We have previously reported a powerful dynamic resolution of phosphines under asymmetric Appel conditions.1 By exploring the origin of the stereoselection, the involvement of Berry pseudorotation in the selecting step was first ruled out. This was achieved through the synthesis, and use as test substrate, of cyclic phosphine, 2,3-dihydro-1-phenylbenzo<b>phosphole. This allowed us to develop a robust working hypothesis that the stereoselection is via dynamic kinetic resolution in the reaction of rapidly racemising chlorophosphonium salts (CPS) with a chiral auxiliary, leading to a pair of diastereomeric alkoxyphosphonium salts (DAPS). The diastereomeric excess (de) of the DAPS derived from a variety of enantiopure chiral alcohols was measured by 31P NMR, showing it to be consistent with the ultimate ee in the phosphine oxide products.2 In turn this enabled a screen of a variety of racemic  alcohols, allowing use of previously untested cyclohexanols without lengthy enantioselective syntheses. This then allowed us to probe the impact of sterics on stereoselection in a cost and time effective manner leading to a greater understanding of, and significant improvement in, stereoselection.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 product enantiomeric excess (ee)

Mechanistic study of the asymmetric oxidation of phosphines under Appel conditions: Understanding and improving the stereoselection

248th National Meeting (2014)

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