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The wittig rearrangement as a practical method for aldehyde synthesis
Ist Teil von
Tetrahedron, 1989, Vol.45 (9), p.2649-2664
Ort / Verlag
Oxford: Elsevier Ltd
Erscheinungsjahr
1989
Link zum Volltext
Quelle
Elsevier Journal Backfiles on ScienceDirect (DFG Nationallizenzen)
Beschreibungen/Notizen
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.