text: A potential Curtin-Hammett scenario was also encountered during the enantioselective total synthesis of (+)-allocyathin B2 by the Trost group. The pivotal step in the synthesis was a Ru-catalyzed diastereoselective cycloisomerization. The reaction could result in the formation of two possible double bond isomers. The reaction provided good selectivity for the desired isomer, with results consistent with a Curtin-Hammett scenario. Initial oxidative cycloruthenation and beta-hydride elimination produce a vinyl-ruthenium hydride. Hydride insertion allows for facile alkene isomerization. It is unlikely that the reaction outcome mirrors the stability of the intermediates, as the large CpRu group experiences unfavorable steric interactions with the nearby isopropyl group. Instead, a Curtin–Hammett situation applies, in which the isomer favored in equilibrium does not lead to the major product. Reductive elimination is favored from the more reactive, less stable intermediate, as strain relief is maximized in the transition state. This produces the desired double bond isomer.