Albert Eschenmoser

Albert Eschenmoser is best known for his landmark collaborative work with Robert Burns Woodward of Harvard University on the total synthesis of vitamin B12, completed in 1972 after more than a decade of effort by dozens of researchers across both the ETH Zurich and Harvard groups. This achievement is widely regarded as one of the most complex organic syntheses ever accomplished and led to the formulation of the Woodward–Hoffmann rules for pericyclic reactions.

The Eschenmoser–Tanabe fragmentation is an organic reaction in which an α,β-epoxy ketone is converted into an alkynyl ketone and a smaller carbonyl fragment via cleavage of a diazo intermediate. Developed by Eschenmoser and independently by Tanabe, it has become a valuable tool in natural product synthesis for constructing ring systems bearing alkyne functional groups.

Eschenmoser spent most of his career at ETH Zurich (the Swiss Federal Institute of Technology), where he was a professor of organic chemistry. He also held a long-term visiting position at the Scripps Research Institute in California in his later career.

During the vitamin B12 synthesis, Eschenmoser and Woodward encountered unexpected stereochemical outcomes in certain ring-closure reactions, which led Woodward and Roald Hoffmann to formulate the general principle that the stereochemistry of pericyclic reactions is governed by the orbital symmetry of the reacting system. The resulting Woodward–Hoffmann rules, published in 1965, earned Hoffmann the 1981 Nobel Prize in Chemistry (shared with Kenichi Fukui).