Stereochemistry of bertyadionol and related compounds

Abstract Irradiation of the macrocyclic diterpene bertyadionol resulted in a single photoisomer (2) the formation of which was rationalised in terms of a novel photorearrangement resulting in transannular bond formation. The structure of this photoproduct was elucidated by a combination of chemical and spectroscopic methods. Two related compounds, diterpene B and D, and their acetate derivatives when photolysed underwent E→Z isomerisation of the conjugated double bond and epimerization about one centre of the cyclopropyl moiety.