Cyclopropanones and related compounds. Part II. Adducts from reduction of di-(α-bromobenzyl) ketone in the presence of dienes. Photolysis of α-phenyl ketones

Abstract

Reduction of di-(α-bromobenzyl) ketone with sodium iodide in acetonitrile or acetone in the presence of cyclo-pentadiene yielded the interconvertible cis- and trans-isomers of 2,4-diphenylbicyclo[3,2,1]oct-6-en-3-one. The intermediate cyclopropanone or tautomer added to furan in the same way to form the corresponding 8-oxabicyclo[3,2,1]octanones, which on further treatment with acid isomerised to 1-(2-furyl)-1,3-diphenylpropan-2-one. The only adduct isolated from N-methylpyrrole was the corresponding pyrrolylpropanone. Thiophen and cyclohexa-1,3-diene did not form adducts. The same adducts were produced in lower yield by use of benzyl α-chlorobenzyl ketone and alkaline alumina, which is presumed to generate the same reactive intermediate. Pyrolysis of the furan cis-adduct gave stilbene, perhaps by reversal of its mode of formation, followed by loss of carbon monoxide from the 1,2-diphenylcyclopropanone. Stilbene was also formed by pyrolysis of benzyl α-acetoxybenzyl ketone by elimination of acetic acid and carbon monoxide. Ultraviolet irradiation of the carbocyclic bicyclo-octenones caused cis–trans isomerisation, succeeded by decarbonylation.