Ylide formation of singlet carbene with carbonyl compound—laser flash photolysis of (biphenyl-4-yl)chlorodiazirine in propanone

The ylide formation between a singlet carbene and a carbonyl compound has been studied by laser flash photolysis (LFP) of (biphenyl-4-yl)chlorodiazirine (BCD) in propanone and cyclopentanone, and by product analyses. (Biphenyl-4-yl)chlorocarbene (BCC) adds to the carbonyl compound to yield an equilibrium amount of the carbonyl ylide (CY) which has an absorption maximum around 490 nm. The rate constants of CY formation and dissociation have been determined. CY decays by unimolecular and bimolecular mechanisms. In the photoreaction of BCD with propanone, an aryl olefinic ketone and aryl α-hydroxy ketone were obtained. In the presence of dimethyl fumarate, the photoreaction of BCD in propanone gives a dihydrofuran derivative. The measured ratios of reaction products are in good agreement with ratios calculated from measured rate constants, which indicates that the rate constants are reliable.