4-Chlorophenylboronic acid

Milkiewicz et al. <2003TL4257> prepared a series of novel tetrasubstituted furo[3,2-/ ]pyrroles from the methyl or ethyl 3-bromo-2-phenylfuro[3,2-3]pyrrole-5-carboxylate 336. The compounds 336 were subjected to a Suzuki coupling with 4-chlorophenylboronic acid to form 337, which was treated with a variety of alkylating agents to afford the corresponding esters 338. The esters were then saponified to acids 339 (Scheme 34). 

In 1995, Queguiner reported a new route to antihypertensive 5,6-diarylpyridazin-3(2//)-ones starting from 4-acetyl-6-chloro-5-iodo-3-methoxypyridazine (79) [34]. 79 was synthesized of 79 from 6-chloro-4-(l-hydroxyethyl)-5-iodo-3-methoxypyridazine (37) by oxidation with Mn02 or PCC. The new route involves a chemoselective Suzuki arylation of a C—I over a C—Cl bond on a pyridazine nucleus. In a first Suzuki reaction, C-5 selective arylation of 79 could be obtained using only a slight excess of arylboronic acid. Subsequently, the obtained 4-acetyl-5-aryl-6-chloro-3-methoxypyridazines (80) were transformed into unsymmetrically arylated 4-acetyl-5,6-diaryl-3-methoxypyridazines (81) via a second Suzuki reaction. For this second arylation, an excess of arylboronic acid (2 equivalents) was used. By using 4 equivalents of 4-chlorophenylboronic acid on 79 symmetrically arylated 4-acetyl-5,6-bis(4-chlorophenyl)-3-methoxypyridazine was obtained in 85% isolated yield. 

Biaryls are prepared also by homocoupling of arylmetal compounds using several oxidants. Arylbronic acids undergo efficient oxidative coupling [167]. 4,4 -Dichlorobiphenyl (407) was obtained in 72 % yield from 4-chlorophenylboronic acid (406) using Cu(N03)2 as an oxidant [168]. 

Asymmetric addition of 4-chlorophenylboronic acid (2u) to a,P-unsaturated y-amino ester (26a), followed by deprotection and ester hydrolysis gave optically active 4-amino-3-(4-chlorophenyl)butyric acid (Baclofen) hydrochloride (Scheme 4.10), which plays an important role in various nervous system functions. The best result was observed with a large excess of organoboronic acids (5.0 equiv to 26a) in a 10 1 dioxane-water mixture containing aqueous cesium carbonate [24]. 

Monomethoxy PEG 5000 polymer (1 g) esterified with ortho-iodobenzoic acid (54) (approx. 0.19 mmol) was dissolved in distilled DMF (5 mL). 2,4-Di-chlorophenylboronic acid (55) (73 mg, 0.38 mmol, 2 equiv.), Pd(PPbi)4 (11.6 mg, 0.01 mmol, 0.05 equiv.), and 2 m sodium carbonate (0.25 mL, 0.5 mmol, 2.5 equiv.) were added. The mixture was stirred under argon at 110 °C for 10 h in a screw cap culture tube. Toluene was added and insoluble... 

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