Orthoamides and iminium salts LXXII: N,N,N',N',N'',N'',N''',N'''-octamethyl-(but-2-yne)-bis(amidinium) tetrafluoroborate: the first bis-amidinium salt of acetylenedicarboxyclic acid. A new superelectrophile?

A method for the preparation of the first acetylenedicarboxamidinium salt from a bis-orthoamide derivative of acetylenedicarboxyclic acid has been established. The salt reacted with cyclopentadiene and furan at room temperature to give bicyclic [4+2]-cycloaddition products. The solid compounds were characterized by solution NMR spectroscopy and by single-crystal X-ray diffraction. Quantum-chemical calculations of the isolated N,N,N',N',N'',N'',N''',N'''-octamethyl-acetylene-bis(carboxamidinium) ion showed very good agreement with the spectroscopic and diffraction data.