Depending on conditions, the condensation of 2-amino-3-cyano-4,5,6,7-tetrahydroindole with 8-dicarbonyl compounds leads to 2-methyl-4-oxo-or 4-methyl-2-oxo-10-cyano-6,7,8,9tetrahydropyrimido[l,2-a]indoles via the intermediate compounds: 2-(3-ethoxy-carbonylprop-2-en-2-yl amino) and 2- (l,3-dioxobutylamino)-3-cyano-4,5,6,7-tetrahydroindoles, respectively.
Continuing our investigations on the synthesis of condensed heterocyclic systems containing pyrrole and indole fragments [i-3], we studied the condensation of 2-amino-3cyano-4,5,6,7-tetrahydroindole (I) with acetoacetic ester and diketene.
It is known that reactions of this type are highly dependent on the prevailing conditions and do not always proceed unequivocally (see, for example, [4,5].)
In fact, the reaction of amine I with acetoacetic ester leads to isomeric compounds 2-methyl-4-oxo-lO-cyano-6,7,8,9-tetrahydropyrimido[l,2-a]indole (III) and 4-methyl-2-oxo- lO-cyano-6,7,8,9-tetrahydropyrimido[l,2-a]indole (V), depending on the structure of the intermediates formed: 2-(3-ethoxycarbonylprop-2-en-2-ylamino)-3-cyano-4,5,6,7-tetrahydroindole (II) and 2-(l,3-dioxo-butylamino)-3-cyano-4,5,6,7-tetrahydroindole (IV), respectively.