9a-Phenyl-2,3,3a,3b,9a,9b-hexahydro-4H-furo[3‘,2’:3,4]cyclobuta- [1,2-b]chromen-4-one: A Flavone-Based [2 + 2]-Photocycloadduct

The intermolecular [2 + 2]-photocycloaddition of the parent flavone molecule (4) as triplet energy-accepting species and electron-rich alkene 2, 3-dihydrofuran (5) was performed by visible-light-mediated triplet-sensitization with an iridium-based organometallic sensitizer. reaction proceeds high diastereo- regioselectivity (>98:2 for regiochemical orientation 95% d.s.). In contrast to numerous other ene/enone combinations that are described in literature were also us, between 4 5 almost solely afforded cis-syn-cis cyclobutane 6, whereas analogous conjugated six- five-membered cycloalkenones preferentially react cis-anti-cis cyclobutanes or a mixture both diastereoisomers (e.g., cyclohexanone-derived example 9).