A concise total synthesis of (+/-)-N-methyldibromoisophakellin, a member of the monomeric pyrrole- aminoimidazole alkaloid family isolated from the marine sponge Stylissa carbica, was achieved via a net [3 + 2] cycloaddition to install the cyclic guanidine. This ring annulation employs a 2-amido-1,3 aminoallyl cation obtained under oxidative conditions from variously N-substituted guanidines which in one instance led to isolation of a tetracycle bearing a carbinolamine center through subsequent benzylic oxidation. Finally, the serendipitous formation of a unique, related alkenyl guanidine, N-methy-lugibohlin, achieved via ring opening of cyclic guanidine under acidic conditions suggests that ugibohlin may be an artifact of isolation.(c) 2022 Elsevier Ltd. All rights reserved.