Aldehydes catalyst effect

In the early 1920s Badische Arulin- und Soda-Fabrik aimounced the specific catalytic conversion of carbon monoxide and hydrogen at 20—30 MPa (200—300 atm) and 300—400°C to methanol (12,13), a process subsequendy widely industrialized. At the same time Fischer and Tropsch aimounced the Synth in e process (14,15), in which an iron catalyst effects the reaction of carbon monoxide and hydrogen to produce a mixture of alcohols, aldehydes (qv), ketones (qv), and fatty acids at atmospheric pressure. 

To overcome these problems with the first generation Brmsted acid-assisted chiral Lewis acid 7, Yamamoto and coworkers developed in 1996 a second-generation catalyst 8 containing the 3,5-bis-(trifluoromethyl)phenylboronic acid moiety [10b,d] (Scheme 1.15, 1.16, Table 1.4, 1.5). The catalyst was prepared from a chiral triol containing a chiral binaphthol moiety and 3,5-bis-(trifluoromethyl)phenylboronic acid, with removal of water. This is a practical Diels-Alder catalyst, effective in catalyzing the reaction not only of a-substituted a,/ -unsaturated aldehydes, but also of a-unsubstituted a,/ -unsaturated aldehydes. In each reaction, the adducts were formed in high yields and with excellent enantioselectivity. It also promotes the reaction with less reactive dienophiles such as crotonaldehyde. Less reactive dienes such as isoprene and cyclohexadiene can, moreover, also be successfully employed in reactions with bromoacrolein, methacrolein, and acrolein dienophiles. The chiral ligand was readily recovered (>90%). 

Metal-induced reductive dimerization of carbonyl compounds is a useful synthetic method for the formation of vicinally functionalized carbon-carbon bonds. For stoichiometric reductive dimerizations, low-valent metals such as aluminum amalgam, titanium, vanadium, zinc, and samarium have been employed. Alternatively, ternary systems consisting of catalytic amounts of a metal salt or metal complex, a chlorosilane, and a stoichiometric co-reductant provide a catalytic method for the formation of pinacols based on reversible redox couples.2 The homocoupling of aldehydes is effected by vanadium or titanium catalysts in the presence of Me3SiCl and Zn or A1 to give the 1,2-diol derivatives high selectivity for the /-isomer is observed in the case of secondary aliphatic or aromatic aldehydes. 

Chiral fe-thiourea-type catalysts effectively provide the Baylis Hillman reaction with cyclohexenone and aldehydes.181 In several reactions, thiourea derivatives have been used as significant and specific catalyst because of their intermolecular hydrogen bonding ability (Scheme 74).182 186... 

Rhodium carbonyl catalysts effect hydrocarbonylation under very mild reaction conditions at higher rates and selectivity. Rhodium introduced as Rh4(CO)i2, for example, probably is converted to RhH(CO) , but there is no direct evidence for such species. These rhodium carbonyls are not particularly attractive since they produce mostly branched aldehydes. 

Ito and coworkers found that chiral ferrocenylphosphine-silver(I) complexes also catalyze the asymmetric aldol reaction of isocyanoacetate with aldehydes (Sch. 26) [51]. It is essential to keep the isocyanoacetate at a low concentration to obtain a product with high optical purity. They performed IR studies on the structures of gold(I) and silver(I) complexes with chiral ferrocenylphosphine 86a in the presence of methyl isocyanoacetate (27) and found significant differences between the iso-cyanoacetate-to-metal coordination numbers of these metal complexes (Sch. 27). The gold(I) complex has the tricoordinated structure 100, which results in high ee, whereas for the silver(I) complex there is an equilibrium between the tricoordinated structure 101 and the tetracoordinated structure 102, which results in low enantioselectivity. Slow addition of isocyanoacetate 27 to a solution of the silver(I) catalyst and aldehyde is effective in reducing the undesirable tetracoordinated species and results in high enantioselectivity. 

Thus the chiral BINOL-Ti catalyst effects efficient chiral recognition of the enantio-face of the aldehyde and discrimination between the diastereotopic protons of the ene component in a truly catalytic fashion. 

Eor comparison, ATPH can be used for this kind of differentiation more efficiently in the hetero-Diels-Alder reaction [58]. With ATPH, silyl enol ether Si-1 exhibited adequate potential for the aldolization unlike the observed poor reactivity with KSA alone using the above Eu-catalyst (Scheme 2-26 Table 2-4). Even the /i-sub-stituents of the aldehydes can be differentiated (entries 4 and 5, Table 2-4). The het-ero-atom-containing aldehyde was effectively discriminated, showing non-chelation ability of ATPH (entry 6, Table 2-4). When aldehydes are encapsulated in the ATPH cavity, the hitherto small steric effects turned out in these cases to be dominant. The importance of the effect of the cavity was illustrated further by a comparative experiment with bulky MAD (5 6=3.7 1). 

Sulfur trioxide-Dioxane, 1126-1127 Sulfiir trioxide-Pyridine, 1127-1128 Sulfur trioxide-Trimethylamine, 1128 Sulfuryl chloride, 196,1106,1128-1131 Swamping catalyst effect, 32,33 Synthesis gas, 224 Syringic aldehyde, 430,1047... 

From a practical point of view, Au addition to Pd in carbon-supported catalysts does not give any advantage as to activity in hydrogenation of aromatic aldehydes. Possible effects on the resistance to deactivation are presently being investigated. 

Several Ru complexes under mild conditions catalyze reduction of aldehydes to the corresponding alcohols. Linear and branched aldehydes are effectively hydrogenated by molecular H2 in the presence of RuCl2(CO)2[P(Ph)2]2 or RuCljCPPhj). High catalyst activities and turnover numbers up to 95,000 are observed, with yields up to 99% . The most convenient catalyst precursor is RuHCl(CO)(PPh3) in toluene solutions [equation (d)]. Water and acetic acid accelerate reaction without producing byproducts ... 

A number of metal complexes catalyze the hydrosilylation of various carbonyl compounds by triethylsilane. Stereoselectivity is observed in the hydrosilylation of ketones as in the reactions of 4-t-butylcyclohexanone and triethylsilane catalyzed by ruthenium, chromium, and rhodium metal complexes (eq 4). Triethylsilane and Chlorotris(triphenylphosphine)rho-dium(I) catalyst effect the regioselective 1,4-hydrosilylation of Q ,/3-unsaturated ketones and aldehydes. Reduction of mesityl oxide in this manner results in a 95% yield of product that consists of 1,4- and 1,2-hydrosilylation isomers in a 99 1 ratio (eq 5). This is an exact complement to the use of phenylsilane, where the ratio of respective isomers is reversed to 1 99. ... 

The intramolecular hydroacylation of aldehydic olefins is catalyzed by cationic Rh complexes of chelating phosphines in polar nonprotic solvents. The rate decreases with increasing substrate Rh ratio since the substrate complex with the catalyst inhibits the reaction. However, since this complexation also prevents the decarbonylation of the aldehyde, catalyst deactivation decreases, leading to a higher turnover. The only effective catalytic C—H activations are carried out with [RhCl(CO)(PMe3)2] under photolysis which removes CO. Alkanes are converted to alkenes in the order cyclooctane > cyclohexane > n-decane n-hexane. Up to 200 turnovers cyclooctane per hour are observed. In order to generate terminal... 

Enders also developed, a so-called branehed domino reaetion. In this case a nitroalkene was combined with two equivalents of an aldehyde, catalyst and an oxidant. The most effective oxidation agent IBX oxidised enamine to iminium ion, which served as an acceptor in the last part of the cascade. In this way, cyclohexene derivatives were assembled in good yield and with high diastereomeric and enantiomeric purities (Scheme 8.19). 

Taylor et alP applied an asymmehic variant of this reaction using a Rh-BINAP catalyst and aldehydes, e.g., 296, as aeceptors to yield aldol produets sueh as 298. Although a variety of aromatie, eyelie, and acyelic aldehydes was effective acceptors, the scope of the o,P-unsaturated ester was limited to phenyl acrylate 297, and the enantioseleetivity and syn/anti seleetivities still need to be improved. Shiomi et reported an asymmetrie reduetive eoupling reaction of enones and aromatic aldehydes using ehiral Rh(Phebox) catalysts. Diphenylmethylsilane was used as a hydride donor in this ease, and the desired P-hydroxyketones were produced with up to 93% ee. 

MSA can be used as a powerful, safe, and recyclable catalyst for the condensation reaction of cyclic 1,3-diketones with arylaldehydes (Scheme 3.25). Firstly, synthesis of 2,2-(arylmethylene)bis(3-hydroxycyclohex-2-enone) from reaction of cyclic 1,3-diketones with several aromatic aldehydes was expected, but, as can be seen from Scheme 3.25, under the given conditions, 2,2 -(arylmethylene)bis(3-hydroxycyclohex-2-enone) was not formed and cyclic 1,3-diketones with aldehydes were effectively cyclized to give 9-aryl-substituted 1,8-dioxooctahydroxanthenes. 

Since no reaction occurred at all in the absence of either the aldehyde catalyst or the base or both of them, as well as other proofs such as control reactions using high purity bases (>99.99 % purity), the authors concluded that the reaction is a true TM-free transformation. In addition to the aldehydes catalytic effect, the authors proved that imine intermediates and other TM-free oxidants could also be employed to initiate the reaction, which is consistent with, and further supports, the TM-free N-aUcylation mechanism (Scheme 39). Along with other results of mechanistic studies, the authors proposed a mechanism for the aldehyde-catalyzed A -alkylation reaction (Scheme 41). Firstly, the external aldehydes condense with amines/amides to give imine intermediates, which were then reduced by alcohols via a TM-free MPV-0 transfer hydrogenation process to give product amines and regenerate byproduct aldehydes as the new alkyl source in next reaction cycle. In the key TM-ffee transfer... 

As a mechanism of this MCR process, it is proposed that the Au-catalyst effects (1) a three-component coupling of pyridine-2-aldehyde, amine, and alkyne to give the (2-propargyl)pyridine 33 and (2) enhancement of the triple-bond activity by Au-coordination in favor of the cyclization 33 34 finally the Au-heterocycle 34 should undergo deprotonation ( 35) and demetalation to give the products 32. 

The enhancement of the catalytic activity by the addition of the third component was observed also with this type of catalyst. Effective third components are tertiary phosphines, sulfides, sulfoxides, quinones and N-chlorosuccinimide. Alcohols, ketones and aldehydes, on the other hand, deactivated the catalyst even in... 

For these, several chiral Lewis acid catalysts, which have the C-2 symmetry element, were designed and tested for various asymmetric syntheses, and in 1985 we reported a zinc reagent and in 1988 a bulky aluminum reagent (Scheme 8) [15, 16]. The zinc reagent was used for asymmetric cyclization of unsaturated aldehyde and the aluminum catalyst for asymmetric hetero-Diels-Alder reaction with Danishefsky diene. Both catalysts effectively discriminate the enantioface of aldehydes for reactions. 

David W. C. MacMillan of Princeton University devised Angew. Chem. Int. Ed. 2009, 48, 4349) a remarkable one-pot three-component assembly of the lactone 32. Crossmetathesis of 29 with 30 gave a keto aldehyde. Direct addition of the furan 31 and an chiral imidazolidinone catalyst effected conjugate addition to the unsaturated aldehyde. A third catalyst, (5)-proline, then mediated intramolecular aldol condensation. The crystalline lactone 32 was readily carried on to (-)-Aromadendranediol 33. 

The synthetic utihty of the cationic lanthanide complex [Cp 2Ce][BPh4] as a Lewis acid catalyst, effective with as little as 0.1% loading, for the Diels Alder reaction between Danishefsky s diene and aromatic aldehydes has been demon-strated. s-Caprolactone can be prepared by H2O2 oxidation of cyclohexanone in the presence of catalysts of the type Ln[(02SR) X] (R = perfluoroalkyl n, X = 1,0 2, N 3, Reaction of oxime esters with MejSiCN under the influence of a catalytic amount of La(OPr )3 was found to produce ot-trimethylsilyl oxy-dinitrile derivatives in good yields. ... 

Shibasaki and coworkers have developed lanthanoid-lithium-BINOL complexes (LLB catalysts) as efficient catalysts for the asymmetric nitroaldol (Henry) reaction (59-46). The heterobimetallic asymmetric catalysts effectively mediate the reaction of a variety of aldehydes with nitroalkanes to afford the corresponding desired nitroaldols with high enantioselectivity (Scheme 4). We examined the capability of the LLB complexes as asymmetric catalysts for the nitroaldol reaction of 2,2-difluoroaldehydes with nitromethane (47). 

Knoevenagel reaction. The condensation of an aldehyde with an active methylene compound (usually malonic acid or its derivatives) in the presence of a base is generally called the Knoevenagel reaction. Knoevenagel found that condensations between aldehydes and malonic acid are effectively catalysed by ammonia and by primary and secondary amines in alcoholic solution of the organic amines piperidine was regarded as the best catalyst. 

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