Intramolecular [2+2] photocycloaddition of bichromophoric derivatives of 3,5-dihydroxybenzoic acid and 3,5-dihydroxybenzonitrile

The irradiation of 3-alkenyloxy-5-hydroxybenzoic acid derivatives 1a-d yiel ds highly functionalized alkyloxyenone derivatives when the reaction is car ried out in the presence of acid. A higher reactivity is observed for the c orresponding 3-alkenyloxy-5-hydroxybenzonitrile compounds 7a, b, which also react in neutral reaction media. In the first step of the reaction, a [2+2 ] photocy cloaddition occurs. The following steps, leading to stable final prod ucts, need acid catalysis in the case of the substrates 1a-d. The irra diation of the benzonitrile derivative 7b also furnishes the side product 9 , which results from a [2+3] photocycloaddition.