The Ferrier rearrangement is an organic reaction that involves a nucleophilic substitution reaction combined with an allylic shift in a glycal (a 2,3-unsaturated glycoside). It was discovered by the carbohydrate chemist Robert J. Ferrier.
center|800px|A typical Ferrier rearrangement
Mechanism
In the first step, a delocalized allyloxocarbenium ion (2) is formed, typically with the aid of a Lewis acid like indium(III) chloride or boron trifluoride. This ion reacts in situ with an alcohol, yielding a mixture of the α (3) and β (4) anomers of the 2-glycoside, with the double bond shifted to position 3,4.
Examples
{| class="wikitable" border="1"
|-
! Lewis acid
! Alcohol
! Conditions
! Results
|-
| InCl<sub>3</sub>
| methanol
| in dichloromethane
| α:β = 7:1
|-
| dioxane
| water
| heating
| 75% yield
|-
| SnCl<sub>4</sub>
| methanol
| in dichloromethane, –78 °C, 10 min
| 83% yield, α:β = 86:14
|-
| BF<sub>3</sub>·O(C<sub>2</sub>H<sub>5</sub>)<sub>2</sub>
| isopropanol
| in dichloromethane, RT, 24 hr
| 95% yield
|-
| ZnCl<sub>2</sub>
| ethanol
| in toluene, RT, 30–60 min
| 65–95% yield, α:β = 89:11
|-
| BF<sub>3</sub>·O(C<sub>2</sub>H<sub>5</sub>)<sub>2</sub>
| benzyl alcohol
| in dichloromethane, –20 °C to RT, 1 hr
| 98% yield
|}
Modifications
Forming of C-glycosides
By replacing the alcohol with a silane, C-glycosides can be formed. With triethylsilane (R'=H), the reaction yields a 2,3-unsaturated deoxy sugar.
none|Nitrogen analogue of the Ferrier rearrangement