Synthesis of 3,4‐Dihydro‐2H‐Pyrroles from Ketones, Aldehydes, and Nitro Alkanes via Hydrogenative Cyclization

Syntheses of N‐heterocyclic compounds that permit a flexible introduction of various substitution patterns by using inexpensive and diversely available starting materials are highly desirable. Easy to handle and reusable catalysts based on earth‐abundant metals are especially attractive for these syntheses. We report here on the synthesis of 3,4‐dihydro‐2H‐pyrroles via the hydrogenation and cyclization of nitro ketones. The latter are easily accessible from three components: a ketone, an aldehyde and a nitroalkane. Our reaction has a broad scope and 23 of the 33 products synthesized are compounds which have not yet been reported. The key to the general hydrogenation/cyclization reaction is a highly active, selective and reusable nickel catalyst, which was identified from a library of 24 earth‐abundant metal catalysts.