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Hunter R, Rees-Jones SC, Su H. Beilstein J Org Chem. 2007 Nov
3;3:38.
Vinylogous Mukaiyama aldol reactions with
4-oxy-2-trimethylsilyloxypyrroles: relevance to castanospermine
synthesis.
Department of Chemistry, University of Cape Town, Private
Bag, Rondebosch, Cape Town 7701, South Africa.
Roger.Hunter@uct.ac.za.
ABSTRACT:
BACKGROUND:
The diastereoselectivity of a vinylogous Mukaiyama aldol
reaction of a series of N-substituted
4-oxy-2-trimethylsilyloxypyrroles with a tartrate-based aldehyde
has been explored as a model reaction for castanospermine
synthesis.
RESULTS: The study has revealed that the reaction is
sensitive to the nature of the combination of N- and 4-oxy
substituents. With a N-PMB or N-Bn and 4-methoxy combination,
the reaction generates an aldol adduct with the correct absolute
configurations for C-8 and C-8a of the indolizidine alkaloid
castanospermine. The adduct was transformed to an indolizidine,
whose ketal could not be transformed appropriately for the
target alkaloid.
CONCLUSION: The first successful diastereoselective Mukaiyama
aldol strategy for the C-8 and C-8a stereogenic centres of
castanospermine is presented using silyloxypyrrole chemistry.
The results suggest that a full enantioselective synthesis can
be realized provided that C-1 functionalisation is accomplished
early in the synthesis, post-coupling.
PMID: 17980041
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