Amide enolates 2,3 -Wittig rearrangement

Generally, ester enolates of structure (202 R = M, R = Oalkyl) rearrange via a 3,3-shift, whereas the corresponding amide enolates (202 R = M, R = N(alkyl)2) and acid dianions (202 R = M, R = OM) prefer the 2,3-pathway (equation 20). Both pathways have been observed with ketone enolates (202 R = M, R = alkyl). With substrate (179), Koreeda and Luengo observed only traces of Wittig rearrangement product (205), except for the lithium enolate, where (205) accounted for up to 20% of the reaction mixture (equation 21). ° Thomas and Dubini, however, reported predominant formation of 2,3 Wittig products (207) and (209) under base treatment of ketones (206) and (208) (equation 22). ... 

Pyrrolidinyl amides undoubtedly form Z((9)-enolates, and the [2,3]-Wittig rearrangement of the -alkene (entry 5, [69] is highly selective. The Z-alkene was not tested, and propargylic amide enolates do not rearrange [70]. Entry 5 also shows the highest yield in the Table. As will be seen, amides of C2-symmetric amines can be excellent chiral auxiliaries in this process. 

Scheme 6.14. Possible transition structures for the [2,3]-Wittig rearrangement of the R-allylic ester enolates shown in Scheme 6.13. For amide enolates, see Scheme 6.22.

In a similar fashion, the [2,3]-Wittig rearrangement of amide enolates 78 can be carried out leading to hydroxy acids 79a and 79b, which can... 

Kress MH, Yang C, Yasuda N, Grabowski EJJ. Stereoselective [2,3]-Wittig rearrangement of (15, 2R)-l-amino-indan-2-ol derived amide enolates. Tetrahedron Lett. 1997 38 (15) 2633-2636. 

Potassium Amides. The strong, extremely soluble, stable, and nonnucleophilic potassium amide base (42), potassium hexamethyldisilazane [40949-94-8] (KHMDS), KN [Si(CH2]2, pX = 28, has been developed and commercialized. KHMDS, ideal for regio/stereospecific deprotonation and enolization reactions for less acidic compounds, is available in both THF and toluene solutions. It has demonstrated benefits for reactions involving kinetic enolates (43), alkylation and acylation (44), Wittig reaction (45), epoxidation (46), Ireland-Claison rearrangement (47,48), isomerization (49,50), Darzen reaction (51), Dieckmann condensation (52), cyclization (53), chain and ring expansion (54,55), and elimination (56). 

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