Studies in 2-Naphthol Derivatives

Marks, Robert Barras (1976) Studies in 2-Naphthol Derivatives. PhD thesis, University of Glasgow.

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This thesis consists of two sections. The first section deals with the sodium hydroxide induced rearrangement of l-methyl-2-bromo-3H-naphtho (2,1-b) pyran-3-one. This reaction had already been studied by Dey and Lakshminarayanan, who identified the products as 2-(2-hydroxynaphth-l-yl) propanal and 1-methylnaphtho (2,1-b) furan-2-carboxylic acid: The naphthylpropanal would be a useful starting material for the synthesis of l-alkyl-2-naphthols, so we attempted to repeat this rearrangement. When the Indians' conditions were followed, no clean and tractable products resulted. Air oxidation and dehydration of the initial products seemed to occur. The reaction and work-up were therefore performed under nitrogen and acidification of the reaction mixture was done with carbon dioxide. Under these conditions, two products were isolated. The main product (78%) is 1-(2-hydroxynaphth-1-yl) propan-2-one. The minor product (7%) is 2-methylnaphtho (2,1-b) furan-1-carboxylic acid: These structure assignments are supported by elemental analyses, full spectral data and chemical transformations on both products. A critical review of Dey's published evidence suggests that he had isolated the same products as we did, but assigned an erroneous structure to each as a result of inadequate spectral evidence, uncritical interpretation of chemical evidence and over-reliance on analogies. Mechanisms for the displacement of halides from sp2 hybridised carbons, in a-halolactones and in related systems is reviewed in the Introduction. From this large group of reactions, only the formation of Feist's acid from 2-bromo-4,6-dimethy 1-5-ethoxycarbonylpyrone seems to bear any similarity to the aryl shift wo observe with the methylbromonaphthopyran. The unique occurrence of this rearrangement in this compound is rationalised in terms of the steric congestion due to the methyl group in this particular bromopyrone. The second section deals with synthesis and epoxidation of various 2(1H) naphthalenones. 1-Hydroxy-1-isopropyl-2(1H) naphthalenone has been reported to give on treatment with Na2CO3/H2O2 in aqueous ethanol only one epoxide (90% yield) with the epoxide oxygen on the opposite face (trans) to the hydroxyl group. The same author also reported the 1-acetoxyl analogue to yield the trans epoxide exclusively. There are relatively few such cases of stereospecific epoxidation of dissymmetric enones in the literature and the factors controlling which face of the enone is epoxidised are not all understood. Leppards epoxidations were repeated and the reported results confirmed, save that the 1-acetoxyl compound underwent substantial hydrolysis of the acetoxyl group (only 36% of a single acetoxy-epoxide was isolated). In order to explore the structural requirements for this steric control a range of 2(1H) naphthalenones with different alkyl and oxygen-containing functions on C was made. In addition to the two compounds already mentioned, 2(1H) naphthalenones bearing the following pairs of substituents on C were successfully synthesised: methyl and hydroxyl; methyl and acetoxyl; methyl and methoxyl; ethyl and acetoxyl; isopropyl and trimethylsilyloxyl. Attempts to synthesise and isolate the compound bearing isopropyl and methoxyl on C by alkylation of the 1-hydroxyl compound were unsuccessful. Epoxidation with alkaline hydrogen peroxide of 1-acetoxy-1-methyl-2(lH) naphthalenone and 1-isopropyl-1-trimethylsilyloxy-2(1H) naphthalenone led to the complete hydrolysis of the acetoxyl and trimethylsilyloxyl groups respectively. The epoxide isolated in both cases was the same as that from 1-hydroxy-1-alkyl-2(1H) naphthalenone. Epoxidation of 1-hydroxy-1-methy1-2(1H) naphthalenone and of 1-methoxy-1-methyl-2 (1H) naphthalenone gave one simple epoxide in each case (assumed trans). The 1-hydroxy-1-methyl compound also gave a material which seemed to be a dimer of the simple epoxide. Although in all cases studied only one stereoisomer was formed in the epoxidations it was difficult to prove its stereochemistry. 13C and lanthanide shifts of 1H NMR spectra were studied but no conclusions could be drawn from them about the stereochemistry of the epoxides. The Introduction consists of a selected survey of published examples of epoxidations and related processes in which stereoselective product formation took place. In some cases this outcome might have been anticipated, and in others not. A critical examination of the explanations given does not appear to reveal any underlying unity of cause.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Organic chemistry
Date of Award: 1976
Depositing User: Enlighten Team
Unique ID: glathesis:1976-78768
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 30 Jan 2020 14:55
Last Modified: 30 Jan 2020 14:55

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