Stabilization of singlet ethoxycarbonylnitrene by 1,4-dioxan. Part 3. Stereospecificity for the addition to 4-methylpent-2-ene of the nitrene generated from ethyl azidoformate

Abstract

The addition to cis-4-methylpent-2-ene of ethoxycarbonylnitrene generated by the photolysis of ethyl azidoformate was carried out in 1,4-dioxan–cyclohexane. Both the stereospecificity of addition and the sum of all singlet nitrene products increase with an increase in the concentration of 1,4-dioxan. The relative yield of cis- to trans-aziridine is proportional to the concentration of 1,4-dioxan, and the total triplet nitrene products stay practically constant. This suggests that increased concentration of the singlet state by 1,4-dioxan corresponds to increased concentration of a singlet 1,4-dioxan–nitrene complex, not the free singlet nitrene. For addition using trans-4-methylpent-2-ene in place of the cis-isomer, there was a smaller increase in the stereospecificity induced by 1,4-dioxan. On the other hand, for addition of the nitrene generated by thermolysis, the stereospecificity was almost independent of the concentration of 1,4-dioxan.