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

Abstract

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.

Keywords: Aromatic proton transfer * C-N bond cleavage * Aryne intermediate * [3+2] cycloaddition reaction * Manganese(II) chelation.