De Novo Asymmetric Synthesis of Avocadyne, Avocadene, and Avocadane Stereoisomers.

The de novo asymmetric synthesis of all possible stereoisomers of two polyketide natural products, avocadyne, avocadene, and the saturated variant avocadane, is described. The stereodivergent synthesis of the 12 congeners is accomplished in 4-6 steps from an achiral acylpyruvate derivative, which, in turn, is prepared in five steps from commercially available materials. The approach uses, sequentially, a Noyori asymmetric reduction, a diastereoselective chelate- or directed reduction of a β-hydroxyketone, and an ester reduction to a primary alcohol.