189374-07-0Relevant academic research and scientific papers
Dipolar cycloaddition reactions of dihydropyrimidine-fused mesomeric betaines. An approach toward conformationally restricted dihydropyrimidine derivatives
Kappe, C. Oliver,Peters, Karl,Peters, Eva-Maria
, p. 3109 - 3118 (2007/10/03)
The bimolecular and intramolecular cycloaddition potential of various 4-aryldihydropyrimidine-fused mesomeric betaines was investigated. Dihydropyrimidine-fused isothiomunchnones and isomunchnones were found to undergo 1,3-dipolar cycloaddition reactions with electron-deficient dipolarophiles such as DMAD, methyl propiolate, methyl vinyl ketone, or N-methylmaleimide. In contrast, cross-conjugated mesomeric thiazinium betaines underwent 1,4-dipolar cycloaddition reaction with electron-rich dipolarophiles such as ynamines or ketene acetals. In general, these cycloadditions show a high degree of regioselectivity, facial selectivity, and exo/endo diastereoselectivity. Intramolecular variations of the above processes involving o-alkenylaryl-tethered dihydropyrimidine-fused isomunchnones lead to polycyclic dihydropyrimidine analogs that closely mimic the proposed receptor-bound conformation of dihydropyridine calcium channel modulators. These cycloadducts are the result of an endo-addition of the π-bond to the carbonyl ylide dipole embedded in the isomunchnone system. The relative stereochemistry of these cycloadducts was established by single-crystal X-ray analysis.
