Säurekatalysierte Dienon-Phenol-Umlagerungen von Allylcyclohexadienonen; ladungsinduzierte und ladungskontrollierte sigmatropische Reaktionen

The rearrangement of 10-allyl-2-oxo-Δ^{1(9), 3}-hexahydronaphthalene ( 12 ) catalysed by trifluoroacetic acid and other Bronsted acids yielded almost exclusively the 3s, 3s]-products, 1- and 3-allyl-5,6,7,8-tetrahydro-2-naphthol ( 16 and 15 , respectively). The rearrangement of 12 with trifluoroacetic anhydride or acetic anhydride/sulfuric acid, yields, besides 15 and 16 , appreciable amounts of the 1s, 2s]-rearrangement product, 4-allyl-5,6,7,8-tetrahydro-2-naphthol ( 14 ) (table 1). The CF₃COOH catalysed dienone-phenol-rearrangement of 6-ally-5,6-dimethyl-cyclohexa-2,4-dien-l-one ( 11 ) in hexane at 0° yields4-allyl-2,3-dimethyl-phenol ( 19 ). Rearrangement of d₃- ll containing a specifically deuteriated allyl group proves that the formation of d₃- 19 occurs via a 3s, 3s]-sigmatropic reaction. On the other hand, treatment of 11 with (CF₃CO)₂O at 0° in hexane gives (after saponification) 4-allyl-, 5-allyl- and 6-allyl-2,3-dimethyl-phenol ( 19 , 20 and 21 , respectivcly). This reaction occurs via an acyloxybenzenium-ion intermediate. The reactions performed with d₃- 11 demonstrate that the formation of d₃- 19 occurs both by a direct 3s, 3s]-shift and by a twofold 1s, 2s]-shift, respectively. d₃- 20 is formcd by a 3s, 4s]-sigmatropic reaction. d₃- 21 is obtained with about 95% inversion of the carbon skeleton of the allyl group. Thus d₃- 21 is mainly formed by a 1s, 2s]- followed by a 3s, 4s]-sigmatropic rearrangement. 6-Allyl-6-niethyl-cyclohexa-2,4-dien-1-one ( 4 ) yields with CF₃COOH in hexane 4-allyl-2-methyl-phenol ( 5 ), whereas with (CF₃CO)₂O in hexane 5 , 3-allyl- and 5-allyl-2-methyl-phenol ( 24 and 25 , respectively) are formed in comparable amounts. As a minor product 6-allyl-2-methyl-phenol ( 26 ) was observed. Based on these observations, the concept of charge-induced, e.g. schemes 2 and 3, and charge-controlled, e.g. scheme 7, sigmatropic reactions, has been elaborated. In the former, the charge serves only to accelerate appreciably thermal orbital-symmetry allowed reactions, whereas in the latter, the charge determines the course of the transformations according to the Woodward-Hoffmann rules. Especially in acetylating systems, allylcyclohexdienones undergo charge-induced and charge-controlled reactions simultaneously.