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Iridium-catalyzed intramolecular [4 + 2] cycloadditions of alkynyl halides.

ABSTRACT: Iridium-catalyzed intramolecular [4 + 2] cycloadditions of diene-tethered alkynyl halides were investigated by using [IrCl(cod)](2) as catalyst, and dppe was found to be the most suitable phosphine ligand for the reaction. No oxidative insertion of the iridium into the carbon-halide bond was observed, and the reactions proceeded to provide the halogenated cycloadducts in good yield (75-94%). These results are the first examples of cycloadditions of alkynyl halides using an iridium catalyst.

SUBMITTER: Tigchelaar A

PROVIDER: S-EPMC3511010 | biostudies-literature | 2012

REPOSITORIES: biostudies-literature

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Iridium-catalyzed intramolecular [4 + 2] cycloadditions of alkynyl halides.

Tigchelaar Andrew A Tam William W

Beilstein journal of organic chemistry 20121016

Iridium-catalyzed intramolecular [4 + 2] cycloadditions of diene-tethered alkynyl halides were investigated by using [IrCl(cod)](2) as catalyst, and dppe was found to be the most suitable phosphine ligand for the reaction. No oxidative insertion of the iridium into the carbon-halide bond was observed, and the reactions proceeded to provide the halogenated cycloadducts in good yield (75-94%). These results are the first examples of cycloadditions of alkynyl halides using an iridium catalyst. ...[more]

PMID: 23209510

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Project description:Iron-catalyzed cross-coupling reactions using alkynyl nucleophiles represent an attractive approach for the incorporation of alkynyl moieties into organic molecules. In the present study, a multitechnique approach combining inorganic spectroscopic methods, inorganic synthesis, and reaction studies is applied to iron-SciOPP catalyzed alkynyl-alkyl cross-couplings, providing the first detailed insight into the effects of variation from sp2- to sp-hybridized nucleophiles on iron speciation and reactivity. Reaction studies demonstrate that reaction of FeBr2(SciOPP) with 1 equiv (triisopropylsilyl)ethynylmagnesium bromide (TIPS-CC-MgBr) leads to a distribution of mono-, bis-, and tris-alkynylated iron(II)-SciOPP species due to rapid alkynyl ligand redistribution. While solvents such as THF promote these complex redistribution pathways, nonpolar solvents such as toluene enable increased stabilization of these iron species and further enabled assessment of their reactivity with electrophile. While the tris-alkynylated iron(II)-SciOPP species was found to be unreactive with the cycloheptyl bromide electrophile over the average turnover time of catalysis, the in situ formed neutral mono- and bis-alkynylated iron(II)-SciOPP complexes are consumed upon reaction with the electrophile with concomitant generation of cross-coupled product at catalytically relevant rates, indicating the ability of one or both of these species to react selectively with the electrophile. The nature of the reaction solvent and Grignard reagent addition rate were found to have broader implications in overall reaction selectivity, reaction rate, and accessibility of off-cycle iron(I)-SciOPP species. Additionally, the effects of steric substitution of the alkynyl Grignard reagent on catalytic performance were investigated. Fundamental insight into iron speciation and reactivity with alkynyl nucleophiles reported herein provides an essential foundation for the continued development of this important class of reactions.

Dataset Information

Iridium-catalyzed intramolecular [4 + 2] cycloadditions of alkynyl halides.

Publications

Iridium-catalyzed intramolecular [4 + 2] cycloadditions of alkynyl halides.

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