Synthesis of (+)- and (-)-Gossonorol and Cyclisation to Boivinianin B

The first enantioselective synthesis of gossonorol has been achieved in good overall yield and excellent enantioselectivity, demonstrating the utility of a novel approach to enantiopure tertiary benzylic alcohols. Epoxidation of enantiopure gossonorol followed by acid-catalysed cyclisation gave a diastereoisomeric mixture of boivinianin B, typical of the diastereoisomeric mixtures of this compound found in nature. Separation of the diastereoisomers and determination of their enantiopurity revealed that the stereochemical integrity of the benzylic alcohol of gossonorol had been preserved during the epoxidation/cyclisation reaction.