吡啶-2-基脲两种构象异构体之间的平衡,所述(ê,Ž)和(Ž,Ž)的形式,已经研究了在DMF- d 7在- 70℃。他们中的大多数人都不太喜欢(E,Z)形式,其平衡常数K i在1-2附近。然而,发现1-甲基-2-(3-(吡啶-2-基)脲基)碘化吡啶鎓(12)的K i值为14.2±1.2。那是其他数量级的1个数量级,这表明带正电荷的1-甲基吡啶-2-基取代基将促进(E,Z)形成形式。吡啶-2-基脲与DMF- d 7中的胞嘧啶结合,结合常数K B为30到1700 M - 1。吸电子取代基,例如4-O 2 NC 6 H 4-或1-甲基吡啶-4-基取代基,以较大的结合常数优先促进分子间胞嘧啶的络合。
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.
atom economy has been developed for the synthesis of N-aryl-N′-(4-pyridinyl)ureas. With cheap selenium as the catalyst, carbonmonoxide (instead of phosgene) as the carbonyl reagent, N-aryl-N′-(4-pyridinyl)ureas can be obtained in a one-pot manner mostly in moderate to good yields via oxidative cross-carbonylation of 4-aminopyridine with a variety of aromaticamines in the presence of oxygen under atmospheric