Palladium-Catalyzed Formal (3 + 2) Cycloaddition Reactions of 2‑Nitro-1,3-enynes with Vinylaziridines, -epoxides, and -cyclopropanes

A two-step
Pd-catalyzed (3 + 2) cycloaddition/HNO2 elimination
reaction sequence has been developed to give novel cyclic 1,3-dien-5-yne
systems from Pd-stabilized zwitterionic 1,3-dipoles and 2-nitro-1,3-enyne
substrates. The process is highly atom-efficient and tolerates the
reaction of 2-vinyloxirane, 1-tosyl-2-vinylaziridine, and diethyl
2-vinylcyclopropane-1,1-dicarboxylate derived 1,3-dipoles with a variety
of 2-nitro-1,3-enyne substrates. The stereochemistry of the intermediate
(3 + 2) cycloadducts was determined by single crystal X-ray analysis.
Furthermore, a selective kinetic elimination of the cycloadduct with
an antiperiplanar relationship between the NO2 group and
the participating hydrogen was demonstrated, allowing for efficient
isolation of a single diastereoisomer of the cycloadduct.