Photochemistry of Cyclopropene Derivatives. Synthesis and Photorearrangement of a 3-Acyl-Substituted Cyclopropene

Article abstract of DOI:10.1021/jo00341a001

Two different approaches toward the synthesis of a 3-acyl-substituted 1,2,3-triphenylcyclopropene were investigated.The first involved treating triphenylcyclopropenyl perchlorate with the anion derived from 1,3-dithiane followed by hydrolysis of the resulting dithioacetal.Unfortunately, all attempts to obtain a carbonyl compound from the hydrolysis failed.The only product obtained corresponded to a 1,2-diphenyl-1,2-diacyl-substituted alkene.The second approach utilized for the synthesis involved treating 3-cyano-1,2,3-triphenylcyclopropene with methyllithium.The addition proceeded quite smoothly to give the desired 3-acetyl derivative in high yield.Irradiation of 1,2,3-triphenyl-3-acetylcyclopropene in benzene afforded a mixture of 2,3,4-triphenyl-2-cyclopentenone (60percent), 2-methyl-3,4,5-triphenylfuran (27percent), and 3-acetyl-1,2-diphenylindene (13percent).The formation of the three products obtained can be rationalized in terms of a vinylcarbene intermediate.Several different pathways are available to this species, depending on the stereochemistry about the double bond and on the conformation the oxygen atom assumes in the cis intermediate.The formation of the 2-cyclopentenone derivative provides good support for the mechanism proposed some years ago to rationalize the photochemical rearrangement of 2,5-dimethylfuran.