Oxirenes from diazoketones

Bachmann, C., N Guessan, T. Y., Debu, F., Monnier, M., Pourcin, J., Aycard, J. P., Bodot, H. Oxirenes and ketocarbenes from a-diazoketone photolysis experiments in rare gas matrices. Relative stabilities and isomerization barriers from MNDOC-BWEN calculations. 

Evidence for the involvement of oxirenes in the photolysis and thermolysis of a-carbonyldiazo compounds (54, 56) was obtained from the fate of isotopic labels, as indicated in Scheme 9. Nevertheless, the goal of detecting an oxirene directly proved elusive. The problem was dealt with in a study of the matrix photolysis of diazoketones, from which it was concluded that oxirenes were, at best, intermediates lying in very shallow energy wells. ... 

A persistent question concerning the Wolff rearrangement is whether or not an alternate intermediate, such as an excited state of the diazo precursor " or an oxirene, is involved. Carbonylcarbenes have been detected in low-temperature matrices by electron spin resonance (ESR) and FTIR " spectroscopies. Evidence for the participation of oxirenes - comes from experiments " in which diazoketones labeled at the carbonyl carbon rearrange to form ketenes that possess a label at both carbon atoms (Scheme 3). Similar results were obtained in studies of unsymmetricaUy substituted diazoketones. "- The direct observation of oxirene intermediates, however, has been more elusive. Initial reports of oxirene detection - were later called into question. - Bodot and co-workers have advanced evidence for the existence of dimethyloxirene and its deuterated analogue by low-temperature FTIR methods. - ... 

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