An Aromatic Proton Transfer to the o‐Amine Function: Naphthoquinonyne Intermediate and Cycloaddition Reactions

The article reports a hitherto‐unknown aromatic proton transfer (APT) to the o‐amine function chelated to manganese(II) ion and disintegration of the molecule generating an aryne intermediate. The reaction of (NQ)‐NH(AQ) (o‐HLH) with manganese(II) acetate in boiling DMF generates [MnII(o‐HL‐)2], where the o‐HLH ligands undergo disintegration forming manganese(II) complexes of AQ and an 1,4‐ naphthoquinonyne intermediate based on benzoquinone ring, that has been defined as [NQ‐2H] (NQ and AQ abbreviate respectively 1,4‐naphthoquinone and 8‐aminoquinoline fragments). The disintegration reaction of o‐HLH depends on the metal precursor used, solvent and temperature. A [3+2] cycloaddition of [NQ‐2H] with another o‐HLH affords a carbazolequinone, L[NQ‐2H]. Self‐dimerization and coupling with maleic anhydride by a [2+2] cycloaddition reaction and [4+2] cycloaddition reactions of [NQ‐2H] with furan and isoprene were authenticated by ESI mass spectrometry. Notably, the similar reaction with o‐ClLH generates manganese(II) complexes of o‐ClLH where no disintegration reaction was realized. In MeOH, no APT reaction was accomplished. No such reactions were substantiated even with manganese(II) perchlorate and manganese(II) chloride salts.