An efficient asymmetric addition of pinacolborane to 4‐substituted coumarins proceeded with high enantioselectivity in the presence of a copper(I)‐QuinoxP complex as a catalyst to produce the corresponding 1,4‐hydroboration products. Treatment of the intermediates with electrophiles, without isolation, resulted in enantioenriched dihydrocoumarins. The utility of this protocol was demonstrated in the formal synthesis of biologically active molecules.
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Kim et al. (2010) studied this question.