SYNTHESIS OF INDENO[1,2-B]PYRAZINE N-OXIDES BY REACTION OF NINHYDRIN WITH 1,2-BISHYDROXYLAMINES

The reaction of the ninhydrin (1) with 1,2-bishydroxylamines 2a-c affo rds dihydroindeno[1,2-b]pyrazine N,N'-dioxides 5a-c. The intermediates hexahydro- and tetrahydroindeno[1,2-b]pyrazines 3a and 4c, which have been isolated, are easily transformed into 5a, c. Heating of 5b, c or keeping of 5b on alumina gives indeno[1,2-b]pyrazine N-oxides 6b, c, N,N'-dioxide 7c and indeno[1,2-b]pyrazine 8. Treatment of 5b with a so lution of hydrochloric acid in H2O/MeOH leads to 6b, whereas treatment of 5b with KOH furnishes mono-N-oxides 6b, 9 and dioxide 7b. Compound 8 is prepared by deoxygenation of 6b with TiCl3. The reduction of 6b with c NaBH4 yields alcohol 10 and the reaction of 6b with NH2OH/AcOH gives a mixture of isomeric oximes (E)-11 and (Z)-11.