Intramolecular C-Alkylation Using a Vinyl Thioether. The Regiospecific Synthesis of Methyl 3-Methyl-9-Oxobicyclo [3, 3, 1] Non-2-ene 1-Carboxylate

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Abstract
As a model for the total synthesis of the unusual Lycopodium alkaloid selagine (I) 1,2 we required a convenient and regiospecific route to methyl 3-methyl-9-oxobicyclo [3, 3, 1] non-2-ene 1-carboxylate (II). Whereas the corresponding 3-ene (III) is readily accessible by conventional Michael addition of 2-carbomethoxycyclohexanone enolate to methacrolein followed by aldol cyclization and dehydration,3 construction of the desired 2-ene would require the inverse regiochemistry in the Michaelaldol sequence.