Base-catalysed ring opening of 1,2-diphenylcyclobutanols

Cis- and trans-1,2-diphenylcyclobutanol have been prepared by literature methods and structural assignment confirmed by an X-ray crystal structure determination of the cis isomer. In the crystal structure, the four-membered ring has a pucker angle of 29° and the hydroxy group is pseudo-equatorial with respect to the puckered ring. In aqueous base, both isomers rearrange to 1,4-diphenylbutan-1-one. Rates of this reaction in buffered aqueous dioxane have been measured. The isomers are almost equally reactive. kcis/ktransca. 0.7 at 25 °C, although empirical force field calculations suggest that the cis isomer is more strained by 3.5 kcal mol–1. The solvent isotope effect, kH2O/kD2O, is 0.68, and discrimination isotope effect (kH/kD)in protonation of the benzylic site of the product is 0.99 ± 0.05. These ring openings are compared with those of the related cyclopropanols and with the corresponding reaction in a close acyclic analogue.