Synthesis and reactions of 1,5- and 1,3-dialkyl-(d-manno-pentitol-1-yl)-1H-1,2,4-triazole nucleosides derived from 1-(chloroalkyl)-1-aza-2-azoniaallene salts

1-(Chloroalkyl)1-aza-2-azoniaallene salts underwent cycloaddition with penta-O-benzoyl-d-mannonic acid nitrile to give several intermediates. The salts of these rearranged spontaneously to the protonated 1,2,4-triazoles, which hydrolysed, in situ, to the acyclic 1,2,4-triazole C-nucleosides. Deblocking of the latter afforded the free nucleosides. Analogous treatment of 1,1-tert-butylmethyl derivatives of 1-aza-2-azoniaaallene salts with penta-O-benzoyl-d-mannonic acid nitrile gave, after rearrangment and hydrolysis, acyclic C-nucleosides which on deblocking furnished the free nucleosides. Acetalation of 1-ethyl-3-(d-manno-pentitol-1-yl)-5-methyl-1H-1,2,4-triazole and 5-(d-manno-pentitol-1-yl)-3-methyl-1-(1,2,4-trichlorophenyl)-1H-1,2,4-triazole with acetone and dimethoxypropane in the presence of acid afforded their 2,3:4,5-diacetal derivatives