A convenient one-pot three component synthesis of 3-aminoalkylated indoles catalyzed by 3-chlorophenylboronic acid

An efficient protocol was developed for the synthesis of 3-aminoalkylated indoles using 3-chlorophenylboronic acid as a catalyst under ambient temperature conditions. The three-component reaction of indoles, aromatic aldehydes and N-methyl aniline offered corresponding 3-aminoalkylated indoles in excellent yields. This protocol presents some remarkable features such as mild reaction conditions, simple workup procedure and excellent yields.     

Development of a novel, highly efficient halide-catalyzed sulfenylation of indoles

[reaction: see text] The reaction of a variety of indoles with N-thioalkyl- and N-thioarylphthalimides to produce 3-thioindoles is reported. Catalytic quantities of halide-containing salts are crucial to the success of this reaction. This highly efficient reaction provides sulfenylated indoles from bench-stable, readily available starting materials in good to excellent yields.     

Palladium(0)‐Catalyzed Intermolecular Allylic Dearomatization of Indoles by a Formal [4+2] Cycloaddition Reaction

Bridged indoline derivatives were synthesized by an intermolecular Pd‐catalyzed allylic dearomatization reaction of substituted indoles. The reaction between indoles and allyl carbonates bearing a nucleophilic alcohol side‐chain proceeds in a cascade fashion, providing bridged indolines in excellent enantioselectivity.     

Iodine-promoted selective 3-selanylation and 3-sulfenylation of indoles with dichalcogenides under mild conditions

A simple method was developed for the synthesis of 3-chalcogen indoles via iodine-promoted direct 3-selanyl- and 3-sulfenylation of indoles with dichalcogenides. The reaction was carried out smoothly in EtOH under air at room temperature, selectively giving a series of 3-chalcogen indoles bearing different functional groups in good to excellent yields. The procedure has the merits of environmental friendliness, easy operation, wide substrate scope and mild reaction conditions.     

Facile synthesis of 3,3-di(heteroaryl)indolin-2-one derivatives catalyzed by ceric ammonium nitrate (CAN) under ultrasound irradiation

Ceric ammonium nitrate efficiently catalyzes the reaction of isatin with indoles under sonic waves to afford symmetrical 3,3-di(indolyl)indolin-2-ones in excellent yields, as well as the reaction of 3-hydroxy-3-indolylindolin-2-ones with indoles, pyrrole to afford the corresponding adducts in excellent yields, which provides an efficient route to the synthesis of symmetrical and unsymmetrical 3,3-di(indolyl)indolin-2-one derivatives, respectively.     

Metal Free Mono‐ and 2,3‐Bis‐sulfenylation of Indoles in Water with Sodium Sulfinates as a Sulfur Source

An iodine‐PPh₃ mediated sulfenylation of indoles in water with stable and odorless sodium sulfinates as the sulfur source is described. The reaction could afford monosulfenylated indoles in moderate to excellent yields under metal free conditions. Moreover, double C—H sulfenylation of indoles at 2‐ and 3‐positions has also been achieved by using excess sodium sulfinates under the optimized reaction conditions.     

Direct synthesis of fused indoles by gold-catalyzed cascade cyclization of diynes

A direct, concise, and atom-economical synthetic method for the generation of fused indoles, using a gold-catalyzed cascade cyclization of diynes, has been developed. The reaction gave various fused indoles, such as aryl-annulated[a]carbazoles, dihydrobenzo[g]indoles, and azepino- or oxepinoindole derivatives in good to excellent yields, through an intramolecular cascade 5-endo-dig hydroamination followed by a 6- or 7-endo-dig cycloisomerization, without producing theoretical byproduct. Three of the resulting indoles exhibited potent antifungal activities against T. mentagrophytes and T. rubrum, demonstrating the practical application of the described cascade reaction for drug discovery.     

Highly enantioselective Friedel-Crafts reaction of indoles with 2-enoylpyridine 1-oxides catalyzed by chiral pyridine 2,6-bis(5',5'-diphenyloxazoline)-Cu(II) complexes

The catalytic enantioselective Friedel-Crafts reaction of indoles with 2-enoylpyridine 1-oxides has been studied in the presence of chiral pyridine 2,6-bis(5',5'-diphenyloxazoline)-Cu(II) complexes. The reaction furnished alkylated indoles in excellent yields (up to 97%) and enantioselectivities (up to 99% ee).     

Co/Mn-mediated oxidative cross-coupling of indoles with β-keto esters via dioxygen activation: an efficient access to ketonization-olefination of indoles

The Co/Mn-mediated oxidative cross-coupling of indoles with β-keto esters via dioxygen activation under mild conditions leads to ketonization-olefination of indoles. This reaction furnishes the highly functionalized products with excellent selectivity in good yields.     

A new approach to difficult Fischer synthesis: the use of zinc chloride catalyst in triethylene glycol under controlled microwave irradiation

[reaction: see text]. Application of triethylene glycol with catalytic quantity of zinc chloride (ZnCl2/TEG) is described as a new and efficient reaction medium for a difficult Fischer synthesis, leading to sensitive indoles. Transformation of the 3-acetyl-1-methylthiocycloalka[c]pyridine phenylhydrazones and p-methoxyphenylhydrazones into the 2-(2-pyridyl)indoles and 5-methoxy-2-(2-pyridyl)indoles, which are the synthons in our total synthesis of the sempervirine-type alkaloids, is carried out under controlled microwave irradiation in dry zinc chloride solution (0.16 M) in TEG. This protocol produces indoles from acetophenone or cyclohexanone via their phenylhydrazones in excellent yields.     

Sc(OTf)3: A Highly Efficient and Renewable Catalyst for Michael Addition of Indoles to Nitroolefins in Water

A catalytic amount of scandium trifluoromethanesulfonate [Sc(OTf)₃] (2.5 mol%) was used to catalyze the Michael addition of indoles to nitroolefins in water to afford the corresponding 3-alkylated indoles in good to excellent yields. The short reaction times, excellent yields, and renewability of the catalyst are noteworthy.     

Decatungstate-Photocatalyzed Dearomative Hydroacylation of Indoles: Direct Synthesis of 2-Acylindolines

We report herein a convenient and scalable dearomative hydroacylation reaction of indoles. Employing readily available aldehydes as the acyl source and TBADT as an inexpensive direct HAT photocatalyst, a variety of indoles derivatives were converted into synthetically interesting 2-acylindolines in good to excellent yields as well as great diastereoselectivity under mild conditions. An asymmetric version of the reaction was successfully developed and an experimental mechanistic investigation was carried out in order to gain further insights on the assumed reaction pathway.     

Myoglobin‐Catalyzed C−H Functionalization of Unprotected Indoles

Functionalized indoles are recurrent motifs in bioactive natural products and pharmaceuticals. While transition metal‐catalyzed carbene transfer has provided an attractive route to afford C3‐functionalized indoles, these protocols are viable only in the presence of N‐protected indoles, owing to competition from the more facile N−H insertion reaction. Herein, a biocatalytic strategy for enabling the direct C−H functionalization of unprotected indoles is reported. Engineered variants of myoglobin provide efficient biocatalysts for this reaction, which has no precedents in the biological world, enabling the transformation of a broad range of indoles in the presence of ethyl α‐diazoacetate to give the corresponding C3‐functionalized derivatives in high conversion yields and excellent chemoselectivity. This strategy could be exploited to develop a concise chemoenzymatic route to afford the nonsteroidal anti‐inflammatory drug indomethacin.     

Heterogeneous catalytic hydrogenation of unprotected indoles in water: a green solution to a long-standing challenge

An environmentally benign procedure for the hydrogenation of unprotected indoles is described. The hydrogenation reaction is catalyzed by Pt/C and activated by p-toluenesulfonic acid in water as a solvent. The efficacy of the method is illustrated by the hydrogenation of a variety of substituted indoles to their corresponding indolines which were obtained in excellent yields.     

Asymmetric Friedel-Crafts alkylations of indoles with nitroalkenes catalyzed by Zn(II)-bisoxazoline complexes

[reaction: see text] A novel asymmetric Friedel-Crafts alkylation of indoles with nitroalkenes catalyzed by Zn(II)-bisoxazoline complexes has been developed. The nitroalkylated indoles are synthesized in excellent yields and high enantioselectivities (up to 90% ee). The effects of ligand structure, metal salt, and solvent on the reaction are discussed. The substrates of the reaction can be aromatic, heteroaromatic, and even aliphatic nitroalkenes. The high reactivity and selectivity of the reaction are presumptively attributed to the activation and asymmetric induction of chiral Lewis acids coordinated by nitroalkene substrates through a 1,3-metal bonding model.     

N-Bromosuccinimide mediated synthesis of triazatruxenes from indoles

A new synthetic method for triazatruxenes from indoles is developed using N-bromosuccinimide (NBS) as a user-friendly reagent. Major reaction parameters including the amount of NBS, substrate concentration, temperature, addition rate and addition method are investigated. Additional experiments are also conducted in order to gain access toward the reaction mechanism. Compared to the use of Br₂ in the conventional method, this reaction requires less reaction time, provides better yields, and displays excellent reproducibility. The reaction can be conveniently performed at 10 g scale and it is also applicable to several substituted indoles, benzoindole, and N-alkyl indoles.     

One-pot access to indolo[2,3-b]quinolines by electrophile-triggered cross-amination/Friedel-Crafts alkylation of indoles with 1-(2-tosylaminophenyl)ketones

Activation of C2 and C3 of indoles by molecular iodine (I(2)) and base followed by in situ reaction with 1-(2-tosylaminophenyl)ketones or 2-tosylaminobenzaldehyde can afford highly substituted indolo(2,3-b)quinolines in moderate to excellent yields (up to 99%). The reaction provides a metal-free selective difunctionalization of indoles. The synthetic potential of the protocol has been illustrated by the synthesis of neocryptolepine and its 11-methyl analogue.     

First example of FeCl3-catalyzed alkylation of indoles with pinenes

Indoles undergo smooth alkylation with α- and β-pinenes in the presence of 20 mol % of anhydrous FeCl₃ under mild reaction conditions to produce a wide range of the corresponding 3-alkylated indoles in excellent yields with high trans-selectivity. This is the first example of alkylation of indoles with mono-terpenes.     

有机催化吲哚碳环上的不对称Friedel⁃Crafts烷基化反应

将金鸡纳碱衍生物双功能催化剂用于有机催化羟基吲哚与靛红的不对称Friedel-Crafts反应, 筛选出最佳反应条件: 催化剂为5%(摩尔分数)6′-脱甲基奎尼丁(1b), 溶剂为四氢呋喃, 反应温度 0 ℃. 以67%~91%的产率和最高达97%的对映选择性获得了苯环上取代的羟基烷基化产品. 拓宽了该反应的催化剂类型和底物范围.     

Direct synthesis of 3-arylindoles via annulation of aryl hydroxylamines with alkynes

3-Arylindoles are produced in moderate to excellent yields from the reaction between aryl hydroxylamines and alkynes catalyzed by 10 mol % iron(II) phthalocyanine [Fe(Pc)]. Terminal and internal alkynes afford 3-aryl substituted indoles exclusively. Electron-donating and -withdrawing groups are tolerated on the aryl hydroxylamine. A few bioactive indoles are synthesized as well as several new indoles using this one-step intermolecular annulation procedure.