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.

Rhodium(I)‐Catalyzed Bridged [5+2] Cycloaddition of cis‐Allene‐vinylcyclopropanes to Synthesize the Bicyclo[4.3.1]decane Skeleton

“…[3,4] In 1995, Wender et al first reported the intramolecular rhodium-catalyzed cycloaddition of VCPs with alkynes. [10] In addition, the intermolecular cycloadditions of VCPs with p-systems [11][12][13] and other transition metal catalyzed [5+ +2] cycloadditions [14,15] have been reported. [10] In addition, the intermolecular cycloadditions of VCPs with p-systems [11][12][13] and other transition metal catalyzed [5+ +2] cycloadditions [14,15] have been reported.…”

Cobalt‐Catalyzed Intramolecular Reactions between a Vinylcyclopropane and an Alkyne: Switchable [5+2] Cycloaddition and Homo‐Ene Pathways

“…[3][4][5][6] Meanwhile,t he intramolecular VCP/alkyne cycloaddition has also been catalyzed by other transition metals, such as ruthenium, [7] nickel, [8] iron, [9] and iridium. [10] Depending on the transition metal, the VCP/alkyne cycloaddition is proposed to involve either alkyne/alkene oxidative cyclization to form am etallacyclopentene A (for Ru, [11] Ni, [12] and Fe [9] )orcyclopropane cleavage to form ametallacyclohexene B (for Rh [13] and Ir [10] )a st he initial step (Scheme 1). Intermediates A and B would converge to am etallacyclooctadiene C through b-carbon elimination and migratory insertion, respectively,a nd C À Cr eductive elimination of this common intermediate would lead to the cycloheptadiene product.…”

Control of Enantioselectivity in Rhodium(I) Catalysis by Planar Chiral Dibenzo[a,e]cyclooctatetraenes

“…[1] More recently,d bCOT has found prominence as ab is-h 2 -ligand that confers exceptionalc atalytic activity and stabilityt ol ate transition metals. Notable examples in which dbCOT-metal complexes are known to exhibit superiorp erformance in catalysis spansi ridium(I)-catalyzed allylic substitutions, [2] rhodium(I)catalyzed polymerizations, [3] ruthenium(0)-catalyzed coupling reactions, [4] and rhodium(I)- [5a,b] and iridium(I)-catalyzed [6] cycloaddition reactions. Examples of chiral dbCOTsa sl igandst o transition metals are, on the other hand,s carce.…”