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23.12.1.1.6.3 Variation 3: Monoarylketenes by Photochemical Wolff Rearrangement

DOI: 10.1055/sos-SD-023-00394

Tidwell, T. T.Science of Synthesis, (200623404.

Photolysis of 1-phenyl-2-diazoethanone or 2-diazo-1-(1-naphthyl)ethanone in hydrocarbon solvents gives phenylketene[‌25‌] and 1-naphthylketene,[‌23‌] respectively, as identified by their ketene IR bands near 2120cm1. Mesitylketene is generated by photochemical Wolff rearrangement of 2-diazo-1-mesitylethanone in aqueous solution and it is detected by its ultraviolet absorption, which is used to measure the rate of hydration to mesitylacetic acid.[‌60‌] Photolysis of 13C isotopically labeled 2-diazo-1-phenylethanone shows that the rearrangement is accompanied by oxygen migration via an oxirene intermediate.[‌61‌] When the photolysis is carried out in nucleophilic solvents these reactive ketenes are captured by the solvent. Thus arylketenes 54 are prepared in aqueous solution by photochemical Wolff rearrangement of 1-aryl-2-diazoethanones 53, and their rates of hydration to give arylacetic acids 55 are measured by the change in conductivity (Scheme 22).[‌62‌] Monoarylketenes are also generated by photochemical Wolff rearrangements in acetonitrile, and the kinetics of their reactions with amines are measured by time resolved measurements of the disappearance of their ketene IR absorptions.[‌63‌]

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References