Sulfone Group as a Versatile and Removable Directing Group for Asymmetric Transfer Hydrogenation of Ketones.

The ketone precursor to 11 i (i.e., 10 i ) was prepared by addition of PhSO 2 CH 2 anion to the Weinreb amide PhCH 2 CONMe(OMe). The ATH [using formic acid/triethylamine (FA/TEA) 5:2 azeotrope] of 10 a – d revealed an unexpected trend in which the product ee value increased as the ring became smaller in the series from cyclohexyl ( 11 a , 87 % ee ) to cyclopropyl ( 11 d , 99 % ee ), although it remained high in each case (Figure 4 ).

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