Geometry-Selective Synthesis of <i>E</i> or <i>Z</i> <i>N</i>-Vinyl Ureas (<i>N</i>-Carbamoyl Enamines)
作者:Julien Lefranc、Daniel J. Tetlow、Morgan Donnard、Alberto Minassi、Erik Gálvez、Jonathan Clayden
DOI:10.1021/ol1027442
日期:2011.1.21
N-Vinyl ureas are emerging as a valuable class of compounds with both nucleophilic and electrophilic reactivity. They may be made by capturing the enamine tautomer of an imine with an isocyanate, a reaction which in general leads to the E isomer of the vinyl urea. Deprotonation of such a vinyl urea, or of an allyl urea, generates a dipole stabilized Z-allyl anion which may be protonated to return the Z-vinyl urea. Isomerization of an allyl urea with a Ru complex provides an alternative route to E-vinyl ureas.
Sequential Double α-Arylation of <i>N</i>-Allylureas by Asymmetric Deprotonation and N→C Aryl Migration
作者:Daniel J. Tetlow、Ulrich Hennecke、James Raftery、Michael J. Waring、David S. Clarke、Jonathan Clayden
DOI:10.1021/ol102155h
日期:2010.12.3
On lithiation with lithium amides, N-allyl-N'-aryl ureas undergo rearrangement with transfer of the aryl ring from N to the allylic alpha carbon. From the alpha-arylated products, a further aryl transfer under the influence of a chiral lithium amide allows the enantioselective construction of 1,1-diarylallylamine derivatives. Stereoselectivity in these reactions results from the enantioselective formation of a planar chiral allyllithium under kinetic control.
Reversible aryl migrations in metallated ureas: controlled inversion of configuration at a quaternary carbon atom
作者:Daniel J. Tetlow、Mark A. Vincent、Ian H. Hillier、Jonathan Clayden
DOI:10.1039/c2cc38704b
日期:——
Deprotonation with strong bases of N-vinyl ureas carrying an N′-aryl substituent leads to migration of the N′-aryl group from N to C via an allyllithium; with weaker bases and electron-deficient aryl rings the direction of the migration reverses, and aryl substituents α to the urea N atom may migrate from C to N.
带有 N′-芳基取代基的 N-乙烯基脲在强碱作用下发生去质子化反应,导致 N′-芳基通过烯丙基锂从 N 转移到 C;在弱碱和缺电子芳基环作用下,转移方向发生逆转,脲 N 原子上的α芳基取代基可能会从 C 转移到 N。