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Please login to access the full content or check if you have access via Method 25: Rearrangement of Epoxides Using Other Reagents

DOI: 10.1055/sos-SD-036-00485

Hodgson, D. M.; Humphreys, P. G.Science of Synthesis, (200836645.

Lewis acids are a mild alternative to lithium amides for the rearrangement of epoxides to allylic alcohols[‌337‌] and, due to the decreased basicity of the Lewis acids, more functional groups can be tolerated, including potentially enolizable esters and ketones.[‌338‌,‌339‌] The Lewis acid trimethylsilyl trifluoromethanesulfonate in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene or lutidine is a reagent combination that causes the rearrangement of epoxides to allylic alcohols,[‌338‌] and gives reasonable yields with a variety of cyclic substrates. Here, the least sterically demanding proton is abstracted by the base to give the least substituted E-allylic alcohol; however, mono and acyclic 2,3-dialkyl substituted epoxides fail to react under these conditions.[‌338‌] An alternative silicon-based Lewis acid combination is iodotrimethylsilane and 1,5-diazabicyclo[4.3.0]non-5-ene, although competing deoxygenation reactions, particularly with trisubstituted cyclic epoxides, limit its value.[‌339‌] Boron trifluoridediethyl ether complex with tetrabutylammonium iodide is another mild reagent combination that is used to convert epoxides into allylic alcohols by epoxide ring opening, followed by abstraction of the most accessible β-proton.[‌340‌] An example of this is the synthesis of diol 147 (Scheme 70).

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