Structural Studies of Ylides and Related Derivatives, and of Several Natural Products

Maltz, Abraham (1979) Structural Studies of Ylides and Related Derivatives, and of Several Natural Products. PhD thesis, University of Glasgow.

Abstract

This thesis is essentially divided into two parts, one theoretical (Chapters 1 and 2) and the other experimental (Chapters 3 - 5). A supplement to this thesis includes a listing of all structure factors. The first part (of the thesis) deals with the theory of X-ray diffraction and with various methods for the determination of structures and their refinement. Of these methods, direct methods have been extensively applied in the study of twelve organic molecules and therefore its theoretical basis is described in more detail (Chapter 2). Chapter 3 reports the crystal and molecular structures of two sulphur-nitrogen ylides and of five of their reaction products with electrophilic acetylenes, the reaction products themselves (betaines) having been described as possessing ylide-like skeletons. These investigations were undertaken because the compounds were of chemical interest and because there seemed to be a complete lack of X-ray structural information on N-arylsulphilimines (R1 R2+ S - NAr) and their corresponding sulphur betaines (N-arylsulphilimines + electrophilic acetylene→betaine) while their phosphorus analogues have been long known and investigated. It was also felt that in view of the structural information (from X-ray studies) on N-acylsulphilimines (R1R2+S -N COR3) and N-sulphonylsulphilimines (R1R2+S - N SO2R3) the structural studies on N-arylsulphilimines could be of comparative value. The X-ray analyses revealed unhindered geometries for the sulphilimines whereby the N-S bonding systems are almost coplanar with the aromatic rings. The nitrogen atoms are probably sp2 hybridized and the N-S bonds were found to be 1.622 (2) A and 1.640 (4) A (for the two ylides), thus being similar (within experimental error) to the lengths found for N-sulphonylsulphilimines 1.628 (2) A and significantly below the length of 1.670 (2) A given for N-acylsulphilimines. For the sulphur betaines, steric strain which causes conformational distortions has been observed in all five structures. The bond angles were found to be influenced by this effect while only one C(sp2)-C(sp2) bond length appeared to be influenced appreciably by this effect (1.520 A - 1.549 A). A 'through conjugation' effect was also observed. The structures of a related arsenic betaine and of a C-nitroso-imine- N-oxide are reported in Chapter 4. Interesting conformational distortion originating from the As...O interactions, and a shortened As-C(sp2) bond length [e.g. 1.835 (5) A] are observed for the arsenic ylide. The C-nitroso-imine-N-oxide reveals a planar geometry of the central framework of the molecule which is almost perpendicular to the two aromatic systems. A transoid arrangement of the -N = C - N = O group of atoms is also observed. The structural analyses of two new diterpenoids and a tetranortriterpenoid spiro-lactone are reported in Chapter 5. The novel feature of a fully substituted cresol ring system was shown to exist in one of the diterpenoids while in the other the unique feature of a seven-membered hemiacetal ring B has been established. The tetranortriterpenoid was shown to possess a d -lactone ring system and a cyclic ether in which the oxygen is attached to two secondary carbon atoms.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Organic chemistry
• Date of Award: 1979
• Depositing User: Enlighten Team
• Unique ID: glathesis:1979-78800
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 30 Jan 2020 14:53
• Last Modified: 30 Jan 2020 14:53
• URI: https://theses.gla.ac.uk/id/eprint/78800