Investigation on intramolecular oxidation of oxydiphenols to spirodienones

Abstract

The thesis entitled “Investigations on Intramolecular Oxidative Coupling: Oxidation of Oxydiphenols to Spirodienones and Their Photoisomerizations and Novel Reactions of 1?Bromomethyl?2?naphthol?tetrahydropyranyl Ether” consists of three chapters.

Chapter 1 Chapter 1 is divided into two sections. Section 1 A brief account of various known oxidizing agents used to achieve intramolecular oxidative coupling in phenolic systems and their modes of action. Section 2 This section deals with oxidation studies of several oxydiphenols using high?potential quinones such as:

tetrachloro?o?benzoquinone (o?chloranil) tetrabromo?o?benzoquinone (o?bromanil) 2,3?dichloro?5,6?dicyano?p?benzoquinone (DDQ)

and other oxidants including:

potassium hexacyanoferrate ferric chloride potassium hypobromite manganese dioxide diacetoxyiodobenzene

Oxidation of 1?(2??hydroxy?tetrachlorophenoxy)?2?naphthol (1a) and 1?(2??hydroxyphenoxy)?2?naphthol (1b) with quinone oxidants yielded mainly the rearranged products:

2,2??(tetrachloro?o?phenylenedioxy)?naphthalene?1(2H)?one (IIIa) 2,2??(o?phenylenedioxy)?naphthalene?1(2H)?one (IIIb)

along with the corresponding direct?coupled products, e.g., 1,1??(tetrachloro?o?phenylenedioxy)?naphthalene?2(2H)?one (IVa). The intermediacy of the quinol ether 1,1??(o?hydroxytetrachlorophenoxy, o?hydroxyphenoxy)?naphthalene?2(2H)?one (V) is invoked to explain formation of chlorospirodienones (IIIa) and (IVa). Use of methanol instead of benzene as solvent in o?chloranil oxidation of (1b) produced a colourless compound identified as 1?methoxynaphthalene[3,2?b]?1,4?benzodioxin (VI). In contrast, oxidation of the isomeric oxydiphenols (IIa) and (IIb) under identical conditions produced only the direct?coupled products without rearrangement. Non?quinone oxidants gave exclusively direct?coupled products. Different mechanisms have been proposed based on each oxidant’s mode of action. The rearrangement is suggested to involve intermediates such as 2,2??(1?,2??naphthalenedioxy)?3,6?cyclohexadienone (VII).

Chapter 2 Chapter 2 describes photoisomerization studies of substituted spirodienones of type (I) and (II). The spirodienones were synthesized by oxidation of substituted ??naphthols with o?chloranil and irradiated using a pyrex filter. Key findings:

All ??spirodienones studied undergo isomerization to the corresponding ??spirodienones. Among ??spirodienones, only 6?bromo?2,2??(tetrachloro?o?phenylenedioxy)?naphthalene?1(2H)?one (IIIc) and 6?methoxy?2,2??(tetrachloro?o?phenylenedioxy)?naphthalene?1(2H)?one (IIId) undergo isomerization to their ??isomers. Irradiation in the presence of triplet quenchers did not affect the isomerization, indicating involvement of a singlet excited state. A mechanism involving intermediates of the spirocyclohexadienone type (VII) is proposed.

Chapter 3 Condensation of 1?bromomethyl?2?naphthol?tetrahydropyranyl ether (VIII) with tetrachlorocatechol in acetone and potassium carbonate is known to give novel compounds. This chapter attempts to generalize the reaction using ethyl methyl ketone as solvent. Condensation of the pyranyl ether (VIII) with tetrachlorocatechol in ethyl methyl ketone, in the presence of potassium carbonate, gave a mixture of isomeric products, characterized as isomers of (X). Additional oxidation results for compounds of the type (2??hydroxyphenyl, 2?hydroxynaphthyl)methane (Xa) are provided in the Appendix.