Isoindolinones as Michael Donors under Phase Transfer Catalysis: Enantioselective Synthesis of Phthalimidines Containing a Tetrasubstituted Carbon Stereocenter

Synthesis of 3,3-Disubstituted Allyl Isoindolinones via Pd-Catalyzed Decarboxylative Allylic Alkylation

Herein, we report a mild palladium-catalyzed decarboxylative allylic alkylation of allyl ester-substituted isoindolinone substrates to afford a variety of 3,3-disubstituted isoindolinone derivatives. The decarboxylative coupling reaction tolerates a range of functional groups, including ketones and alkenyl halides, and does not require protection of the isoindolinone nitrogen. Additionally, the reaction was found to proceed in near-quantitative yield for most substrates evaluated. Based on the isolation of competing cyclopropane and protonation products, a reaction mechanism is proposed.

Copper-catalyzed asymmetric 1,2-arylboration of enamines: access to chiral borate-containing 3,3'-disubstituted isoindolinones

An enantioselective copper-catalyzed 1,2-arylboration reaction of enamines has been developed by employing (R)-xyl-BINAP as a chiral ligand. A number of chiral borate-containing 3,3'-disubstituted isoindolinones were obtained in moderate to good yields and good to excellent enantioselectivities from the reactions of N-(o-iodobenzoyl)enamines and bis(pinacolato)diboron (B2pin2) under mild reaction conditions. Synthetic transformations of the products were conducted to demonstrate the practicality of this reaction.

Plausible Pnicogen Bonding of epi-Cinchonidine as a Chiral Scaffold in Catalysis

As a non-covalent interaction of a chiral scaffold in catalysis, pnicogen bonding of epi-cinchonidine (epi-CD), a cinchona alkaloid, was simulated to consider whether the interaction can have the potential controlling enantiotopic face like hydrogen bonding. Among five reactive functional groups in epi-CD, two stable complexes of the hydroxyl group (X-epi-CD1) at C₁₇ and of the quinoline ring (X-epi-CD2) at N₁₆ with pnictide family analytes [X = substituted phosphine (PX), i.e., F, Br, Cl, CF₃, CN, HO, NO₂, and CH₃, and pnictide family analytes, i.e., PBr₃, BiI₃, SbI₃, and AsI₃] were predicted with intermolecular interaction energies, charge transfer (Q_Mulliken and Q_NBO), and band gap energies of HOMO-LUMO (Eg) at the B3LYP/6-31G(d,p) level of density functional theory. It was found that the dominant site of pnicogen bonding in epi-CD is the quinoline ring (N₁₆ atom) rather than the hydroxyl group (O₃₆ atom). In addition, the UV-Vis spectra of the complex were calculated by time-dependent density functional theory (TD-DFT) at the B3LYP/6-31+G(d,p) level and compared with experimental measurements. Through these calculations, two intermolecular interactions (H-bond vs. pnicogen bond) of epi-CD were compared.

5-Annulation of Ketoimines: TFA-Catalyzed Construction of Isoindolinone-3-carboxylates and Development of Photophysical Properties

Herein we have demonstrated the first report on 5-annulation of ketoimines to valuable isoindolinone-3-carboxylates. Instead of commonly used aldimine substrates, relatively less reactive ketoimines are employed for developing a TFA catalyzed organoreductive cyclization to furnish a variety of isoindolinones in excellent yield and reaction rate under mild reaction conditions. This is a metal-free event, which proceeds through a one pot ketoimine formation, hydride transfer from an organic reductant 2-(naphthalen-2-yl)-2,3-dihydrobenzo[ d]thiazole, and followed by five member cyclization sequences through TFA-activation of imine and ester groups. Studies on ESI-MS kinetics, leaving group aptitude, and control experiments led us to propose the mechanistic pathway of the new ketoimine-lactamization reaction. We have shown the synthetic utility of the emerging synthons through easy transformation of isoindolinones to different synthetic analogues. We investigated photophysical properties of the small molecules for their futuristic application as a pharmaceutical and materials, and the heterocycles displayed brilliant fluorescence activity.

Bioactive Indanes: Proof of Concept Study for Enantioselective Synthetic Routes to PH46A, a New Potential Anti-Inflammatory Agent

PH46A is a single enantiomer and a member of the 1,2-indane dimer family. It has two contiguous stereogenic centers with S,S configurations, one of which being a quaternary center, which has been developed as a clinical candidate for the treatment of inflammatory and autoimmune conditions. The current synthetic route to PH46A involves the generation of an unwanted enantiomer (R,R)-7, thus reducing the final yield significantly. Therefore, we have investigated potential alternatives to improve the efficiency of this synthesis. The first phase of the study has demonstrated proof of principle for a chiral alkylation of ketone 3 using phase-transfer catalysis, providing a key intermediate ketone (S)-4. The parent alkaloids required for the synthesis of PH46A, quinine or cinchonidine, have also been identified. Promising enantiomeric excesses of up to 50% have been achieved to date, and the use of an alternative substrate, unsaturated ketone 9, has also opened up further avenues for optimisation in future studies. The second part of the study involved preliminary screening the effects of a panel of hydrolase enzymes on (rac)-4 in order to identify a potential chemo-enzymatic route to optimise the introduction of chirality into PH46A at early stage of the synthesis. The hydrolase module has also yielded positive results; enzyme AH-46 with MtBE providing a selectivity factor of 8.4 with enantiomeric excess of 77%. Overall, positive results were obtained in this proof of concept study described herein. It is believed that conditions of both chiral PTC alkylation and biocatalytic hydrolysis could be optimised to further enhance the selectivity and improve the overall yield. This work is currently ongoing.

Diastereoselective auxiliary- and catalyst-controlled intramolecular aza-Michael reaction for the elaboration of enantioenriched 3-substituted isoindolinones. Application to the synthesis of a new pazinaclone analogue

A new asymmetric organocatalyzed intramolecular aza-Michael reaction by means of both a chiral auxiliary and a catalyst for stereocontrol is reported for the synthesis of optically active isoindolinones. A selected cinchoninium salt was used as phase-transfer catalyst in combination with a chiral nucleophile, a Michael acceptor and a base to provide 3-substituted isoindolinones in good yields and diastereomeric excesses. This methodology was applied to the asymmetric synthesis of a new pazinaclone analogue which is of interest in the field of benzodiazepine-receptor agonists.

Highly diastereo- and enantioselective organocatalytic synthesis of new heterocyclic hybrids isoindolinone-imidate and isoindolinone-phthalide

New heterocyclic hybrids were synthesized in an aldol initiated organocascade reaction of nucleophilic isoindolinones with 2-formyl benzonitriles (2-cyano benzaldehydes).

Bifunctional phase-transfer catalysis in the asymmetric synthesis of biologically active isoindolinones

New bifunctional chiral ammonium salts were investigated in an asymmetric cascade synthesis of a key building block for a variety of biologically relevant isoindolinones. With this chiral compound in hand, the development of further transformations allowed for the synthesis of diverse derivatives of high pharmaceutical value, such as the Belliotti (S)-PD172938 and arylated analogues with hypnotic sedative activity, obtained in good overall total yield (50%) and high enantiomeric purity (95% ee). The synthetic routes developed herein are particularly convenient in comparison with the current methods available in literature and are particularly promising for large scale applications.