Synthetic Studies on Kinamycin Antibiotics: Synthesis of a Trioxygenated Benz[f]indenone and its Diels–Alder Reaction to a Kinamycin Skeleton

Abstract

A benzo[b]fluorene skeleton such as 10, a basic four-ring system in the revised diazo structures 3 of kinamycin antibiotics, was synthesized by Diels-Alder reaction between dienophile 4,7,8-trioxygenated 1H-benz[f]inden-1-one 11 and Danishefsky-type diene 7. The indenone 11 was prepared by deoxygenation of 2,3-dihydro-1H-benz[f]inden-1-one 12 with the inexpensive 1-hydroxy-1,2-benziodoxol-3(1H)-one 1-oxide (IBX) after modification of the known protocol. Indenone 12 in turn was obtained from naphthalene-1,5-diol (14) via an intramolecular Friedel-Crafts cyclization of naphthalene-2-propanoic acid 13 as a key step.