Enantioselective addition of β-functionalized allylboronates to aldehydes and aldimines. Stereocontrolled synthesis of α-methylene-γ-lactones and lactams
We report results regarding the development of condensations of chiral β-alkoxycarbonylallylboronates on aldehydes and imines. These allylboronates add in a highly enantioselective and diastereospecific manner to afford biologically and synthetically useful chiral α-methylene-γ-butyrolactones and lactams. The nature of the electrophile (aldehyde vs imine) is shown to have a dramatic influence on the
2-Methylene-4-butyrolactones were conveniently synthesized by treatment of an aldehyde with 2-carboethoxyallyl(-ic) bromide and metallic tin (and aluminum) in good yields. Protolichesterinic acid was synthesized by employing the method.
[reaction; see text] A general and practical procedure for the highly diastereoselective preparation of either the cis- or trans-beta,gamma-disubstituted-gamma-butyrolactones by appropriate choice of Lewis or Bronsted acid catalysts during crotylboration or lactonization is reported. The cis-stereochemistry of the Z-crotylboration product can be inverted with strong acids during lactonization. A carbocation
Synthesis and cytotoxic activity of γ-aryl substituted α-alkylidene-γ-lactones and α-alkylidene-γ-lactams
作者:Anna Albrecht、Jacek F. Koszuk、Jakub Modranka、Marek Różalski、Urszula Krajewska、Anna Janecka、Kazimierz Studzian、Tomasz Janecki
DOI:10.1016/j.bmc.2008.03.035
日期:2008.5
A series of 5-aryl-3-alkylidenedihydrofuran-2(3H)-ones 6a-g'' and 11a,b as well as 5-aryl-3-methylidenepyrrolidin-2-ones 10a-c and 12 were synthesized starting from 4-aryl-2-diethoxyphosphoryl-4-oxobutanoates 3a-g. Reaction sequence includes reduction or reductiveamination of the carbonyl group, lactonization or lactamization step and finally the Horner-Wadsworth-Emmons olefination of aldehydes using
Triflic Acid-Catalyzed Additions of 2-Alkoxycarbonyl Allylboronates to Aldehydes. Study of Scope and Mechanistic Investigation of the Reaction Stereochemistry
作者:Tim G. Elford、Yuichiro Arimura、Siu Hong Yu、Dennis G. Hall
DOI:10.1021/jo062151b
日期:2007.2.1
The substrate scope and the effect of substrate on the observed inversion of stereoselectivity in the triflic acid-catalyzed allylboration reaction between 2-alkoxycarbonyl allylboronates and aldehydes are presented. A mechanisticinvestigation is described so as to confirm the involvement of a carbocation intermediate as the source of stereochemical inversion. This methodology allows a facile access