Heterogeneous asymmetric aziridination of styrene using Cu2+ exchanged zeolite Y

Jeffs, Laura Ellen 2009. Heterogeneous asymmetric aziridination of styrene using Cu2+ exchanged zeolite Y. PhD Thesis, Cardiff University.

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Abstract

By synthesising S-2-phenyl-Af-(4-nitrophenyl)aziridine from S-phenylglycinol, it has been demonstrated that the aziridination of styrene by N-(4- nitrobenzenesulfonyl)imino phenyliodinane, (nosyliminophenyliodinane, PhlNNs) in the presence of tS',AS'-2,2,-isopropylidene-bis(4-phenyl-2-oxazoline), catalysed by copper(II) triflate in CH3CN solution or heterogeneously by CuHY, has predominantly an /-configuration. The enantioselectivity of the aziridination of styrene by Af-arenesulfonylimino-phenyliodinanes catalysed by copper-exchanged zeolite Y (CuHY), in conjunction with a chiral bis-oxazoline ligand, has been re examined. In the case of PhlNNs, it is shown that the product mixture of enantiomeric aziridines, on treatment with hexane, gives rise to a solid phase of low enantiomeric excess (ee) and a solution phase of high ee. Separation of the solid phase and recrystallisation afforded a true racemate (racemic compound), which has been confirmed by X-ray crystallography. The aziridine obtained from the solution phase could be recrystallised to produce the pure enantiomer originally in excess. A consequence of the new findings is that previous reports on the enantioselectivity of copper-catalysed aziridination, both in heterogeneous and homogeneous conditions, should be regarded with caution if the analytical procedure involved HPLC with injection of the enantiomeric mixture in a hexane-rich solvent. Such a method has been used in previous work from this laboratory, but has also been used elsewhere, following the procedure developed by Evans and co-workers when the (homogeneous) copper-catalysed aziridination by PhlNTs was first discovered. Evidently, the change of substituent in the benzenesulfonyl group reduces the solubility in hexane, affording a solution phase of enhanced ee.

Item Type:	Thesis (PhD)
Status:	Unpublished
Schools:	Chemistry
Subjects:	Q Science > QD Chemistry
ISBN:	9781303222917
Date of First Compliant Deposit:	30 March 2016
Last Modified:	19 Mar 2016 23:32
URI:	https://orca.cardiff.ac.uk/id/eprint/55128

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