Total synthesis of vitamin B12 - a fellowship of the ring

In the synthesis of cobyric acid following an arduous 60-step synthesis of the tetrapyrrole corrigenolide, Woodward demonstrated that ring cyclization yielded unexpectedly the corrin cyclic ether (Fig. 2). Its structure was chosen as the chemistry logo for the 1970 IUPAC meeting. It was a reminder that chemistry can be capricious and beautiful. This article is a tribute to the 50-year career in porphyrins of Professor Kevin M. Smith and describes his early contributions with colleagues in the synthetic quest of a related porphyrin molecule, vitamin B-12 (Fig. 1a).