H-bonding additives act like Lewis acid catalysts.
[reaction: see text] A combination of NMR, IR, and ab initio techniques reveals the striking structural similarities of an exemplary H-bonded complex of an N-acyloxazolidinone with an N,N'-disubstituted electron-poor thiourea and the corresponding Lewis acid complex. Although the H-bond association constant is lower than for the Lewis acid adduct, Diels-Alder reactions are accelerated and stereochemically altered in a fashion similar to weak Lewis acids.
Schreiner
Peter R
PR
Institut für Organische Chemie, Universität Göttingen, Tammannstrasse 2, 37077, Göttingen, Germany. prs@chem.uga.edu
Wittkopp
Alexander
A
D006860:Hydrogen Bonding; D015394:Molecular Structure; D013890:Thiourea / Q000031:analogs & derivatives / Q000737:chemistry; D014508:Urea / Q000031:analogs & derivatives / Q000737:chemistry*
D014508:Urea; D013890:Thiourea