Science of Synthesis

Hodgson, D. M.; Humphreys, P. G., Science of Synthesis, (2008) 36, 647.

Vinyl epoxides bearing a carbonyl, cyanide, sulfonyl, or phosphate group attached to the β-carbon atom act as Michael acceptors and undergo rapid reduction with samarium(II) iodide to give E-allylic alcohols.[‌346‌] As vinyl epoxides can be easily accessed in an asymmetric fashion by Sharpless asymmetric epoxidation of the analogous allylic alcohols, followed by oxidation and alkenation, syntheses of chiral allylic alcohols are possible using this methodology. The reductions proceed rapidly at −90°C with a variety of cyclic and acyclic mono-, di-, tri-, and tetrasubstituted epoxides (typically within five minutes) and give the corresponding E-allylic alcohols in high yields. The probable mechanism for the reductive ring-opening process is illustrated for the synthesis of ethyl (3E)-5-hydroxy-2-methylpent-3-enoate ‌156‌ from the corresponding ester ‌155‌, and a useful feature of this and related conversions is that a E/Z-mixture of the vinyl epoxide gives a single E-isomer of the allylic alcohol (‌Scheme 74‌). Also included in this scheme are representative examples of the reduction of 2-methylene-7-oxabicyclo[4.1.0]heptanes ‌157‌, bearing an electron-accepting function at the exocyclic methylene position, to afford the 3-substituted-cyclohex-2-en-1-ols ‌158‌.[‌346‌]

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References

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• 8.Meeeee-Meee, (8888) 8/8e, 888.
• 8.Meeeee-Meee, (8888) 8/8e, 888.