Synthetic studies relevant to biosynthetic research on vitamin B12. Part 4. Development of the photochemical route to isobacteriochlorins

Abstract

Pigments based on the isobacteriochlorin macrocycle are of great importance for research on the biosynthesis of vitamin B₁₂. A synthesis of the isobacteriochlorin ring system is developed in which a key step is an 18π-photochemical cyclisation. The reaction conditions are extremely mild and are demonstrated to be compatible with the reactive acetic and propionic acid residues present in the natural pigments.