Arylboronic coupling with acid chlorides

The coupling of arylboronic acids with acid chlorides is the basis of a ketone synthesis. It is found that the Suzuki coupling in an ionic liquid has several advantages reduced catalyst concentration, no homocoupling, and reaction in the air. ... 

The two key catalytic intermediates have been observed by electrospray mass spectrometry [394]. Although the exact role and influence of the base remains unclear [395], the transmetallation is thought to be facilitated by base-mediated formation of the tetracoordinate boronate anion [396], which is more electrophilic than the free boronic acid (Sections 1.5.1 and 1.5.2). A useful carbonylative variant has also been developed to access benzophenones (Equation 70) [397], which can also be produced from the coupling of acid chlorides [398] or anhydrides [399], A variant of this method allows the preparation of a, 3-unsaturated esters from alkenylboronic esters [243]. In all of these reactions, one dreaded limitation with some ortho-substituted and electron-poor arylboronic acids is the possible occurrence of a competitive protolytic de-boronation, which is exacerbated by the basic conditions and the use of a transition metal catalyst (Section 1.5.1). Methods to minimize this side reaction were developed in particular the use of milder alternative bases [400] such as fluoride salts [401], and... 

In early studies, it was observed that when the NHG was already attached to the metal center, reaction times were shortened since the time for the deprotonation of the salt and coordination to the metal center was no longer required. The use of well-defined systems also allows for a better understanding of the actual amount of stabilized palladium available in the system. Herrmann reported on two similar Pd(0) complexes bearing two carbenes, 37 and 38. The latter was used in 2002 as the first example of coupling of aryl chlorides (activated and unactivated) with arylboronic acids at room temperature, in high yields, and reaction times between 2 and 24 h in the presence of GsF as base. 

Palladium catalysts have been found which are effective in the Suzuki coupling reaction of arylboronic acids with aryl chlorides carrying electron-withdrawing groups.73 Biaryls may also be synthesized by cross-coupling of arylboronic acids with arenediazonium salts.74,75 There has been a report of the polymer-bound palladium-catalysed Suzuki coupling of aryl triflates with organoboron compounds.76 Arylbor-onates may themselves be synthesized by the palladium-catalysed reactions of... 

Most recently, Fu and co-workers [126] have reported that the use of Pd2(dba)3/PtBu3 as a catalyst for a wide range of aryl and vinyl halides, including chlorides, facilitates their Suzuki cross-coupling with arylboronic acids, giving the coupled products in very good yield, typi-... 

Suzuki and Stille couplings. For coupling of aryl chlorides with arylboronic acids the catalytic system contains (CyjPjjPdClj, CsF in NMP. co-Arylalkanoic acids are prepared by coupling of aryl halides with carboxylic esters bearing a 9-BBN substituent at the other terminus, and saponification. A biaryl synthesis from two different aryl halides is accomplished with in situ boronate formation which depends on the (dppfjPdClj catalyst. For access to aryl boronates either the coupling of aryl triflates with bis(pinacolato)diboron" or that of aryl iodides with pinacolborane may be employed. 

Bromobenzamides couple with arylboronic acids thermal deprotection of the amino group is followed by the formation of a fused pyridin-2-one in good yield. The 4-one ring may be constructed in low yield by stirring at a low temperature (—S °C) a 2-fluorobenzoyl chloride with the lithium derivative of ethyl pyridine-2-acetate. 

Recent work has led to the use of bulk electron-rich phosphine ligands to facilitate palladium-catalyzed processes with problematic oxidative addition. For examples, see (a) Littke, A.F. Fu, G.C. A convenient and general method for Pd-catalyzed Suzuki cross-couplings of aryl chlorides and arylboronic acids. Angew. Chem., Int. Ed. Engl. 1998, 37, 3387-3388. (b) Shen, W. Palladium catalyzed coupling of aryl chlorides with arylboronic acids. Tetrahedron Eett. 1997, 38, 5575-5578. (c) Old, D.W. Wolfe,... 

In the presence of a Pd catalyst, CIPd[P(Cf,Hvinyl iodide couples with mctalatcd aromatics, particularly arylzinc chloride or arylboronic acids. Aryl Grignard reagents, however, couple in very low yield. The resulting C-aryl glucals can be converted to C-aryl glycosides by functionalization of the enol ether double bond.2... 

In promoting the Suzuki coupling of aryl chlorides and bromides with arylboronic acids, the Pd(OAc)2-(i-PrO)3P system is adequate. ... 

Related to the original Suzuki coupling is the ketone synthesis from acid chloride and trialkyl boranes and thiol esters with arylboronic acids. - The latter procedure is Pd-catalyzed and Cu-mediated. 

Aryl chlorides, as the least reactive halides, can be cross-coupled with arylboronic acids by different synthetic methods. Each particular method must include an apropriate catalyst, capable to react with rather unreactive C-Cl function to give a... 

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