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Imine aziridination using diazo-compounds and catalytic quantities of metal salts and sulfides has been investigated. A range of imines derived from benzaldehyde bearing electron-withdrawing groups (N-Ts,CCl 3 ) were prepared and tested in the aziridination process using Me 2 S and phenyldiazomethane. High yields were obtained with all imines but diastereoselectivity varied considerably (3 : 1->10 : 1). A range of N-SES imines were tested with stoichiometric amounts of sulfides and high yields were obtained with both aromatic and aliphatic imines. These imines were subsequently tested with stoichiometric and sub-stoichiometric loadings of enantiomerically pure 1,3-oxathiane 3 with Rh 2 (OAc) 4 and with Cu(acac) 2 . Good yields and high enantioselectivities (89-95%) were observed with Rh 2 (OAc) 4 , although a small reduction in enantiomeric excess was observed with Cu(acac) 2 (85-95%) especially when sub-stoichiometric amounts of sulfide were employed. The same sulfide was also tested with a range of electron-withdrawing groups on the imine nitrogen and in all cases good yields and high enantioselectivities were maintained. Improved diastereoselectivity was observed with carbamate groups.The aziridination process was extended to include diazoester and diazoacetamides with a range of N-Ts imines, and again good yields were obtained although diastereoselectivity varied according to the diazo-compound employed. Although the 1,3-oxathiane 3 could not be employed with these more stable diazo-compounds, (R,R)-2,5-dimethylthiolane 5 was found to be a suitable chiral catalyst and gave moderate enantio-and diastereoselectivities. Rationales for the origin of the diastereoselectivity and enantioselectivity are provided. Scheme 1 Atkinson's aziridination. Scheme 2 Darzens-type addition of a bromoacyl sultam. Reagents and conditions: (i) RCH᎐ ᎐ NP(O)Ph 2 , LiHMDS, THF, Ϫ78 ЊC, 47-87% yield.

A range of 1,3-oxathianes based on camphorsulfonic acid have been prepared and tested in the catalytic asymmetric epoxidation of carbonyl compounds. It was found that the 1,3-oxathiane derived from acetaldehyde 5b gave the highest yield and enantioselectivity in the epoxidation process. The enantioselectivity was independent of the solvent and metal catalyst used (although yields were dependent on both). The optimum conditions were applied to a range of aldehydes, and good enantioselectivities and diastereoselectivities were observed. The origin of the enantioselectivity was probed, and in particular the role of the oxygen of the 1,3-oxathiane was investigated. Thus, the sulfur and carbon analogues of the camphorsulfonic acid based 1,3-oxathiane (derived from formaldehyde) were prepared (i.e., 1,3-dithiane and thiane analogues). With this series of analogues the steric effects are minimized so that the electronic effects can be investigated. The series of compounds was reacted in the catalytic cycle with benzaldehyde and gave stilbene oxides with 44% ee (sulfur analogue), 41% ee (1,3-oxathiane), and 20% ee (carbon analogue). Thus, it was concluded that the oxygen of the 1,3-oxathiane exerted a significant electronic effect in controlling the face selectivity of the ylide reactions. This electronic effect was a result of combined anomeric (higher with the sulfur analogue, not present with the carbon analogue) and Cieplak effects. A strong anomeric effect was observed in the X-ray structures of one of the 1,3-oxathianes, and an even greater one was observed in the corresponding sulfoxide (this was used as an electronic analogue of the ylide). The face selectivity of the ylide was believed to be complete in reactions with 5b. The minor enantiomer resulted from reaction of the minor conformer of the ylide, reacting again with high face selectivity. This was proven by using a more substituted diazo compound, which was expected to give much less of the minor conformer. Indeed, reaction with mesityldiazomethane gave the corresponding epoxide in essentially enantiomerically pure form.

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