Room‐temperature potassium metal reduction of 1‐naphthyl isocyanate in THF results in a rapid cyclotrimerization (initiated by the 1‐naphthyl isocyanate anion radical) that generates two diastereoisomers (atropisomers) of tris(1‐naphthyl) isocyanurate. The formation of the syn and anti diastereoisomers was monitored by 1H and 13C NMR spectroscopy. Upon completion of the cyclotrimerization, the two diastereoisomers were isolated, and their configuration was assigned by NMR spectroscopy. Both compounds crystallize in the monoclinic C2/c space group, and single‐crystal X‐ray diffraction analyses confirm the structures of both isomeric forms. The results from this study prove that alkali metal reduction of isocyanates is a convenient and rapid method for generating isocyanurate compounds even when a sterically bulky substituent is attached to the NCO moiety.