4- phenylboronic

Suzuki coupling reactions with aryl halides. Two as-prepared BaCei cPd c03. ( materials (x = 0.05 and 0.10) were successfully utihzed in several Suzuki coupling reactions. Both aryl iodides and aryl bromides react smoothly with 4-phenylboronic acid, eq 1, to yield the corresponding biatyls in high yields (> 95%). For both 4-bromoanisole and 4-iodoanisole, the biatyl yields reached nearly 100% in 3 min with BaCeo 95Pdoo503 5 as the catalyst, corresponding to an effective TON of ca. 2,000 and an effective TOF of nearly 50,000 h. Resnlts are smmnarized in Table 27.1. 

Maitlis filtration test. To investigate whether the Pd-doped perovskite is the actual catalyst, or a reservoir of soluble Pd, a Maitlis filtration test (10) was performed. The reaction of 4-bromoanisole with 4-phenylboronic acid, catalyzed by BaCeo 95Pdo os02 95, was intemipted at 20 s and 1 min, corresponding to conversions of 16 and 45%, respectively, by filtering the hot reaction mixture to remove the solid perovskite. The filtrates were allowed to cool to room temperature without stirring. After 3 h, the biatyl yields in both samples were estimated to be 100% by H NMR. 

Solvent effect. Several different solvent systems were investigated for the coupling of 4-bromoanisole with 4-phenylboronic acid catalyzed by BaCeo 95Pdoo50295. The resnlts are summarized in Table 27.2. A phase-transfer catalyst (Aliquat 336) was added in the experiment involving toluene/H20. However, only the IPA/H2O solvent system was effective, resulting in a biaiyl yield of 100% all other solvents gave rather low yields. 

Catalyst recycling. The solid Pd-doped perovskite catalysts are easily filtered from the reaction mixtnre for reuse. The activity of the recycled BaCco 95Pdo.o502 95 catalyst was investigated in the coupling of 4-bromoanisole with 4-phenylboronic acid. The results in Table 27.3 show that high activity was retained even after seven cycles of catalyst use. 

In 1956, a ribose diphenylboronate (m.p. 140-142°) was prepared in modest yield by a lusion method,7 but it was later shown26 that an almost quantitative yield of a mono-ester was obtainable by conducting the condensation in hot 2-methoxyethanol, and this was a-D-ribose 2,4-phenylboronate (22), as indicated by p.m.r. and nB-n.m.r. analysis,45 and conversion by selective substitution into the 3-p-toluenesulf-onate.48 It is here suggested that the 2,4-ester (22) might be very sus-... 

Methacrylic anhydride in pyridine, applied to 1,6-anhydro-D-glucose 2,4-phenylboronate, gave the 3-methacrylate, from which an addition polymer was prepared.78... 

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