Synthesis of Spiro Pyrrolidines from Tetrahydropyridinium Salts

Significance

Reported is a strategy for the synthesis of 3,3-heterocyclic ring-fused spiro N-alkyl-3-pyrrolidines involving the key steps of [2,3]-sigmatropic rearrangement of didehydropyridinium ylids to 3-vinyl-substituted pyrrolidines followed by a ring-closing metathesis. Spirocyclic dihydropyran and piperidine systems were prepared in one series starting with readily available tetrahydropyridines; in the other series, a spiro benz­azepinopyrrolide was obtained in modest overall yield.