Synthesis of naphthofuran-3-spirocyclohexanetriones
Abstract
The condensation of 2,3-dichloro-1,4-naphthoquinone with nitrocyclohexane and t-butyl cyclohexane-carboxylate has been studied. The product resulting from reaction of the quinone with t-butyl cyclohexane-carboxylate, 3-chloro-2-(1-t-butoxycarbonylcyclohexyl)-1,4-naphthoquinone (3), was readily hydrolysed to the corresponding acid (4). Thermal cyclisation of this compound gave rise to the two isomeric quinone lactones naphtho[2,3-b]furan-3-spirocyclohexane-2,4,9(3H)-trione (8) and naphtho[1,2-b]-furan-3-spirocyclohexane-2,4,5(3H)-trione (10). Procedures were devised which allowed either (8) or (10) to be obtained exclusively.