Furans, acylation from carbonyl compounds

The double bonds in certain heterocyclic compounds, such as furans, Af-acylpyrroles and A-acylindoles are also susceptible to photoaddition of carbonyl compounds to form oxetanes (equation 106) (77JHC1777). A wide range of carbonyl compounds can be used, including quinones, a-diketones, acyl cyanides, perfluorinated aldehydes and ketones and esters. A remarkable case of asymmetric induction in oxetane formation has been reported from optically active menthyl phenylglyoxylate and 2,3-dimethyl-2-butene the oxetane product obtained after hydrolysis of the ester group had an optical purity of 53% (79AG(E)868). 

The carbanion derived from diethyl l-(trimethylsiloxy)-l-phenylmethanephosphonate 291 served as an acyl anion equivalent. Its reaction with carbonyl compounds afforded the silylated benzoin derivatives 292 (equation 182)443. This reaction was useful for the synthesis of 2-phenylbenzo[h]furans without laborious isolation of the intermediate benzoin. 

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