Three-component spiro heterocyclization of 1H-pyrrole-2,3-diones with dimedone

We previously described spiro heterocyclization of hetareno[a]pyrrole-2,3-dione with dimedone at a ratio of 1 : 1, where the latter acted as 1,3-C,O-binucleophile through initial nucleophilic addition of the CH carbon atom in the enol fragment to C of the 2,3-dioxopyrrole fragment [1]. Reactions of monocyclic 1H-pyrrole-2,3diones with cyclic enols have not been reported so far. Isopropyl 2-(1-aryl-4,5-dioxo-2-phenyl-4,5-dihydro-1H-pyrrol-3-yl)-2-oxoacetates Ia and Ib [2] reacted with dimedone at a ratio of 1 : 2 in boiling anhydrous chloroform to produce in 3–4 h (TLC) isopropyl 2-oxo-2-(1-aryl-3′,3′,6′,6′-tetramethyl-1′,2,8′-trioxo-5phenyl-1,1′,2,2′,3′,4′,5′,6′,7′,8′-decahydrospiro[pyrrole3,9′-xanthen]-4-yl)acetates IIa and IIb. A probable reaction scheme includes initial condensation of the C=O carbonyl group of pyrroledione I with the activated methylene group of dimedone, followed by nucleophilic addition of C and OH group in the enol tautomer of the second dimedone molecule to C and ketone carbonyl carbon atom in the dioxocyclohexane fragment of the primary adduct, respectively. The described reaction is the first example of direct pseudo-three-component spiro heterocyclization of 1H-pyrrole-2,3-diones with cyclic enol, which leads to the formation of difficultly accessible spiro[pyrrole3,9′-xanthene] heterocyclic system. Isopropyl 2-oxo-2-(3′,3′,6′,6′-tetramethyl-1′,2,8′trioxo-1,5-diphenyl-1,1′,2,2′,3′,4′,5′,6′,7′,8′-decahydrospiro[pyrrole-3,9′-xanthen]-4-yl)acetate (IIa). A solution of 1.0 mmol of pyrroledione Ia and 2.0 mmol of dimedone in 15 mL of anhydrous chloroform was heated for 4 h under reflux. The mixture was