Carbenes, nitrogen extrusion diazirines

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. 

Diazirine, fluoromethoxy-nitrogen extrusion, 7, 224 Diazirine, methylvinyl-rearrangement, 7, 221 Diazirines addition reactions to Grignard compounds, 7, 2 0 as carbene precursors, 7, 236 IR spectra, 7, 203 microwave spectrum, 7, 199 molecular spectra, 7, 202-204 nitrogen extrusion, 7, 223 NMR, 7, 202 photoconversion to diazoalkanes, 7, 234 photoisomerization, 7, 221 photolysis, 7, 225-227 quantum chemical investigations, 7, 197 reactions... 

Photolysis of dialkyl- and alkyl-diazirines has been broadly investigated since the products formed gave evidence of shortlived intermediates possessing excess vibrational energy. As shown in Scheme 1 diazirines (3) were photoactivated to (235) by irradiation with a medium pressure mercury lamp with quantum yields smaller than one this means reversibly. Nitrogen extrusion yielded carbenes (236). These rearranged to the primary products, alkenes and... 

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... 

The remaining proposed intermediates involve rearrangement fi om the excited diazirine. This type of explanation was first put forward by Frey and then more recently by Platz and co-workers. - - - In this mechanism, an intermediate is formed from the excited diazirine that leads directly to the rearrangement products (Scheme 5). This second intermediate is not defined in the kinetic scheme, but it has been proposed to be an excited carbene, a biradical, a diazo compound, or the excited diazirine itself AH of these proposed intermediates are thought to allow for concomitant extrusion of nitrogen and rearrangement... 

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