One-Pot Synthesis of Deuterated Aldehydes from Arylmethyl Halides

Mechanistic Analysis of 5-Hydroxy γ-Pyrones as Michael Acceptor Prodrugs

Substituted 5-hydroxy γ-pyrones have shown promise as covalent inhibitor leads against cysteine proteases and transcription factors, but their hydrolytic instability has hindered optimization efforts. Previous mechanistic proposals have suggested that these molecules function as Michael acceptor prodrugs, releasing a leaving group to generate an o-quinone methide-like structure. Addition to this electrophile of either water or an active site cysteine was purported to lead to inhibitor hydrolysis or enzyme inhibition, respectively. Through the use of kinetic nuclear magnetic resonance experiments, Hammett analysis, kinetic isotope effect studies, and density functional theory calculations, our findings suggest that enzyme inhibition and hydrolysis proceed by distinct pathways and are differentially influenced by substituent electronics. This mechanistic revision helps enable a more rational optimization for this class of promising compounds.

Combining tetraphenylethene (TPE) derivative cations with Eu3+-β-diketone complex anions for tunable luminescence

Tetraphenylethene (TPE) derivative cations (TPE⁺) and Eu³⁺-β-diketone complex anions (Eu(ABM)₄^-) were combined to construct a novel dual energy transfer system (TPE⁺ to Eu³⁺ and ABM to Eu³⁺). Our system exhibits tunable luminescence in DMF/water mixtures under different f_w conditions owing to the AIE and ACQ properties of TPE⁺ and ABM, respectively. Its luminescence can be also regulated by adding P-containing oxysalts or polyacrylic acids.

Catalytic Vilsmeier-Haack Reactions for C1-Deuterated Formylation of Indoles

The Vilsmeier-Haack reaction is a powerful tool to introduce formyl groups into electron-rich arenes, but its wide application is significantly restricted by stoichiometric employment of caustic POCl₃. Herein, we reported a catalytic version of the Vilsmeier-Haack reaction enabled by a P(III)/P(V)═O cycle. This catalytic reaction provides a facile and efficient route for the direct construction of C1-deuterated indol-3-carboxaldehyde under mild conditions with stoichiometric DMF-d7 as the deuterium source. The products feature a remarkably higher deuteration level (>99%) than previously reported ones and are not contaminated by the likely unselective deuteration at other sites. The present transformation can also be used to transfer other carbonyl groups. Further downstream derivatizations of these deuterated products manifested their potential applications in the synthesis of deuterated bioactive molecules. Mechanistic insight was disclosed from studies of kinetics and intermediates.

Recent Advances in Practical Synthesis of C1 Deuterated Aromatic Aldehydes Enabled by Catalysis and Beyond

C 1 -selective deuteration of aromatic aldehydes is of great importance for isotopic labeling and for improving the characteristics of drug molecules. Due to the recent increase in the use of deuterated pharmacological drugs, there is a pressing need for synthetic procedures that are efficient to produce deuterated aromatic aldehyde analouges. Deuterium labeling approaches are typically used as an effective tool for researching pharmaceutical absorption, distribution, metabolism, and excretion (ADME). Furthermore, deuterium-labeled pharmaceuticals are intended to increase therapeutic effectiveness and reduce side effects by extending the half-life of drug response. In the last few years, several catalytic or non-catalytic methods have been developed to synthesize deuterated aromatic aldehydes. In this concern, we offer a brief overview of the various synthetic strategies and practical methods for the formyl-selective deuterium labeling of aromatic aldehydes using different deuterium sources.

Synthesis of C-1 Deuterated 3-Formylindoles by Organophotoredox Catalyzed Direct Formylation of Indoles with Deuterated Glyoxylic Acid

Direct formylation of feedstock indoles with newly developed, cost-effective deuterated glyoxylic acid as formylation agent under visible light and air (O₂) as terminal oxidant has been developed. An isatin byproduct produced from the corresponding indole reactant serves as a facilitator for the formylation process. The simple, mild, metal- and oxidant-free protocol enables the synthesis of structurally diverse C1-deuterated 3-formylindoles with broad functional group tolerance and late-stage functionalization at a high level of D-incorporation (95-99%).

Programmable iodization/deuterolysis sequences of phosphonium ylides to access deuterated benzyl iodides and aromatic aldehydes

Herein, a tunable iodization/deuterolysis protocol for phosphonium ylides by employing D₂O as the deuterium source was designed. Notably, this process could be manipulated by tuning the base, thus leading to two valuable deuterated building blocks - benzyl iodides and aromatic aldehydes with broad substrate scope, good functional group compatibility and excellent deuteration degree. Concise syntheses of a series of deuterated drug analogues have been achieved based on the developed deuteration reaction platform.

Recent Developments for the Deuterium and Tritium Labeling of Organic Molecules

Organic compounds labeled with hydrogen isotopes play a crucial role in numerous areas, from materials science to medicinal chemistry. Indeed, while the replacement of hydrogen by deuterium gives rise to improved absorption, distribution, metabolism, and excretion (ADME) properties in drugs and enables the preparation of internal standards for analytical mass spectrometry, the use of tritium-labeled compounds is a key technique all along drug discovery and development in the pharmaceutical industry. For these reasons, the interest in new methodologies for the isotopic enrichment of organic molecules and the extent of their applications are equally rising. In this regard, this Review intends to comprehensively discuss the new developments in this area over the last years (2017-2021). Notably, besides the fundamental hydrogen isotope exchange (HIE) reactions and the use of isotopically labeled analogues of common organic reagents, a plethora of reductive and dehalogenative deuteration techniques and other transformations with isotope incorporation are emerging and are now part of the labeling toolkit.

Reassembly and functionalization of N-CF3 pyridinium salts: synthesis of nicotinaldehydes

An unprecedented hydrolyzation-triggered ring opening and recyclization cascade to construct biologically interesting nicotinaldehydes.

Selective oxidation of alcohol-d 1 to aldehyde-d 1 using MnO2

The selective oxidation of alcohol-d₁ to prepare aldehyde-d₁ was newly developed by means of NaBD₄ reduction/activated MnO₂ oxidation. Various aldehyde-d₁ derivatives including aromatic and unsaturated aldehyde-d₁ can be prepared with a high deuterium incorporation ratio (up to 98% D). Halogens (chloride, bromide, and iodide), alkene, alkyne, ester, nitro, and cyano groups in the substrates are tolerated under the mild conditions.

A facile method for deutrium incorporation into aldehydes by mild reduction of NaBD₄ of aldehydes and MnO₂ oxidation (98% D) is disclosed.

Nitrosoarene-Catalyzed HFIP-Assisted Transformation of Arylmethyl Halides to Aromatic Carbonyls under Aerobic Conditions

A rare metal-free nucleophilic nitrosoarene catalysis accompanied by highly hydrogen-bond-donor (HBD) solvent, 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), organocatalytically converts arylmethyl halides to aromatic carbonyls. This protocol offers an effective means to access a diverse array of aromatic carbonyls with good chemoselectivity under mild reaction conditions. The activation of arylmethyl halides by HFIP to generate stable carbocation and autoxidation of in situ generated hydroxylamine to nitrosoarene in the presence of atmospheric O₂ are the keys to success.

Cleavage and Reassembly of the C═O Bond of 2-Alkynylbenzaldehydes: A Metal-Free Access to Inden-1-ones

A metal-free approach to inden-1-ones from 2-alkynylbenzaldehydes mediated by pyrrolidine has been developed. The reaction proceeds under mild conditions in a step- and atom-economy process by cleaving the C═O bond and constructing new C-C as well as C═O bonds. Oxygen-18 and deuterium labeling experiments revealed an aza-Petasis-Ferrier rearrangement of an intermediate 1-amino-3-methylene-dihydroisobenzofuran.

Single-Step Approach toward Nitrones via Pyridinium Ylides: The DMAP-Catalyzed Reaction of Benzyl Halides with Nitrosoarenes

A single-step approach is reported for the preparation of nitrones from benzyl halides and nitrosoarenes via pyridinium ylides, utilizing 4-dimethylaminopyridine (DMAP) catalyst and mild reaction conditions (Li₂CO₃, dimethylacetamide, and room temperature). The reaction provides both keto- and aldonitrones in high yields with a wide scope for benzyl halides and nitrosoarenes. In the same reaction system, 2-methyl-2-nitrosopropane, which does not have an aryl group, also affords the corresponding N-tert-butyl nitrones from primary benzyl bromides that have an electron-withdrawing group. As an application of the reaction, methyl 2-bromo-2-phenylacetate was used to prepare the corresponding isoxazolidine by a sequential one-pot synthesis.

Deuteration of Formyl Groups via a Catalytic Radical H/D Exchange Approach

H/D exchange at formyl groups represents the straightforward approach to C-1 deuterated aldehydes. This transformation has been recently realized by transition metal and NHC carbene catalysis. Mechanistically, all these processes involve an ionic pathway. Herein we report a distinct photoredox catalytic, visible light mediated neutral radical approach. Selective control of highly reactive acyl radical in the energy barrier surmountable, reversible reaction enables driving the formation of deuterated products when an excess of D2O is employed. The power of the H/D exchange process has been demonstrated for not only aromatic aldehydes, but also aliphatic substrates, which have been difficult in transitional metal catalyzed H/D exchange reactions, and for selective late-stage deuterium incorporation into complex structures with uniformly high deuteration level (>90%).

Practical Synthesis of C-1 Deuterated Aldehydes Enabled by NHC Catalysis

The recent surge in applications of deuterated pharmaceutical agents has created an urgent demand for synthetic methods that efficiently generate deuterated building blocks. Here we show that N-heterocyclic carbenes (NHC) promote a reversible hydrogen-deuterium exchange (HDE) reaction with simple aldehydes, which leads to a practical approach to synthetically valuable C-1 deuterated aldehydes. The reactivity of the well-established NHC catalysed formation of Breslow intermediates from aldehydes is reengineered to overcome the overwhelmingly kinetically favorable, irreversible benzoin condensation reaction and achieve the critical reversibility to drive the formation of desired deuterated products when an excess of D₂O is employed. Notably, this operationally simple and cost-effective protocol serves as a general and truly practical approach to all types of 1-D-aldehydes including aryl, -alkyl and -alkenyl aldehydes and enables chemoselective late-stage deuterium incorporation into complex, native therapeutic agents and natural products with uniformly high levels (>95%) of deuterium incorporation for a total of 104 substrates tested.

Trideuteromethylation Enabled by a Sulfoxonium Metathesis Reaction

A conceptually novel sulfoxonium metathesis reaction between TMSOI and cost-effective DMSO- d6 is developed for the efficient generation of a new trideuteromethylation reagent TDMSOI. The new reagent TDMSOI is produced highly efficiently by simply heating a mixture of TMSOI and DMSO- d6 and directly used for subsequent trideuteromethylation in a "one-pot" operation. The preparative power of the new versatile reagent and the "one-pot" protocol is demonstrated by its use to install the -CD3 moiety into broad functionalities including phenols, thiophenols, acidic amines, and enolizable methylene units in high yield and at a useful level of deuteration (>87% D).