@WILEY-VCH
`Edited by
`Dennis C. Hall T
`
`Boronic Acids
`
`Preparatiun. Applications in
`Organic Synthesis and Medicine
`
`X. 2119 - 1/29
`
`CFAD v. Anacor, IPR2015-01776 ANACOR EX. 2119 - 1/29
`
`

`
`Boronic Acids
`
`Preparation and Applications in Organic Synthesis
`and Medicine
`
`Edited by Dennis C. Hall
`
`WILEY-
`VCH
`
`WILEY-VCH Verlag GmbH 8:, Co. KGaA
`
`CFAD V. Anacor, IPR2015-01776 ANACOR EX. 2119 - 2/29
`
`CFAD v. Anacor, IPR2015-01776 ANACOR EX. 2119 - 2/29
`
`

`
`CFAD V. Anacor, IPR2015-01776 ANACOR EX. 2119 - 3/29
`
`CFAD v. Anacor, IPR2015-01776 ANACOR EX. 2119 - 3/29
`
`

`
`Boronic Acids
`
`Edited by
`D. C. Hall
`
`CFAD V. Anacor, IPR2015-01776 ANACOR EX. 2119 - 4/29
`
`CFAD v. Anacor, IPR2015-01776 ANACOR EX. 2119 - 4/29
`
`

`
`Further Titles ofInterest
`
`S.-I. Murahashi (Ed.)
`
`Ruthenium in Organic Synthesis
`2004
`ISBN 3-527-30692-7
`
`A. de Meijere, F. Diederich (Eds.)
`
`Metal-Catalyzed Cross-Coupling
`Reactions
`2004
`ISBN 3-527-30518-1
`
`P. A. Evans (Ed.)
`
`Modern Rhodium-Catalyzed
`Organic Reactions
`2004
`ISBN 3-527-30683-8
`
`M. Beller, C. Bolm (Eds.)
`
`Transition Metals
`
`for Organic Synthesis
`Building Blocks and Fine Chemicals
`2004
`ISBN 3-527-30613-7
`
`A. Berkessel, H. Gréger.
`
`Asymmetric Organocatalysis
`From Biomimetic Concepts to
`Applications in Asymmetric Synthesis
`2004
`ISBN 3-527-30517-3
`
`CFAD V. Anacor, IPR2015-01776 ANACOR EX. 2119 - 5/29
`
`CFAD v. Anacor, IPR2015-01776 ANACOR EX. 2119 - 5/29
`
`

`
`Boronic Acids
`
`Preparation and Applications in Organic Synthesis
`and Medicine
`
`Edited by Dennis C. Hall
`
`WILEY-
`VCH
`
`WILEY-VCH Verlag GmbH 8:, Co. KGaA
`
`CFAD V. Anacor, IPR2015-01776 ANACOR EX. 2119 - 6/29
`
`CFAD v. Anacor, IPR2015-01776 ANACOR EX. 2119 - 6/29
`
`

`
`Editor
`
`Prof Dennis C. Hall
`University of Alberta
`Department of Chemistry
`W5—07 Chemistry Building
`T6G 2G2 Edmonton (Alberta)
`Canada
`
`All books published by Wiley-VCH are carefully pro-
`duced. Nevertheless, authors, editor, and publisher do
`not warrant the information contained in these books,
`including this book, to be free of errors. Readers are
`advised to keep in mind that statements, data, illustra-
`tions, procedural details or other items may inadver-
`tently be inaccurate.
`
`Library of Congress Card No.: Applied for
`
`British Library Cataloguing-in-Publication Data:
`A catalogue record for this book is available from the
`British Library.
`
`Bibliographic information published by
`Die Deutsche Bibliothek
`Die Deutsche Bibliothek lists this publication in the
`Deutsche Nationalbibliografie; detailed bibliographic
`data is available in the Internet at <htt'p://dnb.ddb.de>.
`
`© 2005 WILEY-VCH Verlag GmbH 8: Co. KGaA,
`Weinheim
`
`All rights reserved (including those of translation into
`other languages). No part of this book may be repro-
`duced in any form — nor transmitted or translated into
`machine language without written permission from
`the publishers. Registered names, trademarks, etc.
`used in this book, even when not specifically marked
`as such, are not to be considered unprotected by law.
`
`Printed in the Federal Republic of Germany
`
`Printed on acid-free paper
`
`Typesetting TypoDesign Hecker GmbH, Leimen
`Printing Strauss GmbH, Morlenbach
`Bookbinding Litges 8: Dopf Buchbinderei Gmbl-I,
`Heppenheim
`
`ISBN-13:
`ISBN-10:
`
`978-3-527-30991-7
`3-527-30991-8
`
`CFAD V. Anacor, IPR2015-01776 ANACOR EX .2119 -7/29
`
`CFAD v. Anacor, IPR2015-01776 ANACOR EX. 2119 - 7/29
`
`

`
`28
`
`1 Structure, Properties, and Preparation Of Boronic Acid Derivatives
`
`other unidentified oxidation products are obtained. In view of their unique proper-
`ties, interest in the chemistry of trifluoroborate salts is expected to grow further.
`
`1.3
`
`Synthesis of Boronic Acids and their Esters
`
`The increasing importance of boronic acids as synthetic intermediates has justified
`the development of new, mild and efficient methods to provide access to a large pool.
`Of particular interest is the synthesis of arylboronic acids substituted with a wide
`range of other functional groups. As a consequence of their growing popularity and
`improvements in methods available for their preparation, many functionalized
`boronic acids have become available from several commercial sources. Although sev-
`eral methods, like the oxidation or hydrolysis of trialkylboranes, have significant his-
`torical and fundamental relevance, this section is devoted mainly to modern methods
`of practical value to synthetic chemists.
`
`1.3.1
`
`Arylboronic Acids
`
`Arylboronic acids remain the most popular class of boronic acids. Their popularity in
`medicinal chemistry is due in large part to their role as cross-coupling partners for
`the synthesis of biaryl units (Section 1.5.3.1), which are present in the structure of
`several pharmaceutical drugs. Several methods, summarized generically in Figure
`1.18, are now available for the synthesis of complex arylboronic acids and the follow-
`ing section presents an overview of these methods with selected examples in Table
`1.3.
`
`Electrophilic Trapping ofAry|meta| Intermediates with Borates
`1.3.1.1
`One of the first and, probably, still the cheapest and most common way of synthesiz-
`ing arylboronic acids involves the reaction of a hard organometallic intermediate (i.e.,
`lithium or magnesium) with a borate ester at low temperature. The corresponding
`zinc and cadmium species are much less effective [173].
`
`By Meta|—Ha|ogen Exchange with Aryl Halides
`1.3.1.1.1
`Provided the aryl halide substrate is compatible with its transformation into a strong-
`ly basic and nucleophilic arylmetal reagent, relatively simple aryl, alkenyl and even
`alkylboronic acids can be made from a sequence of metal—halogen exchange followed
`by electrophilic trapping with a trialkylborate. The first such methods for preparing
`phenylboronic acid, which involved the addition of methylborate to an ethereal solu-
`tion of phenylmagnesium bromide at -15 °C, became notorious for providing a low
`yield of desired product [174]. Boron trifluoride was also employed instead ofborates
`[175]. In the early 1930s, Iohnson and co-workers developed the first practical and
`popular method for preparing phenylboronic acid and other arylboronic acids with
`an inverse addition procedure meant to minimize the undesirable formation of
`
`CFAD V. Anacor, IPR2015-01776 ANACOR EX. 2119 - 8/29
`
`CFAD v. Anacor, IPR2015-01776 ANACOR EX. 2119 - 8/29
`
`

`
`1.3 Synthesis ofBororric Acids and their Esters
`1.3.1.1.1 Electrophilic borate trapping of arylmetal intermediates from aryl halides
`
`| 29
`
`R\—
`\ /
`
`X=Br,|
`
`'- '1'“
`x j>“.B(ORI)3
`
`R\—
`\ /
`
`Ha0+
`R\—
`B(OFi)2 —> K:/>—B(OH)2
`
`1.3.1 .1.2 Electrophilic borate trapping of arylmetal intermediates from directed ortho-metallation
`
`DG
`
`R H I" R Ll
`
`DG
`
`R®—B(OR')
`
`+
`_
`__
`_
`m 2 T»
`ii.B(OR')3
`\ /
`\ /
`DG = directing group
`
`DG
`
`H30 R®—a oH
`
`\ /
`
`(
`
`)2
`
`1.3.1.2 Transmetallation of arylsilanes and arylstannanes
`
`R\:
`\ /
`
`BBr3
`:
`H301‘
`j
`SiMe3 T» BBr2 e> \ /
`
`B(OH)2
`
`1.3.1.3 Transition metal-catalyzed coupling between aryl halides/triflates and diboronyl reagents
`
`R
`
`\—
`\ /
`X=Br,|,OTf
`
`(R'O)2B—B(OFt')2
`
`R
`
`+
`
`R _
`
`or HB(OFt')2 8 H30 9
`x T» B(OR') —>
`Pd(O), base
`\ /
`2
`\ /
`
`B(OH)2
`
`1.3.1.4 Direct boronylation by transition metal-catalyzed aromatic C-H functionalizatio
`
`(Ft'O)gB—B(OFt' 2)
`
`orHB(OR')2
`R©_B(0R.)
`m 2 j’
`T.M.cata|yst
`\ /
`
`HaO+ R®B(OH)
`\ /
`
`2
`
`R\— H
`\ /
`X=Br,I
`
`Figure1.18 Common methods for the synthesis ofarylboronic acids (esters).
`
`borinic acid by-product [176, 177]. In this variant, phenylmagnesium bromide is
`added to a solution of t1'i-n-butylborate at -70 °C. Specifically, in the reaction of an
`arylmagnesium bromide with a trialkylborate, exhaustive formation of undesired
`borinic acid and borane via a second and third displacement on the intermediate
`boronate ester is prevented by precipitation of the magnesium trialkoxyphenylborate
`salt (75, M = MgX, in Equation 27, Figure 1.19). The latter is also thought not to dis-
`sociate into the corresponding boronic ester and metal alkoxide at low temperatures,
`which is key in protecting the desired boronate ester from a second displacement by
`the Grignard reagent (Equation 28). Then, the free boronic acid is obtained following
`a standard aqueous workup to hydrolyze the labile boronic ester substituents. Such
`procedures have been used successfully in the kilogram-scale preparation of impor-
`tant arylboronic acids [178, 179].
`
`CFAD V. Anacor, IPR2015-01776 ANACOR EX. 2119 - 9/29
`
`CFAD v. Anacor, IPR2015-01776 ANACOR EX. 2119 - 9/29
`
`

`
`30
`
`1 Structure, Properties, and Preparation OfBoror1ic Acid Derivatives
`
`Selected examples of preparative methods for arylboronic acids
`Table 1.3
`and esters. pin = pinacolato (OCMe2CMe2O).
`
`Entry
`
`Substrate
`
`Conditions
`
`F
`
`1
`
`H2N
`
`Br
`
`0
`
`NHBOC
`
`MeHN
`
`2
`
`M60
`
`Br
`
`1. i. n-BuLi (2 eq), THF, 0 °c
`ii. TMSCI (2 eq)
`2. i. t-BuLi (2.2 eq), B20, -78 °c
`ii. B(OMe)3 (xs), -78 °c
`
`III. O.1N aq. HCI
`
`i. MeMgC| (5 eq)
`THF, 0 °c
`ii. t-BuLi (5 eq)» -78 °c
`iii. B(OMe)3 (10 eq), 0 °c
`
`3
`
`4
`
`5
`
`6
`
`7
`
`Br
`
`OH
`
`Br
`
`i. n-BuLi (2 eq)
`E120, o °c, 2 h; -78 °c
`ii. B(OMe)3 (1 eq)
`iii. aq. HCI
`
`i. I-PrMgBr, THF, -40 °c
`ii. B(OMe)3, THF, -78 °c
`iii. HOCH2CH2OH, toluene
`
`3|’
`
`OB"
`
`\
`N\SEM
`
`(iPr)2N
`
`o
`
`oMoM
`
`g. t-BuLi, THF, -78 °c
`IL
`0\
`/B-0-i-Pr
`0
`
`i. s-BuLi, TMEDA
`THF, -78 °c
`ii. B(OMe)3
`ii. 5% aq. HCI
`
`1. s-BuLi, TMEDA
`THF, -78 °C
`ii. B(OMe)3
`ii. 5% aq. HCI
`
`\
`
`i. n-BuLi (1 eq)
`
`8 \§ THF,<-20°C
`N,NCph3
`u. B(O-I-Pr)3 (1.3 eq)
`ii. iPrOH-NH4C|-H20
`
`Product
`
`F
`
`Reference
`
`H2N
`
`B(0H)2
`
`183
`
`(45%)
`o
`
`MeHN
`
`NHB
`
`QC
`
`MeO
`
`(80%)
`
`B(OH)2
`
`BOH
`|
`o
`
`(86%)
`
`,0
`B\ j
`o
`(85%)
`
`Bpin
`
`QB"
`
`(FPr)2N
`
`\
`N\
`SEM
`(68%)
`
`0
`
`B(OH)
`(8o%)
`
`2
`
`°“"°""
`
`B(OH)2
`
`N
`
`W}!
`\N,NCPh3
`
`B(OH)2
`
`(89%)
`
`134
`
`18
`
`186
`
`187
`
`192
`
`193
`
`195
`
`CFAD V. Anacor, IPR2015-01776 ANACOR EX. 2119 - 10/29
`
`CFAD v. Anacor, IPR2015-01776 ANACOR EX. 2119 - 10/29
`
`

`
`Table 1.3 Continued
`
`1.3 Synthesis of Boronic Acids and their Esters
`
`31
`
`Entry
`
`Substrate
`
`Conditions
`
`Product
`
`Reference
`
`(CH3)3CCH2O
`
`O
`
`R\—
`\ /
`R = p-Br or crBr
`
`c1-(ac:-120
`
`0
`
`OCONEt2
`
`SiMe3
`
`i. LDA (1.2 eq)
`B(O-'rPr)3 (2.6 eq),
`THF
`ii. diethanolamine (1.1 eq)
`
`i. LTMP (1.5 eq)
`B(O-'rPr)3 (2 eq)
`THF, -78 °c
`ii. HOCH2CMe2CH2OH
`
`i. BBr3 (1.5 eq)
`CHQCIQ, -78 °C to RT
`ii. 5% aq. HCI
`
`Br
`
`B2pin2(1.1 eq)
`PdC|2(dppf) (3 mol%)
`KOAc (3 eq),
`DMSO, 80 °C, 1 h
`
`1
`
`OMEM
`
`°\
`
`BH (2 eq)
`
`O’
`Et3N (3 eq)
`Pd(OAc)2 (5 mol%)
`:0°§,’(2:(°('JbE"P|:‘) (‘° '“°'%)
`
`I
`Bgplng
`PdC|2(dppf) (3 mol%)
`KOAc (3 eq),
`DMSO, 80 °C, 3 h
`
`0M6
`
`Ph
`
`Ph
`
`/0
`0‘
`/B—B\
`O
`O
`Ph
`(1.1 equiv)
`Ph
`O.” PdC|2(dppf) (8 mol%)
`KOAc,DMF,1OO 10,3 h
`
`OMe
`
`NH(;b
`
`Z
`
`NHCb
`
`Z
`
`9
`
`10
`
`11
`
`12
`
`13
`
`14
`
`0
`
`MeO
`
`MeO
`
`Meo
`
`0
`
`0
`
`Bno
`
`15
`
`(CH3)3CCH2O
`
`8/w
`F*\— (
`B---NH
`\ /
`(84%,88%)
`
`CH3CH2O
`
`0
`/0
`3
`\O
`
`OCONEt2
`
`(92%)
`
`196
`
`197
`
`B(OH)2
`
`193
`
`(>85%)
`
`0
`
`.
`Bpm
`
`200
`
`(80%)
`
`Bpin OMEM
`
`OMe
`
`(34%)
`
`MeO
`
`MeO
`
`O
`
`NHCbz
`
`MeO
`
`(95%)
`
`O
`
`(me
`
`Bpi n
`
`NHCbz
`
`Bno
`
`,0
`
`1?
`0
`
`(65%)
`
`Ph
`
`202
`
`205
`
`206
`Ph
`
`CFAD V. Anacor, IPR2015-01776 ANACOR EX. 2119 - 11/29
`
`CFAD v. Anacor, IPR2015-01776 ANACOR EX. 2119 - 11/29
`
`

`
`32 |
`
`1 Structure, Properties, and Preparation OfBoronic Acid Derivatives
`Table 1.3 Continued
`
`Entry
`
`Substrate
`
`Conditions
`
`Product
`
`Reference
`
`Meo
`
`3'
`
`16
`
`17
`
`18
`
`OMe
`
`Cl
`
`B2Pl"2 (1-1 eq)
`Pd(dba)2 (3 mol%)
`PCy3 (7.2 mol%), KOAc (1.5 eq)
`dioxane, 80 °C, 48 h
`
`.
`Bgplng (1.1 eq)
`
`1/2[l|’Cl(COD)]2 + bpy
`(3 mol%)
`
`benzene, 80 °C, 16 h
`
`O
`Bu%B’
`\
`O
`THF, 45 °C, 16 h
`
`Cr(CO)5
`0Me
`
`19
`
`Br
`
`1. Hg(OAc)2, ACOH,
`H20, HCIO4
`2. BH3-THF
`3. H20
`
`\
`N
`T5
`
`OMe
`
`.
`3”"
`
`(70%)
`
`MeO
`
`2°7
`
`Bpin
`
`213
`
`B
`
`’
`
`(73%)
`OH
`
`B .pm
`
`(73%)
`
`OMe
`
`B(OH)2
`
`\
`N
`T5
`
`0
`(85 /0)
`
`Br
`
`217
`
`187
`
`AM + B(0R)a —> M[ArB(©R)al .:> ArB(oR>2 + ROM
`75
`
`(27)
`
`ArB(OR)2 + ArM :» M[Ar2B(0R)2l .:> Ar2B(0R) + ROM
`
`(28)
`
`Figure‘l.19 Equilibrium involved in the reaction between arylmetal
`intermediates (Li or Mg) and borates.
`
`Isolation of free boronic acids using an aqueous work up may lead to low yields, es-
`pecially for small or polar ones, which tend to be water-soluble even at a low pH (Sec-
`tion 1.4). In such cases, it is often better to isolate the desired boronic acid as an es-
`ter. In an improved procedure that does not involve an aqueous work-up, Brown and
`Cole reported that the reaction of several types of organolithium intermediates with
`triisopropylborate was very effective for the synthesis of arylboronic esters [180]. To
`help minimize the possible formation of borinic acids and boranes by multiple dis-
`placements (i.e., Equation 28 in Figure 1.19), the reaction protocol involves the slow
`addition of the organolithium to a solution of triisopropylborate in diethyl ether
`cooled to -78 °C. The use of smaller borate esters such as trimethylborate gave large
`proportions of multiple addition products (i.e., borinic acid and borane). With triiso-
`
`CFAD V. Anacor, IPR2015-01776 ANACOR EX. 2119 - 12/29
`
`CFAD v. Anacor, IPR2015-01776 ANACOR EX. 2119 - 12/29
`
`

`
`1.3 Synthesis of Boronic Acids and their Esters
`
`33
`
`propylborate, however, the clean formation of lithium alkoxyboronate salt (75, M = Li,
`R = i-Pr, Figure 1.19) was demonstrated by NMR spectroscopy, and the boronic ester
`can be obtained in high purity as the final product upon addition of anhydrous hy-
`drogen chloride at 0 °C. An improvement to this procedure involves pyrolysis or the
`use of acid chlorides to breakdown the lithium triisopropylboronate salt, thereby
`avoiding the generation of free isopropanol and lithium chloride and facilitating the
`isolation of the boronic ester [181]. Recently, an “in-situ” quench variant whereby tri-
`isopropylborate is present in the flask prior to the addition of butyllithium was de-
`scribed; in many cases this simpler procedure afforded higher yields of aryl- and het-
`eroaryl boronic acids compared to the sequential addition procedure [182]. Provided
`the requisite aryllithium reagent is readily accessible, all these procedures provide the
`corresponding isopropyl boronic esters in high yields. In addition to arylboronic es-
`ters, alkenyl, alkynyl, alkyl and even (oc-haloalkyl)boronic esters were made this way
`[180]. If so desired, the free boronic acid may be obtained by hydrolysis of the ester.
`The metal—halogen exchange route can even be applied to functionalized substrates
`containing acidic hydrogen atoms, provided either temporary protection is effected
`(entry 1, Table 1.3) or a suitable excess of organometallic reagent is employed (entries
`2 and 3). All isomers of hydroxybenzeneboronic acid were synthesized from the cor-
`responding bromophenols using this method [185].
`Recently, a new convenient procedure to synthesize arylboronic esters from Grig-
`nard reagents and trimethylborate was described [186]. This method involves a non-
`aqueous workup procedure in which the resulting solution of aryldimethoxyboronate
`is evaporated to eliminate the excess B(OMe)3, and the residual solid is refluxed
`overnight in a solution of diol in toluene. In particular, several examples of ethylene
`glycol arylboronic esters were described with this method (e.g., entry 4, Table 1.3). A1-
`ternatively, the robust pinacol ester can be obtained directly by electrophilic quench
`of the aryllithium intermediate with a pinacol borate ester (entry 5). The use of bis-
`(diisopropylamino)boron chloride as trapping agent in the reaction of both organo-
`lithium and magnesium compounds provides the corresponding bis(diisopropyl-
`amino)boranes, which can be easily transformed into the corresponding boronic es-
`ters and oxazaborolidines by exchange with a diol or an aminodiol [188].
`
`By Directed ortho-Metallation
`1.3.1 .'| .2
`The metallation of arenes functionalized with coordinating ortho-directing groups
`such as amines, ethers, anilides, esters and amides is yet another popular way to ac-
`cess arylmetal intermediates that can be trapped with borate esters. Early work
`showed the suitability of ortho-lithiation of N,N-dialkylated benzylamines in the syn-
`thesis of ortho-methylamino-benzeneboronic acids [189—191]. Sharp and Snieckus
`further demonstrated the efficiency of this method in the preparation of ortho-car-
`boxamido phenylboronic acids (entry 6, Table 1.3) [192]. This protocol was then gen-
`eralized to many other substrates. For example, methoxymethoxybenzene (entry 7)
`and pivaloylaniline were treated with s-BuLi in the presence of TM EDA in THF at
`-78 °C, and the resulting ortho-lithiated intermediates quenched with trimethyl bo-
`rate followed by an aqueous acidic workup described above (Section 1.3.1.1.1), to give
`the corresponding arylboronic acids in good yields [193, 194]. Although the crude
`
`CFAD V. Anacor, IPR2015-01776 ANACOR EX. 2119 - 13/29
`
`CFAD v. Anacor, IPR2015-01776 ANACOR EX. 2119 - 13/29
`
`

`
`34
`
`1 Structure, Properties, and Preparation Of Boronic Acid Derivatives
`
`boronic acids could be used directly in Suzuki cross-coupling reactions, they were
`characterized as their stable diethanolamine adducts. The ortho-metallation route to
`
`arylboronic acids constitutes a reliable process in pharmaceutical chemistry where it
`can be applied to heterocyclic intermediates such as a tetrazole required in the syn-
`thesis of the antihypertensive drug Losartan (entry 8, Table 1.3) [195]. The use of es-
`ters as directing groups is more problematic as the metallated intermediate can un-
`dergo condensation with the benzoate substrate, giving a benzophenone. In one pro-
`tocol, the metallation step is performed in the presence of the electrophile [196]. This
`in situ metallation-boronylation procedure employs LDA as base, and neopentyl es-
`ters were found to be particularly suitable because of their stability in the presence of
`this base. Most importantly, LDA is compatible with borate esters under the condi-
`tions employed, and its inertness to bromide-substituted benzoates provides another
`significant advantage over the use of BuLi for the deprotonation step. Thus, a solu-
`tion of bromo-substituted neopentyl benzoate esters and excess triisopropylborate
`treated with LDA (1.1—1.5 equiv.) in THF led to the isolation of crude ortho-carboxy
`arylboronic acids, which were isolated as diethanolamine adducts in high yields (en-
`try 9, Table 1.3). A limitation of this method using LDA as base is the requirement for
`an electron-withdrawing substituent to activate the arene substrate. Neopentyl ben-
`zoate, for example, does not undergo directed metallation and gives, rather, the cor-
`responding diisopropyl carboxamide. A recent variant of this in situ trapping proce-
`dure using 2,2,6,6-tetramethylpiperidide (LTMP) as the base led to a more general
`methodology, allowing the presence of other substituents normally incompatible
`with standard ortho-metallation procedures with alkyllithium bases [197]. For exam-
`ple, ethyl benzoate, benzonitrile, fluoro- and chlorobenzene were transformed in
`high yield into the corresponding ortho-substituted boronic acids as neopentylglycol
`esters. As demonstrated in particular in the case of ethyl benzoate (entry 10), the use
`of LTMP as base is quite advantageous because LDA fails to metallate this substrate
`and provides instead the carboxamide product of addition to the ester.
`
`1.3.1 .2 Transmetallation ofAry| Silanes and Stannanes
`One of the earliest methods for preparing aromatic boronic acids involved the reac-
`tion between diaryl mercury compounds and boron trichloride [198]. As organomer-
`curial compounds are to be avoided for safety and environmental reasons, this old
`method has remained unpopular. In this respect, trialkylaryl silanes and stannanes
`are more suitable and both can be transmetallated efficiently with a hard boron halide
`such as boron tribromide [199]. The apparent thermodynamic drive for this reaction
`is the higher stability of B—C and Si(Sn)—Br bonds of product compared to the re-
`spective B—Br and Si(Sn)—C bonds of substrates. Using this method, relatively simple
`arylboronic acids can be made following an aqueous acidic workup to hydrolyze the
`arylboron dibromide product [193]. For example, some boronic acids were synthe-
`sized more conveniently from the trimethylsilyl derivative than by a standard ortho-
`metallation procedure (entry 11, Table 1.3).
`
`CFAD V. Anacor, IPR2015-01776 ANACOR EX. 2119 - 14/29
`
`CFAD v. Anacor, IPR2015-01776 ANACOR EX. 2119 - 14/29
`
`

`
`1.3 Synthesis of Boronic Acids and their Esters
`
`35
`
`1.3.1.3 Coupling of'Ary| Halides with Diboronyl Reagents
`The traditional method involving the trapping of aryllithium or arylmagnesium
`reagents with borate esters is limited by the functional group compatibility of these
`hard organometallic species as well as the rigorously anhydrous conditions required.
`In search of milder conditions amenable to a wider scope of substrates and func-
`tionalities, Miyaura and co-workers found that diboronyl esters such as Bzpinz (58,
`Figure 1.14) undergo a smooth cross-coupling reaction with aryl bromides, iodides,
`and triflates under palladium catalysis [Z00]. This new reaction process is described
`in Chapter Z; thus only a brief summary is presented here. A detailed mechanism has
`been proposed [139b, Z00], and several diboronyl reagents are now commercially
`available, including diborylpinacolate (Bzpinz). Despite the obvious appeal of this
`cross-coupling method [139], the prohibitive price of the diboronyl reagents current-
`ly restrains its use for the large-scale preparation of boronates. Standard conditions
`for the coupling reaction involve PdCl2(dppf) as catalyst, with potassium acetate as
`the base in a polar aprotic solvent [200]. The mildness of these conditions is evidenced
`by the use of carbonyl-containing substrates such as benzophenones (entry 12, Table
`1.3) or benzaldehydes [83], which would be unsuitable in the Brown—Cole procedure
`using organolithium intermediates. The cheaper reagent pinacolborane (53, Figure
`1.13) can also serve as an efficient boronyl donor in this methodology (entry 13) [Z01].
`Cedranediolborane has also been proposed as an alternative to pinacolborane, which
`gives pinacol esters that are notoriously difficult to hydrolyze (Section 1.Z.3.Z.2) [Z03].
`The scope of haloarene substrates in coupling reactions with diboronyl esters or pina-
`colborane is very broad. A recent example described the preparation of peptide
`dimers using a one-pot borylation/ Suzuki coupling [Z04]. Hindered or electron-rich
`aryl halides may also be used with high efficiency (entries 13, 14, Table 1.3). Of par-
`ticular significance is the use of pinacolborane with aryltriflates, which can be made
`with ease from phenols [201]. For instance, 4-borono-phenylalanine is now easily ac-
`cessible from tyrosine using this approach (entry 15). This example also shows that
`the use of diboronyl reagents with hydrolytically labile substituents is advantageous
`if the desired product is the free boronic acid. Aryl chlorides are more attractive sub-
`strates than bromides and iodides due to their low cost and wider commercial avail-
`
`ability. In this regard, the development of modified conditions with Pd(dba)2 and tri-
`cyclohexylphosphine as catalyst system has expanded the scope of this coupling
`methodology to aryl chlorides — even electron-rich ones (entry 16, Table 1.3) [Z07].
`Alternatively, a microwave-promoted procedure for aryl chlorides using a palladium/
`imidazolium system has been described [Z08]. Recently, a similar procedure em-
`ployed aryldiazonium salts as substrates [Z09].
`
`1.3.1.4 Direct Boronylation by Transition Metal-catalyzed Aromatic C—H
`Functionalization
`
`In terms of atom-economy, a very attractive strategy for accessing arylboronic acids is
`the direct boronylation of arenes through a transition metal promoted C—H func-
`tionalization. In addition to the catalyst, a suitable boron donor is required, and both
`diboronyl esters and dialkoxyboranes are very appropriate in this role. The concept of
`this type of direct borylation was first demonstrated on alkanes using photochemical
`
`CFAD V. Anacor, IPR2015-01776 ANACOR EX. 2119 - 15/29
`
`CFAD v. Anacor, IPR2015-01776 ANACOR EX. 2119 - 15/29
`
`

`
`36
`
`1 Structure, Properties, and Preparation Of Boronic Acid Derivatives
`
`conditions [210]. For arene substrates, several research groups, including those of
`Smith [211], Hartwig [212], Miyaura/Hartwig [213] and Marder [214] have recently re-
`ported a number of efficient procedures using iridium and rhodium catalysts (entry
`17, Table 1.3). This new reaction process has also generated much interest for its
`mechanism [215]. Regioselectivity remains a major challenge in aromatic C—H acti-
`vation with mono- and polysubstituted arenes, and, not surprisingly, new advances
`are reported at a rapid pace [216]. This recent and emerging approach to the synthe-
`sis of boronic acid derivatives is discussed in detail in Chapter 2.
`
`1.3.1.5 Other Methods
`
`I-Iarrity and co-workers described the application of 2-substituted 1-alkynylboronic
`esters in the D6tz cycloaddition of Fisher chromium carbene complexes, affording in
`a highly regioselective fashion a novel class of hydroxy-naphthyl boron pinacolates
`(entry 18, Table 1.3) [217]. These reaction products also provided, upon treatment with
`ceric ammonium nitrate, the corresponding quinone boronic esters.
`
`1.3.2
`Diboronic Acids
`
`The preparation of all three substitution patterns of benzenediboronic acid has been
`reported (Figure 1.20). Whereas the preparation of the 1,4- and 1,3-benzenediboron-
`ic acids 76 and 77 from the corresponding dibromides were Well described [157a, 218],
`that of the ortho isomer 78 is more tedious [72, 219]. Several other mono- and poly-
`cyclic aromatic diboronic acids, such as 79 [150], 80 [220], and 81 [221], have been de-
`scribed.
`
`(H0)2B
`
`(H0)2B@B(OH)2
`
` B(OH)2
`
`76
`
`(HOW
` O2H
`‘How
`
`79
`
`77
`
`O
`
`0
`
`B(OH)2
`
`so
`
`(HO)2B
`
`Figure‘l.20 Selected examples ofdiboronic acids.
`
`B(0H)2
`
` B(OH)2
`
`78
`
`(HO)2B
`
`—
`
`B<oH)2
`
`31
`
`CFAD V. Anacor, IPR2015-01776 ANACOR EX. 2119 - 16/29
`
`CFAD v. Anacor, IPR2015-01776 ANACOR EX. 2119 - 16/29
`
`

`
`l .3 .3
`
`Heterocyclic Boronic Acids
`
`1.3 Synthesis of Boronic Acids and their Esters
`
`37
`
`Heterocyclic aromatic boronic acids, in particular pyridinyl, pyrrolyl, indolyl, thienyl,
`and furyl derivatives, are popular cross-coupling intermediates in natural product
`synthesis and medicinal chemistry. The synthesis of heterocyclic boronic acids has
`been reviewed recently [22Z], and will not be discussed in detail here. In general,
`these compounds can be synthesized using methods similar to those described in the
`above section for arylboronic acids. Of particular note, all
`three isomers of
`pyridineboronic acid have been described, including the pinacol ester of the unstable
`and hitherto elusive 2-substituted isomer, which is notorious for its tendency to pro-
`todeboronate [223]. Improvements and variants of the established methods for syn-
`thesizing heterocyclic boronic acids have been constantly reported [13, 182]. For ex-
`ample, a Hg-to-B transmetallation procedure was recently employed to synthesize a
`highly functionalized indolylboronic acid (entry 19, Table 1.3) [187].
`
`l .3 .4
`
`Alkenylboronic Acids
`
`Alkenylboronic acids constitute another class of highly useful synthetic intermedi-
`ates. They are particularly popular as partners in the Suzuki—Miyaura cross-coupling
`reaction for the synthesis of dienes and other unsaturated units present in many
`natural products (Section 1.5.3.1). Several methods are available for the synthesis
`of a wide range of alkenylboronic acids with different substitution patterns. These
`approaches are summarized in Figure 1.21 and are described in the sub-sections
`below.
`
`Electrophilic Trapping ofA|kenymeta| Intermediates with Borates
`1.3.4.1
`Alkenylboronic acids can be synthesized from reactive alkenylmetal species in a way
`similar to that described above for arylboronic acids (Section 1.3.1.1.1) [ZZ4]. Typical-
`ly, alkenyl bromides or iodides are treated sequentially with n-BuLi and a trialkylbo-
`rate (entry 1, Table 1.4). A nonpolar trienylboronic acid was synthesized using this ap-
`proach [ZZ6]. As described in Section 1.2.2.2, small boronic acids tend to be highly
`soluble in water and may be difficult to isolate when made using the traditional ap-
`proach involving an aqueous workup. In these cases, exemplified with the polymer-
`ization-prone ethyleneboronic acid synthesized from vinylmagnesium bromide, it
`has proved more convenient to isolate the product as a dibutyl ester by extraction of
`the acidic aqueous phase with butanol [2Z7]. Recently, alkoxy-functionalized butadi-
`enyl- and styrenyl boronic esters were synthesized from 0c,|3-unsaturated acetals by
`treatment with Schlosser’s base and subsequent trapping with triisopropylborate (en-
`try 2) [228].
`
`1.3.4.2 Transmetallation Methods
`
`The treatment of trialkylsilyl derivatives with boron halides described in Section
`1.3.1.2 is applicable to alkenyltrimethylsilanes [ZZ9]. It was employed as a method for
`
`CFAD V. Anacor, IPR2015-01776 ANACOR EX. 2119 - 17/29
`
`CFAD v. Anacor, IPR2015-01776 ANACOR EX. 2119 - 17/29
`
`

`
`38 |
`
`1 Structure, Properties, and Preparation OfBoronic Acid Derivatives
`1.3.4.1 Electrophilic trapping of alkenylmetal intermediates with borates
`
`i. R"M
`X
`: T, *
`ii. B(OFl')3
`R
`X = Br, I
`
`R
`
`B(0R')2
`
`B(0H)2
`H3o+
`T» /:/
`R
`
`1.3.4.2 Transmetallation methods
`
`MLn
`
`BX3
`
`BX2
`
`H3O*
`
`B(OH)2
`
`R
`ML” = ZrCp2, SiMe3
`
`R
`
`1.3.4.3 Transition metal catalyzed coupling between aryl halides/triflates and diboronyl reagents
`
`(R'O)2B—B(OR')2
`X
`,_/: T» :
`Pd(O), base
`
`R
`
`X = Br, I
`
`B(OR')2
`
`H3o+
`T» :
`
`B(OH)2
`
`R
`
`[O] and/or
`1.3.4.4.1 Thermal cis-hydroboration of alkynes
`H36
`Hsxz
`H
`BX2
`R—:—R' —> >=< 4»
`R
`R‘
`
`B(0H)2
`
`R
`
`R‘
`
`1.3.4.4.2 Indirect trans—hydroboration using alkynyl bromides
`
`i.HBBr2—SMe2
`[Br 4»
`
`ii. R'OH
`
`H
`
`R
`
`B(OR')2
`
`i.KBH(i—Pr)e.
`T»
`
`Br
`
`ii. H3o+
`
`R
`
`B(OH)2
`
`1.3.4.4.3 Transition metal-catalyzed cis-hydroboration of alkynes
`
`H3O+
`BX2
`H
`HBX2
`HER‘ L» >:(: T» ,:<:
`T.M.
`R
`R-
`R
`
`B(OH)2
`
`R.
`
`1.3.4.4.4 Rhodium and iridium catalyzed trans—hydroboration of alkynes
`
`R
`H—B(OR')2
`_
`RT‘! H ‘
`TM"
`H
`
`1.3.4.5 Alkene metathesis
`
`:
`
`B(OR')2
`
`B(OH)2
`R
`+
`H 0
`#4 \:/
`
`H
`
`H3O+
`
`R
`
`Ru=CH2
`
`R
`
`R
`
`Figure‘l.2‘l Common methods for the synthesis ofalkenylboronic
`acids (esters).
`
`CFAD V. Anacor, IPR2015-01776 ANACOR EX. 2119 - 18/29
`
`CFAD v. Anacor, IPR2015-01776 ANACOR EX. 2119 - 18/29
`
`

`
`1
`
`2
`
`3
`
`4
`
`5
`
`6
`
`3
`
`9
`
`OEt
`
`_
`
`i. n—BuLi/KO—t-Bu (2.5 eq),
`NTHF, —95°C, 2 h
`
`?€
`0
`
`O
`
`iii. H20, extraction
`iv. HOCH2CMe2CH2OH (1 eq)
`toluene, rt, 12 h
`
`/\/KGB
`(93%)
`
`\ / N
`3
`-
`.
`.
`eq
`)
`(2 2
`1 BCI
`S'Me2
`CHZCI2, -40 °C, 5 h
`E‘
`H 2. pinacol, Et3N
`Ph
`Ph
`
`Zr(Cp)2C|
`
`catBC|
`CHZCI2, 0 °C
`
`/=/
`“'3”
`
`B,
`(,,-c8H,,)
`\ _ /
`
`Bgpinz (1.1 eq)
`
`PdC|2(dppf) (3 mol%)
`PPh3 (6 mol%)
`KOPh (1.5 eq),
`toluene, 50 °C, 5 h
`
`Bpin
`Et
`>—<
`Ph
`Ph
`(82%, Z/E 9822))
`B
`1
`_ °a
`/
`(57%)
`
`n—Bu
`
`Bpin
`(n.c3H,,)
`\ _ /
`
`(74%)
`
`on
`
`/—<—
`
`EtO2C
`
`Bgpinz (1.1 eq)
`PdC|2(PPh3)2 (3 mol%)
`PPh3 (6 mol%)
`KOPh (1.5 eq),
`toluene, 50 °C, 1 h
`
`Bpm
`/=<
`B020
`(93%, >990/. z;E)
`
`'
`
`7 d
`
`HBpin (1.5 eq)
`PdC|2(dppf) (3 mol%)
`
`AsPh3 (12 mol%) Et3N (3 eq)
`
`dioxane, 80 °C, 16 h
`
`PhS
`)—:
`
`1. Cy2BH (1 eq), DME, rt, 1 h
`ii. Me3NO (2 eq), reflux
`iii. HOCMe2CMe2OH (1 eq),
`n, 12 h
`
`PhS
`
`BPi“
`
`(86%)
`
`,BP'"
`
`(95%)
`
`1.3 Synthesis of Bororiic Acids and their Esters
`
`39
`
`Table 1.4 Selected examples of preparative methods for a|keny|-
`boronic acids and esters. pin = pinacolato (OCMeZCMe2O),
`cat = catecholato
`
`Entry
`
`Substrate
`
`Conditions
`
`Product
`
`Reference
`
`Br
`
`*
`
`i. s-BuLi, THF, -78 °c
`ii. B(OR')3» -78 °C, 1 h
`iii. HCI/E120, -78 °C to I’!
`iv. H20
`. HO CH CH
`(
`2)a
`
`V
`
`Cl
`
`>
`
`0\
`B-0
`_
`
`225
`
`Cl
`
`(72%)
`
`231
`
`232
`
`234
`
`235
`
`236
`
`244
`
`244
`
`_
`/ *
`
`Bn0
`
`1. Cy2BH (1 eq), DME, rt, 1 h
`Me3NO (2 eq), reflux
`III. l:O1C2Mhe2CMe2OH (1 eq),
`
`_ '3P‘"
`_/—/
`(70%)
`
`Bno
`
`CFAD V. Anacor, IPR2015-01776 ANACOR EX. 2119 - 19/29
`
`CFAD v. Anacor, IPR2015-01776 ANACOR EX. 2119 - 19/29
`
`

`
`40
`
`1 Structure, Properties, and Preparation Of Boronic Acid Derivatives
`
`Table 1.4 Continued.
`
`Entry
`
`Substrate
`
`Conditions
`
`Product
`
`Reference
`
`|pc2BH, THF, -35 °c too °c
`1.
`1o MeO2C : 11. c1-1301-1o (1o eq), 01040 °c
`”'.HOCM CM OH1
`,rt,12h MOC
`111
`e2
`e2
`(
`eq)
`e 2
`
`_ Bpi”
`/—’
`(84%)
`
`W30
`1.
`|pc2BH, THF, -35 °c to rt, 5 h
`11 F 11. c1-1301-10 (xs), 0 °c;
`reflux 12 h
`111. HO(CH2)3OH
`
`W50
`
`:
`13-0
`
`O\
`—
`
`(
`
`74%
`
`)
`
`12
`
`/ —
`
`AC0
`
`1. 37 (1 eq)
`9: H20‘ "’ °'5 h
`111. aq. CHZO (1 eq), rt, 1 h
`IV. HOCMe2CMe2OH
`(1.1. eq), rt, 12 h
`
`_ 31”"
`_/—/
`Aco
`(55%, 97:3 regio)
`
`13
`
`: 1. CBH (1 eq), 70 °c, 1 h
`/_/—— 11. H20, 25 °c, 1 h
`III. flltratlon
`
`Cl
`
`Z HBpin (2 eq),
`14 f CH2C|2, 25 °c, 6 h
`I
`
`15 Ph%siMe3
`
`1. HBCI2 (1 eq), BCI3 (1 eq)
`pentane, -78 °C; 11, 12 h
`ii. MeOH, Et3N, 0 °C
`
`Cl
`
`I
`
`B(OH)2
`
`—
`
`(95%)
`
`Bpin
`
`(84%)
`
`B(°Me>2
`/=<
`ph
`Sm/(ea
`(46%)
`
`: Br
`
`16 _/
`Cl
`
`i. HBBr2—SMe2, CHZCIQ
`
`ii. MeOH, pentane
`iii. K(i-PrO)3BH, E120,
`0 °C to rt, 0.5 h
`iv. H20, 0 °C
`v. HO(CH2)3OH
`
`>
`
`O\
`B_o
`C|_/_\:/
`(89%)
`
`_ 0'
`
`17
`
`_
`
`n_HeX
`
`1. n—BuLi (1.05 eq),
`THF, -90 °c, 15 min
`ii. PhMe2SiB(OCMe2)2,
`warm up to rt, 12 h
`
`_
`
`n_HeX
`
`BP‘"
`
`—
`
`SiMe2Ph
`(89%)
`
`18
`
`p_T°| :
`
`HBcat (1 eq),
`Cp2T1(CO)2 (4 mol%)
`C5H5, 25 °C, 2 h
`
`;—’
`
`Bcat
`
`(96%)
`
`p_T°|
`
`246
`
`247
`
`248
`
`249"
`
`134
`
`253
`
`256