The insertion of methanesulfonylnitrene into C–H and O–H bonds was investigated by the photolysis of methanesulfonyl azide In hydrocarbons and in alcohols. The relative reactivity of the sulfonylnitrene toward C–H bonds of hydrocarbons was found to be smaller than that of ethoxycarbonylnitrene, whereas the reactivity of the sulfonylnitrene toward O–H bonds of alcohols was larger than that of the carbonylnitrene.
Ethoxycarbonyl nitrene, generated by the photolysis of ethyl azidoformate (I), were inserted preferentially into the α C–H bonds of cyclic ethers. The α C–H bonds of cyclic ethers were much more reactive than the corresponding C–H bonds of hydrocarbons for the insertion of the nitrene. In addition, the reactions in cyclic ethers with an alkyl group at the α-position gave unsaturated alkoxyurethanes via a cleavage of the ring C–O bond. It was found that the nitrene insertion into the α C–H bonds of cis- and trans-2,5-dimethyltetrahydrofurans proceeded non-stereospecifically, while the insertion into the C–H bonds of hydrocarbons proceeded stereospecifically. The formation of the alkoxyurethanes can be explained by a mechanism in which an O–N ylide is included as an intermediate of the nitrene reaction; the non-stereospecific insertion of the nitrene give support to this mechanism.
Ethoxycarbonyl nitrene, generated by the photolysis of ethyl azidoformate (I), was inserted preferentially into the α C–H bonds of acyclic ethers. Each of the reactions with acyclic ethers gave N-alkoxyurethane via a cleavage of the C–O bond, indicating that an O–N ylide is an intermediate of the nitrene reaction. Comparing sensitized photolysis with direct photolysis of I in ethers and in alcohols, it was found that the nitrene insertion into the α C–H bonds of ethers proceeds for both singlet and triplet and that the insertion into the β and γ C–H bonds of ethers and the O–H bonds of alcohols proceeds only for the singlet.
The reactions of N,N-dichloromethanesulfonamide (I) with substrates such as hydrocarbons and ethers gave the N-substituted methanesulfonamide (II) and methanesulfonamide (III) in the presence of copper. The reaction with 2-methylbutane gave the product only with a tertiary C–H bond, though the singlet nitrene which was generated from methanesulfonyl azide reacted with the primary, secondary, and tertiary C–H bonds in the ratio of 1 : 4.2 : 9.6. The reactions with the tertiary C–H bonds of cis- and trans-1,4-dimethylcyclohexanes proceeded non-stereospecifically, in contrast to those of the nitrene with them. The addition of a radical inhibitor, hydroquinone, reduced the yield of II, while it increased the yield of III. The reaction with alcohols led to a quantitative yield of III, accompanied by the corresponding aldehydes. These results suggest that the reaction proceeds not by a nitrene mechanism, but by a metal-radical mechanism.
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