Pergamon Tetrahedmn Letters 40 (1999) 371-372 TETRAHEDRON LETTERS A Mild and Rapid Regeneration of Alcohols from their Ailylic Ethers by Chlorotrimethylsilane/Sodium Iodide Ahmed Kamai* , E. Laxman and N. Venugopai Rao Division of Organic Chemistry Indian Institute of Chemical Technology, Hyderabad 500 007, India Received 9 September 1998; accepted 26 October 1998 Abstract: A new extremely facile and efficient cleavage of allyl ethers is developed employing chlorotrimethylsilane/sodium iodide. © 1998 Elsevier Science Ltd. All rights reserved. The protection of alcohols by allyl protecting groups is an important step in the preparation of many organic compounds.I Several new methods have been developed for the removal of the allyl group under different condition; these include; SmCl3/e-, 2 Ti(O), 3 PdCIz/CuCI/O2, 4 Cp~_Zr, 5 NBS/ha), 6 Ti(O-i-Pr)4/n- BuMgCI, 7 DDQ, 8 NaBHJI2, 9 TolSO2H/Pd(PPh3)4, I° and I(CF2)6F/Zn. 11 In comparison to classical procedures which involve a two-step sequence using strongly basic as well as acidic conditions, t2 the recently introduced procedures are better. Nevertheless, there is scope for milder and improved methods for the cleavage of allyl ethers. In this communication, we wish to report a new practical regeneration of alcohols from their allylic ethers employing chlorotrimethylsilane and sodium iodide (hi situ generation of iodotrimethylsilane). In recent years, the use of organosilicon reagents has gained much importance in organic synthesis. Furthermore, the use of the chtorotrimethylsilane and sodium iodide reagent system has been found to be a convenient and inexpensive alternative to iodotrimethylsilane.~3 Recently, we found a new use of the above reagent system for the reduction of azido functionality. '4 In continuation of this effort, particularly for the total synthesis of natural products, the present investigation describes a facile cleavage of allyl ethers. Although, cleavage of esters and lactones has been reported employing the chlorotrimethylsilane-sodium iodide system under reflux conditions, 15 the cleavage of allyl ethers by this reagent system remained unexplored. This led us to utilise this reagent system for the cleavage of allyl ethers following this procedure: To a solution of allyl ether (1 mmol) in acetonitrile (10 ml), NaI (1.5 mmol) was added and the mixture stirred for 2 min. To this stirred suspension, a solution of chlorotrimethylsilane (1.5 mmol) was added and the stirring continued for another 2 min (for entt'y 7, 4.5 equivalent of the reagents were used). On completion of the reaction, as indicated by TLC, the reaction mixture was quenched using sodium thiosulphate and extracted 0040-4039/99/$ - see front matter © 1998 Elsevier Science Ltd. All rights reserved. PH: S0040-.4039(98)02314.-4
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`372 with ethyl acetate. The organic layer was dried over anhydrous Na2SO 4 and concentrated under reduced pressure to give the product which was purified by column chromatography (EtOAc-hexane, 2 : 3) to give the final product. The generality of this method is illustrated in the following Table: Entry Substrate Time(min) Product Yield(%) 1 Me.-~..O ''~ 2 MeSH 98 2 CI--O-O''~ 2 CI--~H 98 3 ~C~ "0''''~ 2 ~,.OH 98 CH3 C H 3 4 ~)"~,~ 3 [~'~DH 96 0 0 6 -~,~.0~ 3 ~H 95 7 =~)~ 0--..~_ 3 HO"~HH OH 95 '6 M eO --,,,,~ MeO.-.,,~ 8 ~,~.0" ~'0~ 2 93 HO ~..,.o HO In summary, the method described in this communication is rapid and efficient and proceed under mild conditions. Therefore, it will find applications in organic synthesis which require deprotection of allyl ethers. References I. a) Greene, T. W.; Wuts, P. G. M. Protective Groups in Organic Synthesis; 2rid ed.; John Wiley ; New York, 1991. b) Kocienski, P.J.; Protecting Groups; Thieme; Stuttgart, 1994. 2. Espanet, B.; Bunach, E.; Perichon, Y.Tetrahedron Lett. 1992, 33, 2485. 3. Kadam, S.M.; Nayak, S.K.; Banerji, A. Tetrahedron Lett. 1992, 33, 5129. 4. Mereyala, H.B.; Guntha, S. Tetrahedron Lett. 1993, 34, 6929. 5. Ito, H.; Taguchi, T.; Hanzawa, Y. J. Org. Chem. 1993, 58, 774. 6. Diaz, R. R.; Melagatejo, C. R.; Espinosa, M. T.. P. L.; Cubero, I. I. J. Org. Chem. 1994, 59, 7928. 7. Lee, J.; Cha, J. K.Tetrahedron Lett.. 1996, 37, 3663. 8. Yadav, J. S.; Chandrasekhar, S.; Sumitra, G; Kacke, R. Tetrahedron Len. 1996, 37, 6603. 9. Thomas, R. M.; Mohan, G. H.; Iyengar, D.S. Tetrahedron Lett. 1996, 38, 4721. 10. Honda. M.; Morita, H.: Nagakura, I. J. Org. Chem. 1997, 62, 8932. l I. Yu, B.; Li, B.; Zhang, J.; Hui; Y. Tetrahedron Lett. 1998, 39, 4871. 12. a) Schelhaas, M.; Waldmann, H. Angew. Chem., Int. Ed. 1996, 35, 2056 b) Ranu, B.C.; Bhar, S. Org. Prep. Proc. Int. 1996, 28, 371. 13. Olah, G. A.; Narang, S. C.; Gupta, B. G. B.; and Malhotra, R., J. Org. Chem 1979, 44, 1247. 14. Kamal, A.; Rao N. V.; Laxman, E. Tetrahedron Lett.. 1997, 38,6945. 15. Ho, T. L.; Olah, G. A. Proc. Natl. Acad. Sci., 1978, 75, 4. 16. Conversion monitored by HPLC. ................................ IICT Commun. No. 4134
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