Formation of 3-amino-1,5,6,7-tetrahydro-4H-indol-4- ones from 2-(2-Oxo-2-arylethyl)-l ,3-cyclohexanediones and N,N-disubstituted-hydrazines

Abstract

Phenacyldimedones (ia -d) undergo an anomalous reaction with N,N-dlsubstitut'ed-hydrazines to afford 3-amino-l,5,6,7-tetrahydro-4H-indol-4-ones (3), with only Id, additionally yielding the normal' product 2a. A mechanism is postulated for the novel reaction of la with N,N-dimethylhydrazine involving species 16 and 17 as intermediates. This is substantiated by reaction of 1 a with N,N dimethylhydrazine and excess of other amines like morpholine, N,N-dibenzylamine. aniline and n-propylamlne Jeading to products 3d, 3f, 3j and 4 respectively. 3f is hydrogenolysed to 3i and thence deaminated to known 2-phenyltetrahydroindole (9a), Reaction of aminocyclohexenone (10) with phenylglyoxal and morpholine affords 3d. N-Aminopiperldine reacts with the acyclic triketone (7) to afford only the 'normal' product 8, while with 18, ketotetrahydroindoles 9b and 23 "are formed through a complex sequence of reactions.