Diazirines photoisomerization

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... 

In all cases the formation of carbenes was accompanied by partial photoisomerization of the precursor diazirines [53] into the corresponding diazo compounds [55] which possess a higher photochemical stability than the diazirines. 

An additional complication is the known (and theoretically expected53) photoisomerization of diazirines to their open diazo isomers. Thus, ben-zylchlorodiazirine 9a photoisomerizes with low efficiency to its diazo isomer 38,23,25 and adamantyldiazirine 41 has long been known to photoisomerize to diazoadamantane, 42.54... 

The photoisomerization of diazirines to diazomethanes has been observed in other liquid-phase photolyses and will be discussed later, but its occmTence in the case of diazirine itself presents quite unique problems. On the basis of the appearance potentials of diazomethane and diazirine, the heats of formation of these compounds have been esti-... 

Recently, Moore and Pimentel have photolyzed diazirine isolated in a solid nitrogen matrix. They found that the photolysis did produce diazomethane. In order to decide whether the diazomethane arose by a photoisomerization reaction or by the reaction of methylene with the nitrogen of the matrix, experiments were carried out in a nitrogen matrix enriched in N. On the basis of these experiments they conclude that the photolysis of the diazirine produces methylene and nitrogen, and that the diazomethane arises from the reaction of the methylene with the matrix and not by photoisomerization. Photolysis of diazomethane does not... 

Besides giving volatile products, the photolysis of methyldiazirine results in the formation of relatively small amounts of a nitrogen-containing oil. This is particularly noticeable with fairly high pressures of the diazirine. It is quite possible that a photoisomerization reaction does occur and that the oil is an azine formed from the diazoethane. 

No gas-phase photolyses have yet been reported with these diazirines. Pyrolysis of the cycloheptyldiazirine yields a mixture of hydrocarbons, and the relative yields of these products are very close to the values obtained by the pyrolysis of diazocycloheptane. Photolysis of these diazirines in the liquid phase yields a hydrocarbon mixture similar to that obtained by pyrolysis, but with small increases in some of the minor products. The photoisomerization reaction leading to the normal diazo compound is readily observed for these two diazirines since the diazo compounds formed are relatively stable. In both cases, during photolysis of the (colorless) diazirines, a deep orange solution develops, and ultraviolet and infrared absorption spectra indicate the formation of the diazo compounds. Photolysis of cycloheptyldiazirine in the presence of acetic acid yields 47% of cycloheptylacetate, which indicates that the photoisomerization reaction under these conditions is a major primary reaction. Under the same conditions cyclooctyldiazirine yields 28% of the corresponding acetate. 

The photodecompositions of 3,3-bis(l,l-difluorohexyl)diazirine and 3-(l,l-difluoro-octyl)-3//-diazirine have been examined. On irradiation in cyclohexane or methanol, competing photoisomerization to linear diazo-compounds and photofragmentation via carbene intermediates to cyclopropanes and alkenes has been observed and is illustrated for 3,3-bis(l,l-difluorohexyl)diazirine (6) in Scheme 1. The majority of investigations of nitrogen photoelimination in cyclic... 

Diazirines can be formed by photoisomerization of diazo compounds. Irradiation of perfluoro-3-diazo-2-butanone (272) at wavelengths >320 nm either at RT in carbon tetrachloride solution or at 77K in an argon matrix yielded perfluoroacetyhnethyl-diazirine (273), together with products resulting from decomposition of the diazo compound to a carbene. ... 

Fluorodiazirines may photoisomerize to diazo compounds, as illustrated with diazirine 278. Photolysis of 278 at 334 nm in a nitrogen matrix at 8K primarily... 

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