Free Radical Fragmentation of Photoadduct Derivatives. Formal Synthesis of Pentalenene

Article abstract of DOI:10.1021/jo00112a043

A series of <2 + 2> photoadducts 3a-d are converted to cyclobutylcarbinyl iodides 6a-d.Free radical fragmentation of the iodides yields bicyclo carbon skeletons 7a-d which are present in a variety of natural products.Application of this methodology to terpenoid synthesis is illustrated by the preparation of unsaturated ketone 19 in only six steps (33percent overall yield).As 19 has been converted to pentalenene (1) this constitutes a formal synthesis of the angular triquinane sesquiterpenoid.