| Abstract: | Heating of 1-(o-hydroxyaryl)-2-propen-1-ols ( 9–13 ; see scheme 1) in diglyme solution at 147° leads to a 1,4-elimination of water to yield ω-vinyl-o-quinomethides ( b ; see scheme 2) as intermediates which cyclise rapidly to form 2H-chromenes ( 17–21 ). 1-(o-Hydroxyphenyl)-5-hexen-1-ol ( 14 ) on heating at 147° is transformed into o-(1,5-hexadienyl)-phenol ( 23 ). This phenol rearranges at higher temperature (270°) in N,N-diethylaniline to yield a mixture of 2,4-propanochromane ( 25 ) and cis- and trans-3,4-propanochromane (cis- and trans- 26 ). The kinetically controlled ratio of these compounds is 2,8:1:2,9. The formation of 25 and 26 can be explained by an intramolecular Diels-Alder reaction (see scheme 3). |
