An Efficient Synthesis of Novel Pyridothieno‐Fused Thiazolo[3,2‐a]pyrimidinones via Pictet—Spengler Reaction.

Title compounds (V) are efficiently synthesized using a Pictet—Spengler reaction of key intermediate (III), which is obtained by condensation reaction of compound (I) with 3-cyanopyridine-2-thione (II) via Thorpe—Ziegler isomerization, and aromatic aldehydes (IV) under sulfamic acid catalysis in good yields.