| dc.description.abstract | The thesis entitled "STUDIES IN TERPENOIDS" embodies synthetic as well as reaction studies in terpenoids and consists of seven chapters, each of which is prefaced by an introductory survey consisting of a comprehensive account of earlier work in the area.
In Chapter 1, the synthesis of pterosin E (2,5,7-trimethyl-1-oxoindan-6-ylacetic acid), a naturally occurring sesquiterpenoid isolated from the Japanese bracken, is described for the first time. The synthesis makes use of the readily available aromatic hydrocarbon mesitylene. A special feature of the synthetic strategy employed is the regio-specific introduction of a chloromethyl function in the aromatic ring after elaboration of one of the methyl groups of mesitylene.
Chapter 2 deals with the extension of Koch-Haaf (K-H) carboxylation to acyclic 4-enones and 4,5-dihydropyrans. Saturated and ?,?-unsaturated ketones are found to resist carboxylation under K-H conditions. Characterisation of the bicyclic lactones from the K-H reaction of 6-methylhept-5-ene-2-one, and of the isomeric tricyclic ?-lactones from 6,6-dimethyl-2,3-tetramethylene-4,5-dihydropyran are discussed. A new route for the preparation of the above dihydropyran has been described. A possible mechanism for the formation of the ?-lactones has been suggested.
Chapter 3 describes the study of manganese(III) acetate oxidation of camphene, longifolene, and ?-pinene. Skeletal rearrangements were observed in the lead tetraacetate oxidation of such bi- and tricyclic terpenoids. However, on manganese(III) acetate oxidation, camphene gives a mixture of stereoisomeric spirotones and longifolene gives a ?,?-unsaturated acid, involving no skeletal rearrangement. ?-Pinene does not, however, incorporate the ‘COOH’ moiety. Instead, under the reaction conditions, it undergoes acetolysis with Wagner-Meerwein rearrangement. The structures of the various reaction products have been established.
With a view to finding out the possibility of dehydrogenation in the seven-membered ring of ?-himachalene, the major product of chloranil dehydrogenation of ?- and ?-himachalene, the products of this reaction were investigated and the results presented in Chapter 4. The presence of bisdehydro-?-himachalene was established, and indirect evidence was provided for the existence of a monodehydro-?-himachalene.
Chapter 5 deals with the synthesis of 1,2,3,4-tetrahydro-1,1,4,7-tetramethylnaphthalene (prepared so far only as a mixture along with 1,2,3,4-tetrahydro-1,1,4,6-tetramethylnaphthalene). Facile cyclodehydration of an alcohol, whose olefinic counterpart was needed for a contemplated synthesis of ?-himachalene, gave unambiguously 1,2,3,4-tetrahydro-1,1,4,7-tetramethylnaphthalene. Its acylation and nitration reactions were studied with a view to assessing the musk properties of such derivatives and also establishing their orientation pattern.
The synthesis of the vermifugal lactone 5,7-dimethylphthalide, starting from mesitoic acid and involving essentially two steps in contrast to the multistep sequence reported in the literature, and its conversion to 1,3-dimethyl-4,5-bisbromomethylbenzene, are presented in Chapter 6.
In Chapter 7, a novel method for the regeneration of ketones from their 2,4-dinitrophenylhydrazones, based on the facile hydration of the >C=N— group by p-toluenesulfonic acid hydrate, is described.
PUBLICATIONS
"Studies in Terpenoids. Part XXX. Synthesis of pterosin E, a sesquiterpenoid from bracken," M.E.N. Nambudiry and G.S. Krishna Rao, J. Chem. Soc. Perkin I, 317 (1974) [Chapter 1].
"Extension of Koch-Haaf carboxylation to acyclic 4-enones and 4,5-dihydropyrans," M.E.N. Nambudiry and G.S. Krishna Rao, Tetrahedron Lett., 4707 (1972). [Part of Chapter 2].
"5,7-Dimethylphthalide, a short synthesis," M.E.N. Nambudiry and G.S. Krishna Rao, Indian J. Chem. (In Press) [Chapter 6].
"Hydration of the >C=N— group by p-toluenesulfonic acid hydrate. Ready regeneration of ketones from their 2,4-dinitrophenylhydrazones," M.E.N. Nambudiry and G.S. Krishna Rao, Austr. J. Chem., 24, 2183 (1971) [Chapter 7].
Two communications, "Manganese(III) acetate oxidation of terpenoids" (Chapter 3) and "Dehydrogenation of ?- and ?-himachalene" (Chapter 4), are under preparation | |
