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Entropy‐Driven 1,2‐Type Friedel–Crafts Reaction of Phenols with N ‐ tert ‐Butoxycarbonyl Aldimines
Author(s) -
Kato Masaru,
Hirao Shogo,
Nakano Katsuhiro,
Sato Makoto,
Yamanaka Masahiro,
Sohtome Yoshihiro,
Nagasawa Kazuo
Publication year - 2015
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201503280
Subject(s) - friedel–crafts reaction , aldimine , phenols , entropy (arrow of time) , chemistry , organic chemistry , mathematics , medicinal chemistry , catalysis , thermodynamics , physics
Differential activation entropy (ΔΔ S ≠ ) is revisited as an important parameter that governs catalytic stereodiscrimination processes by investigating temperature effects on the basis of the Eyring theory. However, correlating the ΔΔ S ≠ effect and the molecular structure of the asymmetric catalyst is still an underdeveloped area. Efforts to identify factors (including catalyst structure, reactants, and reaction conditions) that contribute to the attainment of large ΔΔ S ≠ values for enantioselective 1,2‐type Friedel‐Crafts reactions of phenols with N ‐ tert ‐butoxycarbonyl aldimines catalyzed by conformationally flexible guanidine bisthioureas are described. First, we uncover an interesting property of the ΔΔ S ≠ ‐driven stereodiscrimination process: maximum enantioselectivity is obtained at around room temperature. Second, a plausible transition‐state model accounting for the characteristic ΔΔ S ≠ effect and the structural dynamics of the conformationally flexible organocatalyst in the stereodiscrimination process is discussed.