1 research outputs found
Asymmetric Catalysis with Ethylene. Synthesis of Functionalized Chiral Enolates
Trialkylsilyl
enol ethers are versatile intermediates often used
as enolate surrogates for the synthesis of carbonyl compounds. Yet
there are no reports of broadly applicable, catalytic methods for
the synthesis of chiral silyl enol ethers carrying latent functionalities
useful for synthetic operations beyond the many possible reactions
of the silyl enol ether moiety itself. Here we report a general procedure
for highly catalytic (substrate:catalyst ratio up to 1000:1) and enantioselective
(92% to 98% major enantiomer) synthesis of such compounds bearing
a vinyl group at a chiral carbon at the β-position. The reactions,
run under ambient conditions, use trialkylsiloxy-1,3-dienes and ethylene
(1 atm) as precursors and readily available (bis-phosphine)-cobalt(II)
complexes as catalysts. The silyl enolates can be readily converted
into novel enantiopure vinyl triflates, a class of highly versatile
cross-coupling reagents, enabling the syntheses of other enantiomerically
pure, stereodefined trisubstituted alkene intermediates not easily
accessible by current methods. Examples of Kumada, Stille, and Suzuki
coupling reactions are illustrated