STEREOCONTROLLED SYNTHESYS OF 22-HYDROXY-23-ACETYLENIC STEROIDS, KEY INTERMEDIATES IN STEROID SIDE CHAIN CONSTRUCTION. OBSERVATION OF A DIRECTIVE EFFECT BY AN α-CHIRAL SITE DURING ASYMMETRIC REDUCTION WITH B-3-PINANYL-9-BBN (ALPINE-BORANE)

Article abstract of DOI:10.1016/S0040-4039(01)81738-X

An efficient stereoselective synthesis of 22-R- and 22-S-hydroxy-23-acetylenic steroids has been developed using R-Alpine-Borane (125:1, R:S) and L-Selectride (1:11, R:S) to reduce the 22-keto-steroid.S-Alpine-Borane provides an unexpectedly low 1:2.7, R:S ratio due to the influence of the α-chiral center at C-20 of the steroid.