One-step synthesis of a novel heterocyclic system: Spiro[[1,4]thiazino-[4,3-a]quinoline-5,5′-pyrimidine]

A review of the synthetic strategies toward spirobarbiturate-fused 3- to 7-membered rings

Spiro-connected hexahydropyrimidine-2,4,6-trione heterocyclic rings have received increasing attention from the viewpoint of biological activity and synthetic methods due to the importance of the rigid heterocyclic system and unique orientation of the functional substituents. Since 1900, numerous studies have exploited the synthesis of various spirobarbiturate-fused carbo- and heterocycles by applying different strategies. Due to the importance of barbiturate-based olefins as activated alkenes, these substrates have been utilized in many reactions. In addition, the nucleophilic addition of 1,3-disubstituted barbituric acid to different electrophiles has been applied to prepare highly functionalized spirobarbiturate scaffolds. This short review highlights various strategies for synthesizing spirobarbiturate-fused 3- to 7-membered carbo- and heterocyclic rings and some catalytic diastereoselective and enantioselective chemical reactions to access chiral compounds. The sections are divided by the incorporation of 3- to 7-membered heterocyclic or carbocyclic rings into a spirobarbiturate scaffold, and are presented in different subsections depending on the mechanistic details.

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.