Pd-Catalyzed Dearomative [3 + 2] Cycloaddition of 3‑Nitroindoles with 2‑Vinylcyclopropane-1,1-dicarboxylates

A trans-diastereoselective Pd-catalyzed dearomative
[3 + 2] cycloaddition between vinylcyclopropane dicarboxylates and
3-nitroindoles has been developed. The reaction provides densely functionalized
cyclopenta­[b]­indolines with versatile vinyl and nitro-groups.
The addition of a halide additive was found to be critical for the
diastereoselectivity of the reaction, which is proposed to be a result
of a rapid π-σ-π interconversion between the intermediates
allowing for Curtin–Hammett control. A switch in diastereoselectivity
to afford products with the vinyl and nitro groups cis to each other is observed with a 4-substituted 3-nitroindole.