Diboronic acid esters

The method consists of the one-step synthesis of (Z)-l,2-(bis-benzo-dithienyl)ethenes 10 using double Suzuki coupling between stereochemi-caUy defined diboronic acid esters 11 and 2-iodo-benzodithiophene 12. The (Z)-alkenes thus obtained can be easily and efficiently photochemicaUy cyclized to the corresponding substituted tetrathia[7]helicenes. This methodology can also be applied to the synthesis of stilbenoid derivatives with two different heterocyclic systems such as the phosphole 13 (Figure 3) (2014CEJ12373). 

A recent example of diasteromeric amplification with achiral guests and a racemic library can be seen in the work of Iwasawa and coworkers. The library members consisted of a racemic polyol and l,4-benzenedi(boronic acid) [2], When these components were mixed in an equimolar ratio in methanol, a precipitate formed, which was insoluble in other organic solvents and thought to be a polymeric boronate. However, when the library members were mixed in the presence of toluene or benzene, a precipitate again formed, but it was soluble in several (nonprotic) organic solvents where boronic ester exchange is slow. With toluene a [2 2] complex of the polyol and diboronic acid formed, as evidenced by NMR and FAB-MS data. X-ray crystallography confirmed that a cyclic structure formed with... 

A solution of the pinacol ester of diboronic acid (1 mmol), l-bromo-3,4-methylenedioxy benzene (2 mmol), 10% Pd/C (80mg) and CS2CO3 (3.7 mmol) were dissolved in 10ml methyl alcohol and heated to 55 °C 16 hours. GC analysis indicated that the product constituted of 83.5% 2-(bisl,3-benzodioxole and 16.5% l-bromo-3,4-methylenedioxy)benzene. 

In fact, one boronic acid can reversibly form a boronate ester with two OH groups (one diol group), and one diboronic acid can immobilize two suitably positioned diol units to form a saccharide-containing macrocycle. Selectivity can be achieved by controlling the relative spatial position of the two boronic acids in relation to the cis-diol moieties on the saccharide. A given monosaccharide possesses at least two binding sites that differ from other monosaccharides. 

The Pd-catalyzed cross-coupling reaction of the pinacol ester of diboronic acid with aryl halides and triflates gives a direct procedure for various functionalized arylboronic esters (Table 6), which are useful for highly efficient and selective carbon-carbon bond formation by Pd catalysts (Sect. III.2.2). The combination of PdCl2(dppf) with KOAc (and dppf) is effective in the carbon-boron bond formation. KOAc is essential not only to accelerate the reaction but also to prevent the formation of biaryl by-products. 

Several years later, Reynolds and co-workers [179] extended this work to prepare another sulfonated poly(p-phenylene) using the same approach by replacing 1,4-diboronic acid with 4,4 -biphenyl diboronic ester ... 

Esterification of arylboronic acids Preparation of phenyl-1,4- diboronic acid bis-pinacol ester (266) 18/... 

An efficient green-emitting fluorene copolymer 65a was synthesized by Shim and co-workers via Suzuki coupling of 2,5-dibromothieno[3,2-fc]thiophene with 9,9-dioctylfluorene-2,7-diboronic acid bis(pinacol ester) [103]. The authors compared the EL properties of this copolymer with those of PEO and PEO-bithiophene copolymer 52a. The absorption and emission spectra of 65a are red shifted compared with PFO but slightly blue shifted compared with 52a. A PLED fabricated in the configuration ITO/PEDOT/ 65a/LiF/Al showed a pure green emission (CIE x = 0.29, y = 0.63) with a turn-on voltage as low... 

An improved procedure for benzene diboronic acid and ester (50-60%) Todd, M. H. Balasubramanian, S. Abell, C. Tetrahedron Lett. 1997,38, 6781. 

The Suzuki polymerization is the AA-BB type, and the monomers are usually diarylbromide compounds and diarylboronate esters. It is possible to use diboronic acids as monomers, but the diboronate esters are generally used because they are more easily purified than diboronic acids. 

This monomer, also named 9,9-dihexylfluorene-2,7-diboronic acid bis(l,3-propanediol) ester, is commercially available. The propanediol or pinacol boronate esters of dialkylfluorenes with different alkyl chain lengths are also commercially available products, and these compounds can be used directly in the following Suzuki polymerization. However, the given synthetic procedures for boronate ester monomers will be useful for preparing new fluorene monomers, which are not commercially available. 

The aoss-coupling reaction of bis(pinacolato)diboron with allyl acetates provides the pinacol esters of allylboronic acids in high yield (Scheme The reaction is effectively catalyzed by Pd(dba)2 in DMSO at 50 °C. The reaction more or less accompanies the formation of biallyl, the amount of which markedly depends on the kind of leaving group of the al-lyhc substrates. E)- and (Z)-Cinnamyl acetate and a-phenylallyl acetate aU provide trans-cinnamylboronic acid ester selectively and in almost the same yield, which suggests that the reaction proceeds via ir-allylpalladium as a common intermediate. 

---