Synthesis of (Pyrido[3ʹ,2ʹ:4,5]thieno[3,2-d]pyrimidin-2-ylthio)acetic Acids Esters by the Reaction of N-(Thieno[2,3-b]pyridin-3-yl)-α-chloroacetamides with Potassium Thiocyanate

The reaction of 3-amino-4-aryl-2-acyl-6-phenylthieno[2,3-b]pyridines with chloroacetyl chloride in toluene yielded the corresponding chloroacetamides. The latter underwent a cascade rearrangement upon treatment with KSCN in an acetone–EtOH mixture to form previously undescribed ethyl esters of (pyrido[3′,2′:4,5]thieno[3,2-d]pyrimidin-2-ylthio)acetic acids. Under similar conditions, 4-(4-methoxyphenyl)-6-phenyl-3-(chloroacetamido)thieno[2,3-b]pyridine-2-carbonitrile produced only the isomerization product of the intermediately formed thiocyanatoacetamide—3-(2-imino-4-oxothiazolidin-3-yl)-4-(4-methoxyphenyl)-6-phenylthieno[2,3-b]pyridine-2-carbonitrile.