Reactivity of mixed organozinc and mixed organocopper reagents: 12. Three component reaction of mixed (n-alkyl)(diaryl)zincates, chloroformates and phosphines for the synthesis of esters

The reaction of mixed n-butyldiphenylzincate, n-BuPh2ZnMgBr with ethyl chloroformate, CICOOEt in the presence n-Bu3P in THF takes place with quantitative yield and phenyl group transfer to give PhCOOEt. Ethoxycarbonylation of n-BuPh2ZnMgBr is preferable to the reaction of PhMgBr forming ester and triphenylcarbinol and also to the reaction of triphenylzincate, Ph3ZnMgBr for atom economy. Group selectivity in the phosphine catalyzed C COOR coupling of n-BuPh2ZnMgBr and n-Bu2PhZnMgBr can be controlled by changing reaction parameters. n-Bu3P catalyzed reaction of n-BuPh2ZnMgBr with CICOOEt takes place with phenyl selectivity whereas reaction of n-Bu2PhZnMgBr with CICOOPh results in n-butyl transfer. Catalysis by Ph3P increases n-butyl group:phenyl group transfer ratio in the ethoxycarbonylation of both zincates. Selective transfer of aryl groups in n-Bu3P catalyzed reaction of n-butyl(aryl)(2)ZnMgBr reagents with CICOOEt in THF provides a new procedure for the organometallic synthesis of arenecarboxylic acid ethyl esters at room temperature. (C) 2015 Elsevier By. All rights reserved.