15 B(C6F5)3 toluene 52 31 In(OTf)3 HFIP 99 With the above two sets of optimal reaction conditions established, we first examined the substrate generality and limitations for the synthesis of aza-BCOs under condition A (Scheme 2). A diverse range of aryl BCB ketones successfully underwent this transformation (3a and 3c-p). In these cases, replacing the 2naphthyl BCB ketone with the bulkier 1-naphthyl one did not affect the reaction, yielding the corresponding cycloadduct 3c in 62% yield. The phenyl BCB ketone as well as those bearing a single electron-donating (methyl, methoxy) or electron-withdrawing (halogen, trifluoromethyl) substituent at random position of the phenyl ring was compatible with this transformation, producing the target aza-BCOs in moderate to good yields (3d-k). Particularly noteworthy is 3h, which contains an Ar-Br moiety available for further modifications via cross-couplings. The structure of 3h was comfirmed by X-ray structure analysis (CCDC 2363142). Moreover, both multi-substituted aryl and heteroaromatic (furan, thiophene) BCB ketones participated well in the reaction to furnish the desired products 3l-p in 38-67% yields. Encouragingly, alkyl BCB ketones, such as n-butyl-and cyclopentyl-substituted ones, were also suitable for the reaction, affording the aimed cycloadducts in 45% (3q) and 30% (3r) yields, respectively. Unfortunately, when 1,3-disubstituted BCB ketone was employed under condition A, no product 3s was detected.