Synthesis of 2-Substituted Indoles via Migration Reaction of 3-Substituted Indoles with Triflic Acid.

This study showcases the 1,2-migration reactions of alkyl and aryl groups on the indole molecule. Trifluoromethanesulfonic acid effectively facilitates the migration of the substituent from C3- to C2-position of the indole structure. The resulting C2-substituted indoles offer a valuable pathway for the synthesis of natural products and medicinal compounds.

Fluorescent Rotary Switches: Four- vs Three-Substituted Phthalimide Boron Difluoride Schiff Base Complexes.

The influence of the substitution pattern in phthalimide boron difluoride Schiff base complexes as fluorescent molecular rotors has been investigated. Due to their ground-state zwitterionic structures, they have exhibited negative solvatochromism in absorption and blue-green emission with moderate to satisfactory photoluminescence quantum yields in solution. Ground-state and excited-state theoretical calculations and time-resolved emission spectroscopy revealed that the excited-state rotation is triggered by planar-induced charge transfer, resulting in switched emission toward the green region. Fluorescence lifetime measurements and species-associated emission spectra exhibited two emitting excited species in equilibrium via a planar transition-state barrier. The substitution pattern models showed different behavior in solid-state mechanochromic switching and were analyzed by subcell unit packing obtained from X-ray structure data. We have attempted to gain in-depth insight into the fluorescence mechanism and photoluminescence properties associated with the substitution pattern of the phthalimide motif in order to understand the structure-property-function relationship.

Solvent-Triggered Long-Range Proton Transport in 7-Hydroxyquinoline Using a Sulfonamide Transporter Group.

The ability of long-range proton transport by substitution of 7-hydroxyquinoline at the eighth position with sulfonamide and sulfonylhydrazone rotor units to act as a crane-arm has been studied. Different proton transport pathways triggered by different stimuli have been established depending on the structure of the crane-arms. Solvent-driven proton switching from OH to the quinoline nitrogen (Nquin) site, facilitated by a sulfonamide transporter group in polar protic and aprotic solvents, has been confirmed by optical (absorption and fluorescence) and NMR spectroscopies as well as by single-crystal X-ray structure analysis. Photoinduced long-range proton transport to the Nquin site upon 340 nm UV light irradiation has been estimated in sulfonylhydrazone, which is not sensitive to solvent-driven switching. Both compounds have exhibited acid-triggered switching by trifluoroacetic acid due to the formation of a stable six-membered intramolecular hydrogen bonding interaction between the protonated Nquin and crane-arm. The structures of acid-switched form were confirmed by NMR spectroscopy and single-crystal X-ray structure analysis. The behavior of the compounds suggests a big step forward in the advanced proton pump-switching architecture because they cover three distinct driving forces in the switching process: solvent, light, and acid.

Acylhydrazone Subunits as a Proton Cargo Delivery System in 7-Hydroxyquinoline.

The reimagined concept of long-range tautomeric proton transfer using crane subunits is shown by designing and synthesising two new acylhydrazones containing a 7-hydroxyquinoline (7-OHQ) platform. The acylhydrazone subunits attached to the 7-OHQ at the 8th position act as crane arms for delivering proton cargo to the quinoline nitrogen. Light-induced tautomerization to their keto forms leads to Z/E isomerization of the C=C axle bond, followed by proton delivery to the quinoline nitrogen by the formation of covalent or hydrogen bonds. The axle's being either an imine or ketimine bond is the structural difference between the studied compounds. The -CH3 group in the latter provides steric strain, resulting in different proton transport pathways. Both compounds show long thermal stability in the switched state, which creates a tuneable action of bidirectional proton cargo transport by using different wavelengths of irradiation. Upon the addition of acid, the quinoline nitrogen is protonated; this results in E/Z configuration switching of the acylhydrazone subunits. This was proven by single-crystal X-ray structure analysis and NMR spectroscopy.

Asymmetric Conjugate Addition of Phosphonates to Enones Using Cinchona-Diaminomethylenemalononitrile Organocatalysts.

Asymmetric conjugate additions of phosphonates to trans-crotonophenone and chalcone derivatives using a diaminomethylenemalononitrile organocatalyst resulted in the generation of the corresponding chiral γ-ketophosphonates in high yields with excellent enantioselectivities (up to 95% ee). This report is the first successful example of asymmetric 1,4-additions of phosphonate to α,ß-unsaturated ketones using an organocatalyst.

Asymmetric Conjugate Addition of α-Cyanoketones to Enones Using Diaminomethylenemalononitrile Organocatalyst.

A diaminomethylenemalononitrile organocatalyst efficiently catalyzed the asymmetric conjugate addition of α-cyanoketones to vinyl ketones to give the corresponding 1,5-dicarbonyl compounds, which bear an all-carbon quaternary stereogenic center with high enantioselectivities. This report is the first example of the asymmetric conjugate addition of α-cyanoketones to vinyl ketones using an organocatalyst.

Stereoselective conjugate addition of ketones to alkylidene malonates using thiourea-sulfonamide organocatalyst.

In this study, stereoselective conjugate addition of ketones to alkylidene malonates using organocatalyst has been developed. The reaction in the presence of 20 mol% of a novel thiourea-sulfonamide organocatalyst afforded conjugate adducts in moderate to high yields (up to 81%) under mild reaction conditions. Excellent diastereoselectivity (up to 98:2 dr) and enantioselectivity (up to 88% ee) were achieved.

Asymmetric Conjugate Addition of Nitroalkanes to Enones Using a Sulfonamide-Thiourea Organocatalyst.

The asymmetric conjugate addition of nitroalkanes to α,ß-unsaturated ketones in the presence of a catalytic amount of a novel sulfonamide-thiourea organocatalyst resulted in the corresponding γ-nitro carbonyl products in high yields with excellent enantioselectivities (up to 97% ee).

Squaramide-Sulfonamide Organocatalyst for Asymmetric Direct Vinylogous Aldol Reactions.

Asymmetric direct vinylogous aldol reactions of furan-2(5H)-one with aldehydes in the presence of a catalytic amount of novel squaramide-sulfonamide organocatalyst resulted in the corresponding addition products with high to excellent enantioselectivities. This is the first successful report illustrating an example of highly stereoselective reactions using a squaramide-sulfonamide organocatalyst.

Asymmetric Conjugate Additions of Carbonyl Compounds to Nitroalkenes under Solvent-Free Conditions Using Fluorous Diaminomethylenemalononitrile Organocatalyst.

The novel fluorous organocatalyst bearing a diaminomethylenemalononitrile motif is prepared. The fluorous organocatalyst efficiently promotes asymmetric conjugate additions of ketones to nitroalkenes and results in high yields of these addition products with excellent enantioselectivities under solvent-free conditions.

Asymmetric Chlorination of ß-Keto Esters Using Diaminomethylenemalononitrile Organocatalyst.

Diaminomethylenemalononitrile organocatalysts promote the asymmetric chlorination of simple cyclic ß-keto esters such as methyl, ethyl, and benzyl esters of 1-oxo-2,3-dihydro-1H-indene-2-carboxylic acid. This affords the corresponding chiral α-chlorinated carbonyl products in excellent yields with high enantioselectivities.

Vicinal All-Carbon Quaternary Stereocenter Construction with Trifluoromethyl Groups via Organocatalytic Asymmetric Cascade Michael/Michael Reaction.

A thiourea organocatalyst efficiently promoted the asymmetric cascade Michael/Michael reactions between isatin-derived trifluoromethylacrylate and α-alkylidene succinimide, resulting in high yields of spirooxindole derivatives. These compounds exhibit vicinal all-carbon quaternary stereocenters and bear a trifluoromethyl group, with excellent enantioselectivities reaching up to 99 % ee. This work represents the first successful organocatalyst application for the direct construction of vicinal all-carbon quaternary stereocenters, featuring a trifluoromethyl group.

Regioselective One-Pot Synthesis of Vicinal Bisphosphine Derivatives from Nitroalkenes by Hydrophosphinylation/Elimination/Hydrophosphinylation.

Herein, a facile method is developed for the synthesis of vicinal bisphosphine derivatives based on a cascade of hydrophosphinylation, elimination, and hydrophosphinylation of secondary phosphine oxides with nitroalkenes. This cascade reaction provides step-economy access to a series of vicinal bisphosphine derivatives with high to excellent yields (up to 99%). This method was further extended to prepare, in one-pot, regioselective vicinal bisphosphine derivatives that incorporated two different phosphorus functional groups.

Perfluoroalkanesulfonamide organocatalysts for asymmetric conjugate additions of branched aldehydes to vinyl sulfones.

Asymmetric conjugate additions of branched aldehydes to vinyl sulfones promoted by sulfonamide organocatalyst 6 or 7 have been developed, allowing facile synthesis of the corresponding adducts with all-carbon quaternary stereocenters in excellent yields with up to 95% ee.

Direct aerobic photo-oxidative syntheses of aromatic methyl esters from methyl aromatics using anthraquinone-2,3-dicarboxylic acid as organophotocatalyst.

This paper reports a useful method for facile direct syntheses of aromatic methyl esters from methyl aromatics by aerobic photo-oxidation using anthraquinone-2,3-dicarboxylic acid as an organophotocatalyst.

Synthesis of Chiral α-Substituted ß-Aminophosphine Derivatives through Asymmetric Hydrophosphinylation Utilizing Secondary Phosphine Sulfides.

The organocatalytic enantioselective hydrophosphinylation of various secondary phosphine sulfides with aromatic and aliphatic nitroalkenes is presented in this study. The reaction produced chiral ß-nitrophosphine sulfides with excellent yields and enantioselectivities (up to 99% yield and 99% ee). Furthermore, the chiral ß-nitrophosphine sulfides can be easily converted into α-substituted ß-aminophosphine, which is a family of useful P, N-ligands and phosphine catalysts.

Asymmetric Henry Reaction of Trifluoromethyl Enones with Nitromethane Using a N,N-Dibenzyl Diaminomethylenemalononitrile Organocatalyst.

A novel N,N-dibenzyl diaminomethylenemalononitrile organocatalyst efficiently promoted asymmetric Henry reactions of trifluoromethyl enones with nitromethane, affording corresponding highly functionalized products in high yields with excellent enantioselectivities (up to 90% ee). This study is the first to report the successful example of the asymmetric 1,2-additions of nitromethane to trifluoromethyl enones.

[Development of Green Asymmetric Organocatalytic Synthesis].

Organocatalysts, which are less toxic than metal catalysis, as well as inexpensive, environmentally benign, and stable against moisture and oxygen compared to metal-based catalysts, have received considerable attention for being efficient and clean catalysts. With respect to green chemistry, the development of organocatalysis is a significant research subject for a sustainable society. This article reviews studies on the development of novel organocatalysts and the reactions achieved from using them. Focusing on the push-pull ethylene moiety, in which two electron-withdrawing groups (EWGs) were introduced, we proposed that the vinylogous amide proton (N-H) will lead to the design of organocatalysts. We have developed the diaminomethylenemalononitrile (DMM) organocatalysts, which are push-pull ethylenes having two cyano groups as EWGs, and proved that they are effective for highly stereoselective hydrophosphonylation with aldehydes. The catalytic ability of the DMM organocatalyst was demonstrated in the development of the first asymmetric hydrophosphonylation of ketones using organocatalysts. The DMM organocatalyst can be applied to the selective 1,4-addition asymmetric hydrophosphonylation of enones. In addition, we designed and synthesized novel organocatalysts bearing squaramide-sulfonamide motif as multiple hydrogen bond donors. Squaramide-sulfonamide organocatalysts efficiently catalyzed the asymmetric direct vinylogous aldol reactions of furan-2(5H)-one with aldehydes. Successively, we achieved the synthesis of γ,γ-disubstituted-δ-hydroxy-γ-butenolide via asymmetric direct vinylogous aldol reaction of furanone derivatives using the squaramide-sulfonamide organocatalysts.

Asymmetric Direct Vinylogous Conjugate Addition of Substituted Furanone Derivatives to Benzoyl Acrylonitrile: Stereoselective Synthesis Toward Bicyclic γ-Lactams.

A diaminomethylenemalononitrile organocatalyst efficiently promotes the asymmetric direct vinylogous conjugate additions of α-angelica lactones to benzoyl acrylonitrile derivatives, resulting in the corresponding addition products bearing vicinal tertiary and quaternary stereogenic centers with excellent enantioselectivities (up to 99% ee). This report is the first successful example of the asymmetric conjugate additions of α-angelica lactone to benzoyl acrylonitriles. The chiral γ,γ-disubstituted γ-butenolides obtained can be readily transformed to the bicyclic γ-lactam derivative as a valuable synthetic intermediate.

Diaminomethylenemalononitrile as a Chiral Single Hydrogen Bond Catalyst: Application to Enantioselective Conjugate Addition of α-Branched Aldehydes.

An improved diaminomethylenemalononitrile organocatalyst, bearing a N,N-disubstituted structure, promoted enantioselective conjugate addition reaction of α-branched aldehydes with vinyl sulfone, affording adducts with excellent enantioselectivities (up to 96% ee). Mechanistic studies revealed that the diaminomethylenemalononitrile motif holds the vinyl sulfone substrate using a single hydrogen bond accompanied by multiple weak interactions, including electrostatic C-H⋅⋅⋅O interactions.