Matsumoto N, Hwang T, Romo D. Total Synthesis of (±)-
N-Methyldibromoisophakellin and
N-Methylugibohlin via Net [3+2] Cycloguanidinylations Employing 2-Amido-1,3-Diamino-Allyl Cations.
Tetrahedron Lett 2023;
115:154304. [PMID:
36777739 PMCID:
PMC9914522 DOI:
10.1016/j.tetlet.2022.154304]
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Abstract
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-methylugibohlin, achieved via ring opening of cyclic guanidine under acidic conditions suggests that ugibohlin may be an artifact of isolation.
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