Studies in terpendids transformation reaction of of-pinene : Physico chemical studies of some cyclobutane compounds

Abstract

The pioneering role of the chemistry of terpenes in the development of organic chemistry is well recognized, and in terpene chemistry ??pinene occupies a coveted position because of the attention it commanded in the early days from pioneers like Baeyer. In the structure elucidation of ??pinene, extensive studies on its degradation products held the key role. The thesis entitled “Studies in Terpenoids: Transformation Reactions of ??Pinene and Physico?chemical Studies of Some Cyclobutane Compounds” consists of four parts (Chapters 1 to 7).

Part I The thesis begins with a brief but up?to?date survey of the degradation products (gem?dimethyl substituted cyclobutanoids related to pinonic acid, Chapter 1), in which their preparation, properties, and reactions are described.

Part II Chapter 2 discusses the isolation of (+)-??pinene (1), used in the present work, from the turpentine oil of Pinus wallichiana. An estimation of ??pinene in this oil by a spectrophotometric (IR) method revealed that the oil contains about 90% of (+)-??pinene. Chapter 3 deals with the preparation, properties, and reactions of ethyl (–)-2,2?dimethyl?3?ketocyclobutyl acetate (2) obtained from (+)-??pinene (1) by a sequence of reactions, and chiefly its conversion—via the bromoketoester (3)—to trans?homocaronic acid and its derivatives (4a–f) by the Favorskii rearrangement. Other synthetic possibilities of the ketoester (2) are also mentioned. The interesting gelling property of the cyclopropane carboxamidoester (4e) and its possible applications are indicated. The structural elucidation of two by?products (5 and 6) encountered in the preparation of ketoester (2) is described in Chapters 4 and 5. A novel Baeyer–Villiger?type oxidation by chromic acid of the cyclobutanones (2 and 7) to the corresponding ??lactones (6 and 8) is also reported in Chapter 5, and the possible mechanism of the oxidation is discussed.

Part III The Optical Rotatory Dispersion (ORD) and Circular Dichroism (CD) of a number of cyclobutanones encountered during this work were studied, and the results obtained are interpreted in Chapter 6. Since the number of known optically active cyclobutanones is very limited, the data reported in this chapter will be a useful addition to the existing collection.

Part IV The final section of the thesis, Chapter 7, deals with the Nuclear Magnetic Resonance (NMR) data of a number of cyclobutane systems and their application in assigning the stereochemistry and conformation of pinonic, pinononic, and pinic acids. This has not been done so far by the application of purely physical methods. Suitable illustrations are also provided to show the elegant way in which NMR can be employed in assigning the configuration of other gem?dimethyl cyclobutanoids, whether naturally occurring or synthetic.

Publications Part of the work embodied in this thesis has resulted in the publication of the following two papers:

L. R. Subramanian and G. S. Krishna Rao, Tetrahedron, 4167 (1967). L. R. Subramanian and G. S. Krishna Rao, Tetrahedron Letters, 5643 (1967).

The material in Chapters 1, 5, 6, and 7 is being suitably processed for publication as a review and two full papers.