Aza-Darzens asymmetric synthesis of N-(p-toluenesulfinyl) aziridine 2-carboxylate esters from sulfinimines (N-sulfinyl imines)

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.