The total synthesis of octalactins A and B has been achieved in 15 steps (longest linear sequence) and 10% overall yield from commercially available materials. Key steps include the Paterson-Aldol reaction for the rapid assembly of the carbonate 46, methylenation of 46 and subsequent Claisen rearrangement of the corresponding alkenyl-substituted cyclic ketene acetal to provide the core unsaturated medium-ring lactone 47, and the use of enzyme-mediated acetate deprotection in the presence of a medium-ring lactone.
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β-Hydroxy Esters as Malonic Semialdehyde Proelectrophiles in Enantioselective Butadiene-Mediated Crotylation: Total Synthesis of Octalactins A and B.
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Department of Chemistry, University of Texas at Austin, Austin, Texas 78712, United States.
Tractable and commercially available esters (and amides) of β-hydroxypropionic acid serve as malonic semialdehyde proelectrophiles in enantioselective ruthenium-catalyzed hydrogen autotransfer crotylations mediated by butadiene. Through iterative asymmetric butadiene-mediated crotylations of ethyl 3-hydroxypropanoate, total syntheses of the polyketide natural products octalactin A and B were achieved in fewer steps than previously possible.
View Article and Find Full Text PDFAn effective use of benzoic anhydride and its derivatives for the synthesis of carboxylic esters and lactones: a powerful and convenient mixed anhydride method promoted by basic catalysts.
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Department of Applied Chemistry, Faculty of Science, Tokyo University of Science, Kagurazaka, Shinjuku-ku, Tokyo 162-8601, Japan.
Various carboxylic esters are obtained at room temperature in excellent yields with high chemoselectivities from nearly equimolar amounts of carboxylic acids and alcohols using 2-methyl-6-nitrobenzoic anhydride with triethylamine by the promotion of a basic catalyst such as 4-(dimethylamino)pyridine. A variety of lactones are also prepared in high yields at room temperature from the corresponding omega-hydroxycarboxylic acids with use of 2-methyl-6-nitrobenzoic anhydride in the presence of 4-(dimethylamino)pyridine. A similar reaction occurs with triethylamine when using a catalytic amount of 4-(dimethylamino)pyridine 1-oxide as an effective promoter for the intramolecular condensation reaction.
View Article and Find Full Text PDFA concise synthesis of the octalactins.
J Am Chem Soc
February 2004
Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, UK.
The total synthesis of octalactins A and B has been achieved in 15 steps (longest linear sequence) and 10% overall yield from commercially available materials. Key steps include the Paterson-Aldol reaction for the rapid assembly of the carbonate 46, methylenation of 46 and subsequent Claisen rearrangement of the corresponding alkenyl-substituted cyclic ketene acetal to provide the core unsaturated medium-ring lactone 47, and the use of enzyme-mediated acetate deprotection in the presence of a medium-ring lactone.
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