Enantioselective approaches to the synthesis of terpenoids and terpenoid derived alkaloids

Mahmood, A 1999, Enantioselective approaches to the synthesis of terpenoids and terpenoid derived alkaloids , PhD thesis, Salford : University of Salford.

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Previous work at Salford involved the deprotonation of meso epoxide (Ha) with chiral lithium amide bases, to produce the crural allylic alcohol (Ilia) and the enantioselective deprotonation of meso ketone (I) to provide chiral silyl enol ether (V). In this thesis the potential utility of highly functionalised [3.3.0]bicyclooctane systems (Illb) and (VI) as flexible precursors to biologically active natural products is investigated. Meso epoxide (lib), was prepared stereoselectively in the exo form. Conditions were explored for transforming the epoxide to allylic alcohol (Illb), using a variety of chiral lithium amide bases to provide optically active material. The e.e. of the product was determined by conversion of the alcohol (Illb) to the corresponding benzoate ester and then analysis by HPLC on chiral phase. The highest e.e. (54%) was achieved when (-)- sparteine^BuLi complex (IV) was used for deprotonation. In the first part of the thesis the construction of the linear triquinane skeleton was investigated. Allylic alcohol (Illb) was converted to aldehyde (VII) via a 1,4- conjugate addition. Cyclisation of the third cyclopentane ring provided (IS*, 8R*)-cis-anti-cis-10,10-dimethyltricyclo[]undec-3-one (VIII). This constitutes a formal synthesis of the target triquinane hirsutene (IX). The triethylsilyl enol ether (V) was employed in the synthesis of the intermediate (VI). Several methods were attempted to generate intermediate (X) as a potential precursor to a range Corynanthe alkaloids via condensation with tryptamine. The ester (VI) was converted to the piperidone ring systems (Xlla) and (Xllb) by a Beckmann rearrangement of the corresponding tosylates (XI). The highly functionalised piperidone (Xlla) has potential utility for the construction of a great number of Corynanthe type monoterpenoid alkaloids.%3B&utm

Item Type: Thesis (PhD)
Contributors: Leonard, J (Supervisor)
Schools: Schools > School of Computing, Science and Engineering
Depositing User: Institutional Repository
Date Deposited: 03 Oct 2012 13:34
Last Modified: 04 Aug 2022 11:25
URI: https://usir.salford.ac.uk/id/eprint/26791

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