The first synthesis of pyrido[2,1‐ a ]phthalazinium system and its three thieno‐fused analogues

Substituted biaryl compounds 9, 14–16 were synthesized through Pd(0)‐catalyzed cross coupling reactions between boronic acids or tin derivatives and aryl halides. N ‐Amination, and subsequent ring closure resulted in the new angularly‐fused pyrido[1,2‐ b ]pyridazinium systems 1–4 . The use of silver oxide as a cocatalyst in the couplings of tin derivatives was essential in order to obtain rapid reaction and better yields. Structures were determined by 1 H nmr and 13 C nmr spectra.