Reductions of Heterocycles Containing Two Nitrogen Atoms

Bohlmann97 reported that an ethereal solution of quinoxaline (99) on treatment with lithium aluminum hydride resulted in partial reduction of the nitrogenous heterocyclic ring, 1,2,3,4-tetrahydro-quinoxaline (100) being the sole product of the reaction. Similar 

The reduction of 1-methyl- or ethyl-quinoxalinium salts with aqueous sodium borohydride formed the l-substituted-l,2,3,4-tetra-hydroquinoxaline.131 The tetrahydroquinoxalines were the sole products and were obtained in good yield. 

The reduction of a series of l,3-disubstituted-2-oxo-l,2-dihydro-quinoxalines (104) with lithium aluminum hydride to the corresponding 1,2,3,4-tetrahydroquinoxalines (105) has also been reported.132 Under mild reaction conditions an intermediate was isolated which retained a double bond in the ring, but the intermediate was not sufficiently stable to be characterized. 

Birkofer and Birkofer133 and Bohlmann97 have independently reported that the lithium aluminum hydride reduction of phenazine 

Treatment of an ethereal solution of 4-oxo-dihydro-l,3-diaza-anthracene (108) with lithium aluminum hydride reportedly resulted in the reduction of only the 1,2-carbon-nitrogen double bond with 4-oxo-l,2,3,4-tetrahydro-l,3-diazaanthracene (109) being the only product isolated.134 Apparently conditions were not sufficiently vigorous for the further reduction of the tautomeric form of 109, or possibly the formation of a complex with the aluminohydride pre- 

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REDUCTION OF HETEROCYCLES CONTAINING TWO NITROGEN ATOMS AND ONE OXYGEN ATOM... 

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. 

Reductive cleavage of the N-N bond in bicyclic systems containing a ring junction hydrazine subunit presents a facile route to medium-sized heterocycles containing two or more nitrogen atoms and the subject was duly covered in CHEC-II(1996) <1996CHEC-II(8)747>. No substantial progress has been reported since its publication. 

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