Carbonyl compounds, from nitro reductive amination

Secondary amines can be prepared from the primary amine and carbonyl compounds by way of the reduction of the derived Schiff bases, with or without the isolation of these intermediates. This procedure represents one aspect of the general method of reductive alkylation discussed in Section 5.16.3, p. 776. With aromatic primary amines and aromatic aldehydes the Schiff bases are usually readily isolable in the crystalline state and can then be subsequently subjected to a suitable reduction procedure, often by hydrogenation over a Raney nickel catalyst at moderate temperatures and pressures. A convenient procedure, which is illustrated in Expt 6.58, uses sodium borohydride in methanol, a reagent which owing to its selective reducing properties (Section 5.4.1, p. 519) does not affect other reducible functional groups (particularly the nitro group) which may be present in the Schiff base contrast the use of sodium borohydride in the presence of palladium-on-carbon, p. 894. 

Compounds of formula 63 are readily cyclized by reduction of the nitro group with Raney nickel and hydrogen. The amine thus formed condenses intramolecularly, with the carbonyl function providing the 3,4-dihydro system 64. This may be smoothly oxidized with iodine or an acetone solution of potassium permanganate. " " This route has been used for the unambiguous synthesis of compounds 65, 66, 67, and 68 48.49 Qf particular interest are compounds 66 and 67, which have been used to confirm the orientation of products from the reaction of polyaminopyridines with pyruvaldehyde and p-chlorophenylglyoxal. ... 

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