Dienone-phenol rearrangement of naphthalenetriones. A route to 10-acetoxy5,6,7,8-tetra hydrophenanthrene-1,4-diones

Abstract

Naphthalene-1,4,5(8H)-triones (17) and (18) prepared in a three-step approach from the corresponding acylbenzoquinones (1) and (2), undergo an unusually rapid dienone-phenol rearrangement in acetic anhydride–sulphuric acid solution to give 5-acetoxy-7,8-dimethyl- and 5-acetoxy-6,7,8-trimethyl-1,4-naphthoquinone (19) and (20) in good yields.

Starting from the acylbenzoquinones (1), (2), and (3) the spironaphthalenetriones, (30), (31), and (32) were synthesized through the following sequence: (a) addition of enamine (6) to acylquinones, (b) acid-catalysed rearrangement of the spirobenzofurans (23), (24), and (25), and (c) oxidation, with silver carbonate–Celite reagent, of spironaphthalenones (27), (28), and (29) generated in the latter step. Quinones (30), (31), and (32) were subjected to dienone-phenol rearrangement to produce the corresponding angular tricyclic quinones (33), (34), and (35) in high yields.

The dihydroxyspironaphthalenone (27) afforded the substituted phenanthrene (36) under diendnephenol rearrangement conditions. However, the structurally related naphthalenones (13) and (14) are unreactive to this isomerisation.