Scope and limitations in sulfur ylide mediated catalytic asymmetric aziridination of imines: use of phenyldiazomethane, diazoesters and diazoacetamides

Imine aziridination using diazo-compounds and catalytic quantities of metal salts and sulfides has been investigated. A range of imines derived from b enzaldehyde bearing electron-withdrawing groups (N-Ts, N-SO2CH2CH2SiMe3 (SE S), N-P(O)Ph-2, N-CO2Bn, N-CO2But, N-CO2(CH2)(2)SiMe3, N-CO2C(CH3)(2)CCl3) were prepared and tested in the aziridination process using Me2S and phenyl diazomethane. High yields were obtained with all imines but diastereoselect ivity varied considerably (3 : 1--> 10 : 1). A range of N-SES imines were t ested with stoichiometric amounts of sulfides and high yields were obtained with both aromatic and aliphatic imines. These imines were subsequently te stedwith stoichiometric and sub-stoichiometric loadings of enantiomerically pure 1,3-oxathiane 3 with Rh-2(OAc)(4) and with Cu(acac)(2). Good yields a nd high enantioselectivities (89-95%) were observed with Rh-2(OAc)(4), alth ough a small reduction in enantiomeric excess was observed with Cu(acac)(2) (85-95%) especially when sub-stoichiometric amounts of sulfide were employ ed. The same sulfide was also tested with a range of electron-withdrawing g roups on the imine nitrogen and in all cases good yields and high enantiose lectivities were maintained. Improved diastereoselectivity was observed wit h carbamate groups. The aziridination process was extended to include diazoester and diazoaceta mides with a range of N-Ts imines, and again good yields were obtained alth ough diastereoselectivity varied according to the diazo-compound employed. Although the 1,3-oxathiane 3 could not be employed with these more stable d iazo-compounds, (R,R)-2,5-dimethylthiolane 5 was found to be a suitable chi ral catalyst and gave moderate enantio- and diastereoselectivities. Rationa les for the origin of the diastereoselectivity and enantioselectivity are p rovided.