THE WITTIG REARRANGEMENT AS A PRACTICAL METHOD FOR ALDEHYDE SYNTHESIS

Article abstract of DOI:10.1016/S0040-4020(01)80095-8

If the rearrangement of metalated allyl ethers 2 (or 4) is accomplished in the presence of potassium tert-butoxide, primary alkyl groups preferentially migrate to the unsubstituted allylic terminus (γ-position).Enolates 7 and 1-vinylalcoholates 6 (by alkyl migration to the α-position, adjacent to the oxygen atom) are produced in an approximate ratio of 9 : 1.Because of the endo-configuration of their organometallic precursors, the enolates exclusively emerge in the (Z)-configuration as shown by trapping with chlorotrimethylsilane and isolation of the resulting O-silyl (Z)-enethers.Hydrolysis of the latter affords the corresponding aldehydes with good yields. -The rearrangement is mechanistically still obscure.A concerted process as the main reaction mode is unlikely.The intermediacy of zwitterionic metallomers 18 and solvent caged radical pairs 17 is tentatively suggested.