TY - JOUR
T1 - Mechanistic insights into entropy-driven 1,2-type Friedel-Crafts reaction with conformationally flexible guanidine-bisthiourea bifunctional organocatalysts
AU - Nakano, Katsuhiro
AU - Orihara, Tatsuya
AU - Kawaguchi, Masaki
AU - Hosoya, Keisuke
AU - Hirao, Shogo
AU - Tsutsumi, Ryosuke
AU - Yamanaka, Masahiro
AU - Odagi, Minami
AU - Nagasawa, Kazuo
N1 - Funding Information:
This research was funded by Grants-in-Aid for Scientific Research on Innovative Areas “Middle Molecular Strategy” ( 18H04387 to K.N.), “ Hybrid Catalysis ” ( 20H04828 to M.Y.), Grants-in-Aid for Scientific Research (B) (17H03052 to K.N.), and the A3-foresight program from the Japan Society for the Promotion of Science ( JSPS ). T. O thanks DAICEL Co. Ltd. for the financial support. K.H. was supported by Grants-in-Aid for a JSPS fellowship ( 19J13325 ). M.O. is grateful for JSPS KAKENHI Grant Number 20K05488 . This work was inspired by the international and interdisciplinary environment of the JSPS Asian CORE Program of ACBI (Asian Chemical Biology Initiative) and the A3 program.
Publisher Copyright:
© 2021 Elsevier Ltd
PY - 2021/7/16
Y1 - 2021/7/16
N2 - In some asymmetric catalytic reactions, the enantio-discrimination step is dominated by the change in entropy, in contrast to the usual enthalpy-driven process, but the origin of this entropy-dependent behavior is unclear. Here, we first conducted Eyring analysis to confirm the entropy-driven character of our previously reported 1,2-type Friedel-Crafts (FC) reaction of sesamol with imine, catalyzed by conformationally flexible guanidine-bisthiourea bifunctional organocatalyst, and then we carried out computational studies to compare the transition states leading to the two enantiomers. We found no significant temperature dependence of ΔH or -TΔS for TS-R, the transition state leading to the R enantiomer. In TS-S, on the other hand, -TΔS was increased at higher temperature, although ΔH was unchanged. Furthermore, the benzyl groups of the catalyst increase the contribution of the enthalpy term to the enantioselectivity, albeit with retention of the entropy-driven behavior arising from the conformationally flexible catalyst structure.
AB - In some asymmetric catalytic reactions, the enantio-discrimination step is dominated by the change in entropy, in contrast to the usual enthalpy-driven process, but the origin of this entropy-dependent behavior is unclear. Here, we first conducted Eyring analysis to confirm the entropy-driven character of our previously reported 1,2-type Friedel-Crafts (FC) reaction of sesamol with imine, catalyzed by conformationally flexible guanidine-bisthiourea bifunctional organocatalyst, and then we carried out computational studies to compare the transition states leading to the two enantiomers. We found no significant temperature dependence of ΔH or -TΔS for TS-R, the transition state leading to the R enantiomer. In TS-S, on the other hand, -TΔS was increased at higher temperature, although ΔH was unchanged. Furthermore, the benzyl groups of the catalyst increase the contribution of the enthalpy term to the enantioselectivity, albeit with retention of the entropy-driven behavior arising from the conformationally flexible catalyst structure.
KW - DFT calculation
KW - Entropy
KW - Friedel-crafts reaction
KW - Guanidine
KW - Organocatalyst
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U2 - 10.1016/j.tet.2021.132281
DO - 10.1016/j.tet.2021.132281
M3 - Article
AN - SCOPUS:85108545628
VL - 92
JO - Tetrahedron
JF - Tetrahedron
SN - 0040-4020
M1 - 132281
ER -