Allyl ethers, -Wittig rearrangement mechanisms

Asymmetric induction of the same kind controls the configuration at the allylic methine carbon in compound (134) (134) results from a chain-elongating Wittig rearrangement (mechanism Scheme 6) of sulfone (133 equation 35). Surprisingly, the sense of the asymmetric induction in the rearrangement of silyl ether (135 equation 36) is opposite to that of more than a dozen other ( )-ethers. ... 

Makisumi, Y., Notzumoto, S. Wittig rearrangement of allyl ethers of 2-quinolinemethanol and 9-fluorenol. SNi mechanism. Tetrahedron Lett. 1966, 6393-6397. 

Hauser noted that diallyl ether (8) also undergoes Wittig rearrangement upon base treatment and suggested that product formation could involve either a 1,2-shift or a cyclic mechanism (equation 3). Later studies by Schdllkopf and Makisumi with substituted allylic ethers (10,11 and 14-16 equations 4 and 5) pointed to a cyclic (SnO mechanism a process allowed by the Woodward-Hoffmann rules. The diastereoselectivity of the reaction was not determined in these cases, but Schollkopf subsequently found that benzyl rrans-crotyl ether (20 equation 6) affords mainly the anti products upon rearrangement of ether (20) with BuLi in THF. Rautenstrauch observed a 1 1 mixture of syn and anti products upon rearrangement of ether (20) in the presence of TMEDA, whereas the cis isomer (23) gave only the syn product (22 equation 7). ... 

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