Sommelet-Hauser Rearrangement and Sulfur-Mediated Ring Expansion

Sommelet-Hauser Rearrangement and Sulfur-Mediated Ring Expansion 

These rearrangement reactions are interpretable in terms of [2.3] sigmatropic shifts of the intermediate ylides. A number of such rearrangements of open-chain systems have been described, involving sulfonium ylides [43] [44] [45], ammonium ylides [46] [57], anions in a-position to oxygen (Wittig rearrangement) [48] [49], and fluorenyl carbanions [50]. 

The Sommelet-Hauser rearrangement has rarely been used as a tool in organic synthesis and then only for very special systems [54], The reason is undoubtedly that the Hofmann elimination and the dealkylation reaction of quaternary nitrogen atoms are in direct competition with the ring expansion reactions of these substrates. 

Through sulfur ylide reactions rings can be enlarged by three atoms, two from the vinyl side chain and a third one from the a-alkyl substituent of the sul-fonium ion. The reaction product is, like the starting material, a thiacycloalkane 

3) Both V/107 and V/108 undergo irreversible thermal conversion to V/106 (= 100°, several hours). 

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V3. Sommelet-Hauser Rearrangement and Sulfur-Mediated Ring Expansion... 

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

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