N-Heterocycles from chromium aminocarbenes.

The initial [2 + 2]-cycloadduct between a chromium aminocarbene and a tethered alkene undergoes a ß-hydrogen elimination very efficiently when triphenylphosphine is added as a ligand. The reaction gives cyclic enamines or homoenamines depending on the substitution on the alkene.

N-Heteropolycyclic compounds from the formal intramolecular (4 + 1)-cycloaddition of chromium aminocarbenes.

Chromium aminocarbenes tethered to dienes of all three electronic natures undergo an efficient intramolecular (4 + 1)-cycloaddition to give N-heteropolycyclic compounds. Ligands on chromium had a profound effect on the course of the reaction.