Enantio- and diastereoselectivities in chiral sulfur ylide promoted asymmetric aziridination reactions

Janardanan, Deepa ; Sunoj, Raghavan B. (2008) Enantio- and diastereoselectivities in chiral sulfur ylide promoted asymmetric aziridination reactions Journal of Organic Chemistry, 73 (21). pp. 8163-8174. ISSN 0022-3263

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Official URL: http://pubs.acs.org/doi/abs/10.1021/jo800652c

Related URL: http://dx.doi.org/10.1021/jo800652c

Abstract

Density functional theory investigation on the factors controlling enantio- and diastereoselection in asymmetric aziridination reaction by the addition of chiral bicyclic sulfur ylides to substituted aldimines is presented. High levels of enantioselection are predicted toward the formation of (2S,3S)-cis and (2R,3S)-trans aziridines by the addition of stabilized ylide (R = COMe) respectively to SO2Me and CO2Me protected aldimines. Similarly, high %ee is predicted for the formation of (2S,3R)-cis aziridines from semistabilized (R = Ph) ylide. Moderate to high levels of diastereoselectivity is noticed as well. The present study highlights that a correct prediction on extent of enantioselection requires the knowledge of the activation barriers for elementary steps beyond the initial addition step. In the case of stabilized ylides the ring-closure (or elimination of sulfur compound) is found to be crucial in controlling enantio- and diastereoselection. A cumulative effect of electronic as well as other weak interactions is identified as factors contributing to the relative energies of transition states leading to enantio- and diastereomeric products for the stabilized ylide addition to aldimines. On the contrary, steric control appears quite dominant with semistabilized ylide addition. With the smallest substituent on ylide (R = Me), high enantioselectivity is predicted for the formation of (2R,3R)-trans aziridines although the %de in this case is found to be very low.

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ID Code:109799
Deposited On:02 Aug 2017 11:30
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