Carbonyl compounds quaternary ammonium catalysts

Darzens condensation of chloroacetonitrile and carbonyl compounds to give glycidic nitriles can be carried out in the presence of aqueous sodium hydroxide and a quaternary ammonium catalyst, such as triethylbenzylammonium chloride (TEBA equation 32). In a subsequent study, interesting stereochemical control was obtained in an interfacial Darzens condensation. Condensation of a-chloro-phenylacetonitrile (93) with benzaldehyde, conducted in benzene in the presence of 50% aqueous sodium hydroxide and TEBA as a phase transfer catalyst, affords predominantly the traru-glycidonitrile (94) accompanied by the corresponding cis isomer (95 equation 33). Similar results are obtained when... 

Carbonyl Compounds. Cychc ketals and acetals (dioxolanes) are produced from reaction of propylene oxide with ketones and aldehydes, respectively. Suitable catalysts iaclude stannic chloride, quaternary ammonium salts, glycol sulphites, and molybdenum acetyl acetonate or naphthenate (89—91). Lactones come from Ph4Sbl-cataly2ed reaction with ketenes (92). 

Polk et al. reported27 that PET fibers could be hydrolyzed with 5% aqueous sodium hydroxide at 80°C in the presence of trioctylmethylammonium bromide in 60 min to obtain terephthalic acid in 93% yield. The results of catalytic depolymerization of PET without agitation are listed in Table 10.1. The results of catalytic depolymerization of PET with agitation are listed in Table 10.2. As expected, agitation shortened the time required for 100% conversion. Results (Table 10.1) for the quaternary salts with a halide counterion were promising. Phenyltrimethylammonium chloride (PTMAC) was chosen to ascertain whether steric effects would hinder catalytic activity. Bulky alkyl groups of the quaternary ammonium compounds were expected to hinder close approach of the catalyst to the somewhat hidden carbonyl groups of the fiber structure. The results indicate that steric hindrance is not a problem for PET hydrolysis under this set of conditions since the depolymerization results were substantially lower for PTMAC than for die more sterically hindered quaternary salts. 

Some chiral quaternary ammonium salts are also effective in Michael addition reactions. The Merck catalysts 7 (R=4-CF3, X=Br) and 9 (R=4-CF3, X=Br, 10,11-dihydro) were used tor the Michael additions of 59,61, and 64 to vinyl ketones to give the adducts 60,62, and 65 (isolated as 66), respectively,148,491 with excellent enantioselectivity, as shown in Scheme 19. The Michael addition of the O Donnell imine 23 to the a,(3-unsaturated carbonyl compounds also efficiently proceeded by use of the N-anthracenyl-methyl catalyst 12 (R=allyl, X=Br), giving the Michael adducts 67 (Scheme 20).1251... 

Rozwadowska and coworkers carried out the asymmetric alkylation of isoquino-line Reissert compounds under phase-transfer conditions using cinchonine-derived quaternary ammonium salts as catalysts. The best enantioselectivity was achieved in the benzylation and allylation of 1 -cyano-2-phenoxy carbonyl-1,2-dihydroisoquinoline (17) catalyzed by 2a (Scheme 2.14) [34]. 

In a series of papers [30-35], Blum and co-workers reported the hydrogenation of alkenes, alkynes, and arenes in the presence of a hydrated ion-pair [0ct3NMe] [RhCl4(H20)n] . The quaternary ammonium tetrachlororhodate also catalyzes HTR of alkynes, alkenes and a,j6-unsaturated carbonyl compounds with polymethylhydrosiloxane [36, 37]. Recently, heterogenized and therefore recyclable quaternary ammonium halometallates, namely glass-encapsulated catalysts [38] and polymer-bound tetrachlororhodate [39], have been described. Both types of the insoluble catalysts effectively promote various processes including the hydrogenation of alkenes and the HTR of a,/9-unsaturated carbonyl compounds [40]. 

The strongly basic Dowex 1-XIO (a quaternary ammonium hydroxide resin) has been used to condense carbonyl compounds with cyclopentadiene to produce I lilvenes. " The system has the advantage that the reaction time can be controlled by regiiliiting the time of contact of the catalyst with the reactants. 

The Darzens reaction (tandem aldol-intramolecular cyclization sequence reaction) is a powerful complementary approach to epoxidation (see Chapter 5) that can be used for the synthesis of a,P-epoxy carbonyl and a,p-epoxysulfonyl compounds (Scheme 8.32). Currently, all catalytic asymmetric variants of the Darzens reactions are based on chiral phase-transfer catalysis using quaternary ammonium salts as catalysts. 

In 1994, the first enantioselective trifluoromethylation reaction was achieved with the Ruppert-Prakash reagent, TMSCF3, in the presence of the cinchona-based quaternary ammonium fluoride 140 [65]. The chiral induction can arise from the dual activation mode of the catalyst, that is, the fluoride anion acts as the nucleophilic activator of (TMS)CF3 and the chiral ammonium cation activates the carbonyl group of 141. However, the observed ee values of the obtained carbinols 142 do not exceed 51 % and decrease considerably when nonaromatic carbonyl compounds (15% ee for R1 = n-C7H15 R2 = H) are used, which implies that 7t-7t stacking interactions between the carbonyl compound and cinchoninium occur (Scheme 8.54). 

A process for the coproduction of acetic anhydride and acetic acid, which has been operated by BP Chemicals since 1988, uses a quaternary ammonium iodide salt in a role similar to that of Lil [8]. Beneficial effects on rhodium-complex-catalyzed methanol carbonylation have also been found for other additives. For example, phosphine oxides such as Ph3PO enable high catalyst rates at low water concentrations without compromising catalyst stability [40—42]. Similarly, iodocarbonyl complexes of ruthenium and osmium (as used to promote iridium systems, Section 3) are found to enhance the activity of a rhodium catalyst at low water concentrations [43,44]. Other compounds reported to have beneficial effects include phosphate salts [45], transition metal halide salts [46], and oxoacids and heteropolyacids and their salts [47]. 

Trifluoromethylation. Carbonyl compounds are converted into the trifluoro-methyl carbinols in excellent yields by this reagent in the presence of a quaternary ammonium fluoride. Moderate asymmetric induction is observed when a chiral catalyst is used. 

Quaternary ammonium salts derived from ephedrine have been used as catalysts for the addition of dialkylzinc to carbonyl compounds (Section D.1.3.1.4.) and are useful as phase-transfer catalysts for alkylation of carbonyl compounds17 and reductions18. N-Benzyl-A -methylephedri-nium salts 10 have found varied application they are easily prepared from A -methylephedrine 913 by reaction with benzyl halide in toluene1 or chloroform/methanol (1 1)18 in high yield. Ref 18 also gives the preparation of other ephedrinium and pseudoephedrinium salts. 

We have recently discovered a new, very active and selective catalytic system able to catalyze the N-carbonyl at i on o-f aromatic nitro compounds [28<. The catalyst comprises Ru3quaternary ammonium salt as co-catalyst. Under optimal experimental conditions (160"C, 60 atm at room temperature, NEt Cl" as co-catalyst, in toluene with small amounts o-f methanol) 100% conversion was observed, with a selectivity -for PhNHC02Me up to 95%, the other product being aniline. The reaction... 

Mukaiyama-Michael Reactions. 1,4-Addition of ketene alkyl silyl acetals to a./S-unsaturated carbonyl compounds (eq 10) is promoted by a variety of Lewis acids (for example, TiCU, Ti(OR)4, SnCU, trityl perchlorate, lanthanide salts, Al-montmo-rillonite clay), or Lewis bases such as fluoride ion (eq 11), or quaternary ammonium carboxylates. Lanthanide salts are particularly effective catalysts, and in the case of ytterbium(III) tri-fluoromethanesulfonate, the catalyst can be recovered (eq 10). ... 

Another calixarene-based phase-transfer catalyst was designed by Srivastava and Srivastava [20]. In that study, two different quaternary ammonium salts of calix [4]arene (Calix[4]arene 2a and 2b) were employed as a catalyst in the Darzens condensation to synthesize a,p-epoxy carbonyl compounds (see Fig. 27.5). It was found that these phase-transfer catalysts exhibited significant catalytic activity, especially when the calix[4]arene with long aUcyl chain ( -butyl) was chosen (see Table 27.3). 

In the 1990, Chauvin and coworkers have introduced ionic liquids (ILs) - especially those derived from the combination of quaternary ammonium salts and weakly coordinating anions - as immobilizing agents for various classical transition metal catalyst precursors in reactions [1]. In particular, these liquids provide more adequate and favorable environment for carbonylation reactions as compared to those performed in classical organic solvents or water. The vast majority of these compounds a) are effectively nonvolatile (most of them exhibit negligible vapor pressure) ... 

The cation fragment nature exerts negligible impact on selectivity of the Michael reactions that involve enamine intermediates and commonly the stereochemical outcome remains high. Indeed, pyrrolidine derivatives (Figure 22.6) containing pyridinium 87a,b [98], isoquinolinium 88a,b [99], 1,2,3-triazolium 89a,b [100], benzimidazolium 90 [101], and linear 91 [102] or cyclic 92 [103] quaternary ammonium cations in combination with various anions proved efficient catalysts of asymmetric additions of carbonyl compounds to a-nitro alkenes. Desymmetriza-tion of prochiral 4-substituted cyclohexanones can be achieved by analogy [101]. The reaction efficacy was similar under neat conditions in the presence of acidic additives (catalysts 87, 89, 90, 91) or in the IL medium (commonly in [bmim]BF4) (catalysts 88a,b, 92). 

The reaction mechanism is proposed to consist of four steps (Fig. 5.43). In the first step, a bromo carbonyl compound 1 is bound to the tertiary amine catalyst 3, forming a quaternary ammonium salt I. Formation of the yHde II requires deprotonation with a mild base (CS2CO3). Conjugate addition of aUcene 2 to the yHde leads to a complex III, which undergoes 3-exo-tet cychzation generating cyclopropane 4 as the product. 

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