Dehydration studies of α- and β-ionol. II. With Toluene-p-sulfonic acid

Abstract

α-Ionol (2), when made to react with a 5% solution of toluene-p-sulfonic acid at 20º for 120 h, gave in 20% yield one major dehydration product (1'E)-6-(buta-1',3'-dienyl)-1 ,5,5-trimethylcyclohex- 1-ene (4a) together with trace quantities of the (1'Z)-isomer (4b). β-Ionol (3) under similar conditions gave after 10 min in 84% yield (6E,2'E)- and (6Z,2'E)-6-(but-2'-enylidene)-1,5,5-trimethylcyclohex-1-ene (la) and (1b). Minor products from this reaction included the isomeric trienes (1c) and (1d). However, at 80º the alcohols (2) and (3) gave in about 60% yields complex mixtures of dehydration products which included 1-butyl-2,3,6-trimethylbenzene (7), 1-butyl-2,4,6-trimethylbenzene (8), 1,1,6-trimethyl-1,2,3,4-tetrahydronaphthalene (9) and 1,1,4,4-tetramethyl-2,3,4,5,6,7-hexahydro- 1H-indene (10). Minor products obtained at 80ºincluded 1,1,4,4-tetramethyl-,4,5,6 tetrahydro- 1H-indene (11) and 1,4,4,7a-tetramethyl-5,6,7,7a-tetrahydro-4H-indene (12). The trienes (la-d) and (4a,b) when treated with toluene-p-sulfonic acid at 80º also yielded the compounds (7), (8), (9) and (10). Reaction pathways are suggested for the formation of all identified compounds.