The cyanide catalyzed dimerization of 2,3 naphthalenedicarboxaldehyde: a unique oxidative condensation product and derivatives

Abstract

2,3 Naphthalenedicarboxaldehyde (NDA), in the presence of cyanide, is commonly used for the derivitization of amino acids and peptides to fluorescent 2-substituted 1-cyanobenzo[f]isoindoles, providing high sensitivity in capillary electrophoresis (CE) and high performance liquid chromatography (HPLC) separations. CE studies of the neurotransmitters glutamate and aspartate have shown the formation of a number of competitive side products. Although mentioned in the literature, these side products have not been characterized. The product, 15-hydroxybenzo[g]benzo [6, 7]isochromeno[4,3-c]isochromen- 7(15H)-one (2), is reported here, as a dimerization of NDA in the presence of cyanide and atmospheric oxygen. The structure is confirmed by IR, LRFAB-MS, IRMS, and NMR spectra. Possible mechanisms for the formation of 2, its air oxidation, and an alternative benzoin condensation product are discussed. 15-hydroxybenzo[g]benzo [6,7]isochromeno[4,3-c]isochromen-7(15H)-one (2) is easily converted to full acetals via reflux in an alcohol solvent in the presence of an acid catalyst. Oxidation by NaOCI (aq) yields 3-(3-chloro-1,4-dioxo-3,4-dihydro-1H-benzo[g]isochromen-3-yl)-2-napthaldahyde (4) by capturing hypochlorite at the position æ the enolate. Oxidation by pyridinium chlorochromate (PCC) yields naptho[2,3-c]furan-1,3-dione (5) by multiple oxidations and the formation of the anhydride.