engleski

Sulfur Ylide Promoted Synthesis of N-Protected Aziridines : A Combined Experimental and Computational Approach

A range of N-Ts, N-SES, N-Boc and N-oNs aziridines were prepared in moderate to good yield and with high enantiomeric excess of both isomers starting from N-protected imines, using a sulfonium salt derived from Eliel's oxathiane. Diastereo-selectivities of reactions are influenced by an imine N-protecting group, imine substituent and sulfide structure. An unusual cis selectivity was observed in the formation of N-Ts-2-phenyl-3-tert-butyl-aziridine and N-SES-2-phenyl-3-tert-butyl-aziridine, and was explained using computational investigations. The analysis suggests that betaine formation in the case of N-Ts-tert-butylaldimine aziridination using oxathiane benzyl sulphonium ylide 1’ is reversible and that the selectivity is determined at the rotation step, which is unusual for semistabilized ylide aziridination. We have shown here that the steric bulk of an imine substituent in combination with sterically demanding sulfonium ylide can also affect reversibility of the reaction. This is the first example of the sort in the case of aziridinations using semistabilized ylide.

aziridination ; ylide ; diastereoselectivity ; density functional calculations ; asymmetric synthesis

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