SHORT COMMUNICATIONSMulticomponent condensations offer quite efficient and convenient methods for the synthesis of polynuclear nitrogen-containing heterocycles which can thus be obtained in one step from accessible starting compounds. Three-component condensations involving methylene-active compounds (1,3-diketones, barbituric acid), their nitrogen equivalents (enamino ketones, 6-aminouracil), and aromatic aldehydes have been studied most thoroughly. In particular, oxo derivatives of pyrido[2,3-d]pyrimidine [1] and pyrimido[4,5-b]quinoline [2][3][4][5] have been synthesized in this way.We have examined three-component condensation of cyclic enamino ketones with phenylglyoxal hydrate and barbituric acid. The reactions were carried out by heating the reactants in boiling water or aqueous ethanol for 5-10 min, and the products were functionalized 4,5,6,7-tetrahydroindole derivatives 1a-1g (yield 63-89%). Compounds 1a-1g can also exist as tautomers 2a-2g. Tautomers 1 predominate in the crystalline state; the IR spectra (KBr) contain an absorption band at 3070-3130 cm -1 due to stretching vibration of the enolic hydroxy group in the barbituric acid moiety. According to the 1 H NMR data, tautomers 2 occur in DMSO-d 6 ; they display a singlet at δ 4.5-4.9 ppm from the CH proton.Tetrahydroindole derivatives with a 1,3-dicarbonyl fragment attached to C 3 were previously synthesized by N-heterocyclization of the diketone condensation product of dimedone and phenylglyoxal [6], recyclization of octahydroxanthene derivatives [7], and three-component condensation of substituted enamino ketones with phenylglyoxal and 1,3-dicarbonyl compounds [8].Compounds 1a-1g (general procedure). A mixture of 0.5 mmol of the corresponding enamino ketone, 71 mg (0.55 mmol) of barbituric acid, and 2 mL of water was heated under stirring to 80°C, 2 mL of ethanol was added to complete the dissolution of the enamino ketone (no ethanol was added in the synthesis of 1a and 1b), and a solution of 76 mg (0.5 mmol) of phenylglyoxal hydrate in 2 mL of hot water was added. The mixture was heated for 5-10 min under reflux with stirring and cooled, and the precipitate was filtered off, washed with 50% aqueous ethanol, and dried in air.6-Hydroxy-5-(6,6-dimethyl-4-oxo-2-phenyl-4,5,6,7-tetrahydro-1H-indol-3-yl)pyrimidine-2,4(1H,3H)-dione (1a). Yield 0.125 g (68%), colorless crystals, decomposition point 334-336°C. IR spectrum, ν, cm -1 : 3316 (NH), 3183 (NH), 3067 (OH, R = H (a), Me (b), PhCH 2 (c), Ph (d), 4-MeC 6 H 4 (e), 4-MeOC 6 H 4 (f), 4-ClC 6 H 4 (g).
