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) (LH) with manganese(II) acetate in boiling DMF generates [Mn(L)], where the LH 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 LH depends on the metal precursor used, solvent and temperature. A [3+2] cycloaddition of [NQ-2H] with another LH 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 LH generates manganese(II) complexes of LH 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.