Vinylogous Mukaiyama aldol reactions with 4-oxy-2-trimethylsilyloxypyrroles: relevance to castanospermine synthesis
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2007
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Beilstein Journal of Organic Chemistry
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Biomed Central
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University of Cape Town
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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.
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Hunter, R., Rees-Jones, S. C., & Su, H. (2007). Vinylogous Mukaiyama aldol reactions with 4-oxy-2-trimethylsilyloxypyrroles: relevance to castanospermine synthesis. Beilstein journal of organic chemistry, 3(1), 38.