Synthesis of 1,2,4-oxadiazolylimidazo[1,5-a]thieno[2,3-e]pyrazines as ligands for the gamma-aminobutyric acid A/benzodiazepine receptor complex

Starting from 5-benzoyl-2-chloro-3-nitrothiophene the thieno[2,3-b]pyrazine -2,3-dione ring system (4) was synthesized. This compound was reacted with potassium tert-butoxide and diethyl chlorophosphate to give diethyl 7-benzo yl-4-isopropyl-3-oxo-3,4-dihydrothieno[2,3-b]pyrazin-2-ylphosphate (5), whi ch gave with the desired 5-alkyl-3-isocyanomethyl-1,2,4-oxadiazoles in the presence of additional potassium tert-butoxide the 1,2,4-oxadiazolylimidazo [1,5-a]thieno[2,3-e]pyrazine derivatives (6-10) as ligands for the gamma -a minobutyric acid A / benzodiazepine receptor complex.