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 α-bromoenolates readily affords diversely substituted cis and trans N-sulfinylaziridine 2-carboxylate esters 3 and 7 in good yield and excellent diastereoselectivity. Higher yields, but lower de's, result when a mixture of the α-bromo ester and 2 are treated with base. The N-sulfinyl group is transformed, nearly quantitatively, without ring opening, into the N-tosyl activating group by oxidation with m-CPBA. Selective removal of the N-sulfinyl group in aziridines 3a and 3h with TFA/H2O affords 1H-aziridines 21 which are difficult to prepared by other means. However, C(3) activated azirines such as 3b undergo ring-opening under these conditions. Alternatively, the N-sulfinyl group, even in C(3)-activated aziridines, was selectively and efficiently removed by treatment of the aziridine with 2 equiv of MeMgBr.