Stereodivergent Synthesis of N‐Heterocycles by Catalyst‐Controlled,Activity‐Directed Tandem Annulation of Diazo Compounds with Amino Alkynes

A stereodivergent synthesis of five‐membered N‐heterocycles, such as 2,3‐dihydropyrroles, and 2‐methylene and 3‐methylene pyrrolidines, has been developed through a tandem annulation of amino alkynes with diazo compounds and involves the trapping of in situ formed intermediates. Mechanistic investigations indicate that the copper‐catalyzed tandem annulations proceed by allenoate formation and subsequent intramolecular hydroamination. In contrast, the rhodium‐catalyzed protocol features a carbenoid insertion into the N H bond and subsequent Conia‐ene cyclization.