Singlet carbenes are commonly generated by thermolysis or direct photolysis of nitrogen-containing precursors such as diazo compounds, diazirines, and iV-aziridinylimines.1 (Because of innate instability, diazo species are often prepared and decomposed in situ.) Although carbenes can exist in three singlet electronic configurations ( 2, , p2), the 2 arrangement is favored energetically and in most cases is responsible for the chemistry of singlet carbenes, especially in condensed phases that allow rapid collisional decay of higher energy singlets. Typical reactions of singlet

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Sulfonyl azides in isopropyl alcohol solution give the corresponding sulfonamides, acetone, and nitrogen either on direct irradiation of the azide or on selective irradiation of added benzophenone. Detailed studies with methanesulfonyl azide revealed high quantum yields and rates that showed complex dependences on the light intensity and on the concentrations of azide and benzophenone. A radical chain mechanism, evidently consisting of two propagation sequences, is involved. Chains appear to be terminated by radicals derived from isopropyl alcohol and from benzophenone. e wish to report our discovery and mechanistic W characterization of a photochemical reaction in which sulfonyl azides are reduced to sulfonamides by isopropyl alcohol solvent, according to eq 1. The OH 0 I II I RSOzNa + CHlCCHl + RSOzNHz + C H~C C H B + NP (1) H reaction occurs in the absence of oxygen (1) on direct irradiation of the azide, (2) on selective irradiation of benzophenone added as a sensitizer, (3) on thermal treatment of the solution at its reflux temperature (SO"), or (4) on addition of small amounts of ferrous chloride and hydrochloric acid to a solution of the azide in the alcohol.3 We optimized the conditions only for the photochemical transformations 1 and 2, which are the chief topics of this paper.Because of its representative behavior, methanesulfonyl azide was chosen as the substrate for most of our mechanistic investigations, although the reaction appears general for aliphatic and aromatic sulfonyl azides.Methods and Product Studies. A deoxygenated solution of the azide in peroxide-free isopropyl alcohol was irradiated at ca. 20" with a mercury lamp. The acetone produced was isolated (as its 2,4-dinitrophenylhydrazone) from the distillate of the irradiated solution. The sulfonamide and benzophenone (in those cases where the latter was employed as a sensitizer) were obtained from the distillation residue.A. Direct Photolyses. These irradiations were conducted with unfiltered light in both anhydrous and aqueous isopropyl alcohol. Methanesulfonyl azide, either in the anhydrous solvent or in the presence of 10 vol z water, reacted quantitatively, according to the stoichiometry of eq 1. The photolysis of p-methoxybenzenesulfonyl azide under anhydrous conditions gave the related sulfonamide in at least 9 4 z yield, but the behavior of m-nitrobenzenesulfonyl azide, in (1) (a) Abstracted from the dissertation submitted by M. T. R. in partial fulfillment of the requirements for the degree of Doctor of Philosophy. (b) Presented in summary at the 150th National Meeting of the American Chemical Society, Atlantic City, N. J., Sept 13, 1965, Abstract 23s. (c) This work was supported by the National Institutes of Health (Grants GM-06304 and GM-9693) and by a grant-in-aid from the H. A. B. Dunning Foundation.(2) To whom inquiries should be addressed. (3) H. Kwart and A. A. Kahn, J . Am. Chem. Soc., 89, 1950 (1967), report that the reaction can be effected catalytically with copper.anhydrous solvent, was anomalous. Prolonged irradiation g...

31) See Experimental Section for a substantiation of the structural assignments which are based on NMR analyses and comparison of the data of our compounds and those of the authors cited in ref 30. (32) For related examples of Intramolecular cycloadditions, see H. Prlnz-bach and H.