Stereodivergent Synthesis of Chromanones and Flavanones via Intramolecular Benzoin Reaction

The strategy of stereodivergent
reactions on racemic mixtures (stereodivergent
RRM) was employed for the first time in intramolecular benzoin reactions
and led to the rapid access of chromanones/flavanones with two consecutive
stereocenters. The easily separable stereoisomers of the products
were obtained with moderate to excellent enantioselectivities in a
single step. Catechol type additives proved crucial in achieving the
desired diastereo- and enantioselectivities.