Buchwald-Hartwig-type coupling reactions

BuchwaM-Hartwig and Related Reactions. The Pd(OAc)2-catalyzed Buchwald-Hartwig-type couplings of both electron-poor and electron-rich aryl triflates have been shown to proceed efficiently with various amines provided the appropriate base is used. NaOfBu is usually employed for electron-rich systems while CS2CO3 is preferred for electron-deficient and neutral species (eq 130). ... 

Orr/zc- em-Dihalovinylanilines 278 were also used in another example of a Buchwald-Hartwig-type/Mizoroki-Heck reaction for the synthesis of 2-vinylic indoles 279 (Scheme 8.69). Lautens and coworkers [140] recently illustrated a domino coupUng under Jeffery s condition where the aniline nitrogen undergoes an amination step followed by a Mizoroki-Heck coupling with various alkenes. In this process, electronic factors and steric hindrance of the different substituents had only a small effect on the yield however, in the formation of 3-substituted indoles using this method only very poor yields were obtained. The procedure can also be performed in an intramolecular mode leading to tricycUc compounds such as pyridino and azepino indoles 281 and 282 (Scheme 8.69). 

Carbon-carbon bond formation reactions and the CH activation of methane are another example where NHC complexes have been used successfully in catalytic applications. Palladium-catalysed reactions include Heck-type reactions, especially the Mizoroki-Heck reaction itself [171-175], and various cross-coupling reactions [176-182]. They have also been found useful for related reactions like the Sonogashira coupling [183-185] or the Buchwald-Hartwig amination [186-189]. The reactions are similar concerning the first step of the catalytic cycle, the oxidative addition of aryl halides to palladium(O) species. This is facilitated by electron-donating substituents and therefore the development of highly active catalysts has focussed on NHC complexes. 

Hartwig-Buchwald, Suzuki, and Stille type cross-coupling reactions with key intermediate 46 led to a wide range of substituted sulfoximines such as 47-49 [37]. In order to demonstrate the synthetic utility of the resulting products, pseudo tripeptide 50 was prepared from a related intermediate. 

Clearly, the use of stoichiometric amounts of organo tin compounds is the main disadvantage of this type of C-N coupling reaction both for ecological reasons and with regard to practicability. Thus, from an industrial point of view the aim was to replace the tin amides by simpler amino sources, ideally the amines themselves. Again independently, Buchwald et al. [8] and Hartwig et al. [9] reported... 

Almost all Suzuki polycondensations published to date in the literature use 1-3 mol% of catalyst, mostly Pd[P(p-tolyl)3]3, Pd(PPh3)4 or in situ prepared Pd[P(o-tolyl)3]2. Most catalysts for the Suzuki polycondensation employ tri-arylphosphine ligands. New ligands, which include Buchwald s biaryl-based phosphines, Beller s diadamantyl phosphines, Fu s tri(tert-butyl)phos-phine, and Hartwig s pentaphenylated ferrocenyl phosphines, have been developed for Suzuki-Miyaura cross-coupling reactions. Buchwald-type ligand has been applied to polymerize dichloro monomers using Suzuki polycondensation. 

The palladium-catalyzed amination of aryl halides and sulfonates has emerged as a valuable method for the preparation of aromatic amines [2], Numerous ligands and catalysts have been reported to effect this type of cross-coupling. This reaction, known as the Hartwig-Buchwald amination, is shown in Eq. (1). 

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