Zinc-Catalyzed Esterification of N -β-Hydroxyethylamides: Removal of Directing Groups under Mild Conditions

Isothiourea-Catalysed Acylative Dynamic Kinetic Resolution of Tetra-substituted Morpholinone and Benzoxazinone Lactols

The development of methods to allow the selective acylative dynamic kinetic resolution (DKR) of tetra-substituted lactols is a recognised synthetic challenge. In this manuscript, a highly enantioselective isothiourea-catalysed acylative DKR of tetra-substituted morpholinone and benzoxazinone-derived lactols is reported. The scope and limitations of this methodology have been developed, with high enantioselectivity and good to excellent yields (up to 89 %, 99 : 1 er) observed across a broad range of substrate derivatives incorporating substitution at N(4) and C(2), di- and spirocyclic substitution at C(5) and C(6), as well as benzannulation (>35 examples in total). The DKR process is amenable to scale-up on a 1 g laboratory scale. The factors leading to high selectivity in this DKR process have been probed through computation, with an N-C=O⋅⋅⋅isothiouronium interaction identified as key to producing ester products in highly enantioenriched form.

[Development of Unactivated Bond Cleavage Reactions Under Mild Conditions Based on Stabilization of Addition Intermediates]

Cleavage of unactivated bonds, such as amides, often requires challenging reaction conditions with strong acids and bases, and the tolerance of functional groups is limited. Therefore, the development of cleavage reactions for unactivated bonds under mild reaction conditions is essential. Herein, I report our recent developments in the cleavage of unactivated bonds under mild conditions. We achieved cleavage of unactivated amides, carbamates, ureas, and esters, as well as chemoselective cleavage of directing groups. Furthermore, we conducted mechanistic studies and found that these reactions proceed through the stabilization of addition intermediates.

Fully lignocellulose-based PET analogues for the circular economy

Polyethylene terephthalate is one of the most abundantly used polymers, but also a significant pollutant in oceans. Due to growing environmental concerns, polyethylene terephthalate alternatives are highly sought after. Here we present readily recyclable polyethylene terephthalate analogues, made entirely from woody biomass. Central to the concept is a two-step noble metal free catalytic sequence (Cu20-PMO catalyzed reductive catalytic fractionation and Raney Ni mediated catalytic funneling) that allows for obtaining a single aliphatic diol 4-(3-hydroxypropyl) cyclohexan-1-ol in high isolated yield (11.7 wt% on lignin basis), as well as other product streams that are converted to fuels, achieving a total carbon yield of 29.5%. The diol 4-(3-hydroxypropyl) cyclohexan-1-ol is co-polymerized with methyl esters of terephthalic acid and furan dicarboxylic acid, both of which can be derived from the cellulose residues, to obtain polyesters with competitive Mw and thermal properties (T_g of 70–90 °C). The polymers show excellent chemical recyclability in methanol and are thus promising candidates for the circular economy.

‘Polyethylene terephthalate is a widely used polymer with a concerning environmental impact, and alternatives are now highly sought. In this article, the authors present a biorefinery strategy for constructing polyester analogues of polyethylene terephthalate from woody biomass, which are promising candidates for the circular economy.

A Guide to Directing Group Removal: 8-Aminoquinoline

The use of directing groups allows high levels of selectivity to be achieved in transition metal-catalyzed transformations. Efficient removal of these auxiliaries after successful functionalization, however, can be very challenging. This review provides a critical overview of strategies used for removal of Daugulis' 8-aminoquinoline (2005-2020), one of the most widely used N,N-bidentate directing groups. The limitations of these strategies are discussed and alternative approaches are suggested for challenging substrates. Our aim is to provide a comprehensive end-users' guide for chemists in academia and industry who want to harness the synthetic power of directing groups-and be able to remove them from their final products.

Runge–Kutta analysis for optimizing the Zn-catalyzed transesterification conditions of MA and MMA with diols to maximize monoesterified products

Terminal hydroxylated acrylate derivatives were prepared by transesterification using zinc catalyst. The time to reach the equilibrium state was analyzed by curve-fitting analysis based on the Runge–Kutta method for optimizing the best conditions.

Esterification of Tertiary Amides: Remarkable Additive Effects of Potassium Alkoxides for Generating Hetero Manganese-Potassium Dinuclear Active Species

A catalyst system of mononuclear manganese precursor 3 combined with potassium alkoxide served as a superior catalyst compared with our previously reported manganese homodinuclear catalyst 2 a for esterification of not only tertiary aryl amides, but also tertiary aliphatic amides. On the basis of stoichiometric reactions of 3 and potassium alkoxide salt, kinetic studies, and density functional theory (DFT) calculations, we clarified a plausible reaction mechanism in which in situ generated manganese-potassium heterodinuclear species cooperatively activates the carbonyl moiety of the amide and the OH moiety of the alcohols. We also revealed details of the reaction mechanism of our previous manganese homodinuclear system 2 a, and we found that the activation free energy (ΔG≠ ) for the manganese-potassium heterodinuclear complex catalyzed esterification of amides is lower than that for the manganese homodinuclear system, which was consistent with the experimental results. We further applied our catalyst system to deprotect the acetyl moiety of primary and secondary amines.

Discovery, Optimization, and Characterization of ML417: A Novel and Highly Selective D3 Dopamine Receptor Agonist

To identify novel D₃ dopamine receptor (D3R) agonists, we conducted a high-throughput screen using a β-arrestin recruitment assay. Counterscreening of the hit compounds provided an assessment of their selectivity, efficacy, and potency. The most promising scaffold was optimized through medicinal chemistry resulting in enhanced potency and selectivity. The optimized compound, ML417 (20), potently promotes D3R-mediated β-arrestin translocation, G protein activation, and ERK1/2 phosphorylation (pERK) while lacking activity at other dopamine receptors. Screening of ML417 against multiple G protein-coupled receptors revealed exceptional global selectivity. Molecular modeling suggests that ML417 interacts with the D3R in a unique manner, possibly explaining its remarkable selectivity. ML417 was also found to protect against neurodegeneration of dopaminergic neurons derived from iPSCs. Together with promising pharmacokinetics and toxicology profiles, these results suggest that ML417 is a novel and uniquely selective D3R agonist that may serve as both a research tool and a therapeutic lead for the treatment of neuropsychiatric disorders.

Catalytic Cleavage of Amide C-N Bond: Scandium, Manganese, and Zinc Catalysts for Esterification of Amides

Amide C-N bonds are thermodynamically stable and their fission, such as by hydrolysis and alcoholysis, is considered a long-challenging organic reaction. In general, stoichiometric chemical transformations of amides into the corresponding esters and acids require harsh conditions, such as strong acids/bases at a high reaction temperature. Accordingly, the development of catalytic reactions that cleave not only primary and secondary amides, but also tertiary amides in mild conditions, is in high demand. Herein, we surveyed typical stoichiometric transformations of amides, and highlight our recent achievements in the catalytic esterification of amides using scandium, manganese, and zinc catalysts, together with some recent catalyst systems using late-transition metal reported by other groups.

Directed C(sp3)-H arylation of tryptophan: transformation of the directing group into an activated amide

The aminoquinoline-directed C–H activation was used to synthezise unnatural tryptophans for solid phase peptide synthesis for the first time.

The 8-aminoquinoline (8AQ) directed C(sp³)–H functionalization was applied in the synthesis of β-arylated tryptophan derivatives. The laborious protecting group reorganization towards α-amino acids compatible for solid phase peptide synthesis (SPPS) was cut short by the transformation of the directing group into an activated amide, which was either used directly in peptide coupling or in the gram scale synthesis of storable Fmoc-protected amino acids for SPPS. In this work, directed C–H activation and nonplanar amide chemistry complement each other for the synthesis of hybrids between phenylalanine and tryptophan with restricted side chain mobility.

Dinuclear manganese alkoxide complexes as catalysts for C-N bond cleavage of simple tertiary N,N-dialkylamides to give esters

Amide bonds are stable due to the resonance between the nitrogen lone pair and the carbonyl moiety, and therefore the chemical transformation of amides, especially tertiary amides, involving C-N bond fission is considered one of the most difficult organic reactions, unavoidably requiring harsh reaction conditions and strong acids or bases. We report the catalytic C-N bond cleavage of simple tertiary N,N-dialkylamides to give corresponding esters using a catalyst system (2 mol% based on Mn atoms) of a tetranuclear manganese alkoxide, [Mn(acac)(OEt)(EtOH)]4 (1c), combined with four equivalents of 4,7-bis(dimethylamino)-1,10-phenanthroline (L1: Me2N-Phen). Regarding the reaction mechanism, we isolated a dinuclear manganese complex, [Mn(acac)(OEt)(Phen)]2 (6c), which was revealed as the catalytically active species for the esterification of tertiary amides.

The Pd-catalyzed C–H alkylation of ortho-methyl-substituted aromatic amides with maleimide occurs preferentially at the ortho-methyl C–H bond over the ortho-C–H bond

The reaction of ortho-methyl-substituted aromatic amides with maleimides in the presence of Pd(OAc)₂ and AgOAc results in C–H alkylation only at the ortho-methyl C–H bond.

Metal Template Assisted Proximal Arrangement of a Nucleophile and an Electrophile: Site-Selective Acylation of α-Hydroxyamides in Polyols

Site-selective acylation of α-hydroxyl groups in amides has been achieved in the presence of other primary hydroxyl groups with intrinsic high reactivity. In this methodology, a relatively stable pyridine aldoxime ester was exploited as an acyl donor to suppress undesired acylation. The catalytic activation of a pyridine aldoxime ester with a Lewis acid produced a cationic complex, which preferentially attracted the Lewis basic α-hydroxyamide via a template effect, to thus facilitate o-acylation.

A Two-Step Procedure for the Overall Transamidation of 8-Aminoquinoline Amides Proceeding via the Intermediate N-Acyl-Boc-Carbamates

Herein a two-step strategy for achieving overall transamidation of 8-aminoquinoline amides has been explored. In this protocol, the 8-aminoquinoline amides were first treated with Boc₂O and DMAP to form the corresponding N-acyl-Boc-carbamates, which were found to be sufficiently reactive to undergo subsequent aminolysis with different amines in the absence of any additional reagents or catalysts. To demonstrate the utility of this approach, it was applied on a number of 8-aminoquinoline amides from the recent C-H functionalization literature, enabling access to a range of elaborate amide derivatives in good to high yields.

One-pot transition-metal free transamidation to sterically hindered amides

A highly efficient one-pot transamidation of primary amides has been developed under transition-metal free conditions, generating a variety of amides including hindered amides in good yield (up to 86%) catalyzed by CsF.