Synthetic studies in natural products

Abstract

The thesis entitled "Synthetic Studies in Natural Products (Terpenes & Lignans)" is divided into three parts consisting of nine chapters. Chapter 1 gives a review of the chemistry of aromatic hemiterpenoids of 2,2-dimethylchromene type and concludes with a short account of their biogenesis. Chapter 2 describes the Claisen–Haack reaction on some 2,2-dimethylchromenes and the first syntheses of encecalinol, encecalin, and anhydroencecalinol, all naturally occurring aromatic hemiterpenes. Chapter 3 illustrates the application of DDQ in oxidative dehydrogenation leading to the convenient preparation of some useful p-methoxyphenyl carbonyl synthons and the synthesis of desmethoxyencecalin, a naturally occurring aromatic terpene by different routes. In Chapter 4, the synthesis of 6-(3?-methyl-2?-butyl)-2,2-dimethyl-8-methoxychromene (m-encecalin), a naturally occurring isomer of encecalin, has been described. Chapter 5 comprises the syntheses of espeletone and desmethoxyespeletone, two naturally occurring nonchromenoid aromatic hemiterpenes. In Chapter 6, the synthesis of (4,7-dimethyl-1-naphthyl)-propionic acid (carboxycadalene), which has several closely related analogues among sesquiterpenoids, is described. Chapter 7 contains experiments towards the synthesis of some sesquiterpenoid derivatives of Cacalia decomposita and Cineraria albicans. Chapter 8 describes the synthesis of furoguaiacin and dibenzyl furoguaiaoxidin, lignans from Guaiacum officinale. The last chapter gives the synthesis of 3,4-dimethoxy-8-methyl-5-phenyl-1-naphthoic acid, a key intermediate for the synthesis of several naturally occurring phenalenone pigments.