Chiral Brønsted acid catalyzed Friedel-Crafts alkylation reactions

Enantioselective synthesis of cyclic quaternary α-amino acid derivatives by chiral phosphoric acid catalysis

A highly enantioselective aza-Friedel-Crafts reaction of N-sulfonyl cyclic ketimines with indoles catalyzed by chiral phosphoric acids has been developed. This methodology provides an efficient and facile route to indole-containing chiral cyclic α-amino acid derivatives bearing a quaternary stereocenter in high yields and up to 98% enantioselectivity.

Catalytic asymmetric total syntheses of myrtucommuacetalone, myrtucommuacetalone B, and callistrilones A, C, D and E

Herein, we describe a concise catalytic approach to the first asymmetric total syntheses of myrtucommuacetalone, myrtucommuacetalone B, and callistrilones A, C, D and E. The syntheses proceed in only 5-7 steps from the readily available compound 11, without the need for protecting groups. Key features of the syntheses include a unique organocatalytic asymmetric Friedel-Crafts-type Michael addition with high enantioselectivity and a broad substrate scope, a novel Michael-ketalization-annulation cascade reaction, and an oxidative [3 + 2] cycloaddition. Furthermore, the new compound 7 exhibited potent antibacterial activities against several multidrug-resistant strains (MRSA, VISA and VRE), and showed greater potency than vancomycin.

Construction of Benzene Rings by Copper-Catalyzed Cycloaddition Reactions of Oximes and Maleimides: An Access to Fused Phthalimides

A useful Cu-catalyzed cycloaddition protocol for the construction of benzene rings has been achieved. The reactions, utilizing readily available oximes and maleimides as starting materials, proceed under mild reaction conditions to generate a series of structurally interesting fused-phthalimides that are difficult to be prepared by conventional methods.

Regio and Enantioselective Organocatalytic Friedel-Crafts Alkylation of 4-Aminoindoles at the C7-Position

A chiral phosphoric acid catalyzed highly regio- and enantioselective Friedel-Crafts alkylation at the indole C7-position was developed via the introduction of an alkylamine moiety at the C4-position of the indole ring. The methodology is applicable to a wide range of 4-aminoindoles and β,γ-unsaturated α-ketimino esters to furnish the corresponding C7-position functionalized chiral indole derivatives in high yields with moderate to excellent enantioselectivities. Furthermore, the α-ketimino ester moiety in the products is a versatile building block and enables many further transformations.

Enantioselective Friedel–Crafts C2-alkylation of 3-substituted indoles with trifluoropyruvates and cyclic N-sulfonyl α-ketiminoesters

Enantioselective Friedel–Crafts C2-alkylations of 3-substituted indoles with trifluoropyruvates and cyclic α-ketiminoesters were developed, delivering indole-containing α-hydroxyesters and α-aminoesters in excellent enantioselectivities.

Asymmetric organocatalytic synthesis of chiral 3,3-disubstituted oxindolesviaa 1,6-conjugate addition reaction

The chiral spirocyclic phosphoric acid-catalyzed enantioselective 1,6-conjugate addition reaction ofpara-quinone methides derived fromN-unprotected isatins with indoles was developed.

Chemoselective N–H functionalization of indole derivatives via the Reissert-type reaction catalyzed by a chiral phosphoric acid

An asymmetric N-alkylation of indole derivatives via the Reissert-type reaction was realized in the presence of 10 mol% chiral phosphoric acid.

Friedel–Crafts alkylation reaction with fluorinated alcohols as hydrogen-bond donors and solvents

An effective and clean FC alkylation of indoles and electron-rich arenes with β-nitroalkenes in HFIP was reported. The desired products are formed rapidly in excellent yields under mild conditions without the need for any additional catalysts or reagents. Further, this methodology can be applied to one-pot synthesis of biologically active tryptamine derivatives.

Friedel–Craft alkylation of heterocycle derivatives with β-nitroalkenes was performed in HFIP. The one-pot synthesis of tryptamines could be applied.

Development and application of chiral spirocyclic phosphoric acids in asymmetric catalysis

This review describes the synthetic methods for the preparation of chiral spirocyclic phosphoric acids (SPAs), and their dynamically developing application for catalytic enantioselective transformations.

Enantioselective Friedel-Crafts Alkylation between Nitroalkenes and Indoles Catalyzed by Charge Activated Thiourea Organocatalysts

A series of methylated and octylated pyridinium and quinolinium containing thiourea salts with a chiral 2-indanol substituent are reported. These organocatalysts are positively charged analogues of privileged bis(3,5-trifluoromethyl)phenyl substituted thioureas, and are found to be much more active catalysts despite the absence of an additional hydrogen bond donor or acceptor site (i.e., the presence of a heteroatom-hydrogen or heteroatom). Friedel-Crafts reactions of trans-β-nitorostyrenes with indoles are examined, and good yields and enantioselectivities are obtained. Mechanistic studies indicate that this is a second-order transformation under the employed conditions, and is consistent with the dimer of the thiourea being the active catalyst. Charged organocatalysts, consequently, represent an attractive design strategy for catalyst development.

Catalytic asymmetric Friedel–Crafts synthesis of 1,1′-diaryl-2-substituted 4-pentenes enables stereoselective access to functionalized tetrahydronaphthalenes

A series of electron-rich arenes were reacted with 1-alkyl or 1-aryl 1′-allyl benzylic alcohols to give the corresponding 1,1′-diarylalkanes, in the presence of Lewis and Brønsted acids as catalysts. In the presence of HBF4, 1,1′-diarylalkanes containing an allylic chain were shown to form tetrahydronaphthalenes through a rearrangement involving spirocyclic intermediates. The mechanism of the cyclization is discussed.

H2SO4-Mediated Stereocontrolled Annulation of Oxygenated Naphthalenes and 4-Alkenols: One-Pot Synthesis of Tetanthrenes

H₂SO₄-mediated one-pot stereocontrolled (4 + 2) annulation of 4-alkenols and oxygenated naphthalenes provided tetanthrenes in CH₂Cl₂ at 25 °C for 10 h. The use of various Brønsted acids or Lewis acids was investigated for a facile and efficient transformation. A plausible mechanism has been proposed.

Fe(OTf)3-catalysed Friedel-Crafts reaction of benzenoid arenes with α,β-unsaturated carbonyl compounds: easy access to 1,1-diarylalkanes

A simple and efficient method for the synthesis of 1,1-diarylalkanes via the Friedel-Crafts-type alkylation reaction of electron-rich arenes with cinnamic acid ester derivatives or chalcones is reported. Iron triflate has been found to be the best catalyst for the Friedel-Crafts-type alkylation reaction with α,β-unsaturated carbonyl compounds. This reaction afforded β,β-diaryl carbonyl compounds in good yields (65-93%) and with excellent regioselectivities. Remarkably, this method is also compatible with a variety of indoles to provide 3-indolyl-aryl carbonyl compounds in excellent yields. Great efforts have been made to deduce a plausible reaction mechanism based on isotopic labelling experiments.

Chiral Brønsted Acid Catalyzed Enantioselective aza-Friedel-Crafts Reaction of Cyclic α-Diaryl N-Acyl Imines with Indoles

Asymmetric addition of indoles to cyclic α-diaryl-substituted N-acyl imines, which are generated in situ from 3-aryl 3-hydroxyisoindolinones, is described. The transformation proceeds smoothly with a broad range of indoles and isoindolinone alcohols using a SPINOL-derived chiral Brønsted acid catalyst to afford α-tetrasubstituted (3-indolyl)(diaryl)methanamines in excellent yields and enantioselectivities (up to 98% yield, up to >99:1 e.r.). The origin of stereochemical induction is supported by DFT calculations and experimental data.

Phenolic Activation in Chiral Brønsted Acid-Catalyzed Intramolecular α-Amidoalkylation Reactions for the Synthesis of Fused Isoquinolines

An organolithium addition-intramolecular α-amidoalkylation sequence on N-phenethylimides has been developed for the synthesis of fused tetrahydroisoquinoline systems using 1,1'-bi-2-naphthol (binol)-derived Brønsted acids. This transformation is the first in which activated benzene derivatives are used as internal nucleophiles, instead of electron-rich heteroaromatics, generating a quaternary stereocenter. Phenolic substitution on the aromatic ring of the phenethylamino moiety and the use of binol-derived N-triflylphosphoramides as catalysts are determinants to achieve reasonable levels of enantioselection, that is, up to 75% enantiomeric excess, in the α-amidoalkylation step. The procedure is complementary to the intermolecular α-amidoalkylation process, as opposite enantiomers are formed, and to the Pictet-Spengler cyclization, which allows the formation of tertiary stereocenters.

Catalytic Asymmetric Conjugate Addition of Indolizines to α,β-Unsaturated Ketones

A catalytic enantioselective conjugate addition of indolizines to enones is described. The chiral phosphoric acid (S)-TRIP activates α,β-unsaturated ketones, thereby promoting an enantioface-differentiating attack by indolizines. Using this reaction, several alkylated indolizines were synthesized in good yields and with enantiomeric ratios of up to 98:2.

Construction of Chiral Tetrahydro-β-Carbolines: Asymmetric Pictet-Spengler Reaction of Indolyl Dihydropyridines

A highly efficient synthesis of the enantioenriched tetrahydro-β-carbolines was developed by using a chiral phosphoric acid catalyzed Pictet-Spengler reaction of indolyl dihydropyridines. The reaction proceeds under mild reaction conditions to afford the desired chiral tetrahydro-β-carbolines in good to excellent yields (up to 96 %) and high enantioselectivities (up to 99 % ee). With this method, a formal synthesis of tangutorine and a total synthesis of deplancheine were achieved in a highly efficient manner.

Scope of the Reactions of Indolyl- and Pyrrolyl-Tethered N-Sulfonyl-1,2,3-triazoles: Rhodium(II)-Catalyzed Synthesis of Indole- and Pyrrole-Fused Polycyclic Compounds

An efficient synthesis of tetrahydrocarboline-type products and polycyclic spiroindolines has been achieved. The transformation proceeds via rhodium(II)-catalyzed intramolecular annulations of indolyl- and pyrrolyl-tethered N-sulfonyl-1,2,3-triazoles. The reaction could be tuned toward either the formal [3 + 2] cycloaddition or the C-H functionalization reaction depending on the electronic and structural features of the substrates, leading to the production of a variety of structurally related heterocyclic compounds.

Catalytic asymmetric radical aminoperfluoroalkylation and aminodifluoromethylation of alkenes to versatile enantioenriched-fluoroalkyl amines

Although great success has been achieved in asymmetric fluoroalkylation reactions via nucleophilic or electrophilic processes, the development of asymmetric radical versions of this type of reactions remains a formidable challenge because of the involvement of highly reactive radical species. Here we report a catalytic asymmetric radical aminoperfluoroalkylation and aminodifluoromethylation of alkenes with commercially available fluoroalkylsulfonyl chlorides as the radical sources, providing a versatile platform to access four types of enantioenriched α-tertiary pyrrolidines bearing β-perfluorobutanyl, trifluoromethyl, difluoroacetyl and even difluoromethyl groups in excellent yields and with excellent enantioselectivity. The key to success is not only the introduction of the CuBr/chiral phosphoric acid dual-catalytic system but also the use of silver carbonate to suppress strong background and side hydroamination reactions caused by a stoichiometric amount of the in situ generated HCl. Broad substrate scope, excellent functional group tolerance and versatile functionalization of the products make this approach very practical and attractive.

Methods for the asymmetric introduction of organofluorine groups are often limited by the lack of variability in the starting materials. Here the authors report an asymmetric radical process for the introduction of fluoroalkyl groups using readily available fluoroalkylated sulfonyl chlorides.