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Indium- and Zinc-Mediated Acyloxyallylation of Protected and Unprotected AldotetrosesRevealing a Pronounced Diastereodivergence and a Fundamental Difference in the Performance of the Mediating Metal
journal contribution
posted on 2018-01-25, 00:00 authored by Markus Draskovits, Christian Stanetty, Ian R. Baxendale, Marko D. MihovilovicThe
acyloxyallylation of unprotected aldoses was first demonstrated
more than a decade ago as a potentially elegant two-carbon homologation
of reducing sugars (upon ozonolysis); however, its application in
real case syntheses remained scarce. Following up on such a successful
showcase and to answer several pending questions about this attractive
transformation, we engaged in an in depth methodological reinvestigation.
The epimeric tetroses l-erythrose and d-threose
in unprotected and protected form were successfully applied to the
indium and also zinc-mediated acyloxyallylation, with the latter being
a first for an unprotected sugar. The investigation largely benefited
from the choice of these more exotic starting materials as it allowed
unambiguous identification/quantification of the hexose-products which
are available as authentic reference materials. The observed diastereoselectivities
indicate a strong substrate control (stereochemistry at O2), and the influence of the reagent’s structure on the selectivity
was investigated in great detail. A strong facial diastereodivergence
between related protected and unprotected structures was demonstrated
and an unexpected, pronounced principle difference in performance
between indium and zinc was revealed.
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diastereoselectivitiecase synthesesinfluencereference materialszinc-mediated acyloxyallylationreinvestigationPerformanced-threoseFundamental DifferenceozonolysidiastereodivergencelatterdepthapplicationinvestigationidentificationstereochemistrytransformationMediating MetalPronounced Diastereodivergencetwo-carbon homologationchoiceepimeric tetroses l-erythrosereagentProtectedAldotetroseIndiumshowcaseselectivityperformancesubstrate controlaldoseUnprotectedhexose-productprinciple differenceindiumZinc-Mediated Acyloxyallylation
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