Synthesis 2009(7): 1065-1074  
DOI: 10.1055/s-0028-1088011
PAPER
© Georg Thieme Verlag Stuttgart ˙ New York

Umpolung with Sulfur Dioxide: Carbon-Carbon Cross-Coupling of Electron-Rich 1,3-Dienes and Alkenes; Application to the Enantioselective Synthesis of Long-Chain Polyketide Fragments

Mâris Turksa, Claudia J. Exnerb, Cotinica Hamelc, Pierre Vogel*b
a Faculty of Material Science and Applied Chemistry, Riga Technical University, Riga 1658, Latvia
b Laboratory of Glycochemistry and Asymmetric Synthesis (LGSA), Swiss Federal Institute of Technology (EPFL), 1015 Lausanne, Switzerland
Fax: +41(21)6939350; e-Mail: Pierre.vogel@epfl.ch;
c AC IMMUNE, EPFL, PSE-B, 1015 Lausanne, Switzerland
Further Information

Publication History

Received 5 January 2009
Publication Date:
16 March 2009 (online)

Abstract

At low temperature and in the presence of an acid catalyst, sulfur dioxide undergoes hetero-Diels-Alder additions with 1-oxy-1,3-dienes, giving unstable sultines, which are ionized into zwitterionic species and react as 1-oxyallylic cation intermediates (Umpolung with SO2) with electron-rich alkenes such as allylsilanes or enoxysilanes. The β,γ-unsaturated silyl sulfinates so-obtained can be desulfinylated in situ to generate polyketide fragments containing up to three contiguous stereogenic centers in one-pot operations. This reaction cascade can be applied in two-directional chain elongation approaches for the asymmetric synthesis of long chain polyketide fragments using 1-[(S)- or (R)-1-phenylethoxy]-1,3-dienes.