Steroids and related natural products-X: reduction of lactones

Abstract

Boron trifluoride etherate-lithium aluminum hydride reduction of 12β-hydroxy-14ξ-rosane 16-carboxylic acid lactone (IIa), dihydroabietic γ-lactone (IIIa) and 3β-hydroxy-7-oxo-7a-oxa-B- homo-5α-cholestane (Xa) was found to yield the corresponding (IIb and IIIb) and oxepane (Xb, after acetylation) derivatives. Similar reduction of several lactones prepared from primary alcohols resulted in essentially complete conversion to their respective glycols. For example, only 3,4-dihydroxy-3,4-seco-5α-and rostane (IX) was isolated following reduction of 3-oxo-3a-oxa-A-homo-5α-and rostane (VII). The present study suggests that boron trifluoride-lithium aluminum hydride reduction of esters will increasingly favor ether formation as branching adjacent to the ester alkyl-oxygen moiety increases.