New one-pot synthesis of spiro[furo[2,3-d]pyrimidine-6,5'-pyrimidine]pentaones and their sulfur analogues.

Reaction of barbituric acid (BA), 1,3-dimethyl barbituric acid (DMBA) and 2-thiobarbituric acid (TBA) with cyanogen bromide and various aldehydes in presence of triethylamine afforded a new class of heterocyclic stable 5-alkyl and/or 5-aryl-1H, 1'H-spiro[furo[2,3-d]pyrimidine-6,5'-pyrimidine]2,2',4,4',6'(3H,3'H,5H)-pentaones which are dimeric forms of barbiturate (uracil and thiouracil derivatives) at 0 °C to ambient temperatures. Structure elucidation is proved by X-ray crystallography, (1)H NMR, (13)C NMR, FT-IR, CHN and mass analyses techniques. Mechanisms of the formations are discussed.

1,1',3,3',5,5'-Hexamethyl-spiro-[furo[2,3-d]pyrimidine-6(5H),5'-pyrimidine]-2,2',4,4',6'(1H,3H,1'H,3'H,5'H)-penta-one.

In the title mol-ecule, C(15)H(18)N(4)O(6), the fused 2,3-dihydro-furan ring has an envelope conformation and the spiro pyrimidine ring has a half-chair conformation. In the crystal, short inter-molecular O⋯C contacts of 2.835 (4) and 2.