All-carbon-substituted quaternary carbon atoms in oxindoles by an aerobic palladium(II)-catalyzed ring closure onto tri- and tetrasubstituted double bonds

Schiffner JA, Oestreich M

Abstract

Oxidative palladium(II)-catalyzed cyclization of α,β-unsaturated amides derived from electron-rich anilines is reported. The aerobic ring closure of tri- and tetrasubstituted alkenes yields oxindoles with congested all-carbon-substituted quaternary carbon atoms. The ring-size selectivity is excellent. Selected unsymmetrically substituted arenes cyclize with perfect regioselectivity. Experimental evidence indicates that the mechanism is likely to involve Friedel-Crafts-type electrophilic substitution rather than direct C-H bond activation. Oxindoles are formed in an aerobic palladium(II)-catalyzed cyclization of tri- and tetrasubstituted double bonds at relatively low catalyst loading. The mechanism likelyinvolves a Friedel-Crafts-type electrophilic substitution rather than direct C-H bond activation.