Having identified a chiral thiol catalyst, C1, and optimized reaction conditions that led to observation of significant er values, we assessed the mutual influences of different substrate features and selectivity with a number of prochiral substrates (Scheme 7). Namely, we tested a variety of thiazolidines as well as two cyclic ureas, with various functional groups and substituents of varying steric demand. In general, we examined two sets of conditions as defined in Scheme 7. In Conditions A, we used Fe(acac)3, PhSiH3, and dioxane, whereas in Conditions B, we used Fe(dibm)3, PhSi(OiPr)H2, and MTBE as defined by the mechanistically-guided optimization. We found that Conditions B resulted in a near-uniform yield increase across substrates and similar-to-increased er, in comparison to Table . Screening conditions for internal olefin a Percent yield determined by GC-FID with a calibration curve. b Enantiomeric ratio (er) determined by HPLC with a chiral stationary phase. Peaks reported in order of elution. c Percent conversion to product determined by GC-FID as the crude ratio of starting material to product peaks. original Conditions A. These improvements highlight the ability of our mechanistic investigations to improve the enantioselective catalysis.