Unique effects of sulfur and water on the syntheses of thiaheterocycles
作者:Dong-Qing Sun、Jing-Kui Yang
DOI:10.1002/hc.20755
日期:——
A series of thiaheterocycles were produced by the reaction of diethyl 2,3-dibromomaleate or diethyl 2,3-dibromofumarate with different sulfides without any catalyst. The major products shifted in different conditions. Water was found playing a key role in the generation of carbon–carbon single bonds. Meanwhile, the addition of sulfur could accelerate the reaction and greatly improve the yield of certain
Stereodefined unsymmetrically 3,3-disubstituted alkyl 2-bromopropenoates, 5, were regioselectively prepared by Pd-mediated reactions between 3-alkyl, 3-aryl and 3-alkoxycarbonyl substituted (E)-2,3-dibromopropenoates, (E)-7, and aryl or 1-alkynylzinc chlorides. The stereospecificity of these reactions was found to be dependent on the type of substituent present in the 3-position of (E)-7. The (E)-stereochemistry of compounds 5b, 5d and 5i so prepared was confirmed by their conversion into the corresponding 4-substituted 3-bromocoumarins. Tetrasubstituted alpha,beta-unsaturated esters 10 were then synthesized by Pd-mediated reactions either of (E)-7 with a molar excess of an arylzinc chloride or an aryltributylstannane, or of a compound of general formula 5 with an aryltributylstannane. An examination of the parameters which influence the stereochemistry and the yields of these arylations was made.