Kinetic isotope effects for the benzylic hydrogen atom abstraction reactions of the triplet states of several diarylcarbenes with toluene-toluene-d8 in fluid solution were determined by measuring the ratio of 1,2-diphenylethane to 1,2-diphenylethane-d7 produced in the reaction. Eight carbenes were studied: dibenzocycloheptadienylidene (DBC); 1-naphthylphenylcarbene (1-NPC), 4-biphenylphenlcarbene (BPC), 2-chlorodiphenylcarbene (C1DPC), 2-trifluoromethyldiphenylcarbene (FDPC), fluorenylidene (F1), anthronylidene (AN), and diphenylcarbene (DPC). For 1-NPC, C1DPC, and FDPC the differential kinetic isotope effects were much larger than predicted by complete loss of all zero point energy in the transition state, indicating that there is a contribution of quantum mechanical tunneling to the H(D) atom transfer process. For DPC, DBC, and PBC the differential kinetic isotope effects were barely consistent with a completely classical atom-transfer reaction. For F1 and AN the data were completely consistent with a purely classical atom-transfer process.
Enantioselective Diarylcarbene Insertion into Si–H Bonds Induced by Electronic Properties of the Carbenes
作者:Liang-Liang Yang、Declan Evans、Bin Xu、Wen-Tao Li、Mao-Lin Li、Shou-Fei Zhu、K. N. Houk、Qi-Lin Zhou
DOI:10.1021/jacs.0c04725
日期:2020.7.15
enantioselection usually depends on differences in steric interactions between prochiral substrates and a chiral catalyst. We have discovered a carbene Si-H insertion in which the enantioselectivity depends primarily on the electronic characteristics of the carbene substrate, and the log(er) values are linearly related to Hammett parameters. A new class of chiral tetraphosphate dirhodium catalysts was developed
<i>gem-</i>Difluoroolefination of Diazo Compounds with TMSCF<sub>3</sub> or TMSCF<sub>2</sub>Br: Transition-Metal-Free Cross-Coupling of Two Carbene Precursors
作者:Mingyou Hu、Chuanfa Ni、Lingchun Li、Yongxin Han、Jinbo Hu
DOI:10.1021/jacs.5b09888
日期:2015.11.18
fragment resulting from a diazocompound and a difluorocarbene fragment derived from Ruppert-Prakash reagent (TMSCF3) or TMSCF2Br, has been developed. This gem-difluoroolefination proceeds through the direct nucleophilic addition of diazocompounds to difluorocarbene followed by elimination of N2. Compared to previously reported Cu-catalyzed gem-difluoroolefination of diazocompounds with TMSCF3, which possesses
Visible light photocatalytic decarboxylative monofluoroalkenylation of α-amino acids with gem-difluoroalkenes
作者:Jingjing Li、Quentin Lefebvre、Haijun Yang、Yufen Zhao、Hua Fu
DOI:10.1039/c7cc05758j
日期:——
A novel, efficient and general visible-light photocatalytic decarboxylative monofluoroalkenylation of N-protected α-amino acids with gem-difluoroalkenes is reported, affording the corresponding α-amino monofluoroalkenes.
Silver-Catalyzed N–H Functionalization of Aryl/Aryl Diazoalkanes with Anilines
作者:Feifei He、Claire Empel、Rene M. Koenigs
DOI:10.1021/acs.orglett.1c02289
日期:2021.9.3
Herein, we report on the N–H functionalization reaction of primary and secondary anilines with diaryldiazoalkanes using simple AgPF6 as catalyst. We demonstrated broad applicability in the reaction of diaryldiazoalkanes with different anilines (31 examples, up to 97% yield). Furthermore, we propose a possible reaction mechanism for the N–H functionalization.
Proton or Carbene Transfer? On the Dark and Light Reaction of Diazoalkanes with Alcohols
作者:Claire Empel、Chao Pei、Feifei He、Sripati Jana、Rene M. Koenigs
DOI:10.1002/chem.202104397
日期:2022.3.10
O-H Functionalization: In this combined experimental and computational study, the reaction of diaryl diazoalkanes with alcohols is reported. In the ground state, a direct proton transfer governs reactivity with acidic HFIP. On the contrary, photoexcitation leads to formation of a triplet carbene intermediate that undergoes an alcohol-assisted intersystem crossing to a solvent-stabilized carbene that