Cyclization of allene using organometallic reagents

Abstract

A metal mediated acylation-cyclization of -sulfonamidoallenes bearing a protected hydroxyl group in the β position has been developed. The required disubstituted allenes were synthesized starting from glycidol. Treatment of the allenes with acetyl tetracarbonyl cobalt, under suitable condition, yielded a 1:1 the mixture of trans- and the cis-substituted pyrrolidine . The stereochemistry was determined by NOE difference spectroscopy. Alternatively, treatment of a hydroxy allene with palladium (II) chloride and copper (II) chloride in methanol under carbon monoxide, yielded a 2:1 mixture of stereoisomers by NMR spectroscopy. The products could be intermediates for the synthesis of amphorogynine and related alkaloids.