Palladium-Catalyzed Diastereoselective Coupling of Propargylic Oxiranes with Terminal Alkynes
摘要:
A diastereoselective coupling of propargylic oxiranes with terminal alkynes has been developed with use of a palladium catalyst. The stereochemistries of the resulting 4-alkynyl-substituted 2,3-allenols have been altered depending on the palladium catalyst. An optically active anti-substituted allene was synthesized from the reaction of an enantiomerically enriched propargylic oxirane without loss of chirality.
An efficient and generalprotocol for the palladium-catalyzed Heck alkynylation of benzyl chlorides was developed. A catalyst system comprised of PdCl 2 (CH 3 CN) 2 and 2-dicyclohexyl-phosphino-2',4',6'-triisopropylbiphenyl (XPhos), with CS 2 CO 3 as the base, efficiently couples a wide range of functionalized terminalalkynes and substituted benzyl chlorides at 65 °C. We have also demonstrated that
Highly regioselective hydroboration of unsymmetrical internal alkynes remains a significant challenge for synthesizing valuable alkenylboronate esters. Herein, we describe an easily synthesizable pincer NHC-based Co complex as a catalyst for the cis-α selective hydroboration of unactivated internal alkynes and the cis-β selective hydroboration of activated internal alkynes with pinacolborane. The reaction
不对称内炔烃的高区域选择性硼氢化仍然是合成有价值的烯基硼酸酯的重大挑战。在此,我们描述了一种易于合成的钳形 NHC 基 Co 配合物,作为未活化内炔烃的顺α选择性硼氢化和活化的内炔烃与频立硼烷的顺β选择性硼氢化的催化剂。该反应表现出高化学选择性、区域选择性和立体选择性,并且在无碱反应条件下催化剂表现出高效率和极低负载量。反应范围由具有多种官能团的炔烃证明。机理研究表明,一种可行的钴硼基中间体可以解释不寻常的区域选择性。
Palladium-catalyzed cross-coupling reaction of alkynylzincs with benzylic electrophiles
作者:Mingxing Qian、Ei-ichi Negishi
DOI:10.1016/j.tetlet.2005.02.137
日期:2005.4
The reaction of alkynylzinc bromides with benzyl bromides or chlorides in the presence of a catalytic amount of Pd(DPE-phos)Cl-2 in THF at 23 degrees C cleanly produces the corresponding benzylated alkynes in 73-97% yields. With 10(-3) mol% of Pd(DPE-phos)Cl-2, the maximum turnover number of 7.1 x 10(4) has been observed for the formation of PhC CCH2Ph. (c) 2005 Published by Elsevier Ltd.