Visible-light mediated regioselective approach towards synthesis of 7-aroyl-6-methyl-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazines

Visible-light driven regioselective synthesis, characterization and binding studies of 2-aroyl-3-methyl-6,7-dihydro-5H-thiazolo[3,2-a]pyrimidines with DNA and BSA using biophysical and computational techniques

“…Visible light mediated reaction initiates by the homonuclear fission of C–Br bond of α-bromodiketone 3 and S–H bond of tetrahydropyrimidine-2-thione 2 to generate free radicals 8 and 9 which combine to form S-alkylated open chain structure 10 . The bromine and hydrogen free-radicals generated in the step facilitate the homonuclear fission of N–H and C=O bond respectively of intermediate 10 to generate two new free radicals; amine and carbonyl group adjacent to methyl group; the intramolecular combination of these free radicals generated the (3-hydroxy-3-methyl-2,3,6,7-tetrahydro-5 H -thiazolo[3,2- a ]pyrimidin-2-yl)(aryl/heteroaryl)methanone 11 which undergoes dehydration to yield 2-aroyl/heteroaroyl-3-methyl-6,7-dihydro-5 H -thiazolo[3,2- a ]pyrimidines 4 as product compatibility to our previous results 18 , 19 . The regioselective route followed in the reaction can be explained based on less steric hindrance and crowding on acetyl group as compared to aroyl/heteroaroyl group making the former more susceptible to react.…”

“…1,3-Diketones 18 and tetrahydropyrimidine-2-thione were prepared according to the literature procedure. NBS was purchased commercially.…”

“…Considering the immense biological importance of thiazolo[3,2- a ]pyrimidines and in continuation to our previous studies related to the regioselectivity study of the reaction between 1,3-diketones and various binucleophiles 18 – 20 , it was envisaged to undertake the study of regioselectivity pattern in the reaction between 1,3-diketones 1 and tetrahydropyrimidine-2( H )-thione 2 to synthesize the thiazolo[3,2- a ]pyrimidine nucleus. For this purpose, the unsymmetrical 1,3-diketone 1 was reacted with NBS to produce α-bromo-1,3-diketone 3 which was used in situ for condensation with tetrahydropyrimidine-2( H )-thione 2 in presence of visible light.…”

Vision on Synthetic and Medicinal Facets of 1,2,4-Triazolo[3,4-b][1,3,4]thiadiazine Scaffold

“…In recent years, organic reactions under visible-light irradiation are grabbing intense attention as a powerful strategy involving the concept of ‘Green Chemistry’ to reduce hazardous ecological imprints of organic synthesis. In order to achieve a green protocol, Aggarwal et al [ 28 ] developed first visible-light mediated regioselective synthesis of novel acyl derivatives of 1,2,4-triazolo[3,4- b ][1,3,4]thiadiazines 26 involving reaction of binucleophilic 4-amino-3-mercapto-1,2,4-triazoles ( 1 ) with in situ generated α-bromodiketones ( 25 ) from unsymmetrical β-diketones ( 24 ). In principle, reaction of unsymmetrical α-bromodiketones ( 25 ) (having two carbonyl carbon of different electrophilicity) with 4-amino-3-mercapto-1,2,4-triazoles ( 1 ) may lead to the formation of two regioisomers- 7-aroyl-6-methyl-[1,2,4]triazolo[3,4- b ][1,3,4]thiadiazines ( 26 ) and 7-acetyl-6-aryl-[1,2,4]triazolo[3,4- b ][1,3,4]thiadiazines ( 27 ).…”

Bicyclic 5-6 Systems With One Bridgehead (Ring Junction) Nitrogen Atom: Four Extra Heteroatoms 2:2

“…A solvent free protocol was also established with a catalytic amount of p-toluene sulfonic acid with slightly lower yields. 70 As shown in scheme 45, various polycyclic derivatives have also been obtained from 203. 2-bromoindandione 235 and 2-bromo-3-hydroxynaphtalene-1,4-dione 237 produced regioselectively tetracyclic linear derivative 236 and fused indanones 238 in excellent yields.…”