Sommelet—Hauser rearrangement 2,3 sigmatropic shifts

Initial work on the Sommelet-Hauser rearrangement was mechanistically inspired. Hauser and Kantor provided a major contribution to the understanding of this transformation. They showed that two ylides were involved in the rearrangement. The more stable ylide (421) is initially generated but equilibrates with the less stabilized one (422). The latter ylide then undergoes a concerted, symmetry-allowed 3,2-sigmatropic shift, giving the triene (423). Aromatization finally affords the orrAo-substituted benzylic amine (424 Scheme 108). 

SCHEME 3.31 Sommelet—Hauser rearrangement involving [2,3] sigmatropic shifts. 

Ammonium ylides can isomerize to (1,2) rearrangement products (Stevens rearrangement) or to (2,3) shift products (Sommelet-Hauser sigmatropic rearrangement) when allyl or benzyl are located on the nitrogen atom. A strong microwave effect is noticed (Eq. 66) [116]. 

V. The Cope Rearrangement, the [1.3] Sigmatropic Shift, the Sommelet-Hauser Reaction, and Sulfur-Mediated Ring Expansions... 

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