RESUMO
The enantioselective syntheses of several protected 4-substituted syn-3,5-dihydroxy carboxylic esters have been achieved from the corresponding achiral (E,E)- or (E,Z)-1,3-dienoates. The route relies upon an enantio- and regioselective Sharpless dihydroxylation and a palladium-catalyzed reduction to form gamma-substituted delta-hydroxy-1-enoates. The resulting delta-hydroxy-1-enoates are subsequently converted into benzylidene-protected 4-substituted syn-3,5-dihydroxy carboxylic esters in one step. The benzylidene-protected 3,5-dihydroxy carboxylic esters are produced in good overall yields (20-54%) and high enantiomeric excess (73-97% ee).
Assuntos
Álcoois/síntese química , Ésteres/síntese química , Água/químicaRESUMO
A short and highly efficient route to both enantiomers of muricatacin as well as the C-5-epimer has been developed. The key to the overall transformation is the highly regio- and enantioselective Sharpless asymmetric dihydroxylation of an (E,Z)-dienoate. The highly efficient stereoselective synthesis prepares (-)-muricatacin in seven steps and 66% overall yield.
Assuntos
Furanos/síntese química , Furanos/química , Hidroxilação , Lactonas/química , Estrutura Molecular , EstereoisomerismoRESUMO
A short and highly efficient route to various C-4 substituted sugar lactones has been developed. The key to the overall transformation is the sequential osmium-catalyzed dihydroxylation reaction of substituted 2,4-dienoates and an allylic substitution at the C-4 position. When the Sharpless AD-mix procedure is used in a matched sense for the second dihydroxylation reaction, it results in an exceedingly diastereo- and enantioselective synthesis of several C-4-substituted sugars.
Assuntos
Lactonas/síntese química , Gluconatos/síntese química , Hidroxilação , Estereoisomerismo , Açúcares Ácidos/síntese químicaRESUMO
[reaction: see text] A short and highly efficient route to D- and L-talo-gamma-lactones has been developed. The key transformation was the sequential osmium-catalyzed bis-dihydroxylation reaction of substituted 2,4-dienoates. When the first dihydroxylation reaction is performed on (2Z,4E)-dienoates with use of the Sharpless AD-mix procedure, a regio- and enantioselective dihydroxylation resulted along with an in situ lactonization. A subsequent dihydroxylation, using OsO4/NMO in MeOH conditions, resulted in an exceedingly diastereo- and enantioselective synthesis of talo-gamma-lactone.
Assuntos
Lactonas/síntese química , Butiratos/química , Carboidratos/síntese química , Hidroxilação , Nitrocompostos/química , EstereoisomerismoRESUMO
An efficient route to various sugar lactones has been developed. Key to the overall transformation is the sequential osmium-catalyzed dihydroxylation of 2,4-dienoates. The simplest (one-step/racemic) example of this reaction occurs when the dihydroxylation is performed with aqueous NMO in MeOH. When the first dihydroxylation is performed using the AD-mix procedure, an enantioselective variant results. When a matched AD-mix procedure is used for the second dihydroxylation, an exceedingly diastereo- and enantioselective synthesis of galacto-1,4-lactone results. [Reaction: see text]