Synthesis of 20-methyl and 20-cyano isobacteriochlorins: the Witting–photochemical approach
Abstract
20-Methylisobacteriochlorins, important in relation to biosynthetic studies on vitamin B12, and their 20-cyano analogues, have been synthesised by a mild route compatible with the side-chains of natural isobacteriochlorins; this involves assembly of the A–D ring system using a Witting-type reaction and finally photochemical ring-closure to the macrocycle.