1,2-Wittig rearrangement

A 1,2-Wittig rearrangement is a organic reaction and a 1,2-rearrangement of an ether with an alkyllithium compound.

<math>\mathrm{R_1R_2CH0R_3 + R_4Li \rightarrow R_1R_2R_3CH0^-Li^+ + R_4H}<math>

The intermediate product is a alkoxy lithium salt and the final product a alcohol. When R₂ is a good leaving group and electron withdrawing functional group such as a cyanide (CN) group, ^[1] this group is eliminated and the corresponding ketone is formed.

<math>\mathrm{R_1(CN)CH0R_3 + R_4Li \rightarrow R_1R_3C=O + LiCN + R_4H}<math>

The reaction mechanism centers around the formation of a free radical pair with lithium migrating from the carbon atom to the oxygen atom. The R₃ radical then recombines.

<math>\mathrm{R_1R_2CLi0^o + R_3^o \rightarrow R_1R_2C^o0Li + R_3^o}<math>

References

• G. Wittig, L. Löhmann, Ann. 550, 260 (1942)
• G. Wittig, Experientia 14, 389 (1958).
• ^[1] Preparation of aryl benzyl ketones by [1,2]-Wittig rearrangement Alan R. Katritzky, Yuming Zhang, Sandeep K. Singh Arkivoc p. 146–150 2002 (vii)

[1] open access publication