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Title: The elucidation of organic reaction mechanisms involving lithium reagents
Author: Davies, R. P.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 1997
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Lithium reagents are used to effect key deprotonation steps in numerous organic syntheses. In doing so they are often highly specific. However, little is known about how they function, the reasons for their high selectivity, and the natures of the lithiated organics present prior to work-up. This thesis seeks to redress this lack of structural knowledge of lithiated intermediates. It has been by isolating the intermediates in a variety of reactions involving lithiated organic reagents, establishing their precise identities, and studying their structures both in the solid and in solution that the author has been able to present this insight into the true reaction mechanisms involved and the source of any observed specificities. The reaction intermediates, whose syntheses and characterisation are described within this text, are all lithium complexes of the form [(R-)Li+.yL]n or [(R2-)2Li+]n where the lithium cation is bound to an organic anion (R- or R2) through one or more carbon centres and/or through electronegative heteroatoms (typically N, O or S). The lithium cation is often also bound to a Lewis base donor (L) which is a neutral but polar complexant. Chapter 1 gives a general introduction into the structural chemistry of organolithium and lithiated organic compounds and complexes, as well as a synopsis of their use in organic synthesis. General experimental methods are described in Chapter 2, and the synthesis and characterisations of all the complexes and compounds discussed (within Chapters 4 and 5) are presented in Chapter 3. Chapter 4 contains a detailed discussion on the origin of the regioselectivity exhibited in the -NC(OLi)R directed electrophilic substitution reactions of lithium amides (Section 4.1) and the -CO2Li directed electrophilic substitution reactions of lithium carbamates (Section 4.2). Finally, Chapter 5 looks into how deprotonation reactions using lithium reagents could actually proceed. This has been accomplished by studying the deprotonation of model phosphine oxide systems by lithium reagents both experimentally and theoretically using ab initio M.O. calculational results (Section 5.1), and also by studying the effects of reacting a simple organic molecule (Ph2NH) with an excess of lithiating reagent (t-BuLi and nBuLi)(Section 5.2).
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available