(6S,7S,8S,9R,10S)-(--)-Membrenone B was synthesized in nine steps (9.4% overall yield) beginning with two-directional aldol coupling of tetrahydro-4H-thiopyran-4-one with racemic 1,4-dioxa-8-thiaspiro[4.5]decane-6-carboxaldehyde. The first aldol reaction occurs with dynamic kinetic resolution to give a single adduct (>98% ee). The second aldol reaction is highly diastereoselective (three of eight possible adducts), and both major products are converted to membrenone B. The route also constitutes a formal synthesis of membrenone A.
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Iterative direct aldol strategy for polypropionates: enantioselective total synthesis of (-)-membrenone A and B.
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An iterative direct aldol reaction using a C3 propionate unit as an aldol donor offers expeditious access to polyketide assembly in a highly diastereo- and enantioselective manner. An all-syn polyketide array with four consecutive stereogenic centers was efficiently constructed by an aldol reaction of thiopropionamide via soft Lewis acid/hard Brønsted base cooperative catalysis. This iterative aldol strategy led to an enantioselective synthesis of (-)-membrenone A and B.
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Department of Chemistry, University of Saskatchewan, 110 Science Place, Saskatoon SK S7N 5C9, Canada.
(6S,7S,8S,9R,10S)-(--)-Membrenone B was synthesized in nine steps (9.4% overall yield) beginning with two-directional aldol coupling of tetrahydro-4H-thiopyran-4-one with racemic 1,4-dioxa-8-thiaspiro[4.5]decane-6-carboxaldehyde.
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Department of Chemistry, University of Virginia, Charlottesville, Virginia 22904, USA.
[reaction: see text] A synthesis of the polypropionate marine defense substance (+)-membrenone C and its enantiomer that starts from (S)-2-methyl-3-(tert-butyldimethylsilyloxy)propanal is described. Key steps include (1) additions of chiral allenylmetal reagents to effect both chain homologation and the concomitant introduction of four stereo centers, (2) a bis-intramolecular hydrosilylation-oxidation sequence to install beta-hydroxy ketone subunits, and (3) a bis-intramolecular aldol reaction to construct the two dihydropyrone termini.
View Article and Find Full Text PDFTotal synthesis of (-)-(6S,7S,8S,9R,10S,2'S)-membrenone-A and (-)-(6S,7S,8S,9R,10S)- membrenone-B and structural assignment of membrenone-C.
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School of Chemistry, Physics and Earth Sciences, The Flinders University of South Australia, G.P.O. Box 2100, S.A. 5001, Australia.
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School of Chemistry, Physics and Earth Sciences, Flinders University of South Australia, G.P.O. Box 2100, S.A. 5001, Australia.
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