An Aromatic Proton Transfer to the o-Amine Function: A 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 [Mn^II(^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 fragmentation 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 disruption 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.