Fischer-Helferich procedure

Almost thirty years passed before Todd and coworkers applied the Fischer-Helferich procedure to the synthesis of the natural purine nucleosides, adenosine (l)i and guanosine (2). Condensation of tri-O-acetyl-D-ribofuranosyl chloride, prepared from 5-0-benzyl-D-ribose by way of tetra-0-acetyl-D-ribofuranose,i 2 with the silver salt of 2,8-dichloroadenine... 

Deoxyribonucleosides.—Because of the extreme lability of the poly-O-acyl-2-deoxyglycosyl halides, early attempts to prepare 2-deoxy-ribo -nucleosides by the Fischer-Helferich procedure met with only limited success, in that only the two anomeric 2-deoxy-D-ribo -pyranosyl derivatives of theophylline had been prepared until recently. Almost simultaneously, two groups of workers discovered that, by using acyl groups not normally employed, stable di-0-acyl- 2-deoxy-D-ribo -furanosyl halides (50a and 50b) could be obtained. This discovery led to the direct... 

The above procedure is essentially that described in the laboratory manual by Fischer and Helferich.1... 

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