Photochemical and Acid-Catalyzed Dienone-Phenol Rearrangements. The Effect of Substitutents on the Regioselectivity of 1,4-Sigmatropic Rearrangements of the Type A Intermediate

Article abstract of DOI:10.1021/jo00003a037

Birch reduction of isophthalic acid and 3-cyanobenzoic acid followed by (1) methylation of the resulting enolate with methyl iodide and (2) esterification with diazomethane proved 2-carbomethoxy- and 2-cyano-6-methyl-6-carbomethoxy-1,4-cyclohexadienes 9 and 25.Type A photorearrangement of a series of 2-carbomethoxy-, 2-cyano-, 2-methoxy-, and 2-methyl-4-carbomethoxy-4-methyl-2,5-cyclohexadien-1-ones 11, 26, 45a, and 45b gave 4-carbomethoxy-3-methyl-2-substituted-phenols 12, 28, 46, and 31.It has been demonstrated that the regioselectivity of type A photorearrangement of C(2) substituted 2,5-cyclohexadien-1-ones is governed by electronic rather than steric effects to give the intermediate C(1) rather than C(3) substituted bicyclo<3.1.0^1,5>hex-3-en-2-ones.Regioselectivities of the acid-catalyzed dienone-phenol rearrangements of C(2) substituted 2,5-cyclohexadienones 11, 45a, and 45b appear to be dependent upon the relative stabilities of carbocations resulting from migration of the C(4) carbomethoxy group.