C=N bonds hydrogenation

One of the most valuable and widely used applications of C=N bond hydrogenation is in the field of reductive alkylation, in which an aldehyde or ketone is condensed with an amine and reduced in situ with an appropriate catalyst to give a substituted product. This very valuable reaction has most notably been employed for the racemic synthesis of amino acids from a-ketoesters and acids. This type of reduction can be very powerful, as illustrated by the synthesis of tetrahydro-b-carbolines 64 (76% yield) by the reductive coupling of 65 and 66 under conditions of 1 atm of hydrogen and palladium on carbon catalyst277. 

Besides the biocatalytic and hydride reduction methods, two different effective catalytic C=0 and C=N bond hydrogenation methods have been developed ... 

Recent advances in the asymmetric C=N bond hydrogenation also include transfer hydrogenation of those... 

Nowadays enantioselective synthesis of the herbicide (5)-metolachlor (Dual Magnum) is, to our knowledge, one of the most successful commercial applications of asymmetric C=N bond hydrogenation. Developed by Blaser and Spindler as a key step in the technical synthesis of (5)-metolachlor, the enantioselective hydrogenation of an imine intermediate 193 proceeds in the presence of an iridium ferrocenyl-diphosphine catalyst bearing a Solvias Josiphos-type chiral ligand (/ )-Xyliphos to give... 

As a class of compounds, nitriles have broad commercial utility that includes their use as solvents, feedstocks, pharmaceuticals, catalysts, and pesticides. The versatile reactivity of organonitnles arises both from the reactivity of the C=N bond, and from the abiHty of the cyano substituent to activate adjacent bonds, especially C—H bonds. Nitriles can be used to prepare amines, amides, amidines, carboxyHc acids and esters, aldehydes, ketones, large-ring cycHc ketones, imines, heterocycles, orthoesters, and other compounds. Some of the more common transformations involve hydrolysis or alcoholysis to produce amides, acids and esters, and hydrogenation to produce amines, which are intermediates for the production of polyurethanes and polyamides. An extensive review on hydrogenation of nitriles has been recendy pubHshed (10). 

If, however, hydrogen is present in the a-position of the iV-alkyl substituent, 2-alkyl-oxaziridines are easily decomposed by alkali. Base attack on this H atom effects 1,2-elimination at the C—N bond. From (86) and aldimine (87) forms, and a mixture of ammonia and two carbonyl compounds is finally obtained, one of them containing the carbon atom of the original oxaziridine ring, the other originating from the IV-alkyl group (57JA5739). 

KURSANOV PARNES Ionic Hydrogenation A non-calalytK hydrogenation of C C. C O, C N bonds and hydrogenotysis of C-OH, C Hal etc, under the action of an acid and a hydride ion donor... 

A mechanism which is consistent with the various experimental results for olefin formation involves the initial abstraction of the hydrazone proton (103->106) In this case, however, expulsion of the tosylate anion is associated with the abstraction of a second hydrogen from C-16 instead of hydride attack on the C=N bond (compare 97 98 and 106 107). Ex-... 

Heterocyclic compounds that have water bound covalently across a C=N bond behave as secondary alcohols. When subjected to very gentle oxidative conditions, they are converted into the corresponding 0x0 compounds. Potassium permanganate in 0. IN sodium hydroxide at room temperature has been used to oxidize 2- and 6-hydroxypteri-dine to 2,4- and 6,7-dihydroxypteridine, respectively. In contrast, 4-hydroxypteridine was not attacked by this reagent even at 100°. Hydrogen peroxide in acid solution was used to oxidize quinazoline quinazoline 3-oxide 1,3,5-, 1,3,7-, and 1,3,8-triazanaphthalene and pteridine (which hydrate across the 3,4-double bond in the... 

If a methyl group replaces a hydrogen atom on the carbon of the C==N bond across which addition of water occurs, a considerable reduction in the extent of water addition is observed. Conversely, the existence of such a blocking effect can be used as a provisional indication of the site at which addition of water occurs, while the spectrum and acid dissociation constant of the methyl derivative provide a useful indication of the corresponding properties of the anhydrous parent substance. Examples of the effect of such a methyl group on equilibria are given in Table IV. 

The new carbon-carbon double-bond distance corresponds to the value 0.87 for the double-bond factor. Moreover, there are now available three accurately known triple-bond distances 1.204 for C=C in acetylene, 1.154 A. for C=N in hydrogen cyanide, and 1.094 for N==N in the nitrogen molecule, whereas five years ago only the last was known. The ratios of these distances to the corresponding sums of single-bond radii are 0.782, 0.785, and 0.781, respectively. We accordingly now select 0.78 as the value of the triple-bond factor. Revised covalent radii26 for first-row atoms are given in Table XV. 

Hydrogen cyanide can also be added to the C=N bond to give iminonitriles or a-aminomalononitriles. ... 

An attractive alternative to these novel aminoalcohol type modifiers is the use of 1-(1-naphthyl)ethylamine (NEA, Fig. 5) and derivatives thereof as chiral modifiers [45-47]. Trace quantities of (R)- or (S)-l-(l-naphthyl)ethylamine induce up to 82% ee in the hydrogenation of ethyl pyruvate over Pt/alumina. Note that naphthylethylamine is only a precursor of the actual modifier, which is formed in situ by reductive alkylation of NEA with the reactant ethyl pyruvate. This transformation (Fig. 5), which proceeds via imine formation and subsequent reduction of the C=N bond, is highly diastereoselective (d.e. >95%). Reductive alkylation of NEA with different aldehydes or ketones provides easy access to a variety of related modifiers [47]. The enantioselection occurring with the modifiers derived from NEA could be rationalized with the same strategy of molecular modelling as demonstrated for the Pt-cinchona system. 

The presence of different catalytic sites for the first C-N bond breaking of DHQ and the hydrogenation of CHE is confirmed by the -ln(l-XDiKj) versus -ln(l-X(niK) plot. In the simultaneous reactions of A and B, in which A and B are both adsorbed on the same catalytic site and follow a Langmvtir-Hinshelwood mechanism, we have... 

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