Allylation Of Indoles Research Articles

Mn(I)‐Catalyzed C−H Allylation of Indoles with 2‐Vinylaziridines

AbstractMn(CO)5Br‐catalyzed reaction of 1‐(2‐pyrimidyl)indoles with 1‐sulfonyl‐2‐vinylaziridines in THF in the presence of 0.25 equiv. of NaOAc affords 2‐allylated indoles in 31 % to 100 % yields. The protocol suits for 3‐, 4‐, 5‐, 6‐, and 7‐substituted indoles and N‐(2‐pyrimidyl)pyrroles as well as various 1‐(arylsulfonyl)‐2‐vinylaziridines such as 1‐(phenylsulfonyl)‐2‐vinylaziridine, 1‐(naphthalen‐2‐ylsulfon‐yl)‐2‐vinylaziridine, and 1‐(substituted phenylsulfonyl)‐2‐vinylazirid‐ines. Functional groups including alkyl, alkoxy, halogen, CHO, COOMe, CF3, CN, and NO2 groups are tolerated.

Theoretical studies on the mechanism of Ru(ii)-catalyzed regioselective C-H allylation of indoles with allyl alcohols.

The reaction mechanism of the Ru(ii)-catalyzed regioselective C-H allylation of indoles with allyl alcohols has been studied by density functional theory (DFT) calculations. This reaction mechanism involves five major steps: deprotonation of amide-NH, arene C-H activation, allyl alcohol insertion, β-OH elimination and protonation. Our calculation results indicate that C2-H bond allylation is better than C7-H bond allylation, which can be attributed to the stronger nucleophilicity of C2 compared to C7 in the C-Ru bond insertion of indole substrates. Furthermore, we also suggest that C-Ru bond insertion is more favorable than N-Ru bond insertion, which can be attributed to the different hybridization states of the relevant carbon and nitrogen atoms. Meanwhile, we also illustrate that the substrate cinnamyl alcohol cannot give the desired product due to the steric hindrance of the phenyl ring in cinnamyl alcohol with the indole skeleton.

Ruthenium-Catalyzed Stereoselective C–H Allylation of Indoles

Key words ruthenium catalysis - allylation - indoles - allyl alcohols

Ruthenium(II)-Catalyzed Regio- and Stereoselective C-H Allylation of Indoles with Allyl Alcohols.

A ruthenium-catalyzed C-H allylation of indoles with allyl alcohols via β-hydroxide elimination is reported. Without external oxidants and expensive additives, this reaction features mild reaction conditions, compatibility with various functional groups, and good to excellent regioselectivity and stereoselectivity.

Rhodium(iii)-catalyzed C-H allylation of indoles with allyl alcohols via β-hydroxide elimination.

An efficient Rh(iii)-catalyzed dehydrative C-H allylation of indoles with allyl alcohols via β-hydroxide elimination under oxidant-free conditions has been developed. This method features very mild reaction conditions, excellent regioselectivity and stereoselectivity, and compatibility with various functional groups. In addition, the directing group can be removed under mild reaction conditions, which further underscores the synthetic utility of this method.

Manganese-catalyzed direct C2-allylation of indoles

Development of manganese-catalyzed synthesis of functionalized indoles is reported. This method involves direct C–H activation and allylation of indoles with broad substrate tolerance, leading to a series of C2-allylated indole derivatives under mild reaction conditions.

Rhodium(iii)-catalyzed directed C–H benzylation and allylation of indoles with organosilicon reagents

Rhodium(iii)-catalyzed C2-benzylation and allylation of indoles with organosilicon reagents via chelation-assisted C–H activation has been developed.

Catalytic C‐2 Allylation of Indoles by Electronic Modulation of the Indole Ring and its Application to the Synthesis of Functionalized Carbazoles

AbstractWe report a palladium‐catalyzed C‐2 allylation of indoles and subsequent cyclization of the allylated indoles. The electronic effects of chloro and ester groups that can be readily installed at the C‐3 position of indoles facilitated a highly efficient C–H allylation at the C‐2 position. The resulting 2‐allyl‐3‐chloroindoles were found to be suitable substrates for benzannulation reactions with alkynes and norbornadiene as an acetylene synthon. This approach, utilizing readily available indoles, allyl acetates, and norbornadiene, allows a rapid access to complex carbazoles.magnified image

ChemInform Abstract: Ruthenium‐Catalyzed, Site‐Selective C—H Allylation of Indoles with Allyl Alcohols as Coupling Partners.

AbstractThe site‐selectivity of the mono‐selective method is based on the use of an N‐pyridyl directing group which may be cleaved off without or with significant isomerization of the products′ allyl group.

Ruthenium-Catalyzed, Site-Selective C-H Allylation of Indoles with Allyl Alcohols as Coupling Partners.

A new ruthenium-catalyzed, heteroatom-directed strategy for C-H allylation of indoles is described. The use of allyl alcohols as coupling partners as well as pyridine as the removable directing group is highlighted. This methodology provides access to C2-allylated indoles by utilizing a strategy that does not require prefunctionalization of either of the coupling partners.

ChemInform Abstract: Iridium‐Catalyzed C‐3 Allylation of Indoles with Allylic Alcohols Promoted by a Broensted Acid.

AbstractAttempts upon an asymmetric allylation using a chiral bisoxazoline ligand provide only racemic product.

Mild and Efficient Allylation of Indoles and Amides Using Amberlyst-15 as a Recyclable Heterogeneous Catalyst

A mild and efficient allylation of indoles and amides in the presence of a catalytic amount of Amberlyst-15 has been described in this context. The recyclable heterogeneous catalytic system is practical and facile for the synthesis of C- and N-allylated derivatives and would be of importance for the development of the accordingly functional complex molecules.

Efficient and Metal-Free Friedel-Crafts Alkylation of Indoles with Allyl Acetate Mediated by TFE

An efficient, metal-free and chemo-selective Friedel-Crafts allylation of indoles in 2,2,2-trifluoroethanol (TFE) is developed. A possible mechanism has also been discussed to explain the observed competitive pathways in this reaction system.

ChemInform Abstract: Rapid, Selective Ru‐Sulfonate‐Catalyzed Allylation of Indoles Using Alcohols as Substrates.

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Rapid, Selective Ru-Sulfonate-Catalyzed Allylation of Indoles Using Alcohols as Substrates

The Ru-catalyzed allylation of differing indole compounds using ArCH(OH)CH═CH2 (Ar = Ph, 2-CH3C6H4, 2-CH3OC6H4 2-ClC6H4, and 1-naphthyl) is relatively fast (usually <30 min for 100% conversion) at ambient temperature in the presence of [Ru(Cp*)(CH3CN)3](PF6) + a sulfonic acid cocatalyst, RSO3H (R = p-tolyl, a camphor fragment or CH3). The new catalysts allow allyl alcohols rather than carbonates, halides, acetates, etc., to be used as substrates in this allylation chemistry, thereby avoiding the use of a (wasted) leaving group. The branched products are favored, and in a number of examples b/l ratios in excess of 20 are observed. The catalyst is selective in that there is little or no N-allylation. The use of acids such as CF3SO3H or HBF4 results in slower and/or less selective reactions. Although phosphoric acid additives show some promise, carboxylic acids are much less effective or do not catalyze the reaction at all. The preformed isolated complexes [Ru(Cp*)(η3-C3H5)(RSO3)2] are efficient catalyst precursors; however, NMR experiments suggest that one of the active species is the monosulfonate cationic complex [Ru(Cp*)(η3-C3H5)(CH3CN)(RSO3)]+. Stoichiometric oxidative addition reactions are shown to be relatively rapid. New Ru(Cp*) complexes have been generated and characterized by NMR methods. DFT calculations suggest that the large b/l ratios observed have a structural basis in that the Ru−C(allyl) bond length for the substituted terminal allyl carbon, Ru−C(1), is relatively long. X-ray structures for Ru(Cp*)(η3-C3H5)(SO4) and the dication [Ru(Cp*)(η3-C3H5)(H2O)2]2+ (as a camphor sulfonate salt) are reported.