Creation of a Chiral All-Carbon Quaternary Center Induced by CF3 and CH3 Substituents via Cu-Catalyzed Asymmetric Conjugate Addition

Cu-catalyzed asymmetric construction of a chiral quaternary center bearing CH3 and CF3 groups was achieved with high to excellent enantioselectivity using our originally developed ligands. The asymmetric conjugate addition of Me3Al to β-CF3-substituted enones and unsaturated ketoesters proceeded efficiently. The use of unsaturated ketoesters gives optically active furanones in high yields with high enantioselectivities. The perfluoroalkyl-substituted enone does not seem to be favorable in the present reaction.

Phosphine-Catalyzed Domino Annulation of γ-Vinyl Allenoates: Synthesis of Tetrahydrofuro[3,2-c]quinoline Derivatives

A novel phosphine-catalyzed domino annulation reaction of γ-vinyl allenoates and o-aminotrifluoacetophenones for the construction of terahydrofuro[3,2-c]quinoline derivatives has been developed. In this domino reaction, two kinds of terahydrofuro[3,2-c]quinoline compounds containing CF3 groups were obtained with good yields under mild conditions, three new C-N, C-C, and C-O bonds can be built in one step, and the reaction selectivity is achieved by adjusting the reaction conditions. Furthermore, preliminary studies on an asymmetric variant of this reaction proceeded with moderate enantioselectivity.

Copper-Catalyzed Benzylic Functionalization of Lignin-Derived Monomers

Within the field of lignin biorefining, significant research effort has been dedicated to the advancement of catalytic methods for lignocellulose depolymerization. However, another key challenge in lignin valorization is the conversion of the obtained monomers into higher value-added products. To address this challenge, new catalytic methods that can fully embrace the inherent complexity of their target substrates are needed. Here, we describe copper-catalyzed reactions for benzylic functionalization of lignin-derived phenolics via intermediate formation of hexafluoroisopropoxy-masked para-quinone methides (p-QMs). By controlling the rates of copper catalyst turnover and p-QM release, we have developed copper-catalyzed allylation and alkynylation reactions of lignin-derived monomers to install various unsaturated fragments amenable to further synthetic applications.

Copper (I) Chloride-Catalyzed Photoredox Synthesis of Multifunctionalized Compounds at Room Temperature and Their Antifungal Activities

A simple visible-light-induced CuCl-catalyzed synthesis was developed for highly functionalized carbon-centered compounds (α-alk/aryloxy-α-diaryl/alkylaryl-acetaldehydes/ketones) at room temperature using benzoquinone, alkyl/aryl alcohol, and alkyl/aryl terminal/internal alkynes. Late-stage functionalized compounds show good antifungal activities, especially against Candida krusei fungal strain, in in vitro experiments (the Broth microdilution method). Moreover, toxicity tests (zebrafish egg model experiments) indicated that these compounds had negligible cytotoxicity. The green chemistry metrics (E-factor value is 7.3) and eco-scale (eco-scale value is 58.8) evaluations show that the method is simple, mild, highly efficient, eco-friendly, and environmentally feasible.

Visible Light-Mediated In Situ Generation of δ,δ-Disubstituted p-Quinone Methides: Construction of a Sterically Congested Quaternary Stereocenter

An unprecedented visible light-assisted and zinc triflate-catalyzed construction of a diaryl-substituted quaternary stereocenter is reported. 2-(4-Hydroxyphenyl)-substituted aldehydes and ketones have been prepared in moderate to high yields via multicomponent reaction of acetylene, benzoquinone (BQ), and indole/aniline/thiol. The reaction is believed to proceed via in situ generation of p-quinone methide through a [2+2] cycloaddition-retroelectrocyclization of BQ and acetylene in blue light followed by a zinc triflate-catalyzed vinylogous Michael addition reaction with nucleophiles.

Synthesis of difluoromethylated diarylmethanes via Fe(OTf)3-catalyzed Friedel-Crafts reaction of 2,2-difluoro-1-arylethyl phosphates

The Fe(OTf)₃-catalyzed Friedel-Crafts reaction of 2,2-difluoro-1-arylethyl phosphates with electron-rich (hetero)arenes afforded difluoromethylated diarylmethanes. Control experiments showed that Fe(OTf)₃ behaves as the Lewis acid, and that the phosphate leaving group and o- or p-alkoxy substituents on the substrates are necessary for the Fe(OTf)₃-catalyzed reaction to proceed under mild conditions.

Construction of fully substituted carbon centers containing a heteroatom and a CF3 group via in situ generated p-quinone methides

1,6-Conjugate additions of in situ generated δ-CF3-δ-substituted p-quinone methides have been achieved with a variety of heteronucleophiles under mild conditions, which led to facile and practical construction of fully substituted carbon centers including a heteroatom and a CF3 group. In particular, it was revealed that some amines themselves worked for efficient cleavage of the TBS protective group, and addition of a catalytic amount of an appropriate Brønsted acid was found to sometimes improve the progress of the desired process.

Diastereoselective synthesis of CF3-dihydrobenzofurans by [4+1] annulation of in situ-generated CF3-o-quinone methides and sulfur ylides

An efficient and highly diastereoselective synthesis of CF₃-dihydrobenzofurans by the reaction of in situ-generated CF₃-oQMs in the presence of a base with sulphur ylides is put forward. The generality of the present developed method was well studied with diverse substrates to access the corresponding products in excellent yields. The highly reactive CF₃-oQM has been utilized first time for the annulation reaction.

The first [4 + 1] annulation reaction of in situ-generated highly electrophilic CF₃-ortho-quinone methides with sulphur ylides has been put forth under mild reaction conditions to access CF₃-dihydrobenzofurans.

CF3-Containing para-Quinone Methides for Organic Synthesis

A new family of CF3-containing para-quinone methides (CF3-QMs) was systematically investigated for its suitability in organic synthesis. Addition of different nucleophiles gives access to target molecules with a benzylic CF3-containing stereogenic center straightforwardly. The electrophilicity parameter E of the prototypical CF3-QM 2,6-di-tert-butyl-4-(2,2,2-trifluoroethylidene)cyclohexa-2,5-dien-1-one was determined to be -11.68 according to the Mayr scale, making it one of the most reactive quinone methides known so far.

Syntheses of α-CF3-α-quaternary ketones via p-quinone methides and their derivatization to compounds with successively congested stereogenic centers

NHC-catalyzed 1,6-conjugate additions of a variety of aldehydes to δ-CF₃-δ-substituted p-quinone methides and their highly diastereoselective derivatization to compounds with successively congested stereogenic centers were performed.