Arylboronic coupling with anhydrides

The acylpalladium 141 is formed by oxidative addition of acid anhydride to Pd(0), and can be used for synthetic purposes [61]. The mixed anhydride 143 was prepared in situ by the reaction of benzoic acid with dimethyl dicarbonate (142), and the benzoylpalladium methoxide 144 is generated by decarboxylative oxidative addition of 143, and is used for Suzuki coupling with arylboronic acid to yield the diaryl ketone 145 [62]. 

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... 

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