Selective Thiylation of 1-Vinylpyrrole-2-carbaldehydes: Synthesis of the Novel Pyrrole Synthons 2-[Bis(ethylsulfanyl)methyl]-1-vinylpyrroles and 1-(2-Ethylthioethyl)pyrrole-2-carbaldehydes

Abstract

1-Vinylpyrrole-2-carbaldehydes have been selectively thiylated with ethanethiol either at the aldehyde (acid catalysis) or at the N-vinyl group (free-radical initiation) to afford 1-vinylpyrrole-2-carbaldehyde thioacetals (88-99% yield) or 1-(2-ethylthio­ethyl)pyrrole-2-carbaldehydes (68-89% yield), respectively. Both derivatives constitute important new families of pyrrole building blocks. Exhaustive thiylation at both the aldehyde and vinyl functionalities was achieved by acid-catalyzed reaction of the ethylthioethyl derivative of pyrrole-2-carbaldehyde with ethane thiol. An unexpected reduction of the ethylthioacetal group by ethanethiol to give the ethylthiomethyl group under free-radical initiation was also observed and is discussed.

Key words

1-vinylpyrrole-2-carbaldehydes - ethanethiol - thiylation - thioacetals - sulfides - radical initiation - acid catalysis

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