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.
|Autori:||Rossi, Renzo; Bellina, Fabio; Carpita, Adriano; Mazzarella, F.|
|Titolo:||Palladium-mediated cross-coupling reactions involving 3-substituted alkyl (E)-2,3-dibromopropenoates and arylzinc or aryltin derivatives|
|Anno del prodotto:||1996|
|Digital Object Identifier (DOI):||10.1016/S0040-4020(96)00071-3|
|Appare nelle tipologie:||1.1 Articolo in rivista|