ALLYLIC ACETOXYLATION OF DELTA-5-STEROIDS - OBSERVATION OF A COMPETING PATHWAY - A C-13-NMR STUDY OF 5-BETA-BROMO STEROIDS

Abstract

The allylic acetoxylation of (25R)-spirost-5-en-22-alpha-O-3-beta-yl-acetate (1) using bromine/silver acetate/pyridine/-60-degrees has been studied. Besides the expected 4-actoxy derivative 2 (72%), two products in minor amounts, viz. 5-beta, 6-alpha-dibromo-3-beta-acetoxy steroid (3, 12%) and 5-beta-bromo-3-beta,6-beta-diacetoxy steroid (4, 4%) are obtained. The isolation of products 3 and 4 indicate a competing reaction pathway, albeit in small manner. The C-13 NMR spectra of 5-beta-bromo steroids are studied. Influence of bromine on gamma-carbons, the gamma-g effect, is found to be of immense help in deducing the A/B cis-fusion as well as to highlight configurational and conformational factors.