Photochemical reactions of ketene and diazomethane with 2,3-dimethyl-2,3-epoxybutane

Abstract

The photolyses of ketene (λ= 313 and 334 nm) and diazomethane (λ= 366 nm) in the presence of 2,3-dimethyl-2,3-epoxybutane (DMEB), oxygen and 2,2-dimethylpropane (as internal standard) have been investigated. Four main reaction products from DMEB were observed and identified: 2,3-dimethyl-2,3-epoxypentane (DMEP), 2,3-dimethylbut-2-ene, propanone and 2,3-dimethyl-2,3-epoxybutanal.

CH₂(¹A₁), formed from ketene or diazomethane, was found to insert into the C—H bonds of DMEB to give DMEP at 0.4 times the rate it inserted in to the C—H bonds of 2,2-dimethylpropane; however, no CH₂(¹A₁) C—O insertion products were observed. 2,3-dimethylbut-2-ene and propanone were formed by pathways that did not involve methylene radicals and significant loss of 2,3-dimethylbut-2-ene, by secondary reactions, was observed in oxygen scavenged, ketene systems. 2,3-dimethyl-2,3-epoxybutanal was formed in both ketene and diazomethane systems but the amount produced varied with the photolysis wavelength and methylene precursor.

Mechanisms for the formation of all reaction products are discussed.