Molbank

We report an efficient and transition-metal-free protocol for the propargylation of 4-(4-chlorophenyl)-2-oxo-6-phenyl-1,2-dihydropyridine-3-carbonitrile using propargyl bromide in the presence of cesium carbonate in dimethylsulfoxide under mild conditions. This synthetic transformation proceeds with marked chemoselectivity, furnishing the O-propargylated pyridine and the N-propargylated 2-pyridone in 75% and 8% yields, respectively. Both products were fully characterized by IR and NMR spectroscopy, as well as high-resolution mass spectrometry, confirming their molecular structures.

The 1,4-dipolar cycloaddition of the ylidene derivative of 1H-pyrrole-2,3-dione to a dipole generated in situ from 1-benzylbenzimidazole and dimethyl acetylenedicarboxylate proceeds via the exocyclic multiple bond of the ylidene derivative and affords a mixture of diastereomeric spiro[benzo[4,5]imidazo[1,2-a]pyridine-3,3’-pyrroles], which slowly epimerized in a solution.

The reaction of aliphatic aldehydes with the tautomers 6,6-dimethyl-4-hydroxy-2H-thiopyrane-2-thione and 6,6-dimethyl-2-mercapto-4H-thiopyrane-4-one is reported to yield spiro compounds. However, the spiro compound of the reaction with formaldehyde is postulated, but has not been isolated to date. Due to a change in reaction conditions, we managed to isolate (RS)-6,6,7′,7′-Tetramethyl-2-sulfanylidene-5,6,6′,7′-tetrahydro-2H,2′H,4H,4′H,5′H-spiro[thiopyran-3,3′-thiopyrano [2,3-b]thiopyran]-4,5′-dione for the first time. The structure was proven with the help of a single X-ray crystal analysis. Furthermore, the new compound was fully characterized using one- and two- dimensional NMR techniques such as ¹H, ¹³C, DEPT, COSY, HSQC and HMBC spectra, as well as IR and HRMS measurements.