Intramolecular Cobalt Porphyrin-Catalyzed Alkylation of 1-Isoindolinones by Site-Selective Insertion into a C(sp)-H Bond.

1-Isoindolinones with a reactive hydrazone tether attached to the nitrogen atom underwent an intramolecular alkylation in the presence of cobalt(tetraphenylporphyrin) and a base. Products display saturated heterocyclic rings of various sizes ( = 5-7), and the method was applied to a short synthesis of the azepane alkaloid lennoxamine. The reaction likely involves a diazoalkane intermediate that undergoes dediazotation and a formal insertion into the C3-H bond. If a stereogenic center is present in the tether, a high degree of diastereoselectivity is recorded.