Reexamination of Aluminum Hydride as a Stereoselective Reducing Agent for Reduction of Cyclic Ketones to Thermodynamically More Stable Alcohols

Aluminum hydride, a very interesting and valuable reducing agent, has been widely used in numerous applications in organic syntheses. Jorgenson first reported the comparison in the reducing properties between lithium aluminum hydride and aluminum hydride on the reduction of cinnamaldehyde, and Brown and Yoon reported a systematic study on the reducing properties of aluminum hydride in THF. Finally, Cha and Brown introduced a very stable solutions of aluminum hydride triethylamine complex (AHTEA) and showed this complex possesses actually the same reducing properties as does aluminum hydride alone. Nevertheless, we have believed that this reagent can not be applicable for the stereoselective reduction of cyclic ketones, because the stereoselectivity achieved by the reagent at 0 is quite similar to that by lithium aluminum hydride and hence is insignificant. However, in the course of reexamining the reducing characteristics of aluminum hydride, we have found that this reagent possesses a potentiality to be used as a stereoselective reducing agent to provide thermodynamically more stable alcohols. This report describes such stereoselective reduction.