Thia-Wittig rearrangement

A thia-Wittig rearrangement in the methylenecyclopentane (154) proceeded to (155) without formation of the epimer (equation 45). Obviously, the reaction proceeds on the less hindered (convex) face of the bicyclic framework. Equally high diastereoselectivity — unassigned, but presumably also on the less hindered (exo) face — is recorded for the 2,3-rearrangement of a methylenecyclopentane-derived sulfur ylide. ... 

The pioneering work on thia-[2,3]-Wittig rearrangement was reported by Rautenstrauch in 1971 °. The reaction of allyl sulfides 137 with n-BuLi at —30°C for 1.5-4 h gave homoallyl sulfide or thiol 138 ([2,3]-product) exclusively (equation 81). In contrast, a similar reaction of vinyl sulfide 139 gave no [1,2]-rearrangement product 141 albeit a-thio-carbanion was generated as shown by its methylation to 140 (equation 82) °. 

TABLE 7. Thia-[2,3]-Wittig rearrangements of stannylated precursors and i, i -acetals ... 

Snider and colleagues have developed the sequential ene reaction/thia-[2,3]-Wittig reaction which provide appropriately functionalized product 152 at allylic position on simple alkene 150 in two steps involving intermediate 151 (equation 87) . Thia-[2,3]-Wittig rearrangement was often utilized as a key step of natural product synthesis. Masaki and colleagues have demonstrated that the potassium enolate thia-[2,3]-rearrangement of aUyl sulfide 153 to 154 is useful for the synthesis of terpenoid diol component 155 of the pheromonal secretion of the queen butterfly (equation 88) . 

Recently, the asymmetric thia-[2,3]-Wittig rearrangement using di-(Z)-menthyl phos-phonate 156 as the chiral auxiliary to 157 has been developed by Masson and colleagues (equation... 

Some examples of the related thia-Wittig or aza-Wittig rearrangement, in which a sulfur or ifitrogen atom is located in place of the ether oxygen atom have been... 

Thia-[2,3]-Wittig sigmatropic rearrangement of lithiated carbanions 47, obtained by deprotonation of the S-allylic sulfides 46, affords the thiols 48 or their alkylated derivatives 49. The corresponding sulfonium ylides 51, prepared by deprotonation of the sulfonium salts 50 also undergoes a [2,3]-sigmatropic shift leading to the same sulfides 49 [36,38] (Scheme 13). As far as stereochemistry is concerned, with crotyl (R R =H,R =Me) and cinnamyl (R, R =H,R =Ph) derivatives, it has been shown that the diastereoselectivity depends on the nature of the R substituent and on the use of a carbanion or an ylide as intermediate. 

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