Oxirene Wolff rearrangement

The intermediacy of a ketocarbene species 4 is generally accepted for the thermal or photochemical Wolff rearrangement oxirenes 8 that are in equilibrium with ketocarbenes, have been identified as intermediates ... 

Zeller, K.-P. Blocher, A. Haiss, P. Oxirene participation in the Photochemical Wolff Rearrangement Mlnl-Revlewx in Organic Chemistry 2004,1, 291-308. (Review). 

When the Wolff rearrangement is carried out photochemically, the mechanism is basically the same,162 but another pathway can intervene. Some of the ketocarbene originally formed can undergo a carbene-carbene rearrangement, through an oxirene intermediate.168 This was shown by l4C labeling experiments, where diazo ketones labeled in the carbonyl group... 

Widman-Stoermer synthesis, 3, 43 Wild-fire toxin, 7, 249 Willardiine, synthesis, 3, 146 Willgerodt reaction thiophene synthesis by, 4, 883 Williamson reaction oxetane synthesis by, 7, 390-391 Withasomnine occurrence, 5, 302 Wittig reaction crown ethers and, 7, 759 Wittig-Homer reactions crown ethers and, 7, 759 Wolff rearrangement oxirenes in, 7, 120, 126... 

Hopkinson in 1973175 investigated the Wolff rearrangement of diazo-ketones and a-diazo-esters to form ketens. In particular, an MBS was used to investigate the equilibrium [equation (11)]11 between the parent oxiren (7) and the isomer formyl-... 

The antiaromatic oxirenes 11 are extremely elusive but their potential involvement in photochemical Wolff rearrangements by equilibration with the -oxocarbenes 12 has generated both theoretical and experimental interest and the subject has been reviewed <2004MR0291>. Experimental evidence for participation of oxirenes <2004MR0291> is supported by DFT calculations that suggest that oxirene corresponds to an energy minimum <2003JMT(629)263, CHEC-III(1.03.7)215>. 

Background information on the chemistry of oxirenes is presented in Chapter 1.03, and this area has been reviewed by Zeller <2002SOS(9)19>. The potential antiaromatic character of oxirenes, the strain of the unsaturated three-membered ring, and the possible involvement in important reactions (e.g., oxidation of alkynes, Wolff rearrangement)... 

Oxirenes arising out of cycloalkyne oxidations have been implemented in several transformations (Scheme 61), ultimately resulting in bicyclic ketones, a-dicarbonyls, 0 ,/3-unsaturated ketones, and ring-contracted products via Wolff rearrangement. 

Csizmadia, I. G., Gunning, H. E., Gosavi, R. K., Strausz, O. P. Mechanism of the Wolff rearrangement. V. Semiempirical molecular orbital calculations on a-diazo ketones, oxirenes, and related reaction intermediates. J. Am. Chem. Soc. 1973, 95, 133-137. 

---