Terpene Syntheses Employing Aromatic Precursors

Carnduff, J (1963) Terpene Syntheses Employing Aromatic Precursors. PhD thesis, University of Glasgow.

Abstract

The thesis comprises two parts. In Part I, a review, complete to March, 1963, is given of all known aromatic diterpenes having an octahydrophenanthrene ring system and in particular of the compound totarolone. Aspects of their biogenesis and synthesis are discussed. An account is given of an investigation of a number of naphthalene derivatives which could function as precursors for a synthesis of totarolone. In an attempt to prepare 1,2,3,4-tetrahydro-5-isopropyl-2-keto-6-methoxy-l-methylnaphthalene, 2,6-dimethoxynaphthalene, 1-isonropyl-2-methoxy-naphthalene and l-isopropyl-2,6-dimethoxynaphbhalene were synthesised. 2,6-Dimethoxynaphthalene could be reduced to the 1,4-dihydro-derivative but attempts to methylate this product at the 1-position failed. l-Isopropyl-2-methoxynaphthalene underwent an abnormal nitration reaction giving an a-nitroketone with loss of the O-methyl group. 5-Bromo-6-hydroxytetralin was converted to 5-isopropyl-6-methoxytetralin which has now been converted, elsewhere to totarolone. Methyl 2-hydroxy-1-naphthoate was converted to l-isopropenyl-2-naphthol and 1-isopropyl-2-naphthol. The latter, however, proved to be much more readily available by direct alkylation of sodium 2-naphthoxide. The mechanism, of this process is discussed. l-Isopropyl-2-naphthol showed a remarkable propensity for oxygen absorption, being rapidly converted in air to 1,2-dihydro-1-h-ydropsroxy-l-isoprooyl- 2-keto-naphthalene. Since an autoxidation is possibly a key step in the biogenesis of totarol, this reaction was studied in some detail and comparison made of the reactivity of l-isopropyl-2-naphthol with that of 1-methyl-2-naphthol and 3-isopropyl-2-naphthol, the latter being prepared from 2-hydroxy-3-naphthoic acid. In Part II, the structures, biogenesis and published syntheses of all known iridoid monoterpenes are reviewed. An account is given of a reinvestigation of a synthetic approach to these substances from suitably substituted indanes. Condensation of para-cresol with ethyl acetoacetate gave 4,6-dimethyl-coumarin which was converted to 3-(2-methoxy-5-methylphenyl)butyric acid. Oyclisation of this with polyphosphoric acid gave a methoxyindanone which on Clemmensen reduction and demethylation gave 7-hydroxy-1,4-dimethylindane. This phenol was also obtained by rearrangement of the 3,4-dihydro-derivative of the above coumarin to a hydroxyindanone and reductive removal of the carbonyl group of the latter by the Clemmensen procedure. The degradation of this phenol to nepetalinic acid has been investigated. By a route similar to the first one above, 5,7-dihydroxy-1,4-bimethylindane has been prepared from 4-methylresorcinol and ethyl acetoacetate. It should be possible to convert this relatively simply to nepetalinic acid and research on this subject is continuing.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Organic chemistry
• Date of Award: 1963
• Depositing User: Enlighten Team
• Unique ID: glathesis:1963-79473
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 05 Mar 2020 09:07
• Last Modified: 05 Mar 2020 09:07
• URI: https://theses.gla.ac.uk/id/eprint/79473