A comparative study on the synthesis of pyrazolo-[4,3-c]quinoline oxides by reductive cyclisations

Alternate routes for the reductive cyclisation of 4-acetyl-3-methyl-5-(2-nitrophenyl)-1-phenylpyrazole under different conditions are described. Whereas 3,4-dimethyl-1-phenylpyrazolo4,3-c]quinoline 5-oxide is formed by mild noncatalytic reductions, catalytic and transfer hydrogenation processes cause the diastereoselective formation of cis-4,11-dihydro-3,5-dimethyl-1-phenylpyrazolo4,3-c]quinoline 6-oxide.