Subscribe to RSS
DOI: 10.1055/s-2008-1042703
Synthesis of E-α,β-Unsaturated Esters via Hydration of Propargylic Acetates
Contributor(s):Mark Lautens, Frédéric MénardTokushima Bunri University, Yamashiro-cho, Japan
Virtually Complete E-Selective α,β-Unsaturated Ester Synthesis by Hg(OTf)2-Catalyzed Hydration of sec-Ethoxyalkynyl Acetate
Org. Lett. 2007, 9: 5577-5580
Publication History
Publication Date:
21 February 2008 (online)
Key words
E-alkenes - mercury - alkyne isomerization - ynol ethers
Significance
Although there are several well-established methods to prepare trans-α,β-unsaturated alkenes (stabilized Wittig, HWE, cross-metathesis), depending on the substrates, they can lead to isomeric mixtures. Generally, the olefin isomers arise from reaction under equilibrium conditions, whereas the reaction above is proposed to be stereospecific and can thus lead to only one isomer. The authors report that the E-selectivity of the procedure is higher than that obtained with the commonly used HWE olefination.
Comment
The propargylic acetates 1 are prepared from the corresponding aldehydes by addition of lithium acetylides. Since both the above method and a typical HWE involve the same aldehyde precursor, this procedure should be kept in mind in cases when the olefination is problematic. The Lewis acid catalyst Hg(OTf)2 was a key in promoting the isomerization/hydration of propargylic acetates with perfect stereoselectivity. In contrast, previous methods using Au(III), Lewis or Brønsted acids led to isomeric mixtures.