We initially examined the reaction between N-Bn triazinane 1a and two BCBs (BCB ketone 2a and BCB ester 2A) under B(C6F5)3 catalysis in dichloromethane (CH2Cl2) at room temperature for 24 h. To our delight, for BCB ketone 2a, the formal (4+3) cycloaddition did occur to yield the desired aza-BCO product 3a in 44% yield, while neither (3+2) cycloadduct 6a or cyclobutenyl methanamine 7a was detected (Table , entry 1). Interestingly, for BCB ester 2A, an unexpected butterfly-shaped biscyclobutenyl amine product 5a rather than (4+3) cycloadduct 3b was isolated in 58% yield without any (3+2) cycloadduct 6b or cyclobutenyl methanamine 7b observed (Table ). These outcomes motivated us to evaluate other reaction parameters for both reactions. For the formal (4+3) cycloaddition of 1a with 2a, a variety of Lewis acids were screened (Table ). Although the selected Lewis acids were all effective, none showed improvement over B(C6F5)3. Subsequently, several solvents including 1,2-dichloroethane (DCE), toluene and 1,1,1,3,3,3hexafluoro-2-propanol (HFIP) were evaluated, and toluene was found to be superior (Table , entries 10-12). Various other reaction parameters, such as additive, temperature, concentration and catalyst loading, were further optimized (see Supporting Information and Table , entries 13-15). The key improvement was the addition of 4Å molecular sieves (4Å MS) to prevent the hydrolysis of triazinane 1a and BCB ketone 2a (Table ). A control experiment revealed that no product 3a was formed in the absence of catalyst ). Notably, the competitive products 6a and 7a were not detected throughout the optimization studies. Finally, the optimal conditions were established as 10 mol% of B(C6F5)3 catalyst in CH2Cl2 at room temperature, offering product 3a in 61% yield (Table .