Palladium-catalyzed cross-methylation of aryl triflates by intramolecularly stabilized dialkyl-aluminum, -gallium and -indium reagents

Synthesis and Characterization of Intramolecularly Stabilized Chiral Dimethylindium Alkoxides and their Use as Cross Coupling ReagentsProfessor Joachim Strähle zum 65. Geburtstag gewidmet

“…(ii) Oxidation state of the catalyst precursor. Although the cross-coupling of triflates by group 13-metal containing alkylation reagents is suggested to be catalyzed by Pd(0) rather than by Pd(II) catalysts [4], the reaction of 8 with 1 in the presence of Pd(OAc) 2 and binap as the in situ prepared catalyst system requires an excess of Pd(OAc) 2 to provide good results; i.e. divalent palladium has to be present in the reaction mixture.…”

“…Elemental analyses were performed on a Perkin-Elmer 240 C elemental analyzer. EI mass spectra were obtained using a Varian MAT 311 A spectrometer (70 eV (4). In analogy to the synthesis of 3, a solution of trimethylindium (1,77 g, 11 mmol) in toluene (20 ml) was treated with (S)-2-(dimethylamino)-4-(methyl)-1-pentanol (1,6 g, 11 mmol) in toluene (15 ml (5).…”

“…The same indium complex also smoothly cross-methylates bromophenols to give cresols, whereas the aluminium reagent is destroyed by such hydroxyl-containing substrates [3]. Furthermore, stabilized dimethylindium complexes methylate bromoarenes substituted by further electron withdrawing groups, a result which cannot be achieved by dimethylaluminium reagents [4]. Dialkylaluminium complexes with alkyl moieties containing β-hydrogen atoms tend to disproportionate in the presence of NiCl 2 (PPh 3 ) 2 into alkenes and aluminium hydrides.…”

Palladium-Catalyzed Cross-Methylation of Haloarenes Possessing Active Hydrogen Atoms by Intramolecularly Stabilized Dimethylindium and Dimethylaluminum Reagents

“…1b and 2b) do not attack carbonyl, cyano, bromomethyl or nitro groups, [1] but react rather slowly as cross-coupling reagents, and are often deactivated by electron-releasing groups located in the ortho or para positions. [4] The application of intramolecularly stabilized indium complexes was shown to overcome these shortcomings. Complexes 1c and 2c were found to react nearly as fast as the aluminum compounds, they are not deactivated by ring-bonded alkyl or alkoxyl groups, and do not attack vulnerable groups other than the ring-attached halide or triflate functions.…”

Palladium catalyzed cross‐methylation of bromoheterocycles with intramolecularly stabilized dimethyl indium reagents

“…Upon replacement of one of the alkyl groups by a chelating ligand such as the (3-dimethylamino)propyl group [2,3], the dialkylaluminum complexes, so formed, are safe enough for handling under standard laboratory conditions. [ propyl]dimethylaluminum (1 a) was successfully utilized in the alkylation of various carbonyl compounds [4], as well as in palladium-and nickelcatalyzed cross-methylation of carbocyclic aryl halides and triflates [5][6][7][8][9]. However, in all but one case [6] this mononuclear methylating reagent failed to couple with heterocyclic substrates, probably because of its tendency to form highly stable adducts v i a the lone pairs of the heteroatoms [10].…”