| dc.description.abstract | The thesis entitled “Studies on the Oxidation of Naphthols: Synthesis and Reactions of Dispiro{Naphthalene?1,2??Naphtho[2,1?b]pyran?3?,1???Naphthalene}?2(1H),2??(1??H)?diones (or Bi?spironaphthalenones)” consists of four chapters.
Chapter I
The first chapter deals with the syntheses of bi?spironaphthalenones (1). One synthesis proceeds via the dihydroxy compound (2) by using the Ullmann ether condensation. This synthesis was considered essential for confirming the structure of the bi?spironaphthalenone (1a) as well as that of the dihydroxy compound (2), which was obtained by catalytic hydrogenation or zinc–acetic?acid reduction of (1a).
Another synthesis is via the oxidation of bis(2?hydroxylnaphthyl)methanes (3) with 2,3?dichloro?5,6?dicyanobenzoquinone (DDQ). This approach was taken to study the generality of this unusual oxidative cyclisation and to prepare suitably substituted bi?spironaphthalenones required for photochemical and mass?spectral studies.
During the synthesis of bi?spironaphthalenone (1c) by oxidation of bis(2?hydroxy?6?methoxy?1?naphthyl)methane, an unexpected product was obtained. This product was characterised as 6,6??dimethoxy?1?(2?oxo?1??naphthylidene)?naphth[2,1?b]oxete (4) from its IR, UV, ¹H NMR, and mass spectra. It was established to be a secondary product arising from the primary oxidation product (5c), confirmed by separately oxidising (5c) with DDQ. A mechanism invoking benzylic hydride abstraction, followed by 1,2?shift of the quinol?ether linkage and deprotonation, is discussed.
This chapter also deals with the isolation and characterisation of the diastereoisomers (6) of (1a) and (1b).
Chapter II
Chapter II discusses the results obtained from the photolysis of bi?spironaphthalenones (1a) and (1b), preceded by a brief introduction to photochemical ??cleavages in saturated carbonyl compounds and enones.
The photolysis afforded compounds (6) to (10). Mechanisms invoking ? C–C and C–O cleavages for the formation of compounds (6)–(9) are discussed.
To establish that ? C–O cleavage is a general phenomenon in ??keto spiroquinol ethers, the photolysis of selected mono?spironaphthalenones such as (8a) and (11) was examined. (8a) gave (12), and (11) gave (13). Probable mechanisms involving initial ? C–O cleavage are discussed.
Chapter III
Chapter III deals with the characterisation of products obtained from the borohydride reduction of bi?spironaphthalenone (1a), following a brief introduction to metal?hydride reduction of ?,??enones. The reduction was carried out to prepare the bi?allylic alcohol, required for photochemical studies.
During borohydride reduction, the bi?allylic alcohol and the hemi?ketal were obtained. Additionally, products resulting from intramolecular reductive C–C coupling, such as (14) and (15), were formed, becoming the major products under suitable conditions.
The structures of these novel C–C coupled products were established from IR, ¹H NMR, ¹³C NMR, and mass spectral data. A probable mechanism involving enolate formation through conjugate attack of hydride/alkoxide on one enone system, followed by the enolate acting as a Michael addend, is proposed.
Chapter IV
Chapter IV discusses the mass spectra of various bi?spironaphthalenones (1). The probable mechanism for the formation of the symmetrical dibenzoxanthylium ion (16) in their mass?spectral fragmentation is analysed, with supporting evidence from the mass fragmentation patterns of compounds such as (5) and (3). | |
