Diazo compounds photoreactions

Of the following amine-reactive and photoreactive crosslinkers, the overwhelming majority use an aryl azide group as the photosensitive functional group. Only a few use alternative photoreactive chemistries, particularly perfluorinated aryl azide, benzophenone, or diazo compounds. For general background information on photoreactive crosslinkers, see Das and Fox (1979), Kiehm and Ji (1977), Vanin and Ji (1981), and Brunner (1993). 

Scheme 7) and the reaction was monitored by IR spectroscopy, no significant amount of 33 could be detected [106], Instead, at the initial stage of the irradiation, an intermediate diazo compound was observed, which was assigned the structure 33-D. Further irradiation gave rise to a compound, which was identified with the help of calculations as substituted cyclopropene Z-36 (Scheme 7). Although it is possible that 36 is formed directly from 33-D, it is more likely that 33 is an intermediate of the reaction, as the ESR data imply. ESR spectroscopy is generally more sensitive than IR, and the failure of the latter to detect 33 is likely due to its inherently weak-intensity vibrational absorptions (as indicated by calculations) and/or its high photoreactivity.

This chapter describes photoreactions of nitrogen containing chromophores which are different from the principal reactions of electronically excited carbonyl compounds. Five groups of substrates were included cyclic and acyclic imines, nitriles, amine oxides, azo and diazo compounds, and enamides. 

Due to the complication of alternate pathways involved in the photochemistry of diazo compounds or diazirines, new strategies for carbene generation from non-nitrogenous precursors have been studied. Phenyliodonium ylides" (27) andmethyl-8-chloro-3a,7a-methanoindan-8-carboxylates" (28) are alternative precursors to dicarboethoxycarbene and carbomethoxychlorocarbene, respectively. Photoreactions from these precursors presumably will not be plagued by the excited-state chemistry observed for the diazo compounds and diazirines. 

The most important photoreactions of diazirines are the generation of carbenes and the valence isomerization to linear diazo compounds (Scheme 1). At first glance, these appear to be straightforward processes but under closer scrutiny, several experimental observations introduce complications. 

The photoreactions of bis-diazo ketones have also been examined. Irradiation of l,3-bis(diazo)-2-indanone (52) in an argon matrix at 10 K gave, not unexpectedly, the diazo ketone (53) this was converted on further irradiation into highly strained compounds to which the carbonyl structures (54) and (55) were provisionally assigned. l,2,3-Butatriene-l,4-dione, C4O2, is formed, also in an argon matrix, on photodecomposition of either of the bis(diazo)triketones (56) or (57). ... 

Three major classes of photoreactive compounds have been used to label specific sites of proteins nitrenes, carbenes, and free radicals. Carbenes, generated by photolysis of diazo derivatives, are highly reactive and relatively nonselective in their target sites. Nitrenes, formed by photoactivation of azido derivatives, are less reactive than carbenes and more electrophilic, exhibiting a preference... 

Table I summarizes the quantum yields for the photoreaction of diazo-containing model compounds and those for the benzophenone-oontaining models,...

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