Diastereoselective cyclization of allenes using organocobalt reagents

Abstract

The cobalt mediated acylation-cyclization of gamma-sulfonamidoallenes with a protected hydroxyl group in the alpha position has been developed. The required disubstituted allenes were synthesized starting from acrolein and ethyl acetate. Treatment of the allenes with acetyl tetracarbonyl cobalt, under suitable condition, yielded the trans-substituted pyrrolidine as the major product. The stereochemistry was determined by analysis of the 1H NMR spectra. Silyl protecting groups resulted in the highest yields and diastereoselectivity. The methyl thiomethyl protecting group resulted in the lowest diastereoselectivity