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Synthetic approaches to Diebenz[d,f]azonine alkaloid derivatives and analogous systems.

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Dragar, Charles (1988) Synthetic approaches to Diebenz[d,f]azonine alkaloid derivatives and analogous systems. Unspecified thesis, University of Tasmania.

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Abstract

In the course of this work, the area which received most
attention was the exploration of new synthetic avenues, leading from
medium-ring heterocyclic precursors. A variety of these had become
accessible via a ring-destruction approach from fused 1,2,3,4-tetra-hydroisoquinoline
derivatives. The hitherto unexplored retrosynthetic
relationship between the dibenz[dMazonine and dibenz[d,f]azecine
alkaloids and the 3-benzazonine and 3-benzazecine ring systems was the
primary area to which the present work was addressed. In particular,
derivatives of 2,3,4,5,6,7-hexahydro-9,10-dimethoxy-1H-3-benzazonine
and 1,2,3,4,5,6,7,8-octahydro-10,11-dimethoxy-3-benzazecine, were
available bearing 7- and 8-hydroxyl groups respectively. These known
compounds were converted efficiently, using standard methods, into the
corresponding ketones bearing methyl N-carboxylate, cyanamide and
methyl groups in the 3-position.
These heterocyclic ketones exhibited unusual spectroscopic
properties, previously observed only in medium-ring amino-ketones.
Analysis of their structures as determined by X-ray crystallography
and spectroscopic means, led to the conclusion that in each case,
strong transannular interactions were responsible for their observed
properties. A series of molecular mechanics calculations were also
carried out on two model compounds employing the Allinger MMP1 method,
which assisted in analysis of the spectroscopic properties of these
ketones.
It was envisaged that these ketones might serve as
progenitors for dibenz[d,f]azonine and dibenz[d,f]azecine derivatives,
using one of the many variations of the Robinson annulation reaction.
The results of efforts in this direction are presented in Chapter 2.
Using a cyclopentenone annulation procedure proceeding by way of a
1,4-diketone derivative it was hoped that syntheses of protostephanine
and Cephalotaxusalkaloids might be developed. However little progress
was made beyond the 1,4-diketone stage.
Attempts to apply the classical procedures utilising a
weakly basic catalyst and 3-buten-2-one or some of its synthetic
equivalents, proved fruitless. This was attributed primarily to low
acidity of the ketones. The use of stronger bases was incompatible
with these annulation reagents, so attention was turned away from the
Michael-type alkylations. However, it was found that the ketones
mentioned above could be alkylated in very good yield, employing
low-temperature enolate generation with lithium di-isopropylamide as base, followed by reaction with an appropriate alkyl halide. These
procedures were developed using 3-benzazonin-7-one derivatives and
since the best yields were obtained from alkylation of the methyl
N-carboxylate derivative, this was generally employed. Using either
Wichterle's reagent, 1-iodo-3-chloro-2-butene or Stork's reagent,
(E)-trimethyl-(3-iodo-1-methyl-1-propenyl)silane, it was possible to
prepare 3-benzazonin-7-one derivatives bearing a masked 3-oxobutyl
group in the 6-position. Similarly reaction with 3-iodo-1-propyne
yielded derivatives bearing a masked 2-oxopropyl group. Liberation of
this latent functionality by accepted procedures, was in each case
attended by some problems, which were satisfactorily overcome.

Item Type: Thesis (Unspecified)
Copyright Holders: The Author
Additional Information:

Includes bibliography

Date Deposited: 09 Dec 2014 00:16
Last Modified: 11 Mar 2016 05:55
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