Asymmetric aziridine synthesis by aza-Darzens reaction of N-diphenylphosphinylimines with chiral enolates. Part 2: Inversion of diastereoselectivity

3-Arylaziridine-2-carboxylic Acid Derivatives and (3-Arylaziridin-2-yl)ketones: The Aziridination Approaches

“…The sources of chirality are chiral N-substituents in imines or enolates. Use of chiral enolates and N-diphenylphosphinylimines were explored by Sweeney and co-authors [ 58 , 59 ]. Thus, enolate 16a , generated from 2 R -N-bromoacethylcamphorsultam 15a ( Scheme 12 ) reacts with N-diphenylphosphinyl aldimines 2e1 leading to 3-arylaziridine-2-carboxamides cis - 1b5 .…”

“…There are chiral N-phosphinyl imines 2f1, 2f2 [60,61] and chiral sulfimines 2f3, 2f4 [62][63][64] Chemical yields are good (57-78%) and stereoselectivity excellent, >95% dr in 14 demonstrated examples [58]. However, in some cases depending of the imine aryl substituent structure (using imines 2e2) inversion of stereochemistry has been observed and aziridines trans-1b5 obtained [59]. The mechanism of reaction and transition states were elucidated.…”

2.14 Other Condensation Reactions (Knoevenagel, Perkin, Darzens)

“…115 The Darzens condensation of acyl phosphonates 223 with a-halo ketones 224 in the presence of base at room temperature affords cis-and trans-epoxyphosphonates 225 in good chemical yield (Scheme 63). 116 The diastereoselectivity of this condensation reaction is easily controlled by changing the base.…”

Nucleophilic Aliphatic Substitution

“…54 When the arylimine is substituted in the ortho-position, the product is either a mixture of cis-and trans-aziridine or only the trans-isomer. When the ortho-substituent is H or NO 2 , only a cis-aziridine is obtained.…”

“…The S N 2 reactions of (53), (54), and (55) with bromide ion have been studied in wet CH 2 Cl 2 in the presence of the reversed micelles formed from cetyltrimethylammonium bromide (CTA), cetyltripropylammonium bromide (CTPA), and tetra-n-butylammonium bromide (TBA). 87 The rates of (53) and (54) increase markedly in the presence of the micelles whereas the rate of (55) does not, presumably because the positive (55) does not interact with the cationic micelle. It is suggested that (55) reacts fastest because of the ionic attraction between the charges on the substrate and the bromide ion; (53) reacts the slowest.…”