Preparation of 3-arylmethylindoles as selective COX-2 inhibitors

The 3-arylmethylation of indoles using TMSOTf/Et₃SiH with a wide variety of substituted benzaldehydes has been accomplished. Under these mild Lewis acid mediated reductive conditions, it was demonstrated that indoles bearing both 6-MeSO₂ and 2-methyl substituents could be 3-arylmethylated in good to excellent yields to afford the corresponding 3-arylmethyl indoles, effective as selective COX-2 inhibitors. In addition, the viability of this method for the reductive alkylation of indoles by ketones was demonstrated and shown to be C-3 regioselective. For indoles bearing both a 6-MeSO₂ and 2-cyano substituent where this indole reductive alkylation methodology was unsuccessful, an unprecedented Pd(0) mediated arylorganozinc coupling with the requisite substituted 3-methylcarbonatomethylindole proved successful in affording the desired 2-cyano-6-MeSO₂-3-arylmethylindoles effective as selective COX-2 inhibitors.     

A new synthesis of 3-arylthioindoles as selective COX-2 inhibitors using PIFA

The direct 3-arylthiolation of 2-substituted indoles using phenyliodine(III)bis trifluoroacetate (PIFA) in (CF₃)₂CHOH with a wide variety of benzenethiols has been accomplished. In particular, indoles bearing a 6-MeSO₂ and either a 2-methyl or 2-carboxymethyl substituent could be 3-arylthiolated in good to excellent yields to afford the corresponding 3-arylthioindoles as selective COX-2 inhibitors. In a study varying the electronic nature of the 5-substituent of 2-CO₂Et indoles, it was discovered that the yield of the reaction improved as the substituent became more electron withdrawing. This result was consistent with a proposed mechanism involving benzenethiol displacement of an intermediate 3-IPh indole complex.     

Direct palladium-catalyzed C-3 alkynylation of indoles

The direct palladium-catalyzed coupling reaction of indoles with alkynyl bromides was described in this paper. In the presence of catalytic amount of PdCl₂(PPh₃)₂ and 2.0 equiv. NaOAc, the coupling reaction of indoles with alkynyl bromides proceeded smoothly at 50 °C to give the corresponding 3-alkynylindoles with high regioselectivity in good to excellent yields.     

Indirect regioselective heteroarylation of indoles through a Friedel-Crafts reaction with (E)-1,4-diaryl-2-buten-1,4-diones

A two-step synthesis of 3-heteroaryl indoles has been developed. The first step of the sequence involves a Friedel-Crafts alkylation of indoles with 1,4-diaryl-2-buten-1,4-diones to give the corresponding indoles bearing a 1,4-dicarbonyl moiety. The reaction is catalyzed by InCl₃ and takes place with good yields. Cyclization of the diones under different Paal-Knorr conditions allows to prepare indoles substituted at the C3 position with 3-furanyl, 3-pyrrolyl- and 3-thienyl moieties.     

I2O5 promoted iodosulfenylation of indoles under metal-free conditions

A mild, efficient, and metal-free strategy to construct 2-iodo-3-arylthioindoles was developed via I₂O₅-promoted iodosulfenylation of indoles utilizing simple, cheap and easily available thiophenols as sulfur sources. It is the first time that the iodothiolation difunctionalization of indoles at C-2 and C-3 positions was accomplished with the formation of 2-iodo-3-arylthioindoles in moderate to good yields.     

通过η~3-苄基钯中间体零价钯催化的吲哚苄基化反应(英文)

本文报道了零价钯催化的吲哚苄基化反应,获得了优秀的区域选择性.使用Pd(PPh3)4作为催化剂,在温和反应条件下,以90%–99%的收率获得含有各类取代吲哚片段的三芳基甲烷化合物.     

Highly Efficient InBr3 Catalyzed Michael Addition of Indoles to α, β-Unsaturated Esters

A highly efficient synthetic strategy toward Michael addition of indoles to α,β‐unsaturated esters has been developed using Lewis acid InBr₃ as catalyst. The reactions generated 3‐substituted indoles in high yields with excellent regio‐selectivity in the presence of catalytic amount of InBr₃ under mild reaction conditions. The method is simple, efficient and practical.     

Cs2CO3-catalyzed alkylation of indoles with trifluoromethyl ketones

A Cs₂CO₃-catalyzed alkylation reaction of indoles with trifluoromethyl ketones was presented. Both alicyclic and aromatic trifluoromethyl ketones as well as various substituted indoles are compatible with the methodology. Good to excellent yields of the corresponding trifluoromethyl substituted tertiary alcohols 2,2,2-tritrifluoro-1-(1H-indol-3-yl)-ethan-1-ols were acquired as the sole products.     

Direct Catalytic Asymmetric and Regiodivergent N1- and C3-Allenylic Alkylation of Indoles

Herein we report a Pd-catalyzed asymmetric allenylic alkylation strategy for the direct functionalization of 1H-indoles by employing P-chiral BIBOP-type ligands. The regioselectivity (N1/C3) of this process can be switched efficiently. Using Cs₂CO₃ at elevated temperatures in MeCN, N1-alkylated indoles bearing axial chirality with a stereocenter non-adjacent (β) to the nitrogen are produced in good yields with high enantioselectivity and complete N1-regioselectivity regardless of the electronic properties and substitution patterns of diverse indoles. Using K₂CO₃ at room temperature in CH₂Cl₂, chiral C3-alkylated indoles can also be obtained. Notably, we introduce a new class of tri-substituted allenylic electrophiles that proceeded through different pathways from di-substituted allenylic electrophiles.     

FeCl3 as Lewis acid catalyzed one-pot three-component aza-Friedel-Crafts reactions of indoles, aldehydes, and tertiary aromatic amines

A new strategy for the synthesis of 3-diarylmethyl indoles was developed through FeCl₃ as Lewis acid catalyzed three-component aza-Friedel-Crafts reactions of indoles, aldehydes, and tertiary aromatic amines in one-pot. The reactions generated the corresponding 3-diarylmethyl indoles in good yields under mild reaction conditions by using less expensive, readily available, and environmentally benign iron catalyst. It is important to note that the key feature of this reaction is operational simplicity.     

Ruthenium(II)‐Catalyzed C−H Activation of Imidamides and Divergent Couplings with Diazo Compounds: Substrate‐Controlled Synthesis of Indoles and 3H‐Indoles

Indoles are an important structural motif that is commonly found in biologically active molecules. In this work, conditions for divergent couplings between imidamides and acceptor–acceptor diazo compounds were developed that afforded NH indoles and 3H‐indoles under ruthenium catalysis. The coupling of α‐diazoketoesters afforded NH indoles by cleavage of the C(N₂)?C(acyl) bond whereas α‐diazomalonates gave 3H‐indoles by C?N bond cleavage. This reaction constitutes the first intermolecular coupling of diazo substrates with arenes by ruthenium‐catalyzed C?H activation.     

InBr3 as a versatile and highly efficient catalyst for the synthesis of 3-allyl- and 3-benzylindoles

Indoles undergo smooth alkylation with allylic and benzylic alcohols in the presence of 10 mol % of InBr₃ under mild conditions to produce 3-allyl- and 3-benzyl indoles, respectively, in excellent yields and with high selectivity. This is the first example of the alkylation of indoles with benzylic alcohols using InBr₃ as an acid catalyst.     

Diastereoselective Ruthenium-Catalyzed Michael Addition of Indoles to Hormone Steroids: An Efficient Route to New Indole Derivatives

Diastereoselective conjugate 1,4-addition of indoles to α,β-unsaturated carbonyl compounds (hormone steroids) using Ru(III) as catalyst is reported. It was found that RuCl₃·nH₂O catalyzes the Michael addition of indoles to hormone steroids, providing new 3-alkylated derivatives in good to 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.     

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.     

Novel gallium-mediated C3-allylation of indoles and pyrroles in aqueous media promoted by Bu4NBr

A mild and efficient protocol for the coupling of indoles and pyrroles with allyl halides such as allyl bromide, crotyl bromide and propargyl bromide in the presence of gallium metal in a Bu₄NBr-DMF-H₂O system has been developed. The reaction is equally effective when cadmium is used in lieu of gallium and the corresponding 3-allyl indoles and 3-allyl pyrroles were obtained in almost comparable yields.     

Csp-Csp bond formation via Lewis acid/ammonium salt cocatalyzed tandem addition and oxidative dehydrogenation strategy: alkenylation of indoles with α,β-unsaturated ketones

The alkenylation of indoles with α,β-unsaturated ketones through a tandem addition and oxidative dehydrogenation strategy has been developed. This method provides an alternative approach for C3 alkenylation of indoles with α,β-unsaturated ketones. Using inexpensive and readily available BF₃·Et₂O and an ammonium salt as the efficient cocatalyst constitutes the attractive advantage of this reaction.     

Cyclization Studies with N-Mannich bases of 2-substituted indoles

The synthesis of the indoles 7 , 15 , 16 with a 3-methoxyphenyl group, attached via an α-side chain of 1,2,or 3 CH₂ units, is reported. These compounds, after appropriate protection at C(3), were transformed into the N-[(dimethylamino)methyl]indoles 22 , 23 , and 24 , respectively. When treated with AcCl, these N-Mannich bases gave, in two cases, stable N-(chloromethyl)indoles 25 and 26 . In the presence of SnCl₄, ring closure occurred via electrophilic attack of 1-methylideneindolium ions on the methoxyphenyl group. Formation of seven-membered rings (→ 27 , 28 ) and eight-membered rings (→ 29 ) was found to be a favorable process. Cyclization to six-membered rings did not occur within this series.     

Palladium‐Catalyzed Direct C2 Arylation of N‐Substituted Indoles with 1‐Aryltriazenes

A novel and efficient palladium‐catalyzed C2 arylation of N‐substituted indoles with 1‐aryltriazenes for the synthesis of 2‐arylindoles was developed. In the presence of BF₃ ? OEt₂ and palladium(II) acetate (Pd(OAc)₂), N‐substituted indoles reacted with 1‐aryltriazenes in N,N‐dimethylacetamide (DMAC) to afford the corresponding aryl–indole‐type products in good to excellent yields.     

A rapid stereoselective C-glycosidation of indoles and pyrrole via indium trichloride promoted reactions of glycosyl halides

Various C-glycosyl indoles and pyrroles were synthesized within a few minutes through coupling acetobromo sugars with suitably substituted indoles and pyrrole in the presence of catalytic amounts of InCl₃ at room temperature. Most of the glycosylations proceeded with a high stereoselectivity.