Lewis Base Activation of Lewis Acids: Catalytic, Enantioselective Addition of Glycolate-Derived Silyl Ketene Acetals to Aldehydes
作者:Scott E. Denmark、Won-jin Chung
DOI:10.1021/jo8006539
日期:2008.6.1
A catalytic system involving silicon tetrachloride and a chiral, Lewis basic bisphosphoramide catalyst is effective for the addition of glycolate-derived silyl ketene acetals to aldehydes. It was found that the sense of diastereoselectivity could be modulated by changing the size of the substituents on the silyl ketene acetals. In general, the trimethylsilyl ketene acetals derived from methyl glycolates
Total synthesis of (±)-isoavenaciolide and (±)-avenaciolide
作者:Steven D. Burke、Gregory J. Pacofsky、Anthony D. Piscopio
DOI:10.1016/s0040-4039(00)84792-9
日期:1986.1
The antifungal mold metabolites isoavenaciolide (1b) and avenaciolide (1c) have been synthesized in racemic form from a common precursor, α-methylene lactone 4, obtained via a glycolate ester enolate Claisen rearrangement.
Synthesis of ethisolide, isoavenaciolide, and avenaciolide
作者:Steven D. Burke、Gregory J. Pacofsky、Anthony D. Piscopio
DOI:10.1021/jo00034a009
日期:1992.4
Syntheses of the trio of related mold metabolites ethisolide (1), isoavenaciolide (2), and avenaciolide (3) in racemic and optically active forms are described. Glycolate Claisen rearrangements governed by chelation control of enolate geometry and diastereofacial bias in the [3,3] shifts establish the functional and stereochemical details in butyrolactone precursors (15b, 22, and 19) of the natural products. Lactone rearrangements via complementary bis(transesterification) (22 --> 23) and carboxylate displacement/lactonization (26 --> 27 --> 3) reactions provided the diastereomeric isoavenaciolide and avenaciolide structures. Differential reactivities among potential transacylation substrates 15a, 15b, 21, 22, 24, and 26 are attributed to steric interactions or strain in bridged bicyclic intermediates 32, 34, and 36.