Alkyl sigmatropic, allyl vinyl ethers

The nucleophilicity of sulfur and its ability to stabilize a-carbanions provide sulfur compounds with unique opportunities for sigmatropic processes consecutive rearrangements are no exception. The formation of salt (140) via Sn2 alkylation of ( )-2-butenyl bromide (139) followed by deprotonation leads to the intermediate allyl vinyl ether (141) which, under the conditions of the deprotonation, undergoes a thio-Claisen rearrangement to afford thioamide (143 Scheme 10). Thermolysis of (143) at elevated temperature affords the Cope product (142) in addition to some of its deconjugated isomer. Several unique characteristics of the thio-Claisen sequence should be noted first, the heteroatom-allyl bond is made in the alkylation step, this connection teing not notrtudly practised in the parent Claisen reaction ... 

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