Reduction of Prostaglandin Enone Intermediates with Aluminium Isopropoxide

Abstract

Abstract Because of their enormous therapeutic potential in several, diverse, disease areas the natural prostaglandins and their analogues have been the synthetic target of a large amount of chemical effort in recent years1. A crucial step in many of the successful syntheses is the reduction of an α, β-unsaturated ketone to a mixture of allylic alcohols. For example in Corey's synthesis2 of the natural compounds the enone (Ia) is reduced to the enols (IIa) and (IIIa). This is best achieved using bulky borohydride reducing agents3 with the additional advantage that a preponderance of the required isomer (IIa) is obtained. However, in our experience use of the more convenient sodium or zinc borohydrides is often complicated by the fact that 1,4-reduction occurs to give the saturated ketone and sometimes saturated alcohols.