Sigmatropic rearrangements of anions

Sigmatropic rearrangements of anions of (V-allyl amines have also been observed and are known as aza-Wittig rearrangements.291 The reaction requires anion stabilizing substituents and is favored by (V-benzyl and by silyl or sulfenyl substituents... 

Sigmatropic Rearrangements of Anions The [2,3]-sigmatropic rearrangement pattern is also observed with anionic species. The most important case... 

Sigmatropic Rearrangements of Anions of Allyl Ethers The Wittig and Aza-WUtig Rearrangements... 

Thioallyl anions such as (55) may participate in vis + ttAs cycloadditions as the 47t component. The [2,3]-sigmatropic rearrangements of anions of... 

A final crucial step in this synthesis was an anionic [2,3]-sigmatropic rearrangement of an allylic ether in Step D-4 to introduce the C(l) carbon. 

In the solution proposed by Evans [25], however, the unsaturated ketone is condensed with the anion of an alkyl allyl ether, followed by a [3,3]-sigmatropic oxy-Cope type rearrangement (Scheme 5.22). In the retrosynthetic sense this means a [3,3]-sigmatropic rearrangement of the bis-enol form of the 1,6-dicarbonyl system. 

Sigmatropic rearrangements in anions are more rare, but the isomerization of the conjugated anion 5.42 to the conjugated anion 5.45 probably takes place by a [1,6] shift 5.43 —> 5.44. It is known to be intramolecular, but the stereochemistry (antarafacial is allowed) could not be checked. In order for the reaction to take place at all, it is necessary for the stereochemistry within... 

The anionic [3,3] sigmatropic rearrangement of cyclic diacyl pyrazolidines resulted in poor to good yields of 1,5-diazonane-6,9-diones <2000H(53)151 >. 

Sigmatropic rearrangement of deuterium-labeled bicyclo[3.1.0]hexenyl radicals occur below — 60°C (equation 31) and are faster than ring-opening Lifetimes for ringopening of some cyclopropyl-substituted radical anions (156) have been studied, as well as the ESR spectra of p-cyclopropylnitrobenzene radical anion (157). ... 

Fig. 10.40. Relationship between TS structure and stereoselectivity in [2,3]-sigmatropic rearrangement of alloxy carbanions (a) early TS for unsubstituted allyloxymethyl anion (b) tighter cyclic TS for stabilized allyloxypropargyl anion (c,d) preferred conformation of E-and Z-crotyloxypropargyl anions leading to the E anti and Z syn stereoselectivity (e,f) unchelated and chelated TSs for a-crotyloxy ethanal enolate leading to the E syn stereoselectivity. Reproduced from Tetrahedron, 50, 5917 (1994), by permission of Elsevier.

When nerol oxide (419) is metallated with butyl-lithium, a sigmatropic rearrangement of the anion to (420) occurs. The two isomers of (420) can be trapped in acetic anhydride as the enol acetates (421), hydrolysis of the latter yielding the aldehydes (422). " Additional interest is given to this reaction because the... 

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