Synthesis of Urea Derivatives from CO
<sub>2</sub>
and Silylamines
作者:Maotong Xu、Andrew R. Jupp、Maegan S. E. Ong、Katherine I. Burton、Saurabh S. Chitnis、Douglas W. Stephan
DOI:10.1002/anie.201900058
日期:2019.4.16
A series of thirty‐three N,N′‐diaryl, dialkyl, and alkyl‐aryl ureas have been prepared in pyridine or toluene by reaction of silylamines with CO2. This protocol is shown to provide facile access to 13C‐labeled ureas, as well as chiral and macrocyclic ureas. These reactions proceed through initial generation of the corresponding silylcarbamates, which subsequently react with silylamine under thermal
The conversion of 1,3-bis-(6-amino-pyridin-2yl)-urea (1) with N',N'-carbonyldiimidazole at high temperatures in DMSO yielded a mixture of defined cyclic trimers and tetramers. On the basis of model reactions, exchange reactions were evidenced, which convert the cyclic tetramer into a stable cyclic trimer. Linear even numbered oligomers were obtained in acetone under reflux where side reactions were suppressed. The pronounced tendency of cyclization is attributed to a preferred folded conformation of the urea bond between two pyridyl units.