Decomposition of diazirines

Photolytic decomposition of diazirine 9a in methylcyclohexane led to substantial C-H insertion of PI1CH2CCI into the solvent, although azine was a minor product. At 25°C, there were 74% of 1,2-H shift products and 14% of C-H insertion. Insertion increased to 44% at —75°C. Here too, a curved Arrhenius correlation reflected the competition of two classical reactions, not the incursion of QMT.71... 

Photolytic decomposition of diazirine (25) in the presence of ethyl acetate led to the formation of the ester derived carbonyl ylide (26). Trapping of the ylide with diethyl fumarate led to the formation of the dihydrofuran 28, generated by dehydrochlorination of the initial cycloadduct 27. It occurred with a rate constant... 

The reactivity of palladium and copper cluster models toward diazirine has been compared using the LCGTO-MCP-LSD method <1996SUS11> such calculations were performed to give an insight into the differential bond scission experimentally observed in the thermal decomposition of diazirine on palladium and copper surfaces. Stronger chemisorption was evident with palladium and furthermore, partial diazirine lowest-unoccupied molecular orbital (LUMO) occupation only occurred for the copper cluster model systems. The calculated N-N bond order was significantly decreased in the copper complexes of excited state diazirines, whereas palladium complexes remained unperturbed. 

The thermal decompositions of diazirines appear to be homogeneous, uni-molecular processes " . Cyclic diazirines decompose with a slightly smaller activation energy (Table 14) due to ring strain. Product distributions presumably result from intramolecular rearrangement of carbene intermediates, and the fact that the product ratios differ from those obtained on photolysis supports the hypothesis that the carbenes generated photolytically contain considerable excess vibrational energy. 

Carbene formation. Decomposition of diazirine gives arylchlorocarbenes, which are intercepted by alkenes. 

Reversible electronic relaxation has been found in smaller molecules. In methylene (for which collision-induced intersystem crossing has been extensively studied for many years ) the reversible character of singlet-triplet transitions has been evidenced in a study of pressure effect on the CH2 radical prepared either in the singlet state (by photochemical decomposition of diazirine) or in the triplet state (by photofragmentation of... 

Carbenes can also be generated by decomposition of diazirines, though diazo compounds have been implicated in some of the decompositions, both thermaP and pho-tolytic. There is, however, at least one case of the reverse of this photolysis of 9-diazo-1,8-diazafluorene (202) is believed to proceed via the diazirine (203). 

A kinetic study of the thermal decomposition of 3-chloro-3-methoxydiazirine showed that the reaction was unimolecular both in the gas phase and in solu-tion. A direct two-bond cleavage to carbene was suggested for this reaction, without the formation of a diazo-compound. The authors suggest, however, that the decomposition of diazirine involves both pathways as competitive processes in the general case. 

Akasaka, Effect of substituents on the thermal decomposition of diazirines experimental and computational studies, J. Org. Chem., 2003, 68, 7471-7478. 

Table 10.1 Product distribution from the decomposition of diazirine 56...

Table 10.4 Product distribution resulting from the decomposition of diazirine 90...

The dissociative chemisrapdon of MeOH on a Pd(l 11) surface to give methyl groups was found to be coverage-dependent. Decomposition of diazirine on a Pd(110) surface proceeds by cleavage of C-N and N-N bonds.38l The oxidative addition of CH4 and C2H5 to Pd and Pt has been examined by theoretical methods.268.382.383 Various catalytically important Pd(0) and Pd(II) cmnplexes have been studied by ESCA photoelectron specoosct y. ... 

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