Carbonylation activity

Reactions. The chemical properties of cyanoacetates ate quite similar to those of the malonates. The carbonyl activity of the ester function is increased by the cyano group s tendency to withdraw electrons. Therefore, amidation with ammonia [7664-41-7] to cyanoacetamide [107-91-5] (55) or with urea to cyanoacetylurea [448-98-2] (56) proceeds very easily. An interesting reaction of cyanoacetic acid is the Knoevenagel condensation with aldehydes followed by decarboxylation which leads to substituted acrylonitriles (57) such as (29), or with ketones followed by decarboxylation with a shift of the double bond to give P,y-unsaturated nitriles (58) such as (30) when cyclohexanone [108-94-1] is used. 

The self-condensation is largely suppressed in reactions with those ketones 2, that are activated by an electron-withdrawing substituent or R". The carbonyl activity is then increased, and the enamine-intermediate 5 is favored over the imine 4, by conjugation with the electron-withdrawing group. ... 

Assuming that a carbonyl compound 1 with a substituent Y (which may be either a heteroatomic substituent or an alkyl group) forms enolate 2 exclusively, and that the aldehyde 3 functions as the only carbonyl-active component12, four stereoisomeric products 4a, 4b, 5a, 5 b may result. 

Dihydrothiopyrans have also been prepared by cycloaddition between a,jS-unsaturated thioketones and carbonyl-activated dienophiles under Lewis-acid catalysis [78]. A marked dependence of the reaction yield on the catalyst was observed. The results of the cycloaddition reaction of thioketone 77 with methyl metacrylate, catalyzed by different catalysts, are illustrated in Equation 3.24. 

The presence of halides in the coordination sphere with aldehydes is important as zinc halides are typically used in organic synthesis as organic carbonyl activators. Large excesses of aldehydes and anhydrous zinc halides were necessary. Both monomeric and polymeric structures with halide bridges were observed. Tetrahedral geometries were observed for mixed ligand, aldehyde, and halide complexes.353... 

Nevertheless, /1-carbonylalkyltin chlorides are obtained347 in high yields by reactions of the carbonyl-activated alkenes RR,C=CR"-C(R",)=0 with HC1 and SnCl2, yielding compounds of the type 118, while with tin metal and HC1 compounds of the type 119 are obtained. 

Boeckman, R.K., Kamenecka, T.M., Nelson, S.G., Pruitt, J.R., and Barta, T.E., C-Phosphorylation of enolates an alternate route to complex carbonyl-activated phosphonates, Tetrahedron Lett., 32, 2581, 1991. 

The synthesis of optically active nitrones (95) was carried out by an aldol reaction of aldehydes (93), catalyzed by L- proline, with carbonyl activated compounds (94) and by an in situ reaction with N -alkylhydroxylamines (Scheme 2.36, Table 2.5) (261). 

Scheme 3.14 Dehydrative glycosylation with carbonyl activators.

Commonly Used Carbonyl Activating Reagents in Peptide Synthesis (.. . NHCH(i )C(0)-X)... 

It combines amine protection with considerable carbonyl activation. 

In the Rh systems for MeOH carbonylation to AcOH, it is the property of HI as an acid which is most important in its influence on overall carbonylation activity, through its role in the conversion of [Rh(CO)2l2r to [Rh(CO)2l4] . 

Alkenylboranes are less sensitive to substituents on the diene than are carbonyl-activated dienophiles.33 Relatively hindered dialkylboranes, such as S-vinyl-9-BBN, show steric effects which lead to a preference for the meta regioisomer and reduced endo exo ratios.34... 

The lactone concept is not restricted to the simple model biaryl synthesis presented here. It has been successfully expanded to a broad series of structurally diverse biaryl substrates (e.g., lactones with additional stereocenters and functional groups, configurationally stable lactones, seven-membered lactones, and again configurationally unstable biaryl hydroxy aldehydes ), to different activation modes in the ring-opening step (e.g., use of metallated nucleophiles, carbonyl activation by Lewis acids, (Ti -complexation, etc.), and for various strategies of stereoselection (e.g., external vs. internal asymmetric induction). ... 

Scheme 3.1 Three modes of carbonyl activation toward nucleophilic attack.

Carbonylation of Methyl Acetate on Ni/A.C. Catalysts. Table II shows the catalytic activities of nickel and platinum group metals supported on activated carbon for the carbonylation of methyl acetate. Ruthenium, palladium, or iridium catalysts showed much lower activity for the synthesis of acetic anhydride than the nickel catalyst. In contrast, the rhodium catalyst, which has been known to exhibit an excellent carbonylation activity in the homogeneous system (1-13), showed nearly the same activity as the nickel catalyst but gave a large amount of acetic acid. 

Table V shows the results obtained for the carbonylation of dimethyl ether and methyl acetate with molybdenum catalysts supported on various carrier materials. In the case of dimethyl ether carbonylation, molybdenum-activated carbon catalyst gave methyl acetate with an yield of 5.2% which was about one-third of the activity of nickel-activated carbon catalyst. Silica gel- or y-alumina-supported catalyst gave little carbonylated product. Similar results were obtained in the carbonylation of methyl acetate. The carbonylation activity occured only when molybdenum was supported on activated carbon, and it was about half the activity of nickel-activated carbon catalyst.

Table V. Carbonylation Activities of Supported Molybdenum and Nickel-Activated Carbon Catalysts ...

Other products were dimethyl ether (DME), methane and carbon dioxide. The data in Table I show that high yields of carbonylated products were produced with nickel catalysts supported on activated carbon and carbon black. Other nickel catalysts gave mainly methane and dimethyl ether. It is clear that a carbonaceous carrier is essential for the appearance of carbonylation activity for the nickel catalyst. The role of the carbonaceous carrier will be discussed later. 

Lisinopril (S) -1-A - (l-Carboxy-3-phenylpropyl) -L-lysyl] L-proline dihydrate Pd-catalyzed carbonylation, hydroxylation of a double bond, chemical resolution, amidation, A-protection (using trifluoroacetic anhydride), carbonyl activation (using phosgene)... 

The involvement of the carbonyl group is shown indirectly by the lack of termination in the polymerization of tert.-butyl methacrylate (38). The positive inductive effect of the tert.-butyl group decreases the carbonyl activity and hence the termination rate constant. 

This result appears reasonable, because the carbonyl activity of saturated esters, i. e. the polymer, usually is higher than... 

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