5807-76-1Relevant articles and documents
Medium effects on the direct cis-trans photoisomerization of 1,4-diphenyl-1,3-butadiene in solution
Saltiel, Jack,Krishna, Talapragada R. S.,Laohhasurayotin, Kritapas,Ren, Yanjun,Phipps, Kathleen,Davis, Paul H.,Yee, W. Atom
, p. 2120 - 2129 (2011)
Quantum yields for the photoisomerization of trans,trans-1,4-diphenyl-1,3- butadiene (tt-DPB), determined in benzene, cyclohexane, methylcyclohexane, hexane, and perfluorohexane, confirm the low values reported earlier for benzene and cyclohexane and reveal even lower values in the last two solvents. In contrast to trans-stilbene (t-St), fluorescence and torsional relaxation leading to photoisomerization do not account exclusively for S1tt-DPB decay. Competing radiationless singlet excited-state decay pathways exist in tt-DPB, which do not lead to photoisomerization and may not involve large-amplitude torsional motions. Our results invalidate analyses of tt-DPB fluorescence quantum yields and lifetimes that assign all radiationless decay to the isomerization channel. Gas-phase chromatography analysis of tt-DPB photoisomerization in hexane shows the reaction to be concentration-independent and reveals, for the first time, a significant, two-bond photoisomerization pathway, βtt→tc = 0.092 and βtt→cc = 0.020. The dominant one-bond-twist (OBT) process is accompanied by a bicycle pedal (BP) process that accounts for almost 20% of tt-DPB photoisomerization. The OBT tt-DPB photoisomerization quantum yield is largest in benzene (Bz) and smallest in perfluorohexane (PFH). Contrary to expectations, reduction in medium friction in PFH is accompanied by a decrease in βtt→tc. The 11Bu/21Ag order and energy gap appear to control the contribution of torsional relaxation to radiationless decay. Lowering the 11Bu energy as in Bz favors photoisomerization. Reversal of the 11Bu/2 1Ag order in PFH is accompanied by short τf and small βf and βtt→tc values that suggest the presence of competing 21Ag → 1 1Ag relaxation paths that are unproductive with respect to photoisomerization. We conclude that the Birks extension to diphenylpolyenes of the Orlandi-Siebrand cis-trans photoisomerization mechanism is not valid. Photoisomerization appears to occur in the 1IBu state, and we argue that this applies to t-St as well.
Acetylene as a Dicarbene Equivalent for Gold(I) Catalysis: Total Synthesis of Waitziacuminone in One Step
Armengol-Relats, Helena,Echavarren, Antonio M.,Escofet, Imma,Korber, J. Nepomuk,Scharnagel, Dagmar,de Orbe, M. Elena
supporting information, p. 4888 - 4891 (2020/02/11)
The gold(I)-catalyzed reaction of acetylene gas with alkenes leads to (Z,Z)-1,4-disubstituted 1,3-butadienes and biscyclopropanes depending on the donor ligand on gold(I). Acetylene was generated in situ from calcium carbide and water in a user-friendly p
Carbon-carbon bond forming reactions via Pd-catalyzed detellurative homocoupling of diorganyl tellurides
Zhang, Shaozhong,Kolluru, Lalitha,Vedula, Souseelya K.,Whippie, Drew,Jin, Jin
supporting information, p. 3594 - 3597 (2017/08/23)
A simple and highly efficient method for the constructions of Csp-Csp, Csp2-Csp2 and Csp3-Csp3 bonds is reported. The symmetrical diaryl tellurides undergo detellurative homocouplings to afford symmetrical biaryl products. The reactions are carried out at ambient temperature using PdCl2 as a catalyst in the presence of Ag2O and Na2CO3. Similarly, the detellurative homocouplings of dibenzyl telluride and bis(phenylethynyl)telluride give bibenzyl and the conjugated diyne, respectively.
