Still-Mitra -sigmatropic rearrangement

Still, W. C., Mitra, A. A highly stereoselective synthesis of Z-trisubstituted olefins via [2,3]-sigmatropic rearrangement. Preference for a pseudoaxially substituted transition state. J. Am. Chem. Soc. 1978,100,1927-1928. 

In obtaining all-tram bis-homo-farnesol (7), needed for the synthesis of Cig-JH, Still and co-workers (1979) made use of their former finding (Still and Mitra, 1978) on the [2,3]-sigmatropic rearrangement of alkoxyorganolithium reagents, which provides an efficient method for the preparation of Z-homoallylic alcohols. 

A conceptually interesting approach to the synthesis of CJH involves the reaction of allyUc substrates of type 108 with methyl carbanion equivalents in an 8 2 manner. Several syntheses have followed this approach. The Still-Collum-Mitra synthesis used enforced 8 2 methodology, a 2,3-sigmatropic rearrangement of allylic alcohols (108 where X=OH). The big questions in this approach were (1) what would be used as a CH3" equivalent and (2) would the desired olefin stereocontrol be achieved ... 

Z)-Trisubstitutedalkenes. Still and Mitra have described an efficient synthesis of alkenes of this type from allylic alcohols by a [2.3] sigmatropic Wittig rearrangement. The alcohol 2 is converted into the allyl stannylmethyl ether (3), which can be isolated if desired. Treatment with n-butyllithium results in tin-lithium exchange and rearrangement to the homoallylic alcohol 4 in 95% overall yield. When 3 is transmetalated and immediately quenched with cyclohexanone, 5 is obtained in 73% yield. 

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