Doctor of Philosophy
School of Chemistry
The initial aims of this PhD project were to investigate the Petasis borono- Mannich (PBM) reactions of pinacol allenylboronate in the synthesis of anti-β-allenyl- β-amino alcohols and the application of these products to the synthesis of functionalized piperidines via the aza-Prins cyclization reaction. We also planned to develop a synthetic strategy for the preparation of the pentacyclic alkaloid 9β-hydroxyvertine.
In Chapter 2, the first exploration of the Petasis borono-Mannich (PBM) reactions of pinacol allenylboronate are described. The reactions of glycoaldehyde and chiral α-hydroxyaldehydes with primary and secondary amines gave exclusively anti-β- allenyl-β-amino alcohol products. These reactions are highly regio- and diastereoselective. The anti-stereochemical outcomes of these reactions were determined by conversion of representative compounds to their oxazolidinone derivatives and then NOESY or ROESY NMR analysis. In contrast, the reactions of salicylaldehyde and primary and secondary amines were highly regioselective and gave homopropargylamine and α-allenylamine products, respectively. Possible reactive intermediates were proposed to explain these different product types. A NMR study of the PBM reaction of salicylaldehyde, benzylamine and pinacol allenylboronate indicated that a boron “ate” intermediate was readily formed however ESIMS could not identify this intermediate. The PBM reactions of the aromatic aldehydes lacking an ortho-hydroxy group did not provide PBM products which indicated that the orthohydroxy group was necessary to activate the boron species to allow transfer of the allenyl group to the iminium ion intermediate. The PBM reaction of pincaol allenylboronate, pyridine 2-carboxaldehyde with primary and secondary amines provided exclusively the homopropargyl amine products in poor yields under nonoptimized reaction conditions.
Thaima, Thanaphat, A Study of the Petasis Reactions of Pinacol Allenylboronate and Potential Applications to Bioactive Alkaloid Synthesis, Doctor of Philosophy thesis, School of Chemistry, University of Wollongong, 2018. https://ro.uow.edu.au/theses1/260
Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.