Sigmatropic rearrangements 1,3-benzyl shift

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]. 

Sigmatropic 1,2-shifts of acetylenic groups in RC=CCPh2CH2Li (R=Me or Bu ), produced from RC=CCPh2CH2Cl and Li at -75 °C occurs in THF at 0 C [equation (4a)] in contrast the caesium derivative, prepared analogously, rearranges to (11) [equation (46)]. Metallations of allyl benzyl thioether. 

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). 

The benzyl ether (41) gives o-methylaryl ketones via a [2,3] sigmatropic shift. o-Neopentylbenzenesulphinic acid is obtained in 75% yield from the sulphone (42) in the first example of an alkyl group transfer in a Truce-Smiles rearrangement. ... 

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