Amines, alkylation catalyst

Madsen and co-workers have reported an important extension to the amine alkylation chemistry, in which oxidation takes place to give the amide product [13]. A ruthenium NHC complex is formed in situ by the reaction of [RuCl Ccod)] with a phosphine and an imidazolium salt in the presence of base. Rather than returning the borrowed hydrogen, the catalyst expels two equivalents of H. For example, alcohol 31 and benzylamine 27 undergo an oxidative coupling to give amide 32 in good isolated yield (Scheme 11.7). 

The reaction mechanism including the formation and decomposition of quaternary cations may be a general pathway in amine alkylation processes on acidic zeolites. Pouilloux et al. (247), for example, synthesized dimethylethylamine from ethylamine and methanol on an acidic catalyst. At the reaction temperature of 503 K, trimethylamine was determined by gas chromatographic analysis, which can be explained by the formation and decomposition of trimethylethylammonium ions, (CIl3)3N CH2CH3. 

Reeves and Hilbrich288 have reported the catalysis by pyridines of benzyl ketone alkylation they are less efficient than aliphatic trialkylamines. Reeves and White289 have also described the reaction of alkyl bromides with sodium cyanide, where pyrazine is a better catalyst (99% yield) compared to pyridine (12% yield). Isakawa et al.289 have also carried out addition of dichloro-carbene to cyclohexene under biphasic conditions, using heterocyclic amines as catalysts (e.g., iV-butylpiperidine gives 76% yield). 

Regiocontrol Although Michael additions to [Os]-phenol occur selectively at C4, addition at C2 is thermodynamically favored for phenol complexes that are substituted at C4. For C4-substituted phenol complexes, the regiochemistry can be controlled by varying the time, temperature, and catalyst (Figure 6) [29]. Additions of MVK to the estradiol complex 90 and the p-cresol 94 at —40 °C in the presence of an amine base catalyst result in regioselective C4 alkylation in high yields (91 and 95). However, when this reaction is performed at room temperature in the presence of a Zn2+ co-catalyst, the Michael acceptor adds at C2 to afford... 

A number of (R)- and (,S )-organolanthanide alkyl and amide complexes 1, bearing a homochi-ral substituent R on one cyclopentadienyl ring, were prepared and their catalytic activity in the enantioselective hydroamination-cyclization of 4-pentenylamines 3 was examined 11 113 These complexes are converted to the catalytically active species 2 in the presence of a large excess of the amine. Furthermore, catalyst epimerization (S)-2 to (/ )-2 or vice versa occurs and is complete in the early stages of preparative-scale reactions however, equilibrium homochiralities are frequently high, in some cases >95%. 

The Y zeolites have been identified as active catalysts for various reactions such as isomerisation, amination, alkylation and deamination [1-4]. Cu containing Y zeolites have been found particularly useful to catalyse Diels - Alder cycloaddition [5-6]. Dehydration of t-BuOH has been suggested as a model reaction for estimating the zeolite acidity [7]. The dehydration of t-BuOH has received particular attention as tertiary species gives the most stable carbonium ion. The dehydration of alcohols by zeolites has been extensively studied... 

The catalysts used are usually base catalysts such as an alkyl-imidazole or tertiary amines. The catalysts may be blocked or... 

Denton et al. describe a procedure for aminating alkyl aromatic hydrocarbons, particularly toluene, which is converted to benzonitrile. Toluene and ammonia, at various reactant ratios and liquid space velocities, are passed at atmospheric pressure over a supported molybdenum trioxide catalyst at about 525-550 C. The conversion per pass is -10 per cent, and the yields are 60-85 per cent based on the toluene consumed. The process, as operated commercially, involves the continuous feed of toluene and NHj to one of two reactors followed by continuous removal of ammonia and toluene, for recycle, from the benzonitrile. Catalyst in one reactor is regenerated over a 3-6 hr period by oxidizing carbon deposits with air diluted with an inert gas, while the other reactor is on stream. 

Ethylene oxide adds easlily to an alkyl amine without catalyst forming alkyl diethanol amines or ethoxylated alkyl amines as mentioned previously (pseudocationic nonionics as discussed in Sec. 1.2.6). Primary amine and acylated polyamine ethoxylation brings forth milder and low-toxic surfactants. 

Anthrones [204] and 3-substituted oxindoles [205] possess activated methylenes which have been able to react under asymmetric iminium catalysis with a,p-unsaturated aldehydes. The reaction with 3-substituted oxindoles is especially attractive, since chiral quaternary stereocenters are generated. For this purpose, chiral primary amine thiourea catalyst 132 has been demonstrated as a very efficient promoter for the addition of 3-alkyl substituted oxindoles to P-aryl substituted enals in the presence of benzoic acid as cocatalyst in toluene at rt to afford the corresponding Michael adducts in good diastereoselectivities (dr up to >19/1) and good enantioselectivities (73-93% ee) (Scheme 2.75) [205a], P-Alkyl substituted enals are not suitable partners for the reaction affording very low diastereo- and enanti-... 

In the domino Michael/alkylation reaction applied to the synthesis of 3-(2H)-furanones, the ethyl 4-bromoacetoacetate 203 and nitrostyrene 204 were first trialed with a range of catalysts. In this instance, the so-called modified Feist Binary reaction was completed with an I-threonine bifunctional tertiary amine/thiourea catalyst 205 to produce the furanone 206 in excellent yield and high enantioselec-tivity (Scheme 7.42) [107]. In another report, the furan ring as part of other bicyclic or tricyclic systems was also prepared through an enantioselective Michael addi-tion/nucleophilic substitution reaction (Scheme 7.43) [108]. When diketones and ( )-P,P-bromonitrostyrenes 207 were stirred, again with a bifunctional thiourea... 

A simple enzymic synthesis of barium glucose 6-phosphate from starch has appeared. Ths use of 2-methylthio-4 -l,3,2-benzodioxaphosphorin-2-oxide (MTBO) (see M. Eto et al.. Tetrahedron Letters, 1971, 4263) continues to receive attention. A study of twenty amines as catalysts has shown that primary n-alkyl and alicyclic amines are the most effective, followed by secondary and tertiary amines. Increasing the branching reduced the catalytic efficacy while cyclic imines gave low yields. MTBO has been used to synthesize adenosine 2, 3 -cyclic phosphate in 50% yield from 5 -0-acetyladenosine (Scheme 5). o-Arabinose 5-phosphate and o-xylose 5-phosphate have been... 

In 2015, Seayad and co-workers reported a silica supported palladium complex-catalyzed solvent-free A -alkylation of amines with catalyst loading as low as 0.00196 mol% and TON as high as 469390 (Eq. 41) [146]. The catalyst could be recycled at least four times without obvious loss of activity. 

The aforementioned Pt-Sn/y-AlaOs catalyst developed by Yu and co-workers in 2011 was also effective for self-coupling of aliphatic primary amines with catalyst loading as low as 0.25 mol% (Eq. 80) [142]. In 2012, Shimizu and co-workers found nano-NaPt/Si02 and nano-SPt/Si02 are both effective catalysts for the N-alkylation of anilines, secondary and branched primary amines [223, 224]. In 2013, Shi and co-workers accidentally found that NiCuFeOx complex could catalyze the self-A-alkylation of primary amines [157]. 

Several new applications of crown ethers were developed in performing Gabriel-like transformations for example, high yields of secondary amines are produced, followed by a saponification, when N-alkyl or N-aryl trifluoroacetamides are alkylated in THE using potassium hydride as the base and 18C6 as the alkylation catalyst [218]. 

Hennis and coworkers reported that the reaction of carboxylates with alkyl chlorides is catalyzed by tertiary amines, the combination of tertiary amines and sodium iodide or quaternary ammonium compounds [3, 4]. It was found that the ester formation was catalyzed by quaternary ammonium salts and that these were generated in situ from the amine and alkyl halide. Sodium iodide in 2-butanone converted the alkyl chloride to the more reactive iodide (the Finkelstein reaction) which in turn alkylated amine. Alkyl iodides added directly to the reaction mixture were even more active co-catalysts but the preformed quaternary ammonium salt was the most effective catalyst. It was suggested that the enhanced solubility of the quaternary ammonium carboxylate or the lack of tight ion pairing in this salt might account for the... 

Amines as Catalysts. Some reports have appeared on the use of amines as catalysts in PTC nucleophilic substitution methods. For example, the preparation of alkyl thiocyanates or nitriles from alkyl bromides in two-phase systems may be assisted by a variety of primary, secondary, or tertiary amines as alternatives to quaternary ions. Efficient catalysis seems to require a sterically unhindered amino group with relatively high basicity (J.e. t-alkyl and aromatic amines are not fully efficient), and a total number of carbon atoms in the amine of greater than six to achieve good phase distribution of the catalysts. A similar study on the alkylation of benzyl methyl ketone reached the same conclusions, and from various observations e.g. that the reaction displayed an induction period at low catalyst concentration) it was postulated that initial alkylation of the amine by the alkylating agent (usually a halide) was essential to provide quaternary ions as the actual catalyst,... 

---