Five-Membered Heterocycles with Four Hetero Atoms

Five-Membered Heterocycles with Four Hetero Atoms 

The number of five-membered heterocycles with four hetero atoms is limited to those with nitrogen atoms. Thus, the tetrazole acyclonucleo-sides were formed from sugars N,N -diphenylformazanes by the action of AT-bromosuccinimide or lead tetraacetate [133,134]. The synthesis of the tetra-O-benzoyl-D-lyxononitrile and its conversion to (o-lyxo-tetritol-l-yl)-tetrazole derivatives upon reaction with sodium azide was reported [133, 134]. A pseudo C-nucleoside including a tetrazole ring was achieved by conversion of 3- 0-benzyl- 1,2-O-isopropylidene-D-ribo-pentodialdehydo-1,4-furanose to the respective nitrile and then reaction with sodiiun azide [86]. 

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