Stereochemistry in control of photochemical reactivity: 2,6-Diaryl-4H-spiro[cyclohexane-1,2′-indene]-1′,3′,4-triones

Photochemical reaction of trans-2,6-diaryl-4H-spiro[cyclohexane-1,2′-indene]-1′,3′,4-triones gives rise to the formation of the ylidenephthalide derivatives as previously observed for 2,2-disubstituted 1,3-indandiones. In contrast, the respective cis-isomers afford different products originating from the unprecedented reversible cyclohexanone cycle breaking (photo-induced retro-Michael reaction). The difference between the reaction pathways does not depend on the irradiation wavelengths or the light source power and is observed both in solution and solid state.