Tautomerism and isotopic multiplets in the 13C NMR spectra of partially deuterated 3-arylpyrimido[4,5-c]pyridazine-5,7(6H,8H)-diones and their sulfur analogs--evidence for elucidation of the structure backbone and tautomeric forms

Isotopic splitting patterns in the (13) C NMR spectra of some partially deuterated 1-aryl-2-(phenyldiazenyl)butane-1,3-dione and 4-hydroxy-3-(phenyldiazenyl)-2H-chromen-2-one: evidence for elucidation of tautomeric forms

Nuclear magnetic resonance spectra of synthesized azo dyes derived from aniline derivatives in reaction with benzoylacetone and 4-hydroxycoumarin were studied in both CDCl3 and (CD3 )2 SO (two drops of D2 O were added into solutions of dyes). All dyes showed intramolecular hydrogen bonding. Dyes derived from o-nitro aniline in the reaction with benzoylacetone, and 4-hydroxycoumarin showed bifurcated intramolecular hydrogen bonds. The solvent-substrate proton exchange of dyes derived from benzoylacetone and 4-hydroxycoumarin was examined in the presence of two drops of D2 O. Among ten dye samples, two dyes derived from benzoylacetone did not show deuteration, three dyes showed partial deuteration and five dyes showed full deuteration under similar conditions. For the partially deuterated dyes the β-isotope effect in (13) C splitting was investigated and was used for the determination of the predominant tautomeric form.

An Efficient One-pot Two-component Protocol for Regio- and Chemoselective Synthesis of 5-Aryloyl-1,3,7,9-tetraalkyl-2,8-dithioxo-2,3,8,9-tetrahydro-1H-pyrano[2,3-d:6,5-d′]dipyrimidine-4,6(5H,7H)-diones

Novel symmetric fused pyrano[2,3-d]pyrimidine derivatives were synthesized in 75–92 % yield by a one-pot two-component reaction of arylglyoxals and 1,3-dialkyl-2-thiobarbituric acids in ethanol at room temperature. This is the first protocol to be reported for the synthesis of 5-aryloyl-1,3,7,9-tetraalkyl-2,8-dithioxo-2,3,8,9-tetrahydro-1H-pyrano[2,3-d:6,5-d′]dipyrimidine-4,6(5H,7H)-diones and the significant features of the present protocol are simplicity, high yields, a simple isolation procedure, and high chemoselectivity.

Isotopic effect on tautomeric behavior of 5-(2,6-disubstituted-aryloxy)-tetrazoles

Isotopic effect on tautomeric behaviors of the synthesized 5-phenoxy- (1a), 5-(2,6-dimethylphenoxy)-(1b), 5-(2,6-diisopropylphenoxy)-(1c), 5-(2,6-dimethoxyphenoxy)-(1d) and 5-(4-methylphenoxy)-tetrazole (1e) were investigated in DMSO-d6 by adding one drop of D2O. Among 1a-e, 1a, 1d and 1e show small rotational barrier around C5-O1 and O1-C6 while in 1b and 1c there are distinguishable rotational barrier about that bonds. The (1)H NMR spectra of 1b and 1c show slightly different chemical shifts for two methyl and isopropyl groups on those phenyl ring, respectively, while the chemical shifts difference (Δδ) between two methyl and two isopropyl groups were enhanced by adding D2O. The (13)C NMR spectra of 1b show two overlapped singlets for methyl groups after adding D2O. Representatively, the calculations of compound 1c were performed with GAUSSIAN-03 and the rotational barrier about C5-O1 and between isopropyl group and phenyl ring in 1c was calculated with B3LYP/6-31G(d) basis set.

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.

A Regioselective One-Pot, Three Component Synthesis of 6-Aryl-4-cyano-3(2H)-pyridazinones in Water

A series of 4-cyano-3(2H)-pyridazinones bearing different aryl substituents in the 6-position of the pyridazinone ring was synthesized regioselectively using a novel efficient one-pot three component reaction of alkyl 2-cyanoacetates with arylglyoxals in the presence of hydrazine hydrate at room temperature in water.