Highly Selective Methods for Synthesis of Internal (α-) Vinylboronates through Efficient NHC-Cu-Catalyzed Hydroboration of Terminal Alkynes. Utility in Chemical Synthesis and Mechanistic Basis for Selectivity

被引:278
作者
Jang, Hwanjong [1 ]
Zhugralin, Adil R. [1 ]
Lee, Yunmi [1 ]
Hoveyda, Amir H. [1 ]
机构
[1] Boston Coll, Dept Chem, Merkert Chem Ctr, Chestnut Hill, MA 02467 USA
基金
美国国家科学基金会;
关键词
COPPER(I) BORYL COMPLEXES; OLEFIN CROSS-METATHESIS; DENSITY-FUNCTIONAL THEORY; COUPLING REACTION; ENANTIOSELECTIVE SYNTHESIS; STEREOSELECTIVE-SYNTHESIS; CYCLOADDITION REACTIONS; ORGANOCUPRATE CLUSTERS; HOMOGENEOUS CATALYSIS; ORGANOBORON COMPOUNDS;
D O I
10.1021/ja2007643
中图分类号
O6 [化学];
学科分类号
0703 ;
摘要
Cu-catalyzed methods for site-selective hydroboration of terminal alkynes, where the internal or alpha-vinylboronate is generated predominantly (up to >98%) are presented. Reactions are catalyzed by 1-5 mol % of N-heterocyclic carbene (NHC) complexes of copper, easily prepared from N-aryl-substituted commercially available imidazolinium salts, and proceed in the presence of commercially available bis-(pinacolato)diboron[B-2(pin)2] and 1.1 equiv of MeOH at -50 to -15 degrees C in 3-24 h. Propargyl alcohol and amine and the derived benzyl, tert-butyl, or silyl ethers as well as various amides are particularly effective substrates; also suitable are a wide range of aryl-substituted terminal alkynes, where higher alpha-selectivity is achieved with substrates that bear an electron-withdrawing substituent. alpha-Selective Cu-catalyzed hydroborations are amenable to gram-scale procedures (1 mol % catalyst loading). Mechanistic studies are presented, indicating that alpha selectivity arises from the structural and electronic attributes of the NHC ligands and the alkyne substrates. Consistent with suggested hypotheses, catalytic reactions with a Cu complex, derived from an N-adamantyl-substituted imidazolinium salt, afford high beta selectivity with the same class of substrates and under similar conditions.
引用
收藏
页码:7859 / 7871
页数:13
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