Amines as catalysts for

Heterocyclic tertiary amines as catalysts for the reaction of activated vinyl carbanions with aldehydes 88T4653. 

In conclusion, by using low hindered tertiary amines as catalysts for PO polymerisation, higher reaction rates and a low number of side reactions are obtained, at lower polymerisation temperatures (80-90 °C), where the strong base, quaternary ammonium alcoholate is stable and the predominant catalytic species. 

By propoxylation of the resulting polyols (trimethylolisocyanurate and the Mannich base (15.44), in the presence of a tertiary amine as catalyst (for example dimethylaminoethanol) new heterocyclic polyols for rigid PU foams with a triazinic structure are obtained (reactions 15.45 and 15.46). 

Knoevenagel900 applied weak bases (ammonia or an amine) as catalysts for this type of reaction, thereby enabling the condensation and the decarboxylation of the intermediate arylidene- or alkylidene-malonic acids to be effected at lower temperatures and thus achieving higher yields. 

Asymmetric cyclization (6, 410-411). The use of optically active amines as catalysts for asymmetric cyclizations, as well as an application for synthesis of optically active estrone, has been mentioned previously. This cyclization has now been used in construction of the asymmetric aldehyde (4), a known precursor to 12-methylprostaglandin (5). Thus cyclization of the trione (I) in DMF with i>-proline as catalyst gave the aldol (2), which was dehydrated to the enedione (3), obtained with 96% optical purity. ... 

In 1993, Yamaguchi reported an important milestone in the use of chiral amines as catalysts for enantioselective conjugate addition reactions (Equation 22) [114, 115]. The rubidium salt of proline (120) proved particularly ef ficient by comparison to proline or to its other metal salts. In the course of studies aimed at optimizing the process, beneficial effects were observed in the presence of CsF as an additive. This procedure led to the production of Michael adduct 121 from enone 118 in 88% ee [115]. 

Catalysts. Silver and silver compounds are widely used in research and industry as catalysts for oxidation, reduction, and polymerization reactions. Silver nitrate has been reported as a catalyst for the preparation of propylene oxide (qv) from propylene (qv) (58), and silver acetate has been reported as being a suitable catalyst for the production of ethylene oxide (qv) from ethylene (qv) (59). The solubiUty of silver perchlorate in organic solvents makes it a possible catalyst for polymerization reactions, such as the production of butyl acrylate polymers in dimethylformamide (60) or the polymerization of methacrylamide (61). Similarly, the solubiUty of silver tetrafiuoroborate in organic solvents has enhanced its use in the synthesis of 3-pyrrolines by the cyclization of aHenic amines (62). 

A bifunctional autocatalytic effect of azinones in general is possible in certain nucleophilic reactions such as amination. Zollinger has found that 2-pyridone is the best catalyst for anilino-dechlorination of various chloroazines. It seems likely that examples of autocatalysis will be found when the substrate contains an azinone moiety. The azinone hy-products of displacement reactions may also function in this way as catalysts for the main reaction. 

This reaction pathway explains well the applicability of amines as catalysts. There is evidence for each one of the mechanisms outlined above. Because of the wide scope of the reaction, there may be no uniform mechanism that would apply to all cases. 

A half-sandwich titanacarborane guanidinate complex is formed on treatment of the corresponding amide precursor with 1,3-dicyclohexylcarbodiimide (Scheme 106). The compounds have been employed as catalysts for the guanylation of amines (cf. Section V.C). ... 

Silylation-amination of 4(lH)-quinohnone 255 with a twofold excess of dopamine hydrochloride 256 as amine and an acidic catalyst affords, on heating with excess HMDS 2 for 21 h at 145 °C and subsequent transsilylation in excess boihng methanol, 75% of the crystalline hydrate of 257 (Scheme 4.28). The silylation-amination of 2-thio-6-azauracil 258 with homoveratrylamine 259, HMDS 2, and SnCLj as catalyst for 48 h at 145 °C furnishes 63% of the diamine 260, and MesSiOSiMes 7 and Me3SiSH or Me3SiSSiMe3 601 as leaving groups. 

Regarding bis-NHC chelating ligands, several structures that differ in the motifs used for the enlargement of the tether have been proposed as catalysts for the Mizoroki-Heck reaction. They range from non-functionalised aliphatic chains [23-25] to phenyl [26], biphenyl [27], binaphthyls [28] and to chains containing additional coordination positions like ethers [29], amines [30], and pyridines in an evolution towards pincer complexes [31-35], In most cases, the activity of aryl bromides in Mizoroki-Heck transformations was demonstrated to be from moderate to high, while the activation of chlorides was non-existent or poor (Scheme 6.7). 

Oxidative carbonylation generates a number of important compounds and materials such as ureas, carbamates, 2-oxazolidinones, and aromatic polycarbonates. The [CuX(IPr)] complexes 38-X (X = Cl, Br, I) were tested as catalysts for the oxidative carbonylation of amino alcohols by Xia and co-workers [43]. Complex 38-1 is the first catalyst to selectively prepare ureas, carbamates, and 2-oxazolidinones without any additives. The important findings were the identity of the counterion and that the presence of the NHC ligand influenced the conversions. 2-Oxazohdinones were formed from primary amino alcohols in 86-96% yield. Complex 38-1 also catalysed the oxidative carbonylation of primary amines to ureas and carbamates. n-Propylamine, n-butylamine, and t-butylamine were transformed into the... 

Organic-Base Catalyzed. Asymmetric direct aldol reactions have received considerable attention recently (Eq. 8.98).251 Direct asymmetric catalytic aldol reactions have been successfully performed using aldehydes and unmodified ketones together with chiral cyclic secondary amines as catalysts.252 L-proline and 5,5-dimethylthiazolidinium-4-carboxylate (DMTC) were found to be the most powerful amino acid catalysts for the reaction of both acyclic and cyclic ketones as aldol donors with aromatic and aliphatic aldehydes to afford the corresponding... 

Compounds (L)AuR have been used as precursor molecules for the in situ preparation of the strong nucleophiles [(L)Au]+ X- by treatment with strong acids HX (X = CF3S03, CF3C02, BF4, PF6, SbF6 etc. L = tertiary phosphine R = alkyl) in polar solvents (Equation (2)). The solutions are used as catalysts for the activation of alkenes and alkynes for addition of water, alcohols, and amines (Sections 4 and 10). 

The behavior of 3 toward ether or amines on the one hand and toward phosphines, carbon monoxide, and COD on the other (Scheme 2), can be qualitatively explained on the basis of the HSAB concept4 (58). The decomposition of 3 by ethers or amines is then seen as the displacement of the halide anion as a weak hard base from its acid-base complex (3). On the other hand, CO, PR3, and olefins are soft bases and do not decompose (3) instead, complexation to the nickel atom occurs. The behavior of complexes 3 and 4 toward different kinds of electron donors explains in part why they are highly active as catalysts for the oligomerization of olefins in contrast to the dimeric ir-allylnickel halides (1) which show low catalytic activity. One of the functions of the Lewis acid is to remove charge from the nickel, thereby increasing the affinity of the nickel atom for soft donors such as CO, PR3, etc., and for substrate olefin molecules. A second possibility, an increase in reactivity of the nickel-carbon and nickel-hydrogen bonds toward complexed olefins, has as yet found no direct experimental support. 

In systems where such radicals appear (alcohols, amines, some unsaturated compounds), variable-valence metal ions manifest themselves as catalysts for chain termination (see Refs. [150,151] and Chapter 16). 

Reaction 38 shows that hydroxylamines can cause amination at allylic positions. Fe(II) phthalocyanine (222c) was the most effective catalyst. Other catalysts and substrates were also investigated623. Complexes of Mo(VI) were less effective than 222c as catalysts for amination processes of this type624. 

Epoxides can react with alcohols via acidic or basic catalysed reaction mechanisms. However, since both strong acids and bases will degrade the cell wall polymers of wood, the reaction is usually catalysed via the use of amines, which are more strongly nucleophilic than the OH group. For example, whereas the production of epoxy-phenolic resins requires temperatures in the region of 180-205 °C, reaction between epoxides and primary or secondary amines takes place at 15 °C (Turner, 1967). Reaction of epoxides with wood often involves the use of tertiary amines as catalysts (Sherman etal., 1980). The sapwood is more reactive towards epoxides than heartwood (Ahmad and Harun, 1992). 

Although, from a historical standpoint the cinchona alkaloids also occupy a central position in the field owing to their use as catalysts for the alcoholative ASD of meso anhydrides (a Type II process, see Schane 2), the past few years have witnessed an explosion of interest in the development of other classes of iert-amine-based catalysts primarily for Type I processes. 

Finally, achiral phosphonium salts have been applied as Lewis acid catalysts in some other reactions. The examples will be listed here but not discussed in more detail. Phosphonium salts have been used as catalysts for the A,A-dimethylation of primary aromatic amines with methyl alkyl carbonates giving the products in good yields [123]. In addition acetonyltriphenylphosphonium bromide has been found to be a catalyst for the cyclotrimerization of aldehydes [124] and for the protection/ deprotection of alcohols with alkyl vinyl ethers [125, 126]. Since the pK of the salt is 6.6 [127-130], the authors proposed that, next to the activation of the phosphonium center, a Brpnsted acid catalyzed pathway is possible. 

The base-catalyzed rearrangement of oxadiazolylureas 184 into ben-zoylamino-l,2,4-triazolin-5-ones 185 has been mechanistically examined by using amines as catalysts in acetonitrile and benzene, and borate buffers at various pS in dioxan-water [90JCS(P2)1289]. For the piperidine-... 

The extent of crosslinking in polyurethanes depends on a combination of the amount of polyfunctional monomers present and the extent of biuret, allophanate, and trimerization reactions [Dusek, 1987]. The latter reactions are controlled by the overall stoichiometry and the specific catalyst present. Stannous and other metal carboxylates as well as tertiary amines are catalysts for the various reactions. Proper choice of the specific catalyst result in differences in the relative amounts of each reaction. Temperature also affects the extents... 

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