title: Iridium catalyzed carbocyclizations: efficient (5+2) cycloadditions of vinylcyclopropanes and alkynes.
abstract: Third-row transition metal catalysts remain a largely untapped resource in cycloaddition reactions for the formation of medium-sized rings. Herein, we report the first examples of iridium-catalyzed inter- and intramolecular vinylcyclopropane (VCP)-alkyne (5+2) cycloadditions. DFT modeling suggests that catalysis by iridium(I) proceeds through a mechanism similar to that previously reported for rhodium(I)-catalyzed VCP-alkyne cycloadditions, but a smaller free energy span for iridium enables substantially faster catalysis under favorable conditions. The system is characterized by up to quantitative yields and is amenable to an array of disubstituted alkynes and vinylcyclopropanes.
authors.affiliation: Centre for Analysis and Synthesis, Lund University, Box 124, 22100 Lund (Sweden).
authors.forename: Michaela-Christina
authors.initials: MC
authors.lastname: Melcher
authors.forename: Henrik
authors.initials: H
authors.lastname: von Wachenfeldt
authors.forename: Anders
authors.initials: A
authors.lastname: Sundin
authors.forename: Daniel
authors.initials: D
authors.lastname: Strand
keywords: cycloadditions; density functional calculations; homogeneous catalysis; iridium; seven-membered rings