Photochemical cycloaddition of singlet and triplet diphenylvinylene carbonate with conjugated dienes

Detection of an Energy-Transfer Pathway in Cr-Photoredox Catalysis

“…13 Conversely, the energy-transfer process of triplet sensitization has been used to prepare cyclobutanes. 14 For example, the triplet excited state of 4-methoxychalcone (1, λ em = 480 nm, 2.58 eV) is quenched by isoprene (2), k q = 1.5 × 10 8 M −1 s −1 , to produce a VCB species. 15 Whereas photoredox catalysis often proceeds via electron transfer, excited-state energy transfer has been implicated in select examples.…”

“…Conversely, the energy-transfer process of triplet sensitization has been used to prepare cyclobutanes . For example, the triplet excited state of 4-methoxychalcone ( 1 , λ em = 480 nm, 2.58 eV) is quenched by isoprene ( 2 ), k q = 1.5 × 10 8 M –1 s –1 , to produce a VCB species .…”

Photoadditions of aromatic compounds

“…These systems also form singlet exciplexes, and Lewis and co-workers have utilized the reactions in mechanistic work. 38,200,202 For example, diphenylvinylene carbonate (120) adds to 1,3-dienes and to vinyl ethers to form cyclobutane adducts, the products being the same on direct and on sensitized (Michler's ketone) irradiation. 200,201 Typical products are those from cyclopentadiene and 2,5-dimethylhexadiene (121)(122)(123)(124).…”

“…The ratio 121:122 is 4:1 on direct irradiation and 1:9 on sensitized excitation. 200 When cis or trans dienes are used, e.g., piperylenes, the stereochemistry of the diene is retained in the direct (singlet) irradiation, which is not consistent with a biradical intermediate. However, limiting quantum yields for these additions are less than unity (0.5-0.8), and some intermediate capable of decaying to ground-state reactants is required.…”

“…However, limiting quantum yields for these additions are less than unity (0.5-0.8), and some intermediate capable of decaying to ground-state reactants is required. 200 The reactions can proceed via singlet or triplet states, and exciplex intermediates are apparently involved.…”