Preparation and reductive transformations of vinylogous sulfonamides (β-sulfonyl enamines), and application to the synthesis of indolizidines

Organic & Biomolecular Chemistry Pub Date: 2004-11-04 DOI: 10.1039/B413379J

Abstract

Condensation between the methiodide salts of 1-alkylpyrrolidine-2-thiones and ethyl [(4-methylphenyl)sulfonyl]acetate or 1-[(4-methylphenyl)sulfonyl]propan-2-one afforded several 2-{[(4-methylphenyl)sulfonyl]methylene}pyrrolidines in good yield. These β-sulfonyl enamines are sufficiently nucleophilic for cyclisation with internal electrophiles to give sulfone-substituted indolizines, potentially useful scaffolds for alkaloid synthesis. The carbon–carbon double bond in vinylogous sulfonamides was reduced stereoselectively either by catalytic hydrogenation or by treatment with sodium borohydride to yield β-sulfonyl amines. The sulfone group in β-acyl-β-sulfonyl enamines could be removed by hydrogenolysis with sodium amalgam in THF–methanol to give enaminones.

Graphical abstract: Preparation and reductive transformations of vinylogous sulfonamides (β-sulfonyl enamines), and application to the synthesis of indolizidines
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