Rearrangements of oxo-dicyclopentadienes

Abstract

Dicyclopentadien-8-one (II) has been made by oxidation of syn-dicyclopentadien-8-ol (I). It rearranges to the dicyclopentadien-1-one (III) when melted, and in polar solvents, a rearrangement that is strongly catalysed by Lewis acids. Pyrolysis of these two ketones and of the isomer (VII) formed by ultraviolet irradiation of the 1-ketone gives the same products, but the ratio of cyclopentadiene to cis-3a,7a-dihydroindene (X) decreases in the order 1-ketone > photo-isomer > 8-ketone.

The 1- and 8-alcohols cyclise to cage-alcohols on illumination in acetone, the “α”-1-alcohol (XV) and syn-8-alcohol (I) giving one cage-alcohol (XVII), and the “β”-1-alcohol (XVI) and anti-8-alcohol (XIV) giving the other (XVIII).