studies in terpenoids and vilsmeir formylation on some

Abstract

The thesis entitled “Synthetic Studies in Terpenoids and Vilsmeier Formylation on Some Hydronaphthalene Systems” consists of five chapters dealing with:

a review, for the first time, of the chemistry of vetivalene type naturally occurring sesquiterpenoids, the first synthesis of emmotin H (I), a sesquiterpene naphthaquinone, a new synthesis of (+)-occidol (Va), a naturally occurring sesquiterpene alcohol, via a Vilsmeier intermediate, the synthesis of emmotin G methyl ether (VIIIb), a naphthalenic sesquiterpenoid, also via a Vilsmeier intermediate, and Vilsmeier formylation on some additional hydronaphthalene systems.

Chapter 1 The chemistry of vetivalene type sesquiterpenes, including occidol (Va), rishitinol (Vb), and various emmotins, has been reviewed for the first time, presenting

structure determination, available syntheses, and biogenesis of individual members.

Chapter 2 This chapter illustrates the first total synthesis of emmotin H 3 (2 hydroxyisopropyl) 5,8 dimethyl 1,2 naphthaquinone\] (I), a 1,2 naphthaquinone sesquiterpene isolated from the trunk wood of *Emmotum nitens* (Icacinaceae).

- Selenium dioxide oxidation of **5,8 dimethyl 3 carbomethoxy 1 tetralone (II)**, prepared from *p xylene* in six steps, furnished **5,8 dimethyl 3 carbomethoxy 1,2 naphthaquinone (III)**. - **Thiele’s reductive acetylation** of quinone (III) yielded **1,2 diacetoxy 3 carbomethoxy 5,8 dimethylnaphthalene (IV)**. - Grignard reaction of the diacetoxynaphthalene ester (IV) with excess methylmagnesium iodide furnished **emmotin H (I)**, presumably via aerial oxidation of the intermediate hydroquinone during work up.

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### **Chapter 3** A new synthesis of **(+)-occidol (Va)**, a sesquiterpene alcohol isolated from the essential oil of *Thuja occidentalis* L., is described.

The key intermediate, **5,8 dimethyl 3,4 dihydro 2 naphthaldehyde (VI)**, was prepared using the **Vilsmeier–Haack–Arnold (VHA) reaction**.

- Aldehyde (VI) was oxidized to the corresponding acid and hydrogenated to yield the **tetralin acid (VIIa)**. - Grignard reaction on the tetralin ester (VIIb) with excess MeMgI furnished **(+)-occidol (Va)**.

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### **Chapter 4** This chapter deals with the synthesis of the **methyl ether of emmotin G (VIIIb)**, isolated from the trunk wood of *Emmotum nitens* (Icacinaceae).

- **1,4 Dimethyl 6 methoxytetralin (IX)**, prepared from **7 methoxy 1 tetralone**, was converted into **1,4 dimethyl 6 methoxy 7 formyltetralin (X)** by the VHA reaction. - Dehydrogenation using **DDQ** afforded the **naphthaldehyde (XI)**. - Oxidation with **Jones reagent** furnished the **naphthoic acid (XIIa)**. - Treatment of the methyl ester (XIIb) with excess MeMgI yielded **emmotin G methyl ether (VIIIb)**.

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### **Chapter 5** This chapter provides a brief review of **Vilsmeier formylation** of various systems relevant to this investigation, followed by preparation and identification of several new compounds obtained via Vilsmeier reaction on substrates based on **6 methoxytetralin (XIII)** and related systems.

The formyl compounds prepared and characterised in this study are indicated by structures **XIV–XXV**. Their synthetic potential in elaboration to terpenoids and other natural products is highlighted in the thesis.

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