Selective benzoylation

Jacob et al/12] found that o-xylene can be benzoylated selectively to 3,4-dimethyl-benzophenone using zeolites as catalysts and benzoyl chloride as benzoylating agent. As shown in Scheme 4.2, zeolite H-BEA exhibits higher activity and selectivity for 3,4-dimethylbenzophenone (3,4-DMBP) than that of the other zeolite catalysts (H-ZSM-5, H-Y and H-MOR), due on the one hand to its stronger acid sites compared with the other zeolite catalysts and on the other hand to smaller pore openings (7.6 x 6.4 A and 5.5 x 5.5 A) than H-Y (7.4 x 7.4 A) zeolite, leading to a shape selectivity. In another article on benzoylation of toluene and naphthalene/101... 

Acylation of electron-rich arenes with AC, BC, and benzotrichloride can be performed in the presence of hydrated zirconia. The catalyst is prepared by treatment of an aqueous solution of zirconium(IV) oxychloride octahydrate (ZrOCl2 x 8H2O) with aqueous sodium hydroxide at room temperature, followed by heating the precipitate at 300°C for 5 h. The acetylation is performed in 1,2-dichloroethane at 60°C, whereas benzoylation is carried out under solventless conditions at 120°C (Table 4.16). It is remarkable that naphthalene is benzoylated selectively at the 1-position. The catalyst is recovered by filtration and reused three times with no loss of activity and selectivity in all cases. 

Benzoates. The selective debenzoylation of sucrose octabenzoate [2425-84-5] using isopropylamine in the absence of solvents caused deacylation in the furanose ring to give 2,3,4,6,1/3/6 -hepta- and 2,3,4,6,1/6 -hexa-O-benzoyl-sucroses in 24.1 and 25.4% after 21 and 80 hours, respectively (54). The unambiguous assignment of partially benzoylated sucrose derivatives was accompHshed by specific isotopic labeling techniques (54). Identification of any benzoylated sucrose derivative can thus be achieved by comparison of its C-nmr carbonyl carbon resonances with those of the assigned octabenzoate derivative after benzoylation with 10 atom % benzoyl—carbonyl chloride in pyridine. 

Thiophene is much more easily nitrated than benzene and it is therefore possible to use mild nitrating agents such as acetyl or benzoyl nitrate. Like pyrrole and furan the principal nitration product is the 2-derivative. The a selectivity decreases with increasing vigour of the reagent and up to 15% of the 3-isomer has been obtained. 

BzCl or BZ2O, Pyr, 0°. Benzoyl chloride is the most common reagent for the introduction of the benzoate group. Reaction conditions vaiy depending on the nature of the alcohol to be protected. Cosolvents such as CH2CI2 are often used with pyridine. Benzoylation in a polyhydroxylated system is much more selective than acetylation. A primary alcohol is selectively... 

Me2CHCH2)2AlH, PhCH3, —78°, 80% yield. Since the /V-benzoyl group in this substrate could not be removed by hydrolysis, a less selective reductive cleavage with diisobutylaluminum hydride was used. 

Electrolysis, Me4N Cl , 5°, 65-98% yield. " Acylation of a tosylated amine with BOC or benzoyl reduces the potential required for electrolytic cleavage so that these aryltosyl groups can be selectively removed in the presence of a simple tosylamide. °... 

Bhattacharjee et al. [79] introduced another new catalyst based on a Pd complex containing both acetate and benzoyl pyridine ligands (Table 6). This was developed to hydrogenate liquid carboxylated nitrile rubber (L-XNBR) [80]. Selective hydrogenation of C=C in L-... 

The furanoid vinyl ethers described above are of interest in view of the structure of the nucleoside antibiotic angustmycin A (2) (15) which also contains an exocyclic double bond. As a first step towards the synthesis of analogs of angustmycin A (2), preparation of exocyclic vinyl ethers from hexulofuranoid derivatives was studied. Benzoylation of 2,3 4,6-di-0-isopropylidene-a-L-ryZo-hexulofuranose (44) followed by selective acid hydrolysis of the 4,6-O-isopropylidene group afforded l-0-benzoyl-2,3-0-isopropylidene-a-L-ryZohexulofuranose (45) in 72%... 

This indirect method of selective benzoylation at C-4 is of special interest in the galacto series (47). Reaction of methyl 4,6-O-benzylidene-a-D-galactopyranoside 97 with NBS afforded the corresponding 6-bromo-4-benzoate (98) in over 90% yield. The axial hydroxyl group at C-4... 

The polymerization of vinyl monomers on the surface of silica can be induced also by free radical initiators such as azo-bis-isobutyronitrile (AIBN), di-tert-butylperoxide, benzoyl peroxide etc. The selection of initiator type and method of its introduction in polymerizable systems are determined by the nature of monomers and tasks of investigations. Usually, the following procedures are used ... 

The reaction is less selective than the related benzoylation reaction (/pMe = 30.2, cf. 626), thereby indicating a greater charge on the electrophile this is in complete agreement with the greater ease of nuclophilic substitution of sulphonic acids and derivatives compared to carboxylic acids and derivatives and may be rationalized from a consideration of resonance structures. The effect of substituents on the reactivity of the sulphonyl chloride follows from the effect of stabilizing the aryl-sulphonium ion formed in the ionisation step (81) or from the effect on the preequilibrium step (79). 

---