TOTAL SYNTHESIS OF CRYSTALLINE (+/-)-FREDERICAMYCIN-A - USE OF RADICAL SPIROCYCLIZATION

Crystalline (+/-)-fredericamycin A (1) was synthesized using, as a key step, 5-exo-digonal radical closure of selenide 55. The selenide was generated from the corresponding ketone 54, itself assembled from two components: aldehyde 29 and bromonaphthalene 48. The product of the radical cyclization (56) was converted into spiro diketone 59, and the pentadienyl chain was then formed by a Wittig reaction. Selective deprotection of ring A was accompanied by isomerization of the diene system to the required E,E geometry, and treatment with boron tribromide, followed by aqueous hydrolysis in the presence of air, effected selective demethylation and oxidation to (+/-)-1. The radical spirocyclization used in this synthesis is a general method.