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Linking Conformational Flexibility and Kinetics: Catalytic 1,4‐Type Friedel–Crafts Reactions of Phenols Utilizing 1,3‐Diamine‐Tethered Guanidine/Bisthiourea Organocatalysts
Author(s) -
Sohtome Yoshihiro,
Shin Bongki,
Horitsugi Natsuko,
Noguchi Keiichi,
Nagasawa Kazuo
Publication year - 2011
Publication title -
chemistry – an asian journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.18
H-Index - 106
eISSN - 1861-471X
pISSN - 1861-4728
DOI - 10.1002/asia.201100363
Subject(s) - guanidine , chemistry , enantioselective synthesis , thiourea , friedel–crafts reaction , diamine , catalysis , phenols , organocatalysis , organic chemistry , combinatorial chemistry
Herein, we present details of our conformationally flexible, 1,3‐diamine‐tethered guanidine/bisthiourea organocatalysts for chemo‐, regio‐, and enantioselective 1,4‐type Friedel–Crafts reactions of phenols. These organocatalysts show a unique stereo‐discrimination governed by the differential activation entropy (ΔΔ S ≠ ), rather than by the differential activation enthalpy (ΔΔ H ≠ ). Extensive kinetic analyses using Eyring plots for a series of guanidine/bisthiourea organocatalysts revealed the key structural motif in the catalysts associated with a large magnitude of differential activation entropy (ΔΔ S ≠ ). A plausible guanidine–thiourea cooperative mechanism for the enantioselective Friedel–Crafts reaction is proposed.