Acids phenyl boronic acid synthesis

Phenyl boronic acid synthesis (Clariant/Frankfurt) [10]... 

Temperature profile of the phenyl boronic acid synthesis along the major steps of the process flow scheme. The difference in the temperatures of the conventional batch and the microreactor processes stand for the reduction in energy consumption and respective heat-transfer equipment when using the latter [10]... 

This concept has been applied in the phenyl boronic acid synthesis (Scheme 3.1) [177]. 

Phenyl Boronic Acid Synthesis (Scheme 6.1) (Clariant/Frankfiirt + IMM)... 

The Baccatin III synthesis by K. C. Nicolaou and co-workers is summarized in Scheme 13.54. Diels-Alder reactions are prominent in forming the early intermediates. In Step A the pyrone ring served as the diene. This reaction was facilitated by phenyl-boronic acid, which brings the diene and dienophile together as a boronate, permitting an intramolecular reaction. 

Krische and coworkers [44] developed a Rh-catalyzed asymmetric domino Michael/aldol reaction for the synthesis of substituted cyclopentanols and cyclohex-anols. In this process, three contiguous stereogenic centers, including a quaternary center, are formed with excellent diastereo- and enantioselectivity. Thus, using an enantiopure Rh-BINAP catalyst system and phenyl boronic acid, substrates 2-108 are converted into the correspondding cyclized products 2-109 in 69-88% yield and with 94 and 95% ee, respectively (Scheme 2.24). 

In a more recent study, Wang and coworkers have discussed microwave-assisted Suzuki couplings employing a reusable polymer-supported palladium complex [141]. The supported catalyst was prepared from commercial Merrifield polystyrene resin under ultrasound Bonification. In a typical procedure for biaryl synthesis, 1 mmol of the requisite aryl bromide together with 1.1 equivalents of the phenyl-boronic acid, 2.5 equivalents of potassium carbonate, and 10 mg of the polystyrene-... 

Wulff and his collaborators reported, in 1989, the preparation of imprinted polymers able to perform enantioselective synthesis [11, 12]. The imprinting complex was prepared by reacting 3,4-di-hydroxy-phenyl-alanine methyl-ester (l-DOPA methyl ester) (16) with the 4-vinyl-salicylaldehyde (17) to form the corresponding Schiff s base (18), which was further reacted with the 4-vinyl-phenyl-boronic acid (19) to afford to the corresponding ester (20) (Scheme 4). The imprinting complex obtained was then polymerised and the template removed. The resulting polymers were incubated with sodium glycinate to allow formation... 

Tschierske developed a variety of molecules containing a p-terphenyl unit as backbone equipped with two terminal decyloxy chains and laterally attached crown ethers of different sizes [51-53]. The synthesis was straightforward starting from methyl-2,5-dibromobenzoate 30 that was coupled with [4-(decyloxy)phenyl]boronic acid 31 in a subsequent Pd°-catalyzed Suzuki reaction. The 2-hydroxymethyl crown ethers 32 were attached in the last step (Scheme 18) to yield mesogenic 33. 

Typical industrial process for the synthesis of phenyl boronic acid from phenylmag-nesium bromide and boronic acid trimethoxy ester requires strict temperature control (—25 to —55 °C) to minimize the formation of side products. Recently, Hessel and coworkers reported that a micromixer (width 40 pm and depth 300 pm)/ tubular reactor system gave the phenyl boronic acid at high yield (>80%) even at higher temperatures (22 or 50 °C) with minimum amounts of the side products (Scheme 4.48) [66]. They also achieved a pilot-scale production by employing a caterpillar minimixer (width range 600-1700 pm and depth range 1200-2400 pm). 

Clariant GmbH in Frankfurt, Germany, performed the synthesis of phenyl boronic acid from phenyl magnesium bromide and boronic acid trimethyl ester on a pilot-... 

The (—)-quinine-catalyzed IMA of 40 gave cw-(- -)-methoxy chromanone cou-marin (cA-41) in 67% yield with 98% ee and its trans-41 in 21% yield with lower eantioselectivity (39% ee). The Mgl2-assisted isomerization of cis-(+)-41 accompanied by demethylation followed by the reaction of the formed diastereomeric mixture of chromanone 42 (without separation) with senecioyl aldehyde in the presence of phenyl boronic acid under the same condition to construct the 2,2-dimethyl chromanone ring reported in the synthesis of (+)-inophyllum B (3). The yield of trans-(+)-43 in 61% with 91% ee and its cw-isomer (+)-43 corresponded to the (+)-calanolide D as a minor product in 23% yield with 84% ee. At last, the synthesis of (+)-calanolide A (1) was accomplished by hydride reduction of (+)-43 with... 

A key intermediate required for the synthesis of coelenterazine was described, where aryl 2-aminopyrazines (85, 86, 87) were effectively prepared via Suzuki coupling starting from the corresponding 2-amino-5-bromopyrazines (88, 89, 90) and z-butyl-dimethylsilyloxy-4-phenyl boronic acid (91) [49, 50]. 

Suh et al.65 have reported a formal total synthesis of Mansonone F and this is described in Scheme 12. 5-Methoxy-a-tetralone (127) was converted to 1-methyl-5-hydroxy-naphthalene (128) by the standard organic reactions. Treatment of (128) with phenyl boronic acid, paraformaldehyde and propionic acid followed by catalytic hydrogenation yielded compound (129). This on alkylation gave the compound (130) which on alkaline hydrolysis was converted to acid. The acid halide underwent intramolecular Friedal-Crafts acylation affording an intermediate (131) whose transformation to Mansonone F has been accomplished by Best and Wege.59... 

For carbon nanotubes, organosoluble PS-SWCNT nanocomposites [292] have been prepared that could be efficiently transformed to highly hydrosoluble, pH-responsive materials via direct sulfonation of the grafted PS chains [296]. In another approach, MWCNT-C H was clicked with azide-functionalized poly(glycerol methacrylate) and the final hairy MWCNTs were used for the in situ synthesis and immobilization of monodisperse 3 nm-sized palladium nanoparticles. The final heterostructure had a high catalytic activity (77%) for the C-C coupling Suzuki reaction between 4-bromobenzene and phenyl boronic acid [293],... 

The synthesis of 3-trifluoromethyl-2-phenylindole 117 was accomplished by succeeding palladium catalyzed carbon-carbon cross-coupling of 116 with phenyl-boronic acid and carbon-nitrogen coupUng in the presence of S-Phos [47]. 

Boronic esters (3) can be homologated to a-chloroboronic esters (4) (Scheme 2) replacement of the chlorine atom by carbon nucleophiles, such as Grignard reagents, and oxidation of the carbon-boron bond gives a new route to alcohols/ If the sequence is performed with (+)- or (-)-pinanediol boronic esters it can be made into a directed chiral synthesis of alcohols, as illustrated in Scheme 3 from phenyl boronic acid the homologation steps were found to occur with diastereoselectivities in excess of 90%, the chlorine replacement proceeds with inversion, and the oxidative step with retention of configuration. 

Bumagin, N.A. Bykov, V.V. Beletskaya, I.P. (1989) Synthesis of biaryls from phenyl-boronic acid and aryl iodides in aqueous media, Izv. Akad. Nauk SSSR, Ser. Khim., 2394. 

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