Palladium-catalyzed synthesis of N-aryl carbamates

Electrophilic C(sp2)-H Cyanation with Inorganic Cyanate (OCN-) by PIII/PV=O-Catalyzed Phase Transfer Activation

An organophosphorus -catalyzed method for the direct electrophilic cyanation of C(sp2)-H nucleophiles with sodium cyanate (NaOCN) is reported. The catalytic deoxyfunctionalization of the OCN- anion is enabled by the use of a small-ring phosphacyclic (phosphetane) catalyst in combination with a terminal hydrosilane O-atom acceptor and a malonate-derived bromenium donor. In situ spectroscopy under single-turnover conditions demonstrate that insoluble inorganic cyanate anion is activated by bromide displacement on a bromophosphonium catalytic intermediate to give a reactive N-bound isocyanatophosphonium ion, which delivers electrophilic "CN+" equivalents to nucleophilic (hetero)arenes and alkenes with loss of a phosphine oxide. These results demonstrate the feasibility of deoxyfunctionalization of insoluble inorganic salts by PIII/PV=O catalyzed phase transfer activation.

Direct synthesis of carbamates, thiocarbamates, and ureas from Boc-protected amines: a sustainable and efficient approach

In the quest for sustainable and efficient synthetic methodologies within medicinal chemistry, the synthesis of carbamates and their derivatives holds a pivotal role due to their widespread application in bioactive compounds. This investigation unveils a novel methodology for the straightforward transformation of Boc-protected amines into carbamates, thiocarbamates, and ureas, utilizing tert-butoxide lithium as the sole base. This approach effectively obviates the necessity for hazardous reagents and metal catalysts, presenting marked enhancements compared to traditional synthetic pathways. Notably, the method demonstrates facile scalability to gram-level production. This study contributes to the advancement of sustainable synthetic methodologies, offering a more benign and efficient alternative for the synthesis of key chemical intermediates with implications for broad pharmaceutical and agrochemical applications.

Derivatization of 2,1,3-Benzothiadiazole via Regioselective C-H Functionalization and Aryne Reactivity

Despite growing interest in 2,1,3-benzothiadiazole (BTD) as an integral component of many functional molecules, methods for the functionalization of its benzenoid ring have remained limited, and many even simply decorated BTDs have required de novo synthesis. We show that regioselective Ir-catalyzed C-H borylation allows access to versatile 5-boryl or 4,6-diboryl BTD building blocks, which undergo functionalization at the C4, C5, C6, and C7 positions. The optimization and regioselectivity of C-H borylation are discussed. A broad reaction scope is presented, encompassing ipso substitution at the C-B bond, the first examples of ortho-directed C-H functionalization of BTD, ring closing reactions to generate fused ring systems, as well as the generation and capture reactions of novel BTD-based heteroarynes. The regioselectivity of the latter is discussed with reference to the Aryne Distortion Model.

General cross-coupling reactions with adaptive dynamic homogeneous catalysis

Cross-coupling reactions are among the most important transformations in modern organic synthesis^1-3. Although the range of reported (het)aryl halides and nucleophile coupling partners is very large considering various protocols, the reaction conditions vary considerably between compound classes, necessitating renewed case-by-case optimization of the reaction conditions⁴. Here we introduce adaptive dynamic homogeneous catalysis (AD-HoC) with nickel under visible-light-driven redox reaction conditions for general C(sp²)-(hetero)atom coupling reactions. The self-adjustive nature of the catalytic system allowed the simple classification of dozens of various classes of nucleophiles in cross-coupling reactions. This is synthetically demonstrated in nine different bond-forming reactions (in this case, C(sp²)-S, Se, N, P, B, O, C(sp³, sp², sp), Si, Cl) with hundreds of synthetic examples under predictable reaction conditions. The catalytic reaction centre(s) and conditions differ from one another by the added nucleophile, or if required, a commercially available inexpensive amine base.

Sustainable Route Toward N-Boc Amines: AuCl3 /CuI-Catalyzed N-tert-butyloxycarbonylation of Amines at Room Temperature

N-tert-butoxycarbonyl (N-Boc) amines are useful intermediates in synthetic/medicinal chemistry. Traditionally, they are prepared via an indirect phosgene route with poor atom economy. Herein, a step- and atom-economic synthesis of N-Boc amines from amines, t-butanol, and CO was reported at room temperature. Notably, this N-tert-butyloxycarbonylation procedure utilized ready-made substrates, commercially available AuCl₃ /CuI as catalysts, and O₂ from air as the sole oxidant. This catalytic system provided unique selectivity for N-Boc amines in good yields. More significantly, gram-scale preparation of medicinally important N-Boc amine intermediates was successfully implement, which demonstrated a potential application prospect in industrial syntheses. Furthermore, this approach also showed good compatibility with tertiary and other useful alcohols. Investigations of the mechanisms revealed that gold catalyzed the reaction and copper acted as electron transfer mediator in the catalytic cycle.

Synthesis of 3H-1,2,4-Triazol-3-ones via NiCl2-Promoted Cascade Annulation of Hydrazonoyl Chlorides and Sodium Cyanate

A nickel-promoted cascade annulation reaction for the facile synthesis of 3H-1,2,4-triazol-3-ones from readily available hydrazonoyl chlorides and sodium cyanate has been developed. The transformation occurs through a cascade nickel-promoted intermolecular nucleophilic addition-elimination process, intramolecular nucleophilic addition, and a hydrogen-transfer sequence. The method has been successfully applied for the construction of the core skeleton of the angiotensin II antagonist.

Comparative study of aryl halides in Pd-mediated reactions: key factors beyond the oxidative addition step

The comparative experimental study of Ar–X (X = Cl, Br, I) reactivity and analysis reported herein suggest that oxidative addition cannot be considered the sole reason of the observed low reactivity of aryl chlorides.

Discovery of DS68702229 as a Potent, Orally Available NAMPT (Nicotinamide Phosphoribosyltransferase) Activator

Nicotinamide phosphoribosyltransferase (NAMPT) catalyzes the rate-limiting step of the nicotinamide adenine dinucleotide (NAD+) salvage pathway. Because NAD+ plays a pivotal role in energy metabolism and boosting NAD+ has positive effects on metabolic regulation, activation of NAMPT is an attractive therapeutic approach for the treatment of various diseases, including type 2 diabetes and obesity. Herein we report the discovery of 1-(2-phenyl-1,3-benzoxazol-6-yl)-3-(pyridin-4-ylmethyl)urea 12c (DS68702229), which was identified as a potent NAMPT activator. Compound 12c activated NAMPT, increased cellular NAD+ levels, and exhibited an excellent pharmacokinetic profile in mice after oral administration. Oral administration of compound 12c to high-fat diet-induced obese mice decreased body weight. These observations indicate that compound 12c is a promising anti-obesity drug candidate.

Small-Scale Procedure for Acid-Catalyzed Ketal Formation

A modified procedure for dehydrative ketal protections is disclosed, which serves as an alternative to the classic Dean-Stark protocol. Studies show that this new procedure can outperform the Dean-Stark apparatus on small scales and thus serves as a complementary approach to effect dehydrative ketalizations. A detailed procedure for this apparatus is presented.

One stone two birds: cobalt-catalyzed in situ generation of isocyanates and benzyl alcohols for the synthesis of N-aryl carbamates

An efficient method for the synthesis of N-aryl carbamates from N-Boc-protected amines has been developed. The cobalt-catalyzed in situ generation of isocyanates from N-Boc-protected amines and benzyl alcohols from benzyl formates has been achieved for the first time, which in turn furnished the corresponding benzyl carbamates in moderate to high yields. The reaction was catalyzed by CoI₂ with tris-(4-dimethylaminophenyl)-phosphine as the ligand and zinc powder as the reductant. The developed reaction conditions were found to be compatible for aromatic amines with both electron-donating and -withdrawing substituents.

An Fe3O4@SiO2/Schiff base/Cu(ii) complex as an efficient recyclable magnetic nanocatalyst for selective mono N-arylation of primary O-alkyl thiocarbamates and primary O-alkyl carbamates with aryl halides and arylboronic acids

A convenient and efficient selective mono N-arylation of primary O-alkyl thiocarbamates and carbamates is reported by a recyclable magnetic Cu(ii) nanocatalyst.

Synthesis of N-(Hetero)aryl Carbamates via CuI/MNAO Catalyzed Cross-Coupling of (Hetero)aryl Halides with Potassium Cyanate in Alcohols

An efficient route to N-(hetero)aryl carbamates was developed through CuI/MNAO [2-((2-methylnaphthalen-1-yl)amino)-2-oxoacetic acid] catalyzed cross-coupling of (hetero)aryl chlorides with potassium cyanate in alcohols at 120-130 °C. This method utilizes broadly available substrates to afford various N-(hetero)aryl carbamates in good to excellent yields. Moreover, (hetero)aryl bromides and (hetero)aryl iodides were also reacted at low catalyst loadings and relatively low temperatures to provide N-(hetero)aryl carbamates.

A direct strategy to synthesize hybrid benzothiazole–carbamate moieties via O-acylation of phenols under metal–organic framework catalysis

Cu-CPO-27 was used as an efficient recyclable catalyst for the synthesis of benzothiazole–carbamate structures.

Copper-catalyzed carbonylation of anilines by diisopropyl azodicarboxylate for the synthesis of carbamates

Herein, a simple Cu-catalyzed system for the synthesis of carbamates has been developed using anilines with diisopropyl azodicarboxylate as a carbonyl source under solvent-free conditions.

Fe3O4@SiO2/Schiff base/Pd complex as an efficient heterogeneous and recyclable nanocatalyst for chemoselective N-arylation of O-alkyl primary carbamates

An Fe₃O₄@SiO₂/Schiff base/Pd complex as an efficient, heterogeneous magnetically recoverable and reusable catalyst for the N-arylation of O-alkyl primary carbamates.

Synthesis of acyl carbamates via four component Pd-catalyzed carbonylative coupling of aryl halides, potassium cyanate, and alcohols

A simple and mild method is demonstrated for assembling acyl carbamates through a base-free four-component Pd-catalyzed carbonylation of aryl halides in the presence of potassium cyanate and alcohols in a two-chamber system. This approach produces a wide range of aryl acyl carbamates in good to excellent yields from the corresponding aryl bromides or iodides with near-stoichiometric carbon monoxide. In addition, the method can be extended to the synthesis of primary amides thereby expanding the usefulness of cyanate as an ammonia equivalent.

Quinoline-2-carboimine copper complex immobilized on amine functionalized silica coated magnetite nanoparticles: a novel and magnetically retrievable catalyst for the synthesis of carbamates via C–H activation of formamides

A novel and magnetically recoverable nanocatalytic system consisting of a magnetic silica based copper complex has been fabricated and applied in the synthesis of carbamates via C–H activation of formamides.

PdCl2 catalyzed efficient assembly of organic azides, CO, and alcohols under mild conditions: a direct approach to synthesize carbamates

A simple and readily available PdCl2 catalyzed carbamate synthesis method via isocyanate generation and application in situ has been developed. This chemistry provides an efficient and practical approach to synthesize carbamates from simple organic azides, CO atmosphere and alcohols. The broad scope, mild and neutral conditions, and only N2 as the byproduct make this transformation very useful. Moreover, simple examples of modification of bioactive molecules and construction of macrocycles were achieved through this protocol.

Structural reevaluation of the electrophilic hypervalent iodine reagent for trifluoromethylthiolation supported by the crystalline sponge method for X-ray analysis

Hypervalent iodine λ3-benziodoxoles are common electrophilic transfer reagents known for their enhanced stability compared to their non-cyclic analogues. Herein we present data showing that chlorobenziodoxole reacts with two different thiolate nucleophiles (thiocyanate and trifluoromethylthiolate), resulting in the formation of stable thioperoxy complexes rather than the expected benziodoxole derivatives. We further report a revised structure for the earlier described electrophilic trifluoromethylthiolation reagent (1), which was previously believed to contain the benziodoxole framework. Our findings, which are based on a combination of analytical techniques, including the recently introduced crystalline sponge method for X-ray analysis, unambiguously demonstrate that 1 is a thioperoxy compound both in solution and the solid state.

Metal free oxidative coupling of aryl formamides with alcohols for the synthesis of carbamates

A new method under metal free conditions has been developed for the direct transformation of N-aryl formamides to corresponding N-aryl carbamates with alcohols using hypervalent iodine reagents as oxidants. The reaction has been postulated to go through the formation of isocyanate intermediates.

PLA/POSS nanofibers: a novel system for the immobilization of metal nanoparticles

In this work, a novel catalytic system is developed, consisting of palladium nanoclusters homogenously dispersed on the surface of nanostructured polymer nanofibers based on poly(L-lactic acid) (PLLA) and polyhedral oligomeric silsesquioxanes (POSS). Indeed, PLLA nanofibers containing amino-functionalized silsesquioxane molecules (POSS-NH2), potentially capable of interacting with the metal precursor, are prepared by means of electrospinning. Conversely to the polymer matrix, which does not show any tendency to retain the metal precursor, the submicrometric dispersion of POSS-NH2 in the PLLA nanofibers, as demonstrated by SEM-EDS analysis, turns out to promote the formation of metal nanoclusters. TEM measurements show a uniform distribution of Pd nanoparticles, characterized by an average dimension of ca. 4 nm, along the fibers. The prepared system proves a relevant catalytic activity toward the hydrogenation of stilbene under heterogeneous conditions. Moreover, as demonstrated by XPS measurements, the support is capable of retaining the catalyst during the hydrogenation reaction, thus preventing its leaching.