Transition Metal‐catalyzed Oxidations, 6. – Total Synthesis of Hallachrome and Related 1,2‐anthraquinones

Abstract

Abstract9,10‐Anthraquinones 3b–3k are prepared by Diels‐Alder reaction of juglone (5a) and 7‐methyljuglone (5b) with the dienes 4a and 4b, then reduced to the corresponding 1‐anthracenols 2b–2d, 2f and 2i that are immediately oxygenated to the ortho‐anthraquinones 1b–1d, 1f and 1i with [MoO(O2)2]·py·HMPT. The 1,2‐anthraquinones dimerize in solution or upon BBr3 treatment. The naturally occurring 1,2‐anthraquinone hallachrome (1a) is prepared by selective protection of the bisphenol 3h as monosilyl ether 3i, oxygenation to the silylated ortho‐anthraquinone 1i and fluoride‐mediated deprotection to 1a.