Fa. Davis et al., Aza-Darzens asymmetric synthesis of N-(p-toluenesulfinyl) aziridine 2-carboxylate esters from sulfinimines (N-sulfinyl imines), J ORG CHEM, 64(20), 1999, pp. 7559-7567
The one-step aza-Darzens reaction of sulfinimines 2 with lithium alpha-brom
oenolates readily affords diversely substituted cis and trans N-sulfinylazi
ridine 2-carboxylate esters 3 and 7 in good yield and excellent diastereose
lectivity. Higher yields, but lower de's, result when a mixture of the alph
a-bromo ester and 2 are treated with base. The N-sulfinyl group is transfor
med, nearly quantitatively, without ring opening, into the N-tosyl activati
ng group by oxidation with m-CPBA. Selective removal of the N-sulfinyl grou
p in aziridines 3a and 3h with TFA/H2O affords VI-aziridines 21 which are d
ifficult to prepared by other means. However, C(3) activated azirines such
as 3b undergo ring-opening under these conditions. Alternatively, the N-sul
finyl group, even in C(3)-activated aziridines, was selectively and efficie
ntly removed by treatment of the aziridine with 2 equiv of MeMgBr.