Dehydrogenation by air: Preparation of 1,3-disubstituted-5,1-dioxo-5,10-dihydro-1H-benzo[g] isochromene scaffold

Naphthaquinopyrans 5a-d, 10 and 12 have been converted to benzoisochromene IIb via base-promoted air oxidation. A mechanism is proposed to account for the observed results. Use of peroxide scavenger was found necessary for consistent yields. IIb proved to be a versatile scaffold for diversity expansion.