The Stereo- and Regio-specific Formation of 11-Oxatetracyclo2,4.03,7> undeca-5,9-dienes by the Substituent-directed Photocycloaddition of Furan to the Benzene Ring

Article abstract of DOI:10.1039/P19900000931

Furan undergoes specific 2,5-2',6'(meta)-photocycloaddition to benzonitrile, the toluonitriles, phenylacetylene, and 1-phenylpropyne. 2-Phenylpropene yields exclusively a <2_? + 2_?> cycloadduct with furan whereas both types of addition occur with styrene.In contrast, 1,4-2',5'(para)-photocycloaddition is the sole or principal reaction from 254 nm irradiation of isoprene, 2,3-dimethylbuta-1,3-diene, or 2,3-dimethoxybuta-1,3-diene with benzonitrile; only with the fixed cis-1,3-diene, 1,2-dimethylene cyclohexane, is the meta-cycloadduct formed in significant amounts.The control over the regio- and stereo-chemistries of the meta-cycloaddition is discussed in terms of substituent stabilization of the developing polarity in the electronically excited aromatic ring on approach of the addends and secondary orbital interactions.