Urea arylation with aryl halides in the presence of catalyst precursor Pd(2)dba(3)-CHCl3/Xantphos and Cs2CO3 in dioxane at 100degreesC affords symmetrical N,N-diarylureas in 64-92% yield. With the same catalytic system the reaction between N-phenylurea and aryl bromides containing electron-withdrawing substituents in the para-position provided N-aryl-N'-phenylureas in 64-91% yields.
Preparation and reactions of 2,3,4,6-tetrafluoropyridine and its derivatives
作者:Paul L Coe、Anthony J Rees
DOI:10.1016/s0022-1139(99)00189-x
日期:2000.1
to give 3-chlorotetrafluoropyridine and its subsequent hydrodechlorination using hydrogen over palladium on alumina at 250–270°C. The formation and reactions of the 3-lithio derivative have been studied with the aim of obtaining 3,4-disubstituted trifluoropyridines. Routes to such materials have been developed and their conversion to deazapurine derivatives as potential substrates for the generation