Synthesis of unsymmetrical urea from aryl- or pyridyl carboxamides and aminopyridines using PhI(OAc)<sub>2</sub><i>via in situ</i> formation of aryl- or pyridyl isocyanates
作者:Joydev K. Laha、Neha Singh、Mandeep Kaur Hunjan
DOI:10.1039/d1nj03160k
日期:——
previously, attempts have been made to trap the isocyanates. While the three pyridylisocyanates were trapped as their corresponding carbamates, 3-pyridylisocyanate was isolated and characterized. Unlike closely related previous methods reported for urea synthesis, the current method avoids direct use of isocyanates or eliminates the use of toxic phosgene for the in situ generation of isocyanates.
1H and 13C NMR spectra of some unsymmetric N,N′-dipyridyl ureas: spectral assignments and molecular conformation
作者:Netai C. Singha、Dixit N. Sathyanarayana
DOI:10.1039/a606800f
日期:——
The 1H NMR spectra of N-(2-pyridyl),
Nâ²-(3-pyridyl)ureas and N-(2-pyridyl),
Nâ²-(4-pyridyl)ureas in CDCl3 and
(CD3)2CO have been assigned with the aid of COSY and
NOE experiments and chemical shift and coupling constant correlations. The
13C NMR spectra in CDCl3 were analysed utilizing the
HETCOR and proton coupled spectra. The 1H NMR spectra, NOE
effects and MINDO/3 calculations have been utilized to show that the
molecular conformation of these compounds has the 2-pyridyl ring coplanar
with the urea plane with the NâH group hydrogen bonded to the
nitrogen of the 2-pyridyl group on the other urea nitrogen while the
3/4-pyridyl group rotates rapidly about the
NâC3/NâC4 bond.