Spiro heterocyclization of 3-acylpyrrolo[1,2-c][1,4]benzoxazine-1,2,4- triones with 1,2,3,4-tetrahydroquinoline

We previously described spiro heterocyclization of 3-acylpyrrolo[1,2-c][1,4]benzoxazine-1,2,4-triones in reaction with N-alkylanilines, which involved successive nucleophilic attacks by the ortho-carbon and nitrogen atoms of anilines on C and C, respectively, of pyrrolobenzoxazinetriones with opening of the oxazine ring at the C–O bond. As a result, 3′-aroyl1′-(2-hydroxyphenyl)-4′-hydroxy-1-alkylspiro[indole3,2′-pyrrole]-2,5′(1H,1′H)-diones were obtained [1]. While studying the scope of application of this procedure, we examined reactions of 3-acylpyrrolo[1,2-c][1,4]benzoxazine-1,2,4-triones Ia and Ib with 1,2,3,4tetrahydroquinoline (II) and isolated 3-aroyl-4-hydroxy-1-(2-hydroxyphenyl)-5′,6′-dihydrospiro[pyrrole2,1′-pyrrolo[3,2,1-ij]quinoline]-2′,5(1H,4′H)-diones IIIa and IIIb. Presumably, addition of the C carbon atom of tetrahydroquinoline to C in pyrrolobenzoxazinetrione I is followed by closure of new pyrrole ring via intramolecular nucleophilic attack by the amino group of the tetrahydroquinoline fragment on the lactone carbonyl carbon atom in the oxazine ring and opening of the latter at the C–O bond. The described reaction may be regarded as an example of regioselective formation of a new spiro heterocyclic system, spiro[pyrrole-2,1′-pyrrolo[3,2,1-ij]quinoline], which is structurally related to the heterocyclic skeleton of Vinca alkaloids. 3-Benzoyl-4-hydroxy-1-(2-hydroxyphenyl)-5′,6′dihydrospiro[pyrrole-2,1′-pyrrolo[3,2,1-ij]quinoline]-2′,5(1H,4′H)-dione (IIIa). A solution of 3.1 mmol of compound I and 3.1 mmol of 1,2,3,4-