Reduction of nitrogen heterocycles with complex

The reduction of iminium salts can be achieved by a variety of methods. Some of the methods have been studied primarily on quaternary salts of aromatic bases, but the results can be extrapolated to simple iminium salts in most cases. The reagents available for reduction of iminium salts are sodium amalgam (52), sodium hydrosulfite (5i), potassium borohydride (54,55), sodium borohydride (56,57), lithium aluminum hydride (5 ), formic acid (59-63), H, and platinum oxide (47). The scope and mechanism of reduction of nitrogen heterocycles with complex metal hydrides has been recently reviewed (5,64), and will be presented here only briefly. 

R.E. Lyleu. P. S. Anderson, The Reduction of Nitrogen Heterocycles with Complex Metal Hydrides, Advances in Heterocyclic Chemistry, Vol. 6, S. 45, Academic Press, New York 1966. 

J.G. Keay, The Reduction of Nitrogen Heterocycles with Complex Metal-Hydrides, Adv. Heterocycl. 

Reduction of nitrogen heterocycles with complex metal hydrides, 6, 45 39, 1 Regioselective substitution in aromatic six-membered nitrogen heterocycles, 44, 199... 

Alanes and boranes are initially electrophilic rather than nucleophilic, and coordinate onto free electron pairs in the molecule prior to hydride delivery. The chemistry of metal hydrides has been extensively reviewed, as has the reduction of nitrogen heterocycles with complex metal hydrides. Generally, NBH reductions, carried out in alcohols, produce tetrahydropyridines, whilst LAH generates mainly di-hydropyridines. 

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