Chiral orthoesters in organic synthesis: Novel reagents for the enantioselective acylation of silylenolethers
摘要:
Dialkyl trans-2-alkoxy-2-alkyl-1,3-dioxolan-4,5-dicarboxylates and the corresponding N,N,N,N-tetramethyl-4,5-diamides have been prepared respectively from dialkyl tartrates or tartaric acid diamides. They smoothly reacted with silylenolethers in the presence of Lewis acids to give enantiomerically enriched (up to 90% d.e.) monoprotected 1,3-diketones. A dramatic dependence of the stereochemical outcome from the configuration of the enolic double bond of 4 has been observed. The products can be stereoselectively reduced to give configurationally defined monoprotected 3-ketols.
Chiral orthoesters in organic synthesis: Novel reagents for the enantioselective acylation of silylenolethers
摘要:
Dialkyl trans-2-alkoxy-2-alkyl-1,3-dioxolan-4,5-dicarboxylates and the corresponding N,N,N,N-tetramethyl-4,5-diamides have been prepared respectively from dialkyl tartrates or tartaric acid diamides. They smoothly reacted with silylenolethers in the presence of Lewis acids to give enantiomerically enriched (up to 90% d.e.) monoprotected 1,3-diketones. A dramatic dependence of the stereochemical outcome from the configuration of the enolic double bond of 4 has been observed. The products can be stereoselectively reduced to give configurationally defined monoprotected 3-ketols.
Enantioselective acylation of enolates; the reaction of (4R)-trans-diethyl 2-alkyl-2-methoxy-1,3-dioxolane-4,5-dicarboxylates with E- and Z-silyl enol ethers
The stereoselectivity of the Lewis acid induced acylation of open-chain silyl enoi ethers by chiral orthoesters is strongly affected by the CC bond configuration: both Z and E silyl enol ethers are acylated in good isolated yields, but the Z isomers give rise to a 1 : 1 ratio of diastereoisomeric monoprotected 1,3-diketones, while excellent stereoselectivities are obtained with E enols.
Dialkyl trans-2-alkoxy-2-alkyl-1,3-dioxolan-4,5-dicarboxylates and the corresponding N,N,N,N-tetramethyl-4,5-diamides have been prepared respectively from dialkyl tartrates or tartaric acid diamides. They smoothly reacted with silylenolethers in the presence of Lewis acids to give enantiomerically enriched (up to 90% d.e.) monoprotected 1,3-diketones. A dramatic dependence of the stereochemical outcome from the configuration of the enolic double bond of 4 has been observed. The products can be stereoselectively reduced to give configurationally defined monoprotected 3-ketols.