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Origin of the Superior Performance of (Thio)Squaramides over (Thio)Ureas in Organocatalysis
Author(s) -
Lu Tongxiang,
Wheeler Steven E.
Publication year - 2013
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.201302990
Subject(s) - squaramide , thio , chemistry , hydrogen bond , thiourea , organocatalysis , catalysis , context (archaeology) , anthracene , amide , combinatorial chemistry , molecule , organic chemistry , enantioselective synthesis , paleontology , biology
The Diels–Alder cycloaddition of anthracene and nitrostyrene catalyzed by the squaramide‐derived aminocatalysts ( Sq ) recently reported by Jørgensen and co‐workers ( Angew. Chem. 2012 , 124 , 10 417; Angew. Chem. Int. Ed. 2012 , 51 , 10 271) has been studied by using modern tools of computational quantum chemistry. This catalyst is compared with analogous urea‐, thiourea‐, and thiosquaramide‐derived aminocatalysts. Ultimately, a thiosquar‐amide‐derived catalyst is predicted to result in the lowest free‐energy barrier, while retaining the same high degree of enantioselectivity as Sq . This stems in part from the superior hydrogen‐bonding ability of thiosquaramides, compared to squaramides and (thio)ureas. We also examine the hydrogen‐bonding ability of (thio)ureas and (thio)‐squaramides in model complexes. In contrast to previous work, we show that aromaticity does not contribute significantly to the enhanced hydrogen‐bonding interactions of squaramides. Overall, thiosquaramide, which has not been explored in the context of either organocatalysis or molecular recognition, is predicted to lead to strong, co‐planar hydrogen bonds, and should serve as a potent hydrogen‐bonding element in a myriad of applications.