Enantioselective dearomative [3 + 2] cycloadditions of indoles with azomethine ylides derived from alanine imino esters†

Catalytic, enantioselective [3 + 2] cycloadditions of azomethine ylides derived from alanine imino esters with 3-nitroindoles are reported. The dearomative cycloaddition reactions occur in the presence of a catalyst generated in situ from Cu(OTf)2 and (R)-Difluorphos to form exo’-pyrroloindoline cycloadducts and establish four contiguous stereogenic centers, two of which are fully substituted. The exo’-pyrroloindoline products are formed in moderate-to-good yields (39–85%) with high diastereoselectivities (up to 98 : 1 : 1 dr) and enantioselectivities (up to 96% ee).