- 1,2-functionalized imidazoles as palladium ligands: An efficient and robust catalytic system for the fluorine-free Hiyama reaction
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A variety of hydroxy- and amino-functionalized imidazoles were prepared from 1-methyl- and 1-(diethoxymethyl)imidazole by means of isoprene-mediated lithiation followed by reaction with an electrophile. These compounds in combination with palladium acetate were screened as catalyst systems for the Hiyama reaction under fluorine-free conditions using microwave irradiation. The systematic study of the catalytic system showed 1-methyl-2-aminoalkylimidazole derivative L1 to be the best ligand, which was employed un-der solvent-free conditions with a 1:2 Pd/ligand ratio and TBAB (20 mol-%) as additive. The study has revealed an interaction between the Pd/ligand ratio and the amount of TBAB. The established catalytic system presented a certain degree of robustness, and it has been successfully employed in the coupling of a range of aryl bromides and chlorides with different aryl siloxanes. Furthermore, both reagents were employed in an equimolecular amount, without an excess of organosilane.
- Martinez, Regina,Pastor, Isidro M.,Yus, Miguel
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supporting information
p. 872 - 877
(2014/03/21)
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- 1,2-Functionalized Imidazoles as Palladium Ligands: An Efficient and Robust Catalytic System for the Fluorine-Free Hiyama Reaction
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A variety of hydroxy- and amino-functionalized imidazoles were prepared from 1-methyl- and 1-(diethoxymethyl)imidazole by means of isoprene-mediated lithiation followed by reaction with an electrophile. These compounds in combination with palladium acetate were screened as catalyst systems for the Hiyama reaction under fluorine-free conditions using microwave irradiation. The systematic study of the catalytic system showed 1-methyl-2-aminoalkylimidazole derivative L1 to be the best ligand, which was employed under solvent-free conditions with a 1:2 Pd/ligand ratio and TBAB (20 mol-%) as additive. The study has revealed an interaction between the Pd/ligand ratio and the amount of TBAB. The established catalytic system presented a certain degree of robustness, and it has been successfully employed in the coupling of a range of aryl bromides and chlorides with different aryl siloxanes. Furthermore, both reagents were employed in an equimolecular amount, without an excess of organosilane.
- Martínez, Regina,Pastor, Isidro M.,Yus, Miguel
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supporting information
p. 872 - 877
(2015/10/05)
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- Isoprene-catalysed lithiation: deprotection and functionalisation of imidazole derivatives
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The isoprene-catalysed lithiation of different 1-substituted imidazoles (1) (such as trityl, allyl, benzyl, vinyl, N,N-dimethylsulfamoyl, para-toluenesulfonyl, tert-butoxycarbonyl, acetyl, trimethylsilyl, tert-butyldimethylsilyl derivatives) leads to the
- Torregrosa, Rosario,Pastor, Isidro M.,Yus, Miguel
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p. 947 - 952
(2007/10/03)
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- An Easily Introduced and Removed Protecting Group for Imidazole Nitrogen: A Convenient Route to 2-Substituted Imidazoles
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Orthoamides (3-5) prepared from imidazoles and triethyl or trimethyl orthoformate are rapidly metalated at -40 deg C in THF or ether to give the corresponding 2-lithio anion which reacts with a variety of electrophiles.The dialkoxymethyl protecting group is readily hydrolyzed under neutral or acidic conditions at room temperature, giving the 2-substituted 1H-imidazole 1 (R = H, X = COOH, n-C4H9, COCH3, CHOHC6H5, C(CH3)OH-2-pyridyl,9-hydroxyfluorenyl, 1-hydroxycyclohex-2-enyl, C(OH)(C6H5)2; R = CH3, R' = H, X = CHO) and the tris(2-imidazolyl)phosphines (R = H, CH3, CH(CH3)2).A mechanism for the deprotection of 3 is proposed.
- Curtis, N.J.,Brown, R.S.
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p. 4038 - 4040
(2007/10/02)
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