Next, we considered the choice of silane. As in the mechanistic studies of the racemic reaction, changing to PhSi(OiPr)H2 improved the asymmetric method to increase both yield and rate (Table 5, entry 3 vs 4). A variety of other silanes provided minimal to no conversion (see SI). Additionally, we tested methyl tert-butyl ether (MTBE) and observed a boost in yield of formation of 4d (Table , entry 5). The effects of all three changes were additive, with the highest yield resulting from Fe(dibm)3, PhSi(OiPr)H2, and MTBE with no significant change in er (Table , entry 6). We moved forward with these reaction conditions for an assessment of the impact of variations to the substrate on the overall reaction efficiency and selectivity.