- Fe(III)-Catalyzed, Cyclizative Coupling between 2-Alkynylbenzoates and Carbinols: Rapid Generation of Polycyclic Isocoumarins and Phthalides and Mechanistic Study
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FeCl3 catalyzed, highly regioselective cyclizative coupling of internal alkynes with alcohols has been reported for the rapid synthesis of structurally divergent, complex isocoumarins and phthalides respectively in intermolecular and intramolecular fashion. This strategy exhibited very high substrate scope and efficiency and proceeds through the simultaneous formation of C?O and C?C bonds. Observations from a series of control experiments supported a) the mechanism as Lewis acid catalyzed dual activation of ester and alcohol, b) the role of carbocation for the enhanced rates of cyclization, i. e., activation of alkyne by carbocation, and c) no role of HCl in the reported cascade process. (Figure presented.).
- Gandhi, Soniya,Baire, Beeraiah
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p. 2651 - 2657
(2020/05/25)
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- On homogeneous gold/palladium catalytic systems
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Two substrates containing an aryl iodide and an allenoate ester were prepared and the goldinduced cycloisomerisation to vinylgold(I) species and their proto-deauration as well as the intramolecular palladium-catalysed cross-coupling reactions were investigated. Switching to catalytic amounts of gold and palladium and stoichiometric amounts of silver did indeed furnish the product of a cycloisomerisation/ intramolecular cross-coupling. Control experiments revealed that silver cannot substitute for gold or palladium in these reactions, but a different palladium catalyst in a different oxidation state also afforded the cycloisomerisation/intramolecular crosscoupling products in only slightly reduced yields. By ICP analysis the palladium was shown to contain gold only at the sub-ppm level. This shows how carefully results obtained with such systems have to be interpreted. Then a series of allylic and benzylic o-alkynylbenzoates were investigated in gold-and palladium-catalysed reactions. For esters of benzyl alcohol and cinnamyl alcohol no palladium co-catalyst was needed for the conversion. All reagents were thoroughly checked for palladium traces by ICP analysis in order to thoroughly exclude a gold/palladium cocatalysis. Optimisation of the gold complex, counter ion and solvent showed that gold(I) isonitrile precatalysts and silver triflate as activator in dioxane are suitable to convert a number of substrates with aryl, alkyl and even cyclopropyl substituents. Crossover experiments proved an intermolecular allyl transfer.
- Hashmi, A. Stephen K.,Lothschuetz, Christian,Doepp, Rene,Ackermann, Martin,De Buck Becker, Janosc,Rudolph, Matthias,Scholz, Christian,Rominger, Frank
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p. 133 - 147
(2012/04/10)
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- Gold-catalyzed substitution reaction with ortho-alkynylbenzoic acid alkyl ester as an efficient alkylating agent
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ortho-Alkynylbenzoic acid alkyl esters behave as alkylating agents in combination with gold catalysts. The reaction with alcohols occurs smoothly in the presence of catalytic amounts of Ph3PAuCl and AgOTf under mild conditions to produce the corresponding ether products in high yields. The protocol is also useful for Friedel-Crafts alkylation and N-alkylation of sulfonamides. The reaction likely proceeds through the gold-induced in situ construction of leaving groups and subsequent nucleophilic attack of nucleophiles, such as alcohols, aromatic compounds, and sulfonamides.
- Aikawa, Haruo,Tago, Sakie,Umetsu, Kazuteru,Haginiwa, Naomichi,Asao, Naoki
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experimental part
p. 1774 - 1784
(2009/06/20)
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