Thermal extrusion of nitrogen from diazirines

Diazirines tend to decompose, in some cases without obvious cause. Gaseous methyl-diazirine exploded at normal temperature and liquid a-hydroxyethylmethyldiazirine exploded on taking it from a dry ice bath 67CB2093). Phenylchlorodiazirine is reported to be more shock sensitive than nitroglycerol 79AHC(24)63). 

First order decomposition was established for dimethyldiazirine (215) and ethylmethyl-diazirine (216). The activation energy is 139 kJ moF for (215) the half life at 100 °C is 97 h. On decomposition of (216) the products formed and their respective yields are as indicated. The products correspond qualitatively and quantitatively with the results of thermal decomposition of 2-diazobutane formed in situ in aprotic solvents. Analogous comparisons of decomposition products of diethyldiazirine, isopropylmethyldiazirine, n-butyl- and t-butyl-diazirine agree equally well 66TL1733). 

Diazirines are in most cases more easily available than linear diazo compounds. Moreover, their decomposition via true carbenes is free of side reactions, whereas linear diazo compounds in presence of H-donors may react by a cationic pathway. Only where reactions of linear diazo compounds are optimized for carbene formation do they give the same products as do decomposing diazirines. 

Thermal decomposition of alkyldiazirines proceeds through the lowest singlet state of the carbene 79JA5082). 

The stabilization reactions of alkylcarbenes were used preparatively in some cases. The diazirine derived from adamantanone gave the dehydroadamantane (2l7) thermally in 96% yield 73ZOR430). Alkene formation was reported for a steroid with its C-3 atom part of a diazirine ring. At 140 °C a A-2-unsaturated steroid was formed 65JA2665). 

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Extrusion of nitrogen from arylchlorodiazirines formally gives a carbene. In the presence of an olefin, a sonochemical cyclopropanation occurs smoothly under neutral conditions (Eq. 6). The authors state that the procedure is "extraordinarily simple" a diazirine and an olefin are sonicated in a bath in hexane at 40 C, a temperature at which the compounds are thermally stable.66 The reaction occurs in yields equivalent to the photochemical process, but with much greater ease. Good yields are obtained from allyl bromide, 2,3-dimethyl-2-butene, or diethyl... 

Photolysis of dlazirines to nitrogen and carbenes is a general reaction and plays a greater role in carbene chemistry than photolysis of linear diazo compounds. Whereas the latter are often obtained only under the conditions of their thermal decomposition from suitable precursors, diazirines are obtainable in a pure state in most cases. Photolysis has the further advantage to permit nitrogen extrusion at atmospheric pressure, even with low-boiling materials. 

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