Encouraged by the above success, we then focused on the ringopening of aza-BCOs (Scheme 6). Gratifyingly, cleavage of the aminal group proved to be feasible under acidic conditions (1 M HCl in THF/H2O), and the transformation of 3a to the corresponding cis-cyclobutyl diamine 4a was effectively accomplished in 96% yield. A series of selected aza-BCOs from Scheme 2 were examined, all of which were successfully transformed to the ring-opening cis-cyclobutyl diamines in high yields (Scheme 6A). To prove our hypothesis of a one-pot procedure transforming BCBs into cis-cyclobutyl diamines, we reacted the model N-Bn triazinane 1a with BCB ketone 2a under condition A followed by treatment with acid, providing the target product 4a in 49% yield, albeit with a longer reaction time and more acidic reaction conditions (Scheme 6B). In addition, we noticed that N-PMP cycloadduct 3z was relatively unstable and slowly decomposed to 4z on silica gel or in CDCl3, thus the onepot procedure was more suitable for the reaction of N-PMP triazinane 1b with 2a, leading to product 4z in 80% yield. These results validated the feasibility of our conceptual "cycloaddition/ring-opening" strategy for the synthesis of ciscyclobutyl diamines from BCBs and triazinanes.