Nucleophilic substitution/deoxidation

Intramolecular deoxidative nucleophilic substitution of 2-(Tmethylhydrazino)quinoxaline 4-oxides 62 to tricyclic heteroaromatics has been extensively researched by Kurasawa e( al. <1995JHC1085, 2000JHC1257, 2002H(56)291, 2002H(58)359, 2003JHC837>. The cyclization consists of initial formation of hydrazone followed by nucleophilic... 

There have been reviews of nucleophilic substitution103 and of deoxidative nucleophilic substitution 104 in heterocyclic A -oxidcs. Stable carbon-carbon-bonded adducts, such as (22), have been reported from the reactions of 6-phenyl-1,2,4-triazine 4-oxides with phenols oxidation of the adducts may be achieved by reaction with potassium permanganate in acetone.105... 

This example shows that azinium cations generated from N-oxides are not always attacked by a nucleophile at C-a or C-y positions. In the above-mentioned reaction, it is the C-(3 position that is the preferential site for nucleophilic attack. Reactions of this type are usually accompanied by loss of the N-oxide function. The presence of a substituent able to stabilize the positively charged species (e.g., 4) seems to be an important feature in determining the site selectivity for these deoxidative nucleophilic substitutions (Scheme 6) (78JQC2514). Similar substitution reactions at C-3 (C-0) of the pyridine ring have also been observed in pyridine N-oxides (86H161). 

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