Asymmetric construction of 4H-carbazol-4-one intermediates via the cyclohexadienone annulation of chiral carbene complexes

The quaternary carbon in a 4H-carbazol-4-one can be introduced with high stereoprecision. in the cyclohexadienone annulation of a 2-indolyl chromium carbene complex bearing an imidazolidinone chiral auxiliary. The chiral complex 12 teas found to exist as atropisomers that were readily separated, and each was found to react with the same alkyne to give opposite configurations at the quaternary carbon in the H-4-carbazol-4-one product.