Stille coupling Suzuki reaction

Biaryls have also been prepared by coupling support-bound aryl halides with aryl-zinc compounds (Figure 5.20) or with aryl(fluoro)silanes [203]. As with Suzuki or Stille couplings, these reactions also require transition metal catalysis. An additional strategy for coupling arenes on solid phase is the oxidative dimerization of phenols (Figure 5.20). 

This review is divided into four main sections, covering the Heck, Stille, and Suzuki reactions, with miscellaneous reactions being included at the end. Processes featuring alkynes in copper co-catalyzed Sonogashira-type couplings have been included in the section on Heck reactions. This review does not cover carbon-carbon bond formation processes using immobilized catalysts. Similarly, fluorous-phase syntheses " and those on polyethylene glycol " are excluded. 

A different example of triphasic catalysis for the Heck, Stille and Suzuki reactions relied on a three-phase microemulsion/sol-gel transport system. Gelation of an z-octyl(triethoxy)silane, tetramethoxysilane and Pd(OAc)2 mixture in a H2O/CH2CI2 system led to a hydrophobicitized sol-gel matrix that entrapped a phosphine-free Pd(ii) precatalyst. The immobilized precatalyst was added to a preformed microemulsion obtained by mixing the hydrophobic components of a cross coupling reaction with water, sodium dodecyl sulfate and a co-surfactant, typically zz-propanol or butanol. This immobilized palladium catalyst was leach proof and easily recyclable. 

This reaction is related to the Stille Coupling, Suzuki Coupling, Hiyama Coupling, and Sonogashira Coupling. 

The cross-coupling reactions of aryl- and alkenylsilanols are adequate replacements for the analogous Stille and Suzuki reactions. Yet the scope of organosilanol coupHng extends beyond this. It has also been shown that the use of alkynylsilanols presents a viable alternative to the classic Sonogoshira-type couphngs of alkynes. 

In Chapter 1, Li and Bo provide an overview of the key chemistry, including Stille coupling, Suzuki coupling and direct C-H arylation, for the synthesis of conjugated polymers used for OPVs. The reaction mechanism and... 

Vinylation can also be done by Pd-catalysed cross-coupling in which one component is used as a halide or triflate and the other as a stannane (Stille reaction) or boronic acid (Suzuki reaction). Entry 9, Table 11.3, is an example of the use of a vinylstannane with a haloindole. lndole-3-boronic acids, which can be prepared by mcrcuration/boration, undergo coupling with vinyl triflates (Entry 10). 

Together with reactions named after Heck and Suzuki, the Stille reac-tion belongs to a class of modern, palladium-catalyzed carbon-carbon bond forming reactions. The palladium-catalyzed reaction of an organotin compound 2 with a carbon electrophile 1 is called Stille coupling. 

The mechanism " of the Suzuki reaction is closely related to that of the Stille coupling reaction, and is also best described by a catalytic cycle ... 

AT-acetyltryptamines could be obtained via microwave-assisted transition-metal-catalyzed reactions on resin bound 3-[2-(acetylamino)ethyl]-2-iodo-lH-indole-5-carboxamide. While acceptable reaction conditions for the application of microwave irradiation have been identified for Stille heteroaryla-tion reactions, the related Suzuki protocol on the same substrate gave poor results, since at a constant power of 60 W, no full conversion (50-60%) of resin-bound 3-[2-(acetylamino)ethyl]-2-iodo-lH-indole-5-carboxamide could be obtained even when two consecutive cross-coupling reaction cycles (involving complete removal of reagents and by-products by washing off the resin) were used (Scheme 36). Also under conventional heating at 110 °C, and otherwise identical conditions, the Suzuki reactions proved to be difficult since two cross-coupling reaction cycles of 24 h had to be used to achieve full conversion. 

Transition metal-catalyzed transformations are of major importance in synthetic organic chemistry [1], This reflects also the increasing number of domino processes starting with such a reaction. In particular, Pd-catalyzed domino transformations have seen an astounding development over the past years with the Heck reaction [2] - the Pd-catalyzed transformation of aryl halides or triflates as well as of alkenyl halides or triflates with alkenes or alkynes - being used most often. This has been combined with another Heck reaction or a cross-coupling reaction [3] such as Suzuki, Stille, and Sonogashira reactions. Moreover, several examples have been published with a Tsuji-Trost reaction [lb, 4], a carbonylation, a pericyclic or an aldol reaction as the second step. 

Domino transition metal-catalyzed processes can also start with a cross-coupling reaction most often, Suzuki, Stille and Sonogashira reactions are used in this context They can be combined with another Pd-catalyzed transformation, and a number of examples have also been reported where a pericydic reaction, usually a Diels-Alder reaction, follows. An interesting combination is also a Pd-catalyzed borina-tion followed by a Suzuki reaction. 

A series of potent, linear C2-symmetric HIV-1 protease inhibitors with K, values in the nanomolar range was prepared from a diaryl bromide precursor emanating from a carbohydrate scaffold, by application of Heck, Suzuki, Stille, and cyanation reactions. Included in this series was the first reported microwave-promoted Suzuki coupling with an alkyl borane [41]. A very high-yielding Suzuki coupling is presented... 

Unsymmetrical 3,4-dihalo-l,2,5-thiadiazoles 118 and 119 were prepared from 3-amino-4-chloro-l,2,5-thiadiazole 117 via a Sandmeyer-like reaction involving successively tert-butyl nitrite and either copper bromide or copper iodide in anhydrous acetonitrile (Scheme 17) <2003H(60)29>. The bromo and iodo thiadiazoles 118 and 119 undergo selective Stille and Suzuki C-C coupling chemistry (see Section 5.09.7.6). 

Doi and Mori made excellent use of dihydroindole triflate 189 in Pd-catalyzed cross-coupling reactions. This compound was discussed earlier in the Suzuki section, and it also undergoes Stille couplings as illustrated below [140]. A final dehydrogenation completes the sequence to indoles. 

Nonetheless, to make imidazole-containing molecules, haloimidazoles may serve as electrophilic coupling partners for the Suzuki reaction. As described in section 9.1, regioselective bromination at the C(4) position could be achieved for a 1,5-dialkylimidazole using NBS in CH3CN. The Suzuki coupling of l-benzyl-4-bromo-5-methylimidazole with phenylboronic acid assembled the unsymmetrical heterobiaryl in 93% yield, whereas the corresponding Stille reaction with phenyltrimethyltin proceeded in only moderate yield (51%) [8]. 

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