same title Woodward delivered in the later part of the year 1972 are confined to the A/B approach of the synthesis and do not discuss the ETH A/D approach. Eschenmoser had discussed the ETH contributions to the A/B approach in 1968 at the 22nd Robert A. Welch Foundation conference in Houston, as well as in his 1969 RSC Centenary Lecture "Roads to Corrins", published in 1970. He presented the ETH photochemical A/D approach to the B12 synthesis at the 23rd IUPAC Congress in Boston in 1971. The Zürich group announced the accomplishment of the synthesis of cobyric acid by the photochemical A/D-approach in two lectures delivered by PhD students Maag and Fuhrer at the Swiss Chemical Society Meeting in April 1972, Eschenmoser presented a lecture "Total Synthesis of Vitamin B12: the Photochemical Route" for the first time as Wilson Baker Lecture at the University of Bristol, Bristol/UK on May 8th, 1972. As a joint full publication of the syntheses by the Harvard and ETH groups (announced in and expected in) had not appeared by 1977, an article describing the final version of the photochemical A/D approach already accomplished in 1972 was published 1977 in Science. This article is an extended English translation of one that had already appeared 1974 in Naturwissenschaften, based on a lecture given by Eschenmoser on January 21, 1974 at a meeting of the Zürcher Naturforschende Gesellschaft. Four decades later, in 2015, the same author finally published a series of six full papers describing the work of the ETH group on corrin synthesis. Part I of the series contains a chapter entitled "The Final Phase of the Harvard/ETH Collaboration on the Synthesis of Vitamin B12", in which the contributions of the ETH group to the collaborative work on the synthesis of vitamin B12 between 1965 and 1972 are recorded. The entire ETH work is documented in full experimental detail in publicly accessible Ph.D. theses, almost 1'900 pages, all in German. Contributions of the 14 postdoctoral ETH researchers involved in the cobyric acid syntheses are mostly integrated in these theses. The detailed experimental work at Harvard was documented in reports by the 77 postdoctoral researchers involved, with a total volume of more than 3'000 pages. Representative reviews of the two approaches to the chemical synthesis of vitamin B12 have been published in detail by A. H. Jackson and K. M. Smith, T. Goto, R. V. Stevens, K. C.