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[reaction: see text] Boryl substitution on an olefin activates the olefinic double bond toward addition of an organozinc reagent. Addition of an allylic zinc reagent to an alkenylboronate thus takes place smoothly to afford a variety of gem-zincio/boryl species. Theoretical studies with density functional calculations on the reaction pathway revealed that the reaction proceeds via a zincio-ene reaction rather than a bora-Claisen rearrangement.  相似文献   
2.
Fractionation monitored by the immunomodulatory activity of the AcOEt extract of an Ascomycete, Emericella aurantio-brunnea, afforded two known fungal sesterterpenes, variecolin (1) and variecolactone (2), two new variecolin congeners named variecoacetals A (3) and B (4), and a new sesquiterpenetriol diester named emeremophiline (5), as the immunosuppressive constituents of this fungus. The absolute configuration of 1, which was previously not determined, was determined to be (2S,3S,6R,10S,11R,14S,15R,16S) from the NMR spectral data of the (6R,7R)-dimethyl-1,3,5-trioxacycloheptyl derivative of 1 (7). The absolute configurations of the other variecolin congeners, 2-4, and variecolol (6) are also proposed from biosynthetic considerations.  相似文献   
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