Asymmetric Iridium(I)-Catalyzed Allylic Alkylation of Monosubstituted Allylic Substrates with Phosphinooxazolines as Ligands. Isolation, Characterization, and Reactivity of Chiral (Allyl)iridium(III) Complexes

Abstract

Ir I -catalyzed allylic alkylations of linear aryl-substituted allylic acetates proceed with enantiomeric excess of up to 95% ee using bidentate phosphinooxazolines as chiral ligands. The chiral (π-allyl)Ir III complexes 14 and 15 have been characterized by X-ray crystal structure analysis and spectroscopic data. The stoichiometric reaction between sodium dimethyl malonate and complex 14 proceeded with nucleophilic addition at the central allylic carbon as well as ligand exchange at Ir to give the iridacyclobutane complex 16, which was fully characterized. Complex 16 was transformed into (π-allyl)Ir III complexes by treatment with Lewis acid or iodine.

Mechanistic insights into the iridium-catalyzed hydrosilylation of allyl compounds

“…This is interesting due to reports on dimer opening by simple coordination of the double bond rather than via C-Cl activation [1,33]. However, it does not seem surprising since similar reactivities have been observed for reactions with allyl bromo/chloro derivatives [34,35]. With regard to 1 H NMR spectroscopy, the signals of [Ir(allyl)(Cl) 2 (COD)] at room temperature in CD 2 Cl 2 are particularly broad but measurements at À60°C reveal a very defined spectrum and in combination with 2D NMR experiments, two isomers in a ratio of 10:3 (different orientation of the allyl ligand) can be identified ( Fig.…”

Palladium-catalyzed cross-couplings of allylic carbonates with triarylbismuths as multi-coupling atom-efficient organometallic nucleophiles

“…The metal catalyzed reactions of allylic substrates are useful for a variety of synthetic transformations [1][2][3][4][5][6][7][8][9][10]. The reactivity profile of allylic carbonates differ from other allylic substrates in coupling reactions [11][12][13][14][15][16][17][18][19][20][21][22].…”

Iridium-Catalyzed Allylic Substitution

“…The alkylation products were isolated in nearly quantitative yield and were formed with ratios of branched-to-linear products up to 99:1 and with enantioselectivities up to 95% ee. In this and subsequent studies with PHOX ligands [51,52] [53] occurred with low enantioselectivity, and the regioselectivity was lower for the reactions of alkyl-substituted allylic esters than for the reactions of aromatic allylic esters. Thus, further studies on iridium-catalyzed allylic substitution with complexes of PHOX ligands have not been reported.…”

“…Attempts to generate a p-allyliridium(III) intermediate from the species containing L1 or ethylene as ligand led to complexes that neither catalyzed allylic substitution nor produced the expected branched allylation products upon exposure to a stoichiometric quantity of nucleophile [52].…”