Cross-coupling arylboronic acids

The more utilitarian means for installing an aryl substituent in position 4 onto the 2(5//)-furanone ring, the Suzuki-type cross-coupling of arylboronic acid with... 

Microwave and fluorous technologies have been combined in the solution phase parallel synthesis of 3-aminoimidazo[l,2-a]pyridines and -pyrazines [63]. The three-component condensation of a perfluorooctane-sulfonyl (Rfs = CgFiy) substituted benzaldehyde by microwave irradiation in a single-mode instrument at 150 °C for 10 min in CH2CI2 - MeOH in the presence of Sc(OTf)3 gave the imidazo-annulated heterocycles that could be purified by fluorous solid phase extraction (Scheme 9). Subsequent Pd-catalyzed cross-coupling reactions of the fluorous sulfonates with arylboronic acids or thiols gave biaryls or aryl sulfides, respectively, albeit it in relatively low yields. 

Soluble polymers have also been used as support. These exploit the combined advantage of homogeneous with those of soHd-phase chemistry [36]. PEG linked 5-bromothiophene-2-carboxyUc acid was cross-coupled with several arylboronic acids under microwave irradiation (constant power of 75 W) using water as the solvent (Scheme 17). Interestingly, microwave irradiation gave less ester cleavage than classical heating (70 °C). The polymeric support remained stable under both conditions. 

SUZUKI CROSS-COUPLING OF ARYLCHLORIDES WITH ARYLBORONIC ACIDS... 

The scope of Suzuki-Miyaura reactions is extremely broad, covering practically all types of organic residues. The cross-coupling of arylboronic acids with aryl halides or triflates is the most... 

In cross-coupling with arylboronic acids, some Cu1 carboxylates were found to provide a way to realize a very mild, base-free procedure, which is helpful in cases when added base can induce side reactions (59).222... 

These ligands afford high yields of cross-coupling products in the highly sterically burdened reactions of aryl bromides with arylboronic acids when both contain substituents in the ortho- (or equivalent) positions, although drastic reaction conditions are required (110). 

Amides of phosphorous acid (e.g., P(NMe2)3 and the bicyclic compound (L16)) are useful ligands for cross-coupling of arylboronic acids with aryl bromides and chlorides (system Pd(OAc)2/2L, Cs2C03, toluene, 80 °C), the bicyclic amide being markedly more effective than simple acyclic ones.421 Amides of phosphinous acids are also excellent bidentate ligands with PN coordination mode ((L6), Section 9.6.3.4.2). 

A similarly high performance has been reported for oxime-derived (125) and benzylsulfide-derived (126) palladacycles.438 These precatalysts are effective in the cross-coupling of arylboronic acids,438,439 organotin compounds,440 and terminal acetylenes441 with aryl iodides and bromides, and of activated aryl chlorides. SC-palladacycles can effect the Suzuki-Miyaura reaction even at room temperature. 

The readily available oxazolines (L19) are used in the cross-coupling of arylboronic acids with aryl bromides, including nonactivated ones in the system (Pd(OAc)2/L, Cs2C03, dioxane, 80 °C). It is notable that the system works well at 1 1 Pd L ratio.442 A simple sulfide complex showed similar activity (PdCl2(SEt2)2, K3P04, DMF, 130°C).18 A series of bidentate N,N-donor ligands... 

Simple bidentate ligands involving dipyridyl- or dipyrimidylamino fragment (L23) form Pd catalysts of moderate activity for the cross-coupling of terminal acetylenes (copper-free reaction) or arylboronic acids. Supported versions of such ligands were also reported (see Chapter 9.9 for more details about supported catalysts).449,450... 

Apart from imidazol-2-ylidene carbenes, other electron-rich carbenes such as (L27)—generated by deprotonation of a 4,5-dihydroimidazole—have been tested for cross-coupling reactions, but gave much poorer results. The only reported exception is in the cross-coupling of arenediazonium salts with arylboronic acids, in which (L27) (used as hydrochloride) proved to be efficient.369... 

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