RESUMO
A new reaction system was devised for decarboxylative radical coupling reactions by heterogeneous semiconductor photoredox catalysis. When an α-alkoxy carboxylic acid and Pt-doped TiO2 in EtOAc were irradiated with a violet light-emitting diode at room temperature, the photogenerated electron hole of TiO2 oxidatively induced the ejection of CO2 via the formation of a carboxyl radical to produce the corresponding α-alkoxy radical. C(sp3)-C(sp3) bond formation between the radicals led to dimers with reductive conversion of protons to H2 by the photogenerated electron. Alternatively, in the presence of an electron-deficient olefin, an intermolecular radical addition reaction occurred, resulting in the formation of a 1,4-adduct via single-electron reduction and subsequent protonation. These operationally simple and mild transformations are amenable to the one-step assembly of densely oxygenated linear and branched carbon chains.
RESUMO
A mild radical-based coupling method was devised for intermolecular installation of quaternary carbons. Treatment of α,α-dialkoxyacyl telluride with Et3B/O2 at room temperature promoted the formation of a highly reactive α,α-dialkoxy carbon radical, which coupled with 2-cyano-3-methyl-2-cyclohexen-1-one to forge the sterically cumbersome bond between the tetrasubstituted and quaternary carbon centers. The present convergent strategy was successfully applied to a seven-step total synthesis of 5-epi-eudesm-4(15)-ene-1ß,6ß-diol (1).
