Catalytic hydrogenation heterocycles

Displacement of halogen by isopropylamine gives intermediate 57. High pressure catalytic hydrogenation leads to reduction of the heterocyclic ring... 

Additional data on the use of oxazine (539) and products of its modifications in syntheses of compounds having potential biological activity and their precursors are presented in Scheme 3.274 (541). Catalytic hydrogenation of the imino and oximino fragments is primarily used for this purpose. This approach made it possible to prepare a representative series of nitrogen-containing heterocycles and of other previously unknown compounds. 

Synthesis of the heterocyclic core possessing a fully saturated six-membered ring can be achieved using a catalytic hydrogenation (see Section 11.10.4.5.5). The six-membered ring can also be formed starting from the appropriate... 

Similar procedures to those used for the catalytic hydrogenation of furan and thiophene can usually be applied to the functional derivatives of these heterocycles. 

Aromatic heterocycles containing two nitrogen atoms are best reduced by catalytic hydrogenation. Other reduction methods may cleave some of the rings. Even catalytic hydrogenation causes occasional hydrogenolysis. 

Hydroxylic groups in positions a to heterocyclic aromatics undergo hydro-genolysis in catalytic hydrogenation. In the case of furfuryl alcohol, hydrogenation also reduces the aromatic nucleus and easily cleaves the furan ring giving, in addition to a-methylfuran and tetrahydrofurfuryl alcohol, a mixture of pentanediols and pentanols [38,420]. 

A-Amine oxides can be reduced (deoxygenated) to tertiary amines. Such a reaction is very desirable, especially in aromatic nitrogen-containing heterocycles where conversion to amine oxides makes possible electrophilic substitution of the aromatic rings in different positions than it occurs in the parent heterocyclic compounds. The reduction is very easy and is accomplished by catalytic hydrogenation over palladium [736, 737], by borane [738], by iron in... 

Only two examples of the synthesis pyrimidoazocines have been described. In Ref. 82JHC1257, a three-stage synthesis of a new heterocycle system, pyrimido[5,4-c]benz[l]azocine, has been proposed. Condensation of 4-methyl-2-phenyl-5-pyrimidincarboxylate (112) with 3,4-dimethoxy-6-nitrobenzaldehyde (113) led to the substituted alkene 114, which, after catalytic hydrogenation of the nitro group on Raney nickel and subsequent intramolecular cyclization of product 115, was converted into pyrimidobenz[l]azocine 116 (Scheme 32). 

On the other hand, the presence of a glycosyl group attached to the nucleoside pyrophosphate has been found to influence the reactivity of the heterocyclic base. Thus, the catalytic hydrogenation of uridine and 6-azauridine 5 -(a-D-glucopyranosyl pyrophosphates) to the 5,6-dihydro derivatives proceeds more slowly than that of the respective nucleoside 5 -phosphates or 5 -pyrophosphates.338,339 Such differences have not been observed in comparisons of analogous derivatives of 2 -deoxyuridine, N3-methyluridine, and cytidine. 

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