Stabilization of singlet ethoxycarbonylnitrene by 1,4-dioxan. Part 2. Selectivity for insertion into C–H bonds

Abstract

The selectivity for insertion of ethoxycarbonylnitrene generated thermally or photochemically from ethyl azidoformate into the tertiary, secondary, and primary C–H bonds of iso-octane, cyclohexane, and n-octane were determined at various concentrations of 1,4-dioxan. The relative selectivity for secondary and primary C–H bonds is almost independent of the 1,4-dioxan concentration, whereas that for tertiary and primary C–H bonds decreases with an increase in the quantity of 1,4-dioxan. The tendency for this decrease is greater in photolysis than thermolysis. The results are explained in terms of steric hindrance in the transition state of the reaction between the crowded tertiary C–H bonds and a nitrene–1,4-dioxan complex. The variation of the selectivity with temperature supports formation of this complex.