Matrix photolysis, Wolff rearrangement

Figure 18. Diazonaphthoquinone-novolac resist. The novolac (Novolak) matrix resin is prepared by acid catalyzed copolymerization of cresol and formaldehyde. The base insoluble sensitizer, a diazohaphthoquinone, undergoes photolysis to produce a carbene which then undergoes Wolff rearrangement to form a ketene. The ketene adds water which is present in, the film, to form a base soluble, indenecarboxylic acid photoproduct.

Scheme 8-34 also contains the formation of 2,3-bis(trifluoromethyl)oxirene (8.64), which was found by the group of Strausz (Torres et al., 1983) in the photolysis of l,l,l,4,4,4-hexafluoro-3-diazobutan-2-one (8.58, R = R = CF3) in an Ar matrix. Both the primarily formed ketocarbene and the oxirene could be observed directly. This is an important result in the context of the mechanism(s) of the Wolff rearrangement. 

Thermolysis of N,N-dialkyldiazoacetamides in matrices results in formation of ketenes by Wolff rearrangement, as well as competitive formation of C—H insertion products, with ketenes favored for cyclic precursors. Matrix photolysis in argon of 65 forms an unobserved carbene, which leads mainly to the P-lactam 66 and small amounts of the ketene 67 as identified by IR spectroscopy (Eqn (4.34)). Photolysis of 65 in a CO matrix gives capture of the carbene by CO forming ketene rotational isomers syn-68 and anti-68, similarly identified by IR spectroscopy (Eqn (4.35)), while N,N-dimethyl and N,N-diethyl diazoamides form insertion products. ... 

Flash vacuum thermolysis with Ar-matrix isolation or matrix photolysis of 2-phenylbenzo-l,3-dioxan-4-one as well as other precursors gave the ketene 6-carbonylcyclohexa-2,4-dienone 112, as detected by the IR absorption at 2134 cm Flash vacuum thermolysis above 600 °C or matrix photolysis resulted in formation of the fulvenone 114, proposed to arise by decarbonylation of 112 and Wolff rearrangement. The use of C-labeled precursor gave 114 with scrambling revealing the intermediacy of bisketene intermediates 113 in the reaction (Scheme 4.21). 

An intriguing alternative entry into this type of cyclohexadienylidene chemistry has been provided by matrix isolation studies of the photolysis of a-diazo-2-ethynylacetophenone (46) (Scheme 8). Irradiation of 46 at 403 nm in solid argon gave the ketene 48 as the major product but also the carbene 50 as a minor product. Carbene 50 was reversibly converted into 49 on irradiation at A > 475 nm. Thus, the Wolff rearrangement of ketocarbene 47, which was not observed directly, competed with the intramolecular addition of the carbene center to the triple bond. 

---