Cyclic diazo ketones

Ring contraction of cyclic diazo ketones (Wolff)... 

The photolysis of cyclic diazo ketones in hydroxylic solvents leads to ring contracted carboxylic acid derivatives via this ketocarbene -> ketene rearrangement. Examples of such reactions are given in (2.24)239) and (2.25) 240). In this last example a photoequilibrium between the diazo ketone and its valence isomer, a diazirine, has been observed, both products then eliminating nitrogen to afford the cyclobutane carboxylic acid. 

In five-membered cyclic diazo ketones containing a bivalent sulfur atom, intramolecular ylide formation with subsequent ring contraction becomes... 

Rearrangement of the carbenes generated by photoelimination of nitrogen from cyclic diazo-ketones is frequently accompanied by ring-contraction. This process has found extensive use in synthesis recent examples include the synthesis of the [7]paracyclophane ring system,6 4,8-dihydrodibenzo[cRing-contraction was not observed on irradiation of the unstable... 

The mesomeric structure 9.35a is related to cyclic diazo ketones based on this structure, 1,2-benzoquinone diazide may be called 2-diazocyclohexa-3,5-dien-l-one... 

Scaiano et al. (1989) characterized the parent benzoquinone oxide, various derivatives thereof being obtained from the corresponding cyclic diazo ketones as well as from 9-diazofluorene, and from diazodiphenylmethane by laser flash photolysis at room temperature. The parent benzoquinone oxide has an absorption maximum at 410 nm. The rate constants of 2-diazo-l,2-benzoquinone and of the carbene of this diazo compound with singlet oxygen were found to be 1.0 x 10 m s and... 

---