Next, the scope of the reaction in the aldehyde component was examined using benzylamine (1a) in combination with isopropyl iodide (3a, Figure ). The CAA reaction was welltolerant of alkyl aldehydes featuring a-branching (4q-u), and could accommodate useful functionalities. The successful transformation of an aldehyde containing a cyclopropyl motif to the expected amine product (4v) proceeded without any products arising from b-scission of the strained ring, strongly suggesting that the reaction does not proceed via an a-amino radical intermediate. A series of benzaldehydes also performed well in the CAA reaction (to 4w-y). Although aryl iodides are susceptible to reduction by the silyl radicals generated under our reaction conditions, reduction of alkyl iodides is generally faster; accordingly, we observed that abranched secondary amine product 4y derived from 3iodobenzeldehyde could be obtained in good yield with the aryl iodide moiety intact. Products containing Lewis-basic heterocycles could be readily accessed in good yields through the use of heteroarene-derived aldehydes (4z-aa) with HFIP as co-solvent. Although unbranched aldehydes were generally poor substrates when using benzylamine as the amine (entries 1-5, Table ), while evaluating the scope in the amine component we noticed that the performance of these substrates was markedly improved when a-branching was present in the amine (e.g. 4j-l, 4n-o). Accordingly, with 4-aminotetrahydropyran as the amine, product 4ab containing a remote alkene was formed from (±)citronellal in excellent yield. The use of 4-pentenal as the aldehyde provided a-branched secondary amine 4ac as the sole product, with no products derived from radical 5-exo-trig cyclisation detectable. This result contrasts to our previous study and suggests that, under the present conditions, the isopropyl radical adds to an uncharged imine, rather than cationic iminium, C=N bond. Indeed, performing the same reaction in the presence of 2 equivalents of TMSCl led to the formation of pyrrolidine product 4ac' in addition to 4ac. Pyrrolidine 4ac' presumably arises from a competing mechanism involving formation of an aminium radical cation (Int-II) which, in contrast to the corresponding neutral aminyl radical (Int-I), cyclises with a rate comparable to that of hydrogen atom transfer from the silane reductant (Figure ). The scope in the alkyl iodide component was explored using benzylamine (1a) in combination with hydrocinnamaldehyde (2a) or cyclohexanecarboxaldehyde (2b) (Figure ). Linear alkyl fragments derived from primary alkyl iodides could be added to the in situ-generated imine intermediates to form a selection of a-branched secondary alkylamines displaying a variety of functionality in generally good yields (4ad-aj). In these cases, we found the addition of two equivalents TMSCl to be beneficial-we speculate that this effect originates from the lower nucleophilicity of primary alkyl radicals, wherein full protonation (by in situ generated HCl) of the intermediate aldimine to generate a more electrophilic species is advantageous. Methyl iodide was productive in this process, but the yield of the amine product (4ad) was low and, in our hands, proved inseparable from the reductive amination byproduct. We were pleased to find that the fluoromethyl radical (derived from fluoroiodomethane) engaged in effective radical addition under these conditions, giving b-fluoroamine 4ah in synthetically useful yield. A C-Cl bond was retained through the reaction to deliver 4ai, which contains an electrophilic functional handle suitable for further elaboration, and use of an alkyl iodide derived from ethylene glycol provided protected g-amino alcohol 4aj. Pleasingly, incorporation of a ketone into the iodide component, which could theoretically compete with the aldehyde in the condensation step, resulted in the formation of aminoketone product 4ak in good assay yield, although we were unable to obtain a pure sample of this material. Cyclic secondary alkyl iodides of varying ring sizes and substitution were also good substrates (forming 4ak-al) and even tertiary alkyl iodides generated the hindered amine products (4am-an) in good yield. As observed in the scope of the amine and aldehyde components, classical reductive amination methods to form 4an-o would be challenging due to the difficulty in performing condensations at hindered ketones. Although a range of alkyl iodides are competent in this CAA reaction, our studies highlighted this as the component having the greatest impact on the success of the reaction. Specifically, the reaction is sensitive to the nucleophilicity of the carbon-centred radical; in the case of less nucleophilic radicals (such as primary radicals and/or those bearing proximal electron-withdrawing groups), reductive amination is observed as a significant by-product. For example, the use of 3-iodo-g-butyrolactone gave exclusively the product of reductive amination; none of desired product 4ao was observed.