From Triazoles to Imidazolines through the Sequential N–H Insertion of α‑Imino Rhodium–Carbenes into β‑Enamino Esters/Enamine–Imine Tautomerization/Conjugate Addition Cascade

A rhodium­(II)-catalyzed denitrogenative
coupling of N-sulfonyl-1,2,3-triazoles with ambiphilic
β-enamino esters
affords 2,5-dihydro-1H-imidazoles (3-imidazolines)
with broad functional group tolerance. Mechanistic studies using a
deuterium-labeled triazole suggest that the reaction proceeds in a
cascade through the N–H insertion of an α-imino rhodium–carbene,
followed by enamine–imine tautomerization and conjugate addition.
Moreover, the reaction proceeds with high diastereoselectivity for
α-substituted β-enamino esters (R3 = Me, Ph)
to give a single diastereomer.