Asymmetric [2,3]‐Rearrangement of Glycine‐Derived Allyl Ammonium Ylids.

Abstract

Aminocarboxylic acids (hydrazinocarboxylic acids) and esters P 0270Asymmetric [2,3]-Rearrangement of Glycine-Derived Allyl Ammonium Ylids. -N-Allylic glycine salts bearing a camphorsultam auxiliary undergo [2,3] rearrangement to give allylglycine derivatives with excellent enantiocontrol. Substrates bearing the (2R)-configured auxiliary afford predominantly (2'S)-configured products, while the use of the (2S)-auxiliary gives (2'R)-products. Allyl migration is favored over benzyl migration. For ammonium salts (IX) high diastereoselectivities are observed for the corresponding products. Ammonium salt (XII) having the chiral auxiliary attached to the allyl substituent rather than the glycine moiety also undergoes the rearrangement to give β-ethenyl aspartate derivative (XIII) as major stereoisomer. The route to allylglycine (V) via product (IIb) represents a new and efficient method for this compound. -(WORKMAN, J. A.; GARRIDO, N. P.; SANCON, J.; ROBERTS, E.; WESSEL, H. P.; SWEENEY*, J. B.; J.

Lewis acid–catalyzed domino generation/[2,3]-sigmatropic rearrangement of ammonium ylides to access chiral azabicycles

“…1A) (1)(2)(3). However, the harsh reaction conditions usually required for generation and deprotonation of the quaternary ammonium salts and the problems associated with purification of these salts limit the applicability of this type of reaction (7). To obviate the requirement of synthesizing and purifying problematic quaternary ammonium salts, protocols have been developed for directly generating ammonium ylides from tertiary amino carbonyl compounds by reacting them with a stoichiometric amount of a strong Lewis acid (e.g., BF 3 •Et 2 O and BBr 3 ) and a strong Brønsted base (8,9), or with aryne intermediates formed in situ (Fig.…”