Improved syntheses of thieno[2,3‐ b ]‐ and [3,2‐ b ]‐fused naphthyridines

The preparation of eight isomeric thieno[2,3‐ b ]‐ and [3,2‐ b ]‐fused naphthyridines [1] was improved through the Pd(0) catalyzed cross‐coupling of 3‐formyl‐4‐iodopyridine, 2‐formyl‐3‐iodopyridine, 3‐bromo‐4‐formylpyridine and 2‐bromo‐3‐formylpyridine with t ‐butyl N ‐(2‐trimethylstannyl‐3‐thienyl)car‐bamate and t ‐butyl N ‐(3‐trimethylstanny‐2‐thienyl)carbamate.