A New Route for Installing the Isocyclic Ring on Chlorins Yielding 13¹-Oxophorbines

A new route to 13¹-oxophorbines, the parent macrocycle of chlorophylls, begins with the synthesis of a 13-bromochlorin. Pd-mediated coupling of the latter with tributyl(1-ethoxyvinyl)tin and subsequent acidic hydrolysis afforded the 13-acetylchlorin (1). Treatment of 1 with NBS afforded the 15-bromo analogue in 70% yield. Pd-mediated α-arylation closed the isocyclic ring to give the 13¹-oxophorbine (2) in 85% yield. Facile access to 13¹-oxophorbines should enable a variety of spectroscopic studies and diverse applications.