Suzuki boronic anhydrides

Bisseret recently reported the conversion of dibromoalkenols, a new class of benzofuran precursors, into 2-phosphonylated and 2-aryl benzo furans [174]. For example, reaction of dibromalkenol 213 with phenyl boronic anhydride provides 2-phenylbenzofuran in 80% yield. The proposed mechanism for this transformation starts with a Suzuki coupling of the more reactive E vinyl bromide and the boronic anhydride followed by a second Pd-catalyzed coupling between the Z vinyl bromide and the alcohol oxygen. 

Recently, Davies et al. have observed that boronic acids, esters and boronic anhydrides are partners in Suzuki coupling reactions with various P-chlorovinylamidini-um salts to give the desired P-arylvinylamidinium salts. Among boron partners, boronic anhydrides give better yields (up to 88%). Reduction is a competing reaction pathway (Equation 83) [115]. 

The allylic carbamate 193 formed as shown in Scheme 17 can be exploited in the synthesis of a pancratistatin analogue. Thus, Suzuki-Miyaura cross-coupling of this carbamate with aryl boronic acid 61 (Scheme 18) afforded the expected arylated cyclohexene 200 (87%) that upon sequential treatment with diborane, alkaline hydrogen peroxide, aqueous acid then acetic anhydride gave the triacetate 201 (42%). Subjecting this last compound to the Bischler-Napieralski reaction... 

The synthesis of lapatinib involves a Suzuki-Miyaura coupling of a (5-formylfuran-2-yl)boronic derivative and an aryl iodide and was studied in detail by several teams. " In a recent patent,researchers from Zentiva noticed that in their own attempts to use commercial boronic acid, the excess of this reagent required for optimal conversions and purity was dependent on the source (a common issue with boronic acids, which are often contaminated with anhydrides and borinic acid). Thus, they turned to cyclic boronic esters as a more reliable intermediate, allowing correct control of the amount of boron reagent. Transposition of a process originally developed for the coupling of (5-formylfuran-2-yl)boronic acid was successful. The authors compared... 

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