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31 P NMR Spectroscopically Quantified Hydrogen‐Bonding Strength of Thioureas and Their Catalytic Activity in Diels–Alder Reactions
Author(s) -
Nödling Alexander R.,
Jakab Gergely,
Schreiner Peter R.,
Hilt Gerhard
Publication year - 2014
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.201402871
Subject(s) - chemistry , thiourea , bifunctional , catalysis , diels–alder reaction , chemical shift , proton nmr , amine gas treating , hydrogen bond , carbon 13 nmr , medicinal chemistry , organic chemistry , molecule
The hydrogen‐bonding strength of a variety of commonly employed thiourea catalysts was quantified by using a trialkylphosphine oxide as a 31 P NMR probe. Simple diarylthioureas and more complex bifunctional amine‐ and hydroxy‐substituted thiourea derivatives were examined. Their catalytic activity was determined in a Diels–Alder reaction, and the obtained pseudo‐first‐order rate constants were correlated with the 31 P NMR chemical shifts. A linear correlation between both variables was observed throughout the functionalized thioureas. The 31 P NMR probe correlation fared better in comparison to a p K a correlation. Accordingly, the quantification presented herein by using a 31 P NMR probe offers an elegant way to estimate the catalytic activity of thiourea catalysts in hydrogen‐bond‐activated reactions such as the Diels–Alder reaction.