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Regio and diastereoselective synthesis of tetrahydroimidazo[1,5-b][1,2,4]oxadiazol-2(1H)-thiones via 1,3-dipolar cycloaddition of imidazoline 3-oxides with methylisothiocyanate

Elsevier B.V.
Publication Date
  • Organic Chemistry > Synthetic Chemistry
  • Orgchem/0105001


1,3-Dipolar cycloaddition of imidazoline 3-oxides 1 with methylisothiocyanate proceeds regio- and diastereoselectively to give tetrahydroimidazo[1,5-b][1,2,4]oxadiazol-2(1H)-thiones 3 in high yields. Attempts to hydrolyse compounds 3 in ethanol with diluted HCl to tetrahydroimidazo[1,5-b][1,2,4]oxadiazol-2(1H)-ones 5 were unsuccessful instead the corresponding imidazoles were isolated. The adducts 3 undergo ring opening at heating in the condensed phase or in the presence of secondary amines to give corresponding imidazole, while tertiary amines induce elimination only in the case of C-6 unsubstituted 3a-c but not in the case of C-6 phenyl substituted adducts 3d-e. 3a-c undergo ring opening at reflux in acetonitrile to give imidazoles while 3d undergo retro dipolar cycloaddition to give the starting nitrones 1.

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