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.

Graphical abstract

The chirality of 5,11‐disubstituted dibenzo[a,e]cyclooctatetraene ligands is represented by a two‐fold axis of symmetry in molecular monarch‐butterflies searching for flowers (metal centers). A flap of the butterfly wings will interconvert enantiomeric insects in the same way as dissymmetric cyclooctatetraenes racemize. The symmetry of the butterflies is broken both by the pattern of the wings and through a single antenna on each head. The latter represents the 5,11‐pattern of substitution that gives rise to exceptionally efficient asymmetric catalysis. More information can be found in the Communication by D. Strand et al. on page 2344.

Iridium Catalyzed Carbocyclizations: Efficient (5 + 2) Cycloadditions of Vinylcyclopropanes and Alkynes. -The first examples of iridium-catalyzed inter-and intramolecular vinylcyclopropane-alkyne (5+2) cycloadditions are reported. DFT modeling suggests that catalysis by iridium(I) proceeds through a mechanism similar to that previously reported for rhodium(I)-catalyzed vinylcyclopropane-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. -(MELCHER, M.-C.; VON WACHENFELDT, H.; SUNDIN, A.; STRAND*, D.; Chem. -Eur. J. 21 (2015) 2, 531-535, http://dx.