Synthesis of various arylated trifluoromethyl substituted indanes and indenes, and study of their biological activity

Brønsted-Acid-Catalyzed One-Pot Synthesis of β,β-Diaryl Esters: Direct Regioselective Approach to Diverse Arrays of 3-Aryl-1-indanone Cores

A three-component, solvent-dependent, Brønsted-acid-catalyzed reaction of benzaldehydes, silyl enolates and arene nucleophiles has been developed for the synthesis of potential drug candidate 3-aryl-1-indanones. This reaction features the formation of three C-C bonds, high regioselectivity in a one-pot strategy, broad substrate generality, facile scalability (1.04g), high functional group tolerance and viable substrates. The β-O-silyl ethers generated in-situ from the Mukaiyama aldol reaction were subjected to acid-catalyzed benzylic arylation with strong as well as weak nucleophiles, and the resultant β,β-diaryl esters can undergo a third C-C bond formation with excellent regioselectivity through intramolecular cyclization to afford the indanone products in the same pot. Detailed mechanistic insight leads to a feasible reaction pathway. This transformation opens up a practical and adaptable approach to producing a variety of synthetically valuable transformations and enable the synthesis of medicinally valuable (R)-tolterodine and (+)-indatraline.

Sequential Knoevenagel Condensation/Cyclization for the Synthesis of Indene and Benzofulvene Derivatives

Sequential Knoevenagel condensation/cyclization leading to indene and benzofulvene derivatives has been developed. The reaction of 2-(1-phenylvinyl)benzaldehyde with malonates gave benzylidene malonates, cyclized indenes, and dehydrogenated benzofulvenes. The product selectivity depends on the reaction conditions. The reaction with piperidine, AcOH in benzene at 80 °C for 1.5 h gave a benzylidene malonate in 75% yield as a major product. The reactions with piperidine, AcOH in benzene at 80 °C for 17 h and with TiCl₄-pyridine at room temperature gave an indene derivative in 56 and 79% yields, respectively, as a major product. The reaction with TiCl₄-Et₃N gave a benzofulvene in 40% yield selectively. Indene was transformed to a benzofulvene derivative using the reagents TiCl₄-Et₃N and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). The reaction of variously substituted aryl derivatives with dimethyl malonate gave indene and benzofulvene derivatives. The reactions of 2-(1-phenylvinyl)benzaldehyde with Meldrum's acid or malononitrile also gave cyclized compounds in the suitable sequential or stepwise conditions. Furthermore, the reaction of 2-arylbenzaldehydes has been investigated. The limitation and scope have been described. The reaction mechanism of the cyclization steps has been examined by DFT calculations.

Synthesis of 1-Trifluorometylindanes and Close Structures: A Mini Review

This review describes methods for the synthesis of 1-trifluomethylindanes and close structures, which are still quite rare and scarcely available compounds. There are two main approaches to obtain 1-CF3-indanes. The first one is the construction of an indane system from CF3 precursors; the main methods are acid-mediated Friedel–Crafts cyclization, transition metal-catalyzed [3+2] annulation, and free-radical transformations. The second approach is the trifluoromethylation of a ready-made indane core by various CF3 sources, such as Ruppert–Prakash or Togni reagents. Many of these synthetic procedures possess high regio- and stereo-selectivity, allowing the preparation of unique 1-CF3-indane structures. In recent years, great attention has been paid to the synthesis of 1-CF3-indanes, due to the discovery of important biologically active properties for these compounds.

Machaerium acutifolium compounds with larvicidal activity against Aedes aegypti

BACKGROUND

Plant extracts and isolated compounds are known for their insecticidal activity. The Aedes aegypti mosquito has a significant medical impact as it transmits a number of arboviruses and is able to develop resistance to the commercially available insecticides. This study investigates larvicidal compounds isolated from Machaerium acutifolium, designated by the Brazilian Forest Service as a sustainable species.

RESULTS

A M. acutifolium trunk ethyl acetate extract was fractionated using chromatographic methods with full structural elucidation by mass spectrometry (MS), nuclear magnetic resonance and specific rotation analyses revealing: one new 3-arylcoumarin derivative 1; two flavonoids 2 and 3; a trans-stilbene 4, and an unprecedented natural indene 5. The larvicidal activity against Ae. aegypti after 24 h exposure was: crude extract (median lethal dose, LC₅₀ 205 mg L^-1 ), fraction C (LC₅₀ 27 mg L^-1 ) and 5 (LC₅₀ 24 mg L^-1 ).

CONCLUSION

A M. acutifolium extract showed larvicidal activity, which increased with prolonged exposure, demonstrating LC₅₀ 75 mg L^-1 after 72 h. Although the flavonoids 2 and 3 and trans-stilbene 4 were deemed inactive according to the adopted mortality limit, additional tests revealed their ability to cause 65% Ae. aegypti larvae mortality, suggesting they could contribute to the larvicidal activity. Compound 5, identified by liquid chromatography-MS, was over eight-fold more toxic to larvae than the crude extract after 24 h. Therefore, 5 constitutes a structural model for new prototypes to control Ae. aegypti. These data reinforce the potential of natural products as a source of commercial alternatives for vector control strategies, respecting both sustainability and eco-friendly principles. © 2020 Society of Chemical Industry.

CF3-substituted carbocations: underexploited intermediates with great potential in modern synthetic chemistry

"The extraordinary instability of such an "ion" accounts for many of the peculiarities of organic reactions" - Franck C. Whitmore (1932). This statement from Whitmore came in a period where carbocations began to be considered as intermediates in reactions. Ninety years later, pointing at the strong knowledge acquired from the contributions of famous organic chemists, carbocations are very well known reaction intermediates. Among them, destabilized carbocations - carbocations substituted with electron-withdrawing groups - are, however, still predestined to be transient species and sometimes considered as exotic ones. Among them, the CF3-substituted carbocations, frequently suggested to be involved in synthetic transformations but rarely considered as affordable intermediates for synthetic purposes, have long been investigated. This review highlights recent and past reports focusing on their study and potential in modern synthetic transformations.

TfOH-Promoted Reactions of TMS-Ethers of CF3-Pentenynoles with Arenes. Synthesis of CF3-Substituted Pentenynes, Indenes, and Other Carbocyclic Structures

Trimethylsilyl ethers of 1,5-diaryl-3-(trifluoromethyl)-pent-1-en-4-yn-3-oles [Ar-C≡C-C(CF₃)(OSiMe₃)-CH═CH-Ar'] in the superacid TfOH give rise to reactive conjugated CF₃-allylic-propargylic cations [Ar-C≡C-C⁺(CF₃)-CH═CH-Ar']. These species react with arenes in the presence of 1.5 equiv of TfOH forming regio- and stereoselectively E-1,1,5-triaryl-3-(trifluoromethyl)-pent-2-en-4-ynes [Ar-C≡C-C(CF₃)═CH-CHAr'(Ar″)] in good yields. In the excess of TfOH, these CF₃-pentenynes are further intramolecularly cyclized into CF₃-bicyclic dihydroanthracene derivatives ("helicopter"-like molecules). The CF₃-pentenynes may also react with arenes, as external nucleophiles, leading to CF₃-indenes. These two main reaction pathways depend on internal nucleophilicity of aryl substituents in CF₃-pentenynes and external nucleophilicity of aromatic molecules. Plausible cationic reaction mechanisms have been discussed. CF₃-bicyclic dihydroanthracene derivatives have been studied regarding their cytotoxicity and virus-inhibiting activity against influenza virus A/Puerto Rico/8/34 (H1N1) in MDCK cell line.

Rhodium(iii)-catalyzed synthesis of 3-trifluoromethylindanones from N-methoxybenzamides via C–H activation and Claisen/retro-Claisen reaction

An efficient synthesis of 3-trifluoromethylindanones via C–H annulation of N-methoxybenzamides with β-trifluoromethyl-α,β-unsaturated ketones under Rh(iii)-catalysis is described.

TfOH-promoted transformation of TMS-ethers of diarylsubstituted CF3-allyl alcohols with arenes into CF3-indanes

Novel synthesis of 1,3-diaryl-1-trifluoromethyl indanes, having predominantly a trans-configuration of aryl groups, was developed on the basis of the reaction of TMS-ethers of 2,4-diaryl-1,1,1-trifluorobut-3-en-2-ols with arenes in superacid TfOH.