Beginning with the reaction conditions of the CAA to form tertiary alkylamines, we investigated the synthesis of abranched secondary alkylamines by irradiating (with a 40 W blue LED) a dichloromethane solution of benzylamine (1a, 1 equiv), hydrocinnamaldehyde (2a, 1.2 equiv) and 2iodopropane (3.0 equiv) in the presence of (Me3Si)3Si-H (2.0 equiv), TBSOTf (2.0 equiv) and 4 Å MS. These conditions produced a complex mixture of degradation products, and none of the desired a-branched secondary amine 4a was detected by 1 H NMR analysis of the crude reaction mixture (entry 1, Table ). Surprisingly, when TBSOTf was omitted, 4a was formed in 11% assay yield (entry 2). We subsequently conducted a screen of Lewis acids, the key results of which are presented in Table . The use of 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) as an additive significantly improved the yield of 4a, as did the use of trimethylsilyl chloride (TMSCl) (entries 3 and 4). The combination of these two additives gave 4a with an assay yield of 52%, which proved to be optimal for this combination of amine and aldehyde. To our surprise, changing the linear aldehyde 2a to the a-branched aldehyde cyclohexanecarboxaldehyde (2b) resulted in a greatly enhanced yield of the corresponding a-branched secondary amine 4b in the absence of any additive (entry 6). The use of TBSOTf, again, had a detrimental effect on the reaction and, in contrast to the case of 2a, so did the addition of TMSCl (entries and). The addition of HFIP gave a small boost in the yield (entry 8). Interestingly, the combination of TMSCl and HFIP again proved optimal, providing 4b in 97% assay yield which could be isolated in 86% yield after reverse phase chromatography on C18. Given the efficacy of both HFIP and TMSCl as additives in these studies, we evaluated the use of both additives for the majority of substrate combinations.