Anomaly in Palladium-Catalyzed Phenylethynylation of 2,2'-Dihalobiphenyls: Formation of Alkylidenefluorenes

Article abstract of DOI:10.1021/jo00174a023

2,2'-Diiodobiphenyl and 5,5'-dinitro-2,2'-dihalobiphenyls underwent palladium-catalyzed phenylethynylation with 2 mol of phenylacetylene to yield 3-(fluoren-9-ylidene)-1,3-diphenylpropyne and 3-(3,6-dinitrofluoren-9-ylidene)-1,3-diphenylpropyne, respectively.These fluorenyl compounds exhibited well-defined splitting patterns for the fluorenyl ring protons in the 250-MHz proton NMR spectra.The structure of 3-(fluoren-9-ylidene)-1,3-diphenylpropyne was further confirmed by an independent synthesis via the thermolysis of diethyl 3-(fluoren-9-ylidene)-1,3-diphenylpropen-1-yl phosphate.The mechanistic importance of the complex iodo(fluoren-9-ylidenebenzyl)bis(triphenylphosphine)palladium(II) in the catalytic cycle was established on the basis of its reaction with phenylacetylene to give 3-(fluoren-9-ylidene)-1,3-diphenylpropyne.