Oxidation of bis(2-hydroxy-1-naphthyl)methane and similar bisnaphthols with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone. Structure and synthesis of novel products

Abstract

Oxidation of bis(2-hydroxy-1-naphthyl)methane (4a) with 2,3-dichloro-5,6-dicyano-1,4-benzoqui-none (DDQ) has been shown to give the novel compounds, cis- and trans-dispiro{naphthalene-1,2′(1′H)-naphtho[2,1-b]pyran-3′,1″-naphthalene}-2(1H),2″(1″H)-dione (12a) and (13a) together with the quinone methide dimer (6a) and the spiroketone (5a). Compounds (12a) and (13a) were characterised on the basis of their spectral properties and the structures were finally confirmed by an X-ray crystal structure analysis of (12a). Hydrogenation of compounds (12a) and (13a) has been shown to give the dihydroxy compound (14) via C–C bond cleavage. An alternative synthesis of the dispironaphthalenones (12a) and (13a) was achieved by oxidation of the dihydroxy compound (14), prepared by an independent method. The generality of the oxidation of bisnaphthols of type (4a) to give novel products of the type (12a) and (13a) has been shown by studying the oxidation of the variously substituted bisnaphthols (4b–d,f) with DDQ. A mechanism has been proposed invoking the intermediacy of the quinol ethers (22) and (24).