Catalysts biphenyl alkylation

Preparation of the starting material DIPB is typically achieved by isopropylation of benzene or cumene by use of conventional Friedel-Crafts catalysts [8] although solid acids [9], resins [10] and, more recently, zeolites [11,12] have also been mentioned as catalysts. Likewise, alkylation of polynuclear aromatics, e. g. biphenyl or naphthalene, gives rise to valuable intermediates. 4,4 -DialkyIbiphenyl can be converted into 4,4 -biphenyldicarboxylic acid, a monomer for a variety of... 

The increased activity and stability combined with the shape-selective elfect of these tailored mordenites is illustrated beautifully by comparing results for biphenyl alkylation with those obtained using either a more traditional catalyst or non-modified zeolites. The results are summarized in Table 1 [15]. DHM-2X is a modified mordenite later referred to by Dow as 3-DDM after the more extensive studies described above. The Si02/Al203 molar ratio of this sample was 2600. The Zeolon 100 sample is a standard commercially available mordenite with a Si02/ AI2O3 ratio of 10. 

Pd-catalyzed asymmetric allylic alkylation is a typical catalytic carbon-carbon bond forming reaction [ 126 -128]. The Pd-complex of the ligand (R)-3b bearing methyl, 2-biphenyl and cyclohexyl groups as the three substituents attached to the P-chirogenic phosphorus atom was found to be in situ an efficient catalyst in the asymmetric allylic alkylation of l-acetoxy-l,3-diphenylprop-2-en (4) with malonate derivatives in the presence of AT,0-bis(trimethylsilyl)acetamide (BSA) and potassium acetate, affording enantioselectivity up to 96% and quantitative... 

Dichloroalkyl)chlorosilanes undergo the Friedel-Crafts alkylation type reaction with biphenyl in the presence of aluniinurn chloride catalyst to afford 9-((chlorosilyl)alkyl)fluorenes through two step reactions (Eq. (16)). The results obtained from the alkylation of biphenyl and the cyclization reaction to 5-membered-ring product are summarized in Table XIIE... 

The mechanism for the production of 9-((chlorosilyl)alkyl)(luorenes from the Friedel-Crafts alkylation reaction of biphenyl with (l,2-dichloroethyl)silane in the presence of aluminum chloride as catalyst is outlined in Scheme 4. At the beginning stage of the reaction, one of two C—Cl bondsof (1,2-dichloroethyl)silane (CICH2—CICH—SiXi) interacts with aluminum chloride catalyst to give intermediate 1 (a polar +C-CI - ( +C-C1—Al CI3) or a carbocation C AICU ... 

Fig. 2.22 Combination of chiral imidazolidin-2-ylidenes and biphenyl linkers in the chiral catalysts or catalyst precursors for the asymmetric allylic alkylations...

An enantioselective synthesis of both (R)- and (5)-a-alkylcysteines 144 and 147 is based on the phase-transfer catalytic alkylation of fert-butyl esters of 2-phenyl-2-thiazoline-4-carboxylic acid and 2-ort/ro-biphenyl-2-thiazoline-4-carboxylic acid, 142 and 145 <06JOC8276>. Treatment of 142 and 145 with alkyl halides and potassium hydroxide in the presence of chiral catalysts 140 and 141 gives the alkylated products, which are hydrolyzed to (R)- and (S)-a-alkylcysteines 144 and 147, respectively, in high enantioselectivity. This method may have potential for the practical synthesis of chiral a-alkylcysteines. 

In contrast, there are relatively few publications on the conversion of polynuclear aromatics in zeolite catalysts. Lee et al. [16] found unusually high selectivities for 4,4 -diisopropylbiphenyl when dealuminated mordenite was used as catalyst for the alkylation of biphenyl with propene. The reactions of 1- and 2-methylnaphthalene on acid forms of zeolite X, Y, Omega, mordenite and ZSM-5 were studied byDimitrov etal. [17], S o 1 i n a s et... 

The product distribution in the zeolite-catalysed alkylation of polynuclear aromatics depends on the structure of zeolite pores. High regioselectivities were observed in the HM catalysed isopropylation of polynuclear aromatics, such as biphenyl, naphthalene, p-terphenyl, and dibenzofuran, to yield predominantly the least bulky products e.g., 4,4 -DIPB for biphenyl, and 2,6-DIPN for naphthalene. These reactions are controlled by steric restriction at the transition state inside the pores and by the entrance of intermediate products molecules into the pores. On the other hand, the catalysts with large-pore HY and HL zeolite are controlled at low temperature by the electron density of the reactant molecule and at higher temperature by the stability of the product molecules because their pores have enough space for a transition state, which allow the formation of all corresponding isomers. 

The group of Jew and Park successfully utilized dihydrocinchonidine-derived 6f as an efficient catalyst for the asymmetric alkylation of o-biphenyl-2-oxazoline- and o-biphenyl-2-thiazoline-4-carboxylic acid tert-butyl esters (16a and 16b) under mild solid-liquid phase-transfer conditions (Scheme 2.13) [32,33]. These reactions are... 

The phase-transfer benzylation of 2 with the catalyst (S)-12a having [1-naphthyl group on the 3,3 -position of the flexible biphenyl moiety proceeded smoothly at 0 °C to afford the corresponding alkylation product (R)-3 in 85% yield with 87% ee after 18 h. The origin of the observed chiral efficiency could be ascribed to the considerable difference in catalytic activity between the rapidly equilibrated, diaste-reomerichomo- and heterochiral catalysts namely, homochiral (S,S)-12a is primarily responsible for the efficient asymmetric phase-transfer catalysis to produce 3 with high enantiomeric excess, whereas the heterochiral (R,S)-12a displays low reactivity and stereoselectivity. 

Friedel-Crafts alkylation occurs when biphenyl is treated with tert-butyl chloride and iron (III) chloride (a Lewis acid catalyst) the product of monosubstitution is p-ferf-butylbiphenyl. All the positions of the ring that bears the tert-butyl group are sterically hindered, so the second alkylation step introduces a tert-butyl group at the para position of the second ring. 

Under the usual commercial hydrodesulfurization conditions (elevated temperatures and pressures, high hydrogen-to-feedstock ratios, and the presence of a catalyst), the various reactions that result in the removal of sulfur from the organic feedstock (Table 4-3) occur. Thus, thiols as well as open chain and cyclic sulfides are converted to saturated and/or aromatic compounds depending, of course, on the nature of the particular sulfur compound involved. Benzothio-phenes are converted to alkyl aromatics, while dibenzothiophenes are usually converted to biphenyl derivatives. In fact, the major reactions that occur as part of the hydrodesulfurization process involve carbon-sulfur bond rupture and saturation of the reactive fragments (as well as saturation of olefins). 

Maruoka and co-workers developed an elegant solution by creating phase-transfer-catalysts of type 30 [36], For example, the C2-symmetric N-spiro organocatalyst (S,S)-30, which contains a conformationally flexible biphenyl subunit, efficiently catalyzed the alkylation of glycinate 18 with benzyl bromide, with formation of the product (R)-20b in 95% yield and with 92% ee (Scheme 3.10) [36],... 

Very recently, Maruoka and co-workers described a new N-spiro quaternary ammonium bromide with two chiral biphenyl structures as easily modifiable subunits [37]. These phase-transfer catalysts with biphenyl subunits, containing methyl groups in the 6,6 -position for inducing chirality, and additionally bulky substituents in the 4-position, efficiently catalyzed the alkylation of protected glycinate with high enantioselectivity of up to 97% ee. The substrate range is broad, for example (substituted) benzyl bromide and allylic and propargylic bromides are tolerated [37]. 

An important development followed in 1991,28 when Yus and Ramon showed that naphthalene, biphenyl and DBB could be used catalytically in the reduction of functionalised alkyl chlorides.29 9 Only 1% of the arene catalyst is required, and organolithiums are... 

For the alkylation of pofyaromatics and biphenyls Mordenite with high sihca to alumina ratios seems to be the prrferred catalyst. Lee at d. [64] observed that dealumination of Mord e by add wadiing with 6 N HNO3 modified the pore structure of Mordenite resulting in an increase in the total pore volume and e edalfy an increase in the volume of pores a diameter between 20 and 1000 A. In the isopropylation of b henyl an increase in the yield of diisopropylb henyl was obtained which mi t be ascribed to either the enhanced difiiision of the reactants and produds via the newly created meso-pores or the decrease in the rate of deactivation during the alkylation reaction. 

SbFs reacts with perfluoroindan and trifluoromethylbenzenes to generate benzyhc cations which readily alkylate polyfluorinated arenes [40]. The polyfluorinated a-fluorodiphenyhnefhyl cations thus obtained can be transformed to perfluorinated diphenyldifluoromefhanes by acidolysis (Scheme 14.15) or to benzophenones by hydrolysis (Scheme 14.16) [41]. In fhe presence of the SbFs catalyst, perfluorinated benzenes and olefins undergo electrophihc condensation with fluorinated olefins [42]. Pentafluorobenzene reacts with hexachlorobenzene in SbFs to give an unsymmetrical perhalogenated biphenyl via a radical cation intermediate [43]. 

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