The irradiation of chromone-2-carboxylic esters resulted in the stereo- and regioselective formation of C(2) chiral anti-HH dimers from the triplet excited state. On the contrary, photolysis in the solid-state gave anti-HT dimers exclusively controlled by molecular arrangement in the crystal.

Irradiation of the simple chromone (benzo-gamma-pyrone) resulted in the formation of two types of dimers, anti-HT (head-to-tail) and trans-fused HT isomers, whose structures were established by X-ray structural analysis.

Benzopyran derivatives R 0350Photodimerization of Chromone. -Irradiation of chromone affords the two chromone dimers (II) and (III), whose structures are established by single crystal X-ray diffraction analysis. -(SAKAMOTO*, M.; KANEHIRO, M.; MINO, T.; FUJITA, T.; Chem.