Enantioselective Fujiwara-Moritani indole and pyrrole annulations catalyzed by chiral palladium(II)-NicOx complexes

Schiffner JA, Wöste TH, Oestreich M

Abstract

The catalytic asymmetric Fujiwara-Moritani ring closures of several indole-and pyrrole-based cyclization precursors are reported. These unprecedented oxidative palladium(II)-catalyzed annulations allow for the formation of a stereogenic quaternary carbon atom, and decent levels of enantiocontrol are seen in 5-exo-trig cyclizations (54% ee for an indole and 76% ee for a pyrrole) while 6-exo-trig ring closures afford essentially racemic material. Novel oxazoline ligands with a nicotine platform (NicOx) are pivotal for good catalytic turnover as conventional PyOx ligands failed to produce acceptable chemical yields. The preparation of these NicOx ligands as well as the syntheses of the cyclization precursors are described in detail.