Steroid boranes. Part IV. Hydroboration of a steroid olefin with asymmetric boranes
Abstract
Asymmetric hydroboration of cholest-2-ene with (–)-dipinan-3α-ylborane and with the enantiomeric (+)-dipinan-3α-ylborane is described. The main product from the first reaction is 5α-cholestan-3α-ol and that from the second 5α-cholestan-2α-ol. These results are opposite to those predicted by the model suggested by Brown and Zweifel.