Entropy‐Driven 1, 2‐Type Friedel–Crafts Reaction of Phenols with N‐tert‐Butoxycarbonyl Aldimines. Issue 51 (6th November 2015)

• Record Type: Journal Article
• Authors: Kato, Masaru; Hirao, Shogo; Nakano, Katsuhiro; Sato, Makoto; Yamanaka, Masahiro; Sohtome, Yoshihiro; Nagasawa, Kazuo
• Is Part Of: Chemistry. Volume 21:Issue 51(2015)
• Page Start: 18606
• Page End: 18612
• Publication Date: 2015-11-06
• Subjects: entropy -- Friedel–Crafts reactions -- organocatalysis -- phenols -- transition states; Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201503280
• Languages: English
• ISSNs: 0947-6539

Abstract

Abstract: 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. Abstract : Tip the balance : The enantioselective 1, 2‐type Friedel–Crafts reaction of phenols with N ‐ tert ‐butoxycarbonyl aldimines catalyzed by conformationally flexible guanidine bisthioureas proceeded with a large differential activation entropy (see figure).