Abstract
The photochemical oxetane formation reactions, i.e. the Paternò-Büchi (PB) reactions, of tetrahydrobenzofuranols 1a with benzophenone was investigated to examine the hydroxy-group directivity on the regio- and stereoselectivity. The selectivities were found to be largely dependent upon the concentration of the allylic alcohols and the reaction temperature. The temperature-dependent change of the regioselectivity at high-concentration of the allylic alcohol was similar to that of the hydroxy-protected methyl ether 1b of the alcohol. Thus, the concentration effect on the regioselectivity can be explained by the PB reaction of the hydrogen-bonded aggregates, which mimic the reaction phenomena of the hydroxy-protected methyl ether. The hydroxy-directed cis-selectivity in the oxetane formation 3a at low concentration of alcohol 1a was found to be larger than that of the higher-concentration of the substrate. The cis-selectivity in the higher-substituted oxetane was found to be higher than that in the lower-substituted oxetane.
