Intermolecular Friedel Crafts Alkylation Research Articles

Facile Synthesis and Global Aromaticity of Aza-Superbenzene and Aza-Supernaphthalene at Different Oxidation States.

All-benzenoid polycyclic aromatic hydrocarbons or macrocycles usually display localized aromaticity. On the other hand, incorporation of quinoidal units into the skeleton could lead to effective electron delocalization and global (anti)aromaticity. In this work, fully π-conjugated macrocycle 1 and bismacrocycle 2 containing both para-quinodimethane and triphenylamine units are efficiently synthesized mainly through intermolecular Friedel-Crafts alkylation reaction. They can be considered as a tetraazasuperbenzene and a hexaazasupernaphthalene, respectively, due to their similar geometry and electronic structures to the benzene and naphthalene. X-ray crystallographic analyses reveal a largely planar geometry for both 1 and 2 and variable-temperature NMR measurements disclose slow dynamic processes owing to restricted ring flipping of the phenyl rings. 1 and 2 can be easily oxidized into higher-oxidation-state species. NMR and theoretical calculations indicate that 12+ and 14+ show global anti-aromaticity and aromaticity, respectively, with a dominant 32π and 30π conjugation pathway, while for the bismacrocycle 2, its dication 22+, tetracation 24+ and hexacation 26+ exhibit global aromaticity, antiaromaticity, and aromaticity with a 54π, 52π and 50π conjugation pathway along the outermost backbone, respectively.

Facile synthesis and characterization of aza-bridged all-benzenoid quinoidal figure-eight and cage molecules.

Synthesis of conjugated compounds with unusual shape-persistent structures remains a challenge. Herein, utilizing thermodynamically reversible intermolecular Friedel-Crafts alkylation, a dynamic covalent chemistry (DCC) reaction, we facilely synthesized a figure-eight shaped macrocycle FEM and cage molecules CATPA/CACz. X-ray crystallographic analysis confirmed the chemical geometries of tetracation FEM4+(PF6 -)4 and hexacation CACz6+(SbF6 -)6. FEM and CATPA displayed higher photoluminescence quantum yield in solid states compared to that in solution, whereas CACz gave the reverse result. DFT calculations showed that fluorescence-related frontier molecular orbital profiles are mainly localized on their arms consisting of a p-quinodimethane (p-QDM) unit and two benzene rings of triphenylamine or carbazole. Owing to their space-confined structures, variable-temperature 1H NMR measurements showed that FEM, CATPA and FEM4+ have intramolecular restricted motion of phenyl rings on their chromophore arms. Accordingly, FEM and CATPA with flexible triphenylamine subunits displayed aggregation-induced emission behavior (AIE), whereas CACz with a rigid carbazole subunits structure showed no AIE behavior.

Cyclobis(7,8‐(para‐quinodimethane)‐4,4′‐triphenylamine) and Its Cationic Species Showing Annulene‐Like Global (Anti)Aromaticity

Abstractπ‐Conjugated macrocycles containing all‐benzenoid rings usually show local aromaticity, but reported herein is the macrocycle CBQT, containing alternating para‐quinodimethane and triphenylamine units displaying annulene‐like anti‐aromaticity at low temperatures as a result of structural rigidity and participation of the bridging nitrogen atoms in π‐conjugation. It was easily synthesized by intermolecular Friedel–Crafts alkylation followed by oxidative dehydrogenation. X‐ray crystallographic structures of CBQT, as well as those of its dication, trication, and tetracation were obtained. The dication and tetracation exhibited global aromaticity and antiaromaticity, respectively, as confirmed by NMR measurements and theoretical calculations. Both the dication and tetracation possess open‐shell singlet ground states, with a small singlet–triplet gap.

Cyclobis(7,8-(para-quinodimethane)-4,4'-triphenylamine) and Its Cationic Species Showing Annulene-Like Global (Anti)Aromaticity.

π-Conjugated macrocycles containing all-benzenoid rings usually show local aromaticity, but reported herein is the macrocycle CBQT, containing alternating para-quinodimethane and triphenylamine units displaying annulene-like anti-aromaticity at low temperatures as a result of structural rigidity and participation of the bridging nitrogen atoms in π-conjugation. It was easily synthesized by intermolecular Friedel-Crafts alkylation followed by oxidative dehydrogenation. X-ray crystallographic structures of CBQT, as well as those of its dication, trication, and tetracation were obtained. The dication and tetracation exhibited global aromaticity and antiaromaticity, respectively, as confirmed by NMR measurements and theoretical calculations. Both the dication and tetracation possess open-shell singlet ground states, with a small singlet-triplet gap.

Mild Friedel-Crafts Reactions Enable a Robust Synthesis of Roseophilin.

An 11-step total synthesis of either enantiomer of roseophilin has been developed. The chemistry features effective production of a challenging carbocation on a macrocyclic segment 25 and a highly efficient intermolecular Friedel-Crafts alkylation reaction to integrate a complex furan-pyrrole unit 5 regioselectively with this carbocation under very mild reaction conditions.

Catalytic Selenium-Promoted Intermolecular Friedel-Crafts Alkylation with Simple Alkenes.

A method for conducting selenium-promoted intermolecular Friedel-Crafts (F-C) alkylation reactions has been developed with simple alkenes using trimethylsilyl trifluoromethanesulfonate as a catalyst and N-phenylselenophthalimide as an efficient selenium source. Electron-rich arenes smoothly underwent F-C alkylation with a variety of alkenes to afford alkylated products in good yield and with high regioselectivity and diastereoselectivity. The regioselectivity and stereoselectivity of arenes and alkenes as well as a preliminary mechanism of the F-C alkylation reaction are discussed.

ChemInform Abstract: Chiral Broensted Acid Catalyzed Intermolecular Friedel—Crafts Alkylation of Styrenes with Indoles: Construction of All‐Carbon Quaternary Stereocenters.

AbstractA breakthrough in asymmetric Friedel‐Crafts reactions is achieved by using terminal 1,1‐diarylalkenes as alkylating reagents, which avoids the generation of side products.

A Facile, Superacid-Promoted Sequential Domino One-Pot Dual C–C Bond Formation and Fischer Indole Synthesis: Rapid Access to 10-Phenyl-5,10-dihydroindeno[1,2-b]indoles

A superacid-promoted sequential domino one-pot approach for the synthesis of novel 10-phenyl-5,10-dihydroindeno[1,2-b]indoles, ubiquitous core structure present in many alkaloid natural products, is presented. The entire sequential process involves a domino intermolecular Friedel–Crafts alkylation and intramolecular acylation of simple and easily accessible ethyl cinnamates, to furnish the corresponding indanones, followed by the Fischer indole reaction. Interestingly, this method enabled the synthesis of various dihydroindeno[1,2-b]indoles possessing tertiary or quaternary centers at the 10th position.

Chiral Brønsted acid catalyzed intermolecular Friedel–Crafts alkylation of styrenes with indoles: construction of all-carbon quaternary stereocenters

A chiral Brønsted acid catalyzed Friedel–Crafts reaction of terminal 1,1-diaryalkenes with indoles is described. This reaction provides indole derivatives with acyclic all-carbon quaternary stereocenters in excellent yields and with excellent enantioselectivities, and features high atom efficiency without the generation of side products.

Formal synthesis of (±)-brazilin and total synthesis of (±)-brazilane

A convergent synthesis towards (±)-brazilin and (±)-brazilane has been reported from 3,4-dimethoxy benzaldehyde in <15 reaction steps. Palladium(II)-catalysed intramolecular Friedel–Crafts cyclisation and Lewis acid supported intermolecular Friedel–Crafts alkylation reactions have been demonstrated. A tetracyclic substituted indane common key intermediate is employed to furnish the desired two molecules in good to excellent yield. Pd(OH)2 has played a crucial role in the total synthesis of (±)-brazilane.

ChemInform Abstract: Superacid‐Promoted Dual C—C Bond Formation by Friedel—Crafts Alkylation and Acylation of Ethyl Cinnamates: Synthesis of Indanones.

AbstractThe method affords a series of 3‐substituted or 3,3‐disubstituted indan‐1‐ones.

Superacid-Promoted Dual C-C Bond Formation by Friedel-Crafts Alkylation and Acylation of Ethyl Cinnamates: Synthesis of Indanones

A superacid (triflic acid) promoted dual C–C bond formation via intermolecular Friedel–Crafts alkylation (Michael addition type) and intramolecular acylation for the efficient synthesis of 3-substituted indan-1-ones is presented. This method was successful in activating ethyl cinnamates towards dual aromatic electrophilic substitution. Moreover, it enabled us to synthesize novel spirotetracyclic systems.

Facile synthesis of dihydrochalcones via the AlCl3-promoted tandem Friedel–Crafts acylation and alkylation of arenes with 2-alkenoyl chlorides

Tandem Friedel–Crafts acylation and alkylation of arenes with 2-alkenoyl chlorides were investigated under the catalysis of Lewis acids. The cascade reaction affords dihydrochalcones in good yields accompanying 1-indanone derivatives in some cases, in the presence of anhydrous aluminum chloride. The scope, limitation, and mechanism of the tandem reaction were also explored. The intermolecular Friedel–Crafts alkylation for the formation of dihydrochalcones is more favorable than the intramolecular one for the generation of 1-indanones in the tandem reaction due to a stable six-membered ring transition state. The sequent process was further studied by the DFT computations at the M06-2X/6-31G(d) level, which are in great agreement with the experimental observation and support the proposed mechanism. The current method provides a convenient and economic method to synthesis of dihydrochalcones.

ChemInform Abstract: FeCl3‐Mediated Synthesis of Polysubstituted Tetrahydroquinolines via Domino Mannich/Friedel—Crafts Reactions of Aldehydes and Amines.

AbstractDomino Mannich—intramolecular Friedel—Crafts alkylation—intermolecular Friedel—Crafts alkylation reaction of aliphatic aldehydes with aromatic amines is smoothly catalyzed by FeCl3 to give polysubstituted tetrahydroquinolines in moderate yields and moderate to good diastereoselectivities.

FeCl3-Mediated synthesis of polysubstituted tetrahydroquinolines via domino Mannich/Friedel–Crafts reactions of aldehydes and amines

A useful method to construct highly substituted tetrahydroquinolines has been developed through an iron(III) chloride-mediated domino Mannich and intramolecular Friedel-Crafts alkylation followed by intermolecular Friedel-Crafts alkylation reactions of aliphatic aldehydes with aromatic amines.

Growth of carbon nanospheres through a building block assembly method at 300 °C

Carbon nanospheres (CNSs) with the diameters of 50–250 nm were synthesized through a one-step solvothermal method at about 300 °C. In this process, benzene and hexachloroethane (C 2Cl 6) served as carbon source for the CNSs. The results showed that the CNSs were composed of a mixture of graphitic nanocrystallites and amorphous carbon. It is believed that they formed through intermolecular Friedel–Crafts alkylation and dehydrogenation reactions in the presence of anhydrous aluminum chloride (AlCl 3). The mechanism of carbonization and the effect of Al particles on the morphology of carbon products are discussed.

Friedel–Crafts alkylation of arenes with epoxides promoted by fluorinated alcohols or water

The stereoselective intra- and intermolecular Friedel-Crafts alkylation of electron-rich arenes with epoxides can take place in refluxing 1,1,1,3,3,3-hexafluoroisopropanol owing to its weak acidity and high ionizing power.

Concise Stereoselective Synthesis of (−)‐Podophyllotoxin by an Intermolecular Iron(III)‐Catalyzed Friedel–Crafts Alkylation

Without further ado, the building blocks 1–3 were combined in three CC bond-forming reactions to provide the enantiomerically pure natural product (−)-podophyllotoxin (4). The stereogenic center at C1 was generated in the key reaction, a diastereoselective iron(III)-catalyzed intermolecular Friedel–Crafts alkylation.

Fused Polycyclic Hydrocarbons Through Superacid-Induced Cyclialkylation of Aromatics

Benzene and substituted derivatives (toluene, ortho-xylene, 1,2,3-trimethylbenzene, 1,2,4-trimethylbenzene, anisole), when applied in large excess, react with 1,4 diols (pentan-1,4-diol, hexan-2,5-diol, and 2,5-dimethylhexan-2,5-diol) or an oxolane (2,2,5,5-tetramethyltetrahydrofuran) in the presence of the Bronsted superacid trifluoromethanesulfonic acid (triflic acid, TFSA) to afford substituted tetralins in excellent yields with high selectivity. Reacting benzene with a small excess of alkylating agents yields octahydroanthracenes. The transformation of naphthalene with oxolane leads to a partially saturated octamethyloctahydrotetracene under similar conditions. Product formation is interpreted by intermolecular Friedel-Crafts alkylation followed by cyclialkylative ring closure.

A New Regio‐ and Stereoselective Intermolecular Friedel—Crafts Alkylation of Phenolic Substrates with Aryl Epoxides.

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