Photolysis small ring compounds

Oxiranecarboxylic acids 41 (glycidic acids) can be converted into a,P epoxy diazomethyl ketones 42 via mixed anhydrides. It was found that photolysis of these compounds in the presence of alcohols gave yhyunsaturated esters 44. It is thought that nucleophilic attack of the alcohol on the ketene 43 results in epoxide ring opening. The E olefin isomer is predominately formed, although small quantities of Z esters are also isolated (< 10%). Conveniently non-racemic, chiral substrates are readily prepared via Sharpless asymmetric epoxidation of allylic alcohol 39, followed by... 

The Balz-Schiemann reaction has been used for the preparation of the 4-iluoro-derivatives of pyridine and 2,5-, 2,6-, and 3,5-lutidine it has also been used to obtain 5-fluoronicotinic acid, required for conversion into the corresponding pyridylmethanol via LiAlH reduction of the ethyl ester. The introduction of F into fluoroaromatic compounds has been achieved via isotopic exchange in diazonium tetrafluoroborates. U.v. irradiation of aqueous solutions of the appropriate diazonium tetrafluoroborates has been used to procure the first ring-fluorinated imidazoks, e.g. photolysis of the diazonium solution obtained by adding sodium nitrite to 2-amino-imidazole in aqueous fluoroboric acid provides 2-fluoroimidazole contaminated with only a small amount of 2-azidoimidazole, the sole product of thermal decomposition of imidazole-2-diazonium tetrafluoroborate. 

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