Synthetic studies in terpenoids.

Abstract

The thesis entitled “Synthetic Studies in Terpenoids” consists of seven chapters. The first chapter gives an account, for the first time, of the chemistry of oxygenated compounds of cadalene type. The succeeding four chapters deal with the syntheses of the naturally occurring oxygenated cadalenic sesquiterpenes: mansonone G, pyrocurzerenone, mansonone D, and 3-methoxy-7-hydroxycadalenal. The sixth chapter describes the utilization of pulegone for the construction of a dimethyl isopropyl spiro[4.5]decane acoranoid skeleton, while the last chapter deals with an efficient method for removing sulphur from sulphur-contaminated materials arising from sulphur dehydrogenation of hydroaromatics. In Chapter 1 is given a survey of the chemistry of about forty-one oxygenated compounds of cadalene type, discussed under the headings: (1) Oxy (hydroxy) compounds (2) Oxo compounds (3) Oxy-oxo compounds (4) Oxides (5) Phenols (6) Quinones (7) Biogenesis In view of the large number of these compounds, attention has been principally focused on their structure elucidation, in order to conserve space. Chapter 2 deals with the synthesis of two naturally occurring o-naphthaquinones, mansonone G and its methyl ether, isolated from Mansonia altissima and Zelkova serrata respectively. The structure of an interesting dimer formed in an alternative synthetic approach is described. In Chapter 3 is described the synthesis of pyrocurzerenone, a furanocadalene sesquiterpene isolated from Curcuma zedoaria. 1,5-Dimethyl-6,7,8,9-tetrahydronaphtho[2,3-b]furan-9-one was also synthesized in this connection to serve as a model for the synthesis of pyrocurzerenone. The ambiguity in ring closure to afford the furan moiety was settled by two independent syntheses of the model. Chapter 4 describes a three-step conversion of pyrocurzerenone to mansonone D, a cadalenic furan-o-naphthaquinone, isolated from Mansonia altissima. Chapter 5 contains an account of the synthesis of a phenolic sesquiterpene, 3-methoxy-7-hydroxycadalenal, a constituent of the Ulmus heartwoods, by an interesting sequence of reactions involving oxalylation of 5-isopropyl-6-methoxy-8-methyl-2-tetralone. Attempted preparation of 3-hydroxy-5-methyl-7-methoxy-8-isopropyl-2-naphthoic acid, a key intermediate in the synthesis of the above aldehyde, by the allylic oxidation of methyl 5-methyl-7-methoxy-8-isopropyl-3,4-dihydro-2-naphthoate by t-butyl chromate and chromium trioxide-pyridine complex led to some interesting oxidation products, the structures of which have been elucidated.