Syntheses and Structural Elucidation of Natural Coumarins

Ballantyne, Mary M (1970) Syntheses and Structural Elucidation of Natural Coumarins. PhD thesis, University of Glasgow.

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A short review of natural coumarins is given which incorporates some of the structural features and biosynthetic aspects of those coumarins unsubstituted at positions 3 and 4. All of the 5,7-dioxygenated simple coumarins, known to occur naturally, have been tabulated. Part I The 'Claisen Rearrangement' has been investigated as a method of synthesising ortho-(1,1-dimethylallyl)hydroxy-coumarins. Thus, pyrolysis of 7-0-(3,3-dimethylallyl)scopoletin(61) yielded obliquetin(62) and the corresponding cyclic ether, nieshoutin(63). A third product of this pyrolysis was 3-(1,1-dimethylallyl)scopoletin(76), the result of a triple 'Claisen Rearrangement'. In a similar manner, 7-0-(3,3-dimethylallyl)-5-methoxy-coumarin(120) was converted to a phenol which was trapped as the butyrate. Hydrolysis and methylation yielded the coumarin pinnarin(122). A general study of the 'Claisen Rearrangement' products of the 7-0-(3,3-dimethylallyl) ethers of the following coumarins was made, namely aesculetin(19), 4-methylscopoletin(101), umbelliferone(4) and 4-methylumbelliferone(115). Part II A new method of introducing a 3,3-dimethylallyl unit ortho to a phenol has been developed. The 1,1-dimethylpropargyl ethers of umbelliferone(4) and 7-hydroxy-5-methoxycoumarin were prepared and then selectively reduced to the corresponding 1,1-dimethylallyloxycoumarins. Pyrolyses of the latter ethers enabled the natural coumarins, osthenol(21), 7-demethylsuberosin (22), osthol(146), suberosin(147) and coumurrayin(131) to be prepared. Part III The structure of nieshoutol(160), the only trioxygenated coumarin isolated from the heartwood of Ptaeroxylon obliquum, was deduced from chemical and spectroscopic evidence. The ortho relationship of the phenolic hydroxyl to the oxygen of the 2,3,3-trimethyldihydrofuran ring was determined by n. m. r. shielding effects. Demethylation, ester interchange and cyclic ketal formation showed that the methoxyl of nieshoutol is ortho to the phenolic hydroxyl. Structure 160 was confirmed when a nuclear Overhauser effect was observed between the methoxyl and the C-4 proton.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Organic chemistry
Date of Award: 1970
Depositing User: Enlighten Team
Unique ID: glathesis:1970-78536
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 28 Feb 2020 12:09
Last Modified: 28 Feb 2020 12:09

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