Palladium-Catalyzed Synthesis of 2-(Aminomethyl)indoles from 3-(o-Trifluoroacetamidoaryl)-1-propargylic Alcohols and Amines (original) (raw)
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Heterogeneous palladium catalysts ([Pd(NH 3) 4 ] 2 þ /NaY and [Pd]/SBA-15) were applied to the synthesis of 2-functionalised indoles, giving generally high conversions and selectivities (> 89% yield) using only 1 mol % [Pd]-catalyst under standard reaction conditions (polar solvent, 80 8C). For the synthesis of 2,3-functionalised indoles by crosscoupling arylation, the [Pd]/SBA-15 catalyst was found to be particularly interesting, producing the expected compound with ¼ 35% yield after 12 days of reaction, which is comparable to the homogeneous catalyst, Pd(OAc) 2 (¼ 48% yield). In the course of the study, the dual reactivity of the indole nucleus was demonstrated: aryl bromides gave clean C À C coupling while aryl iodides led to a clean C À N coupling.
Tetrahedron, 2009
a b s t r a c t 3-(o-Trifluoroacetamidoaryl)-1-propargylic esters have been used as common synthetic intermediates for the preparation of a variety of 3-unsubstituted 2-substituted indoles. Treating ethyl 3-(o-trifluoroacetamidoaryl)-1-propargylic carbonates unsubstituted or containing an aryl substituent at the propargylic carbon with piperazines and Pd(PPh 3 ) 4 in THF at 80 C affords 2-(piperazin-1-ylmethyl)indoles in excellent yields. Good to excellent yields of 2-aminomethylindoles are also obtained with other secondary amines. Ethyl 3-(o-trifluoroacetamidoaryl)-1-propargylic carbonates bearing an alkyl substituent at the propargylic carbon and ethyl 3-(o-trifluoroacetamidoaryl)-1-propargylic acetates disubstituted at the propargylic carbon give 2-vinylic indoles with the Pd(OAc) 2 /PPh 3 combination and Et 3 N in THF at 80 C. Formation of 2-vinylic indoles is quite stereoselective, generating trans vinylic derivatives, at least with the substrates that we have investigated. In the presence of formic acid, Et 3 N, and Pd(PPh 3 ) 4 in MeCN at 80 C, ethyl 3-(o-trifluoroacetamidoaryl)-1-propargylic carbonates afford 2-alkylindoles in good to excellent yields. Tetrahedron j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / t e t range of ethyl 3-(o-trifluoroacetamidoaryl)-1-propargylic carbonates into the corresponding 2-aminomethylindoles. Compound 1a
Advanced Synthesis & Catalysis, 2013
The bis(acetonitrile)palladium(II) chloride complex, PdCl 2 A C H T U N G T R E N N U N G (MeCN) 2 , efficiently catalyzes the regioselective alkylation of indoles with various benzylic and allylic alcohols under moisture and air insensitive conditions. Notably the reaction does not require any other co-catalyst, acid, base, additive, or external ligand.
The Journal of Organic Chemistry, 2006
New functionalizations of indoles via palladium-catalyzed reaction of indoles and 2-acetoxymethyl-substituted electrondeficient alkenes are reported. It was found that for Nprotected indoles the reaction proceeded smoothly in the presence of 5 mol % of Pd(acac) 2 and 10 mol % of PPh 3 at 80°C in HOAc, while for N-unprotected indoles, the reaction was carried out by using 5 mol % of Pd(dba) 2 or 2.5 mol % of Pd 2 (dba) 3 ‚CHCl 3 with 10 mol % of 2,2′-bipyridine as the catalyst in toluene. This strategy allows the selective installation of electron-deficient olefin functionality at the 3-position of indoles, which might be difficult to obtain by other methods and can be further elaborated.
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Given the prevalence of the indole nucleus in biologically active compounds, the direct C3functionalization of 2,3-disubstituted indoles represents an important problem. Described is a general, high-yielding method for the palladium-catalyzed β-allylation of carba-and heterocycle fused indoles, including complex natural product substrates.