Preparation of ribosyl derivatives of 1,2,4-triazol-3(2H)-one and 5-methyl-1,2,4-triazol-3(2H)-one

Abstract

Reaction of the silylated triazolone I with 2,3,5-tri-O-benzoyl-D-ribofuranosyl bromide afforded a mixture of the 4-ribosyltriazolone IXa and 2,3-diribosyltriazolone Xa. Under the same conditions the silylated 5-methyltriazolone II gives the 4-ribosyl derivative XIa and 2-ribosyl derivative XIIa. The 4-phenyl and 4-ribosyltriazoles VII, VIII, IXa and XIa were prepared by an alternative synthesis: cyclisation of l-ethoxymethylene-, l-(l-ethoxyethylidene)-4-phenyl- and 4-ribosylsemicarbazides XIII, XIV, XVa,b and XVIa,b in boiling hexamethyldisilazane in the presence of ammonium sulfate. The semicarbazides XIII, XIV, XVa,b and XVIa,b were obtained by reaction of 4-phenyl- or 4-ribosylsemicarbazide with triethyl orthoformate or diethyl orthoacetate. Compounds XIII and XIV were obtained as the (E)-isomers whereas compounds XV and XVI as mixtures of (Z)- and (E)-isomers XVa,b and XVIa,b, respectively. The benzylation of the triazolones I and II was also studied.