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Aza-spirocyclic compounds via oxidative amidation of phenols : application on the studies towards the synthesis of himandrine and the total synthesis of Erythrina alkaloids

University of British Columbia

This thesis illustrates two application of the oxidative amidation of phenols in the synthesis of natural products. The first part focuses on an approach to himandrine via a tandem oxidative cyclization of a phenolic dienylsulfonamide / intramolecular Diels-Alder reaction / epimerization sequence that produces a substituted trans-fused decalone. This material exhibits three of the five rings present in the natural product, but it is made in racemic form. Efforts to prepare said trans-decalone in enantioenriched form are also outlined. The strategy that was explored in that respect relies on a Rh(I)-mediated diastereoselective 1,4-addition of an arylboronic acid to a conjugated ester derived from L-serine. The second part of this dissertation describes the total synthesis of two Erythrina alkaloids, (+)-3-demethoxyerythratidinone and (+)-erysotramidine, via the oxidative cyclization of a phenolic oxazoline. A key step of the synthesis involves the desymmetrization of a dienone through a highly diastereoselective, intermolecular 1,4-addition of the alcohol revealed upon unraveling of the oxazoline. This allows the creation of the aza-spirocenter characteristic of this class of alkaloids with the correct configuration. The degree of stereocontrol achieved in the course of such operations is essentially perfect (no diastereomeric side products detectable). This synthesis also introduces improved techniques to effect a crucial eliminative Curtius-Schmidt rearrangement.

Text

2018-02-14

Attribution-NoDerivatives 4.0 International

http://hdl.handle.net/2429/64633

Chemistry

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nd/4.0/