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.
Novel enantioselective acylating agents. The reactions of chiral ortho esters and silylenol ethers as a route to optically active monoprotected 1,3-dicarbonyl compounds
A novelenantioselectiveroute to monoprotected 2-substituted-1,3-dicarbonyl compounds has been developed via acylation of silylenolethers with chiralorthoesters derived from diethyl or di-isopropyl (R,R)-tartrates; good yields and stereoselectivity can be achieved starting from cyclic enolsilanes.
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.