Kumada couphng

Palladium-catalyzed cross-coupling reaction of organostaimanes with organic halides, triflates, etc. For the catalytic cycle, see Kumada couphng. 

The PEPPSI (pyridine-enhanced, precatalyst, preparation, stabilization and initiation) precatalyst 20 is a very versatile catalyst for Kumada couphngs of highly hindered substrates and heterocycles at ambient temperature (Equation 2.64) [106]. 

More recently, Ackermann has expanded on the use of air-stable H-phosphonates as preligands for palladium-catalyzed processes by demonstrating their effectiveness for Kumada couphngs of aryl tosylates. Both, chlorides and fluorides are tolerated, and heteroaryl tosylates proved also to be excellent substrates when using commercially available preligand 23 (Equation 2.77) [125]. 

Hindered substrates, such as 2-chloro-m-xylene, can also be coupled efficiently, although the utihty of this Kumada cross-couphng process is Hmited by its relatively low functional-group tolerance. Thus, for example the reaction of methyl 4-chlorobenzoate results in the formation of significant amounts of undesired side products. 

K. Tamao, K. Sumitani, Y. Kiso, M. Zembayashi, A. Fujioka, S. Kodama, 1. Nakajima, A. Minato and M. Kumada, Nickel-phosphine complex-catalyzed Grignard coupling. 1. Cross-couphng of alkyl, aryl and alkenyl Grignard reagents with aryl and alkenyl halides General scope and limitations. Bull. Chem. Soc. Jpn., 49, 1958-1969 (1976). 

One of the earliest reports of silicon cross-coupHng by Kumada and Tamao [16] involved the use of the dipotassium salt ofpentafluorostyrylsilicate 1 (Scheme 7.3). Despite the harsh conditions employed, this reaction provided the first indication... 

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