Thermisches Verhalten von o-Dipropenylbenzol,Beispiel einer aromatischen [1,7]-sigmatropischen H-Verschiebung. Vorläufige Mitteilung

cis, cis-, cis, trans- and trans, trans-o-Dipropenylbenzene (cis, cis-, cis, trans- and trans, trans- 1 ) were prepared. At 225° cis, cis- 1 isomerises to give cis, trans- 1 and vice versa. The isomerisation follows 1. order kinetics. At equilibrium 89% cis, trans- and 11% cis, cis- 1 are present. It is shown by deuterium labelling that the isomerisation is due to aromatic [1, 7 a] sigmatropic H-shifts. trans, trans- 1 rearranges at 225° to yield 2, 3-dimethyl-1, 2-dihydronaphthalene ( 3 ). This can be visualized by disrotatory ring closure of trans, trans- 1 followed by an aromatic [1, 5 s] H-shift. When cis, cis- or cis, trans- 1 are heated for 153 hrs at 225° a small amount (3%) of 1-ethyl-1,2-dihydronaphthalene ( 5 ) is formed.