Nitriles, catalytic hydrogenation aldehydes

Catalytic hydrogenation of nitriles may result in several products primary, secondary, and tertiary amines imines hydrocarbons aldehydes amides and... 

Double bonds conjugated with aromatic rings and with carbonyl, carboxyl, nitrile and other functions are readily reduced by catalytic hydrogenation and by metals. These reductions are discussed in the appropriate sections aromatics, unsaturated aldehydes and ketones, unsaturated acids, their derivatives, etc. 

CARBON SKELETON. The technique of precolumn catalytic hydrogenation can be applied to reduce certain unsaturated compounds to their parent hydrocarbons. Compounds analyzed by this technique include esters, ketones, aldehydes, amines, epoxides, nitriles, halides, sulfides, and fatty acids. Fatty acids usually give a hydrocarbon that, is the next lower homolag than the parent acid. For most systems utilizing hydrogenation, hydrogen is also used as the carrier gas. Usually 1% palladium or platinum on a non-adsorptive porous support such as AW-Chromosorb P is used as the catalytic packing material. 

A convenient route to 1-amino-1 //-2,3-benzopyrrolizines (28) was achieved by a Mannich reaction of aldehyde 27. Catalytic hydrogenation of either the base (28a) or trimethylammonium iodide (29) was accompanied by elimination to give compound 30. Treatment of 29 with potassium cyanide gave nitrile 31.28... 

In the synthesis we should not wish to make 21 as it would cyclise and, in any case, we d rather reduce nitrile, nitro and alkene all in the same step by catalytic hydrogenation. The very simple method used for the conjugate addition is possible only because of the slow aldol reaction of the hindered aldehyde 24. The aldol 25, also called a Henry reaction, needs a separate dehydration step but the three functional groups in 26 are reduced in one step in good yield.7... 

The synthesis of aldehydes by the Sommclet reaction, the Rosenmund reduction and the Stephens reaction all involve the conversion of a group already present in the molecule. The Rosenmund reduction (Scheme 6.7) is the catalytic hydrogenation of a benzoyl chloride in the presence of a catalyst poison, quinoline/sulfur, which prevents over-reduction to the alcohol. In the Stephens reaction (Scheme 6.7), a nitrile group is reduced by tin(II) chloride and hydrochloric acid to an imine salt, which is then hydrolysed. 

A few 6- and 8-cyanopurines have been prepared and undergo characteristic nitrile addition reactions rather readily. Thus, alkaline hydrolysis produces carboxamides, then carboxylic acids, alcoholysis leads to imidates, ammonolysis to amidines, hydrazinolysis to amidhydrazines, hydroxylamine to amidoximes, and hydrogen sulfide to thioamides. Acid hydrolysis tends to give the decarboxylated acid derivative. Reduction either by sodium-ethanol or, preferably, by catalytic hydrogenation affords aminoalkylpurines and addition of Grignard reagents produces, in the first place, acylpurines. As with aldehydes, most of the compounds examined have been relatively non-polar derivatives. Table 28 lists some reactions and relevant literature. 

The enantioselective total synthesis of (-)-hemiasterlin, a marine tripeptide with cytotoxic and antimitotic activity, was achieved by E. Vedejs and co-workers. The asymmetric Strecker reaction was used to construct the key tetramethyltryptophan subunit. The aldehyde substrate was first converted to the corresponding chiral imine with (R)-2-phenylglycinol under scandium triflate catalysis. The addition of tributyltin cyanide resulted in the formation of a-amino nitriles as an 8 1 mixture of diastereomers. Subsequently the cyano group was converted to a primary amide, and the chiral auxiliary was removed under catalytic hydrogenation conditions. 

Some reports concern selective catalytic hydrogenations using CO and H20 in the presence of catalytically active metal clusters. Selective reduction at the C=C double bond occurs for a,/ -unsaturated aldehydes, ketones, and nitriles with Rh6(CO)16. As a typical example, yS-phenylacrolein is converted into / -phenylpropion-aldehyde in THF at 130° C and 100 bar after 20 hr the yield is 74% with 100% selectivity (CT 1190) (314) ... 

Formation of an aldimine intermediate is the first step in the catalytic hydrogenation of nitriles. When hydrogenation is carried out in aqueous acidic media, aldehydes may form by hydrolysis of the aldimine. Selective hydrogenation of aromatic nitriles to ben-zaldehydes over finely divided Ni (Raney Ni) is best obtained with an equimolecular amount of H2SO4 in a 10 1 mixture of tetrahydrofuran-water ... 

A simple method of preparing aldehydes is to trap the aldehydes formed as intermediates in the catalytic hydrogenation of nitriles, for which purpose semicarbazide is eminently suitable. The method has been used with particular success with derivatives of benzyl cyanide 583 the resulting phenylacetaldehyde semicarbazones were cleaved by formadehyde solution. 

The oxime 7, prepared from salicyl aldehyde, is converted with iV-chlorosuccinimide into the hydrox-amic acid chloride 8. From this, the nitrile oxide is obtained with KHCO3, which reacts regioselec-tively with styrene to give the 3,5-diaryl-4,5-dihydroisoxazole 9. Catalytic hydrogenation leads to the y -hydroxy ketone 10, which on acid-catalysed cyclodehydration gives the flavanone 11. 

Acid chlorides can be reduced by catalytic hydrogenation to give an aldehyde in what is called the Rosenmund reduction. Nitriles are reduced by catalytic hydrogenation to a primary amine. 

In previous sections, hydride reagents such as NaBH4 or LiAlH4 reduce ketones or aldehydes and most acid derivatives to the corresponding alcohol. LiAlH4 reduces amides to amines and also reduces nitriles to amines. Catalytic hydrogenation reduces alkenes and alkynes, as well as ketones, aldehydes, acid chlorides, and nitriles. Acid chlorides may be reduced to aldehydes, and nitriles are also reduced to amines by catalytic hydrogenation. 

In the presence of a transition metal catalyst, hydrogen gas converts a ketone or aldehyde to an alcohol 14,15,16,17,37,43,44 46. Acid chlorides can be reduced by catalytic hydrogenation to give an aldehyde in what is called the Rosenmund reduction. Nitriles are reduced by catalytic hydrogenation to a primary amine 18,19, 20, 37. 

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