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

Abstract

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

Photosensitized [2 + 2]-Cycloaddition of Complex Acceptor–Donor Combinations: A Regio/Diastereoselectivity Study

“…4.6:1) and dimer formation (24%) remained unchanged. Another example was recently shown for flavone that exhibited different reactivities and selectivities than the cyclohexenone analog …”

From energy to electron transfer photocatalysis (PenT → PET): oxidative cyclobutane cleavage alters the product composition

“…S1-S7, ESI †) using cyclic voltammetry. 8,19 All oxidation and reduction processes were irreversible due to rapid follow-up reactions (see our mechanistic considerations below). Since the peak potentials of irreversible peaks are depending on the solvent, scan rate and concentration, we chose the same conditions for all samples and determined offset potentials as shown in Fig.…”