1,4-Di-o-toly-2,3-naphthoquinone

Abstract

1,4-Di-o-tolyl-2,3-naphthoquinone 1, produced by lead tetraacetate oxidation of 2,3-dihydroxy. -1, 4-di-o-tolylnaphthalene 2 at –30 °C, is sufficiently stable to allow purification involving aqueous work-up and low temperature chromatography. It has been characterised by UV and IR spectroscopy as the adduct 11 formed with norbornadiene and by a comparison of its properties with those of the stable quinone 12. The spectroscopic properties of 1 and 12 are in good agreement but indicate greater conjugation in the true naphthoquinone 1. Whilst 1 gives mainly the cyclopentadiene adduct 20 by addition to C-1 and C-4, the quinone 12 resembles other o-benzoquinones in undergoing addition at both the diene and heterodiene systems. The hydroquinones required as quinone precursors were prepared via the cyclopentadienones 7 and 13. With dichlorovinylene carbonate, 7 gave the adduct 9 which with Zn–HOAc gave the carbonate 10 of the required hydroquinone 2.