Chiral α-silyloxy ketones participate in highly stereoselectiveTiCl4-mediatedaldolreactions that afford diastereomerically pure syn–syn adducts in high yield irrespective of the R1 and R2 substituents flanking the carbonyl or the silicon protecting group. Further manipulation of the resulting aldol adducts provide in a straightforward manner highly functionalized fragments that facilitate the synthesis
Total Synthesis of the Putative Structure of Lucentamycin A
作者:Ujjwal Pal、Sujeewa Ranatunga、Yamuna Ariyarathna、Juan R. Del Valle
DOI:10.1021/ol902251c
日期:2009.11.19
A rapid and stereoselective enolate-Claisen rearrangement provides access to the 4-ethylidene-3-methylproline (Emp) subunit of lucentamycin A. Synthesis of the putativestructure of the cytotoxic natural product suggests the need for structural revision.
The acylation reaction of organolithium reagents with pyrrolidine-derived α-benzyloxy and α-silyloxy carboxamides provides a simple and high-yielding method for the preparation of enantiopure α-benzyloxy and α-silyloxy ketones.
[reaction: see text]Comprehensive analysis of the enolization of alpha-silyloxyketones by Chx2BCl/R3N has allowed us to design stereoselective Chx2BCl-mediated aldol processes that afford syn or anti aldol products and to disclose a hypothesis that accounts for the subtle effects that determine their enolization.