Thieno[3,2-c]pyridazine: synthesis and derivatives

Abstract

Thieno[3,2-c]pyridazine (VII; R = H) has been synthesised by sequential reduction and oxidation of the corresponding thienopyridazin-3-one, (VI; R¹= R²= H), itself prepared from its 6-carboxylic acid (VI; R¹= CO₂H, R²= H). The methyl ester of this acid was made by stepwise oxidation with N-bromosuccinimide of the corresponding tetrahydro-derivative (IV; R = CO₂H) which had resulted from a reaction series requiring the condensation of hydrazine with methyl 2-(5-methoxycarbonyl-3-oxotetrahydro-2-thienyl)acetate, the product of a Dieckmann condensation. Various functional derivatives of the title compound and the foregoing intermediates, including oxidation products, have been made.