N-Heterocyclic Carbene Catalyzed Enantioselective Claisen Rearrangement

Significance

An enantioselective annulation of ynals 2 and enols (e.g. 3) to dihydropyranones (e.g. F) has been achieved via a N-heterocyclic carbene 1 catalyzed variant of the Claisen rearrangement. The catalytic system enabled the synthesis of kojic acid derivatives 4 in high yields and with excellent enantiomeric ratios. The reaction was also effective for other enol substrates: ethyl pyruvate and 2-naphthol, although lower enantio­selectivity was achieved in the naphthol case.