We have previously reported a powerful dynamic resolution of phosphines under asymmetric Appel conditions1 and seek to improve further its stereoselection and substrate scope. Our present working hypothesis is that the stereoselectivity arises from the reaction of the chiral auxiliary with a rapidly racemising chlorophosphonium salt (CPS) resulting in the formation of diastereomeric alkoxyphosphonium salts (DAPS). Initially a study was designed to probe stereoselection in a consistent manner, measuring (by 31P NMR) the diastereomeric excess (de)obtained from a variety of enantiopure commercial chiral alcohols at 0 �C.2 However a very useful aspect of this system is that it allows us to screen synthetic racemic alcohols and still determine de in the same way.The racemic auxiliary approach allowed access to previously untested cyclohexanols. The ability to vary the structure and measure stereoselectivity without lengthy enantioselective synthesis has allowed us to probe directly the impact of steric effects on stereoselection in a cost and time effective manner. This led to improvement in stereoselection from 82% to >90% at -78 �C 1. Bergin, E.; O' Connor, C. T.; Robinson, S. B.; Mc Garrigle, E. M.; O' Mahony, C. P.; Gilheany, D. G., J. Am. Chem. Soc. 2007, 129 , 9566; Rajendran, K. V.; Gilheany, D. G. Chem. Comunn. 2012, 80 , 100402. Diastereomeric excess (de) is used to facilitate comparison with the enantiomeric excess (ee) of the ultimate oxide products

Prediction of enantioselectivity using racemic chiral auxiliary: A study of stereoselectivity

248th National Meeting (2014)

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