An efficient approach to chiral nonracemic trans- and cis-decalin scaffolds for drimane and labdane synthesis

Optically active trans - and cis -ring junction decalinic intermediates, which represent useful precursors for the synthesis of more complex natural targets, have been conveniently prepared starting from the β-ketoester obtained by standard chemistry from β-ionone and dimethyl carbonate. The chiral auxiliary (−)-menthol, easily attached to the β-ketoester through DMAP-catalyzed transesterification, allowed a clean separation of the diastereomers obtained in the key electrocyclization step, which were further elaborated to chiral intermediates already taken to drimane and labdane sesquiterpenes.