An improved synthesis of 3‐deazaeytosine, 3‐deazauracil, 3‐deazacytidine, and 3‐deazauridine

3‐Dcazacytosine (4‐amino‐2‐pyridone, 3 ), 3‐doazauracil (4‐hydroxy‐2‐pyridone, 5 ), 3‐deaza‐cytidine (4‐amino‐1‐β‐D‐ribofuranosyl‐2‐pyridonc, 9 ), and 3‐deazauridine (4‐hydroxy‐1‐β‐D‐ribo‐furanosyl‐2‐pyridone, 11 ) were prepared in high overall yields from 1‐methoxy‐1‐buten‐3‐yne ( 1 ). Ethyl 3,5,5‐triethoxy‐3‐pentenoate ( 2 ), obtained from acylatioti of 1 with diethyl carbonate and subsequent in situ conjugate addition of ethoxide, was cyelized with ammonia to provide 3 . Diazotization of 3 and subsequent in situ hydroxydediazotization afforded 5 . Nucleoside 9 was obtained from the stannic chloride‐catalyzed condensation of bis‐trimethylsilylated 3 and 1‐ O ‐acetyl‐2,3,5‐tri‐ O ‐benzoyl‐β‐D‐ribofuranose ( 7 ), followed by ammonolysis of the blocking groups. Diazotization of 9 and subsequent in situ hydroxydediazotization afforded nucleosidc 11 .