Formation of optically active chromanes by catalytic asymmetric tandem oxa-Michael addition–Friedel–Crafts alkylation reactions

A novel tandem reaction involving an oxa-Michael addition, followed by a Friedel–Crafts alkylation has been developed. This catalytic tandem reaction, which provides facile and efficient access to optically active functionalised chromanes, proceeds under the influence of bisoxazoline-based catalysts to give diastereomerically pure products in enantioselectivities up to 81% and excellent yields. The optimisation studies, the scope of the reaction, and a model that on the basis of PM3 calculations predicts the outcome of the reaction will be detailed.