general and highly efficient organocatalyzed desymmetrization of acyclic meso 1,3-diols through acyl transfer using chiral isothioureas is described. The introduction of π-systems in the acyclic substrates provided new opportunities in terms of reactivity, enantioselectivity and synthetic potential. To reach this high level of enantioselectivity (up to er >99:1), the reaction proceeds through a synergistic
A Facile and Efficient Synthesis of 4-Hydroxy-2,6-<i>cis</i>-tetrahydropyrans via Tandem Cross-Metathesis/Thermal S<sub>N</sub>2′ Reaction: Protecting-Group-Free Synthesis of (±)-Diospongin A
作者:Kiyoun Lee、Hyoungsu Kim、Jiyong Hong
DOI:10.1021/ol902125d
日期:2009.11.19
The tandem cross-metathesis/thermal SN2′ reaction was explored for the facile and efficientsynthesis of 4-hydroxy-2,6-cis-tetrahydropyrans. The mildness of the thermal conditions allowed for the synthesis of 4-hydroxy-2,6-cis-tetrahydropyrans from base-sensitive substrates without the use of protecting groups. The tandem reaction enabled a protecting-group-free synthesis of (±)-diospongin A.
探索了串联交叉复分解/热S N 2'反应的快速有效合成4-羟基-2,6-顺-四氢吡喃。热条件的温和性允许在不使用保护基的情况下从碱敏感的底物合成4-羟基-2,6-顺-四氢吡喃。串联反应使(±)-双倍体皂苷A的无保护基合成成为可能。
Iron-Catalyzed Synthesis of C2 Aryl- and <i>N</i>-Heteroaryl-Substituted Tetrahydropyrans
An iron-catalyzed cyclization of hydroxy allylic derivatives into tetrahydropyrans possessing an N-heteroaryl at C2 is disclosed. The reaction proceeds with good yield and in high diastereoselectivity in favor of the more stable isomer. The diastereoselectivity results from an iron-induced reopening of the tetrahydropyrans, allowing a thermodynamic equilibration. The method allows access to a variety of 2,6-disubstituted as well as 2,4,6-trisubstituted tetrahydropyrans that could be considered as attractive scaffolds for the pharmaceutical industry.