Efficient Palladium-Catalyzed Alkoxycarbonylation of <b><i>N</i></b>-Heteroaryl Chlorides - A Practical Synthesis of Building Blocks for Pharmaceuticals and Herbicides
作者:Matthias Beller、Wolfgang Mägerlein、Adriano Indolese、Christine Fischer
DOI:10.1055/s-2001-14576
日期:——
The alkoxycarbonylation of various N-heteroaryl chlorides was examined in detail. Studies of the butoxycarbonylation of 2- and 3-chloropyridine revealed the importance of selecting both the right phosphine ligand and ligand concentration in order to obtain efficient conversion and selectivity. Amongst the different ligands tested, 1,4-bis(diphenylphosphino)butane (dppb) and 1,1′-bis(diphenylphosphino)ferrocene (dppf) led to the most efficient palladium catalyst systems for the conversion of 2- and 4-chloropyridines and similar heteroaryl chlorides. The best catalytic systems for the alkoxycarbonylation of less activated substrates, such as 3-chloropyridines, were found to be those containing 1,4-bis(dicyclohexylphosphino)butane. Good to excellent yields of a number of N-heterocyclic carboxylic acid esters were realized by applying the appropriate ligand in the right concentration at low catalyst loadings (0.005-0.5 mol% Pd). For the first time catalyst turnover numbers (TON) of up to 13,000 were obtained for the carbonylation of a (hetero)aryl chloride.
详细研究了各种N-杂芳基氯化物的烷氧羰基化反应。对2-和3-氯吡啶的丁氧羰基化研究发现,为了获得高效的转化率和选择性,选择合适的膦配体及其浓度至关重要。在测试的不同配体中,1,4-双(二苯基膦)丁烷(dppb)和1,1'-双(二苯基膦)二茂铁(dppf)为2-和4-氯吡啶及类似杂芳基氯化物提供了最高效的钯催化体系。对于活性较低的底物,如3-氯吡啶,最佳催化体系是含有1,4-双(二环己基膦)丁烷的体系。通过在低催化负载量(0.005-0.5摩尔% 钯)下使用适当浓度的合适配体,实现了多种N-杂环羧酸酯的良好至优异产率。对于(杂)芳基氯化物的羰基化反应,首次获得了高达13,000的催化剂周转数(TON)。