Direct and sensitized irradiation of methyl diazomalonate gives singlet and triplet biscarbomethoxycarbene, respectively. The reactions of these species with carbon-carbon double bonds are described. Cyclopropanes are formed with substantial retention of stereochemistry from the singlet but with complete loss from the triplet. Additions to aliene, norbornadiene, and benzene are also achieved. The reactions of several triplet carbenes with dienes are reported, but even in systems thought to be favorable to 1,4 addition, only the normal cyclopropanes could be found. Reactions with carbon-hydrogen single bonds are also described. Singlet carbene reacts by direct insertion, but the triplet abstracts hydrogen to give radical pairs which undergo recombination and

The 1,4 addition of chlorine to ketazines in methylene chloride at -60" is shown by nmr to proceed stereospecifically so that symmetric (syn,syn or anti,anti) ketazine isomers give meso-a,a '-dichloroazoalkanes and unsymmetric (syn,anri) ketazine isomers give the di product. Studies on equilibrium and nonequilibrium mixtures of ketazine isomers are reported. At low temperature addition is clean and does not involve radical chains, but at room temperature there is solvent dependent competition from ionic substitution of hindered ketazines and, in the light, from radical-induced decomposition of a-arylazoalkanes. Single crystal X-ray diffraction establishes the chlorine-nitrogen eclipsed conformation for meso-1,1 '-dichlofo-1,l '-diphenyl-1,l '-azopropane in the solid state with C-N and N=N bond distances of 1.46 and 1.24 j= 0.02 A, respectively. Thermolysis of this azo compound and of its dl diastereomer gives cage coupling with ~1 0 % stereospecificity.

temperature. The reaction solution was allowed to stand for 1 hr and excess chlorine and solvent were removed under vacuum. The crystalline product, 3,3-dimethyl-l,l-dichloro-2-butanone azine (mp 56°, from hexane at -70°), was obtained in almost quantitative yield: nmr 3.54 (singlet, 2 H), 8.64 (singlet, 18 H).

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A series of α,α′‐dichloro (α DClA), α,α′‐dialkoyloxy‐ (αDAlA) and α,α′‐dibenzoxy‐azoalkanes (αDBeA) without α‐aryl substituents was found to undergo meso ⇄ dl photointerconversion upon direct irradiation through Pyrex in the presence of oxygen in a number of solvents. Furthermore, irradiation of α,α′‐dipropionoxy‐azoalkanes in benzene in the presence of excess acetic acid leads to substitution of the propionoxy groups by acetoxy groups in addition to meso ⇄ dl photointerconversion. Similar irradiation in the presence of CH3CO2D does not lead to deuterium substitution of the β‐hydrogens. The presence of benzenethiol radical scavenger does not affect the course of these photoreactions. Photosolvolysis schemes involving heterolysis (in the case of αDAlA and αDBeA) or an unstable intermediate (in the case of αDClA) are proposed.