A study of electrophilic substitution in the pyrrolo[2,3‐d]pyrimidine ring

Several 4,5‐disubstituted pyrrolo[2,3‐d ]pyrimidines were prepared for the first time via electrophilic substitution, e.g. halogenation, nitration and sulfonation. PMR data for certain pyrrolo[2,3‐d]pyrimidines are included which has furnished conclusive evidence that electrophilic substitution occurred at position 5. These pyrrolo[2,3‐d]pyrimidines, with electron ‐withdrawing substituents at position 5, are of considerable interest as bases for the preparation of nucleoside derivatives related to tubercidin, toyocamcin and sangivamycin.