addition of unsymmetrical dienes to acyl-1,4-benzoquinones and oxidation of the adducts with manganese dioxide: a regiospecific route to mono- and di-methyl-1,4-naphthoquinones

regioselective diels-alder reactions of acyl-1,4-benzoquinones 1 with, severally, isoprene, trans-piperylene,1-acetoxy-1,3-butadiene and 1-methoxy-1,3-butadiene gave the corresponding adducts 2 in high yield. treatment of the adducts 2 with manganese dioxide gave regiospecifically the corresponding 1,4-naphthoquinones 3. in several cases, the adducts of the acetylquinones afforded intermediates of type 4, which subsequently gave the corresponding naphthoquinones by de-acetylation and aromatization.