Reaction of cyclic b-dicarbonyl compounds such as pyrimidine-(1H,3H,5H)-2,4,6-trione (BA), 1,3dimethyl pyrimidine-(1H,3H,5H)-2,4,6-trione (DMBA) and 2-thioxo-pyrimidine-(1H,3H,5H)-4,6-dione (TBA) with cyanogen bromide in acetone and 2-butanone in the presence of triethylamine afforded a new class of stable heterocyclic spiro[furo[2,3-d]pyrimidine-6,5¢-pyrimidine]2,2¢,4,4¢,6¢(3H,3¢H,5H)-pentaones (dimeric forms of barbiturate) at 0°C and ambient temperature. Structure elucidation was carried out by X-ray crystallographic, 1 H NMR, 13 C NMR, two dimensional NMR, FT-IR spectra, mass spectrometry and elemental analysis. The mechanism of product formation is discussed. The reaction of DMBA with cyanogen bromide in the presence of triethylamine also afforded trimeric form of barbiturate of uracil derivatives in good yield. The reaction of selected acyclic b-dicarbonyl compounds with cyanogen bromide in the presence of triethylamine in acetone and/or diethyl ether has also been investigated under the same condition. Diethyl malonate and ethyl cyanoacetate brominated and also ethyl acetocetate both brominated and cyanated on active methylene via cyanogen bromide.
Scheme I Reaction of cyclic b-dicarbonyls (1a-e)with cyanogen bromide and ketones (2)(3)(4)(5) in the presence of triethylamine Scheme II Proposed mechanism for the preparation of 6a as representative
One-pot New Barbituric Acid DerivativesScheme III Knoevenagel condensation, Michael addition and cyclization mechanism for the formation of 7b as representative Scheme IV Reaction of 1b with cyanogen bromide in various ketones (2-5) in the presence of triethylamine for the synthesis of 16b
