Palladium-catalyzed Aminocarbonylation Research Articles

Synthesis of Multisubstituted 2,3-Allenamides via Palladium-Catalyzed Carbonylation of Propargylic Esters.

2,3-Allenamides are an important class of unsaturated group-substituted carbonyl compounds. A palladium-catalyzed aminocarbonylation of propargyl acetates with amines for the synthesized tri-/tetrasubstituted 2,3-allenamides has been developed. A broad range of tri-/tetrasubstituted 2,3-allenamides have been prepared from propargyl acetates in good to excellent yields. The reaction featured mild reaction conditions and good functional group tolerance. The applicability of this methodology was further highlighted by the late-stage modification of several natural products and pharmaceuticals.

Synthesis of p-phenylene-based chiral dicarboxamides via aminocarbonylation of 1’,4-diiodostyrene

Chiral p-phenylene-based dicarboxamides featuring carboxamide and 2-arylacrylamide motifs were synthesised through a synthetic sequence involving conventional organic reactions followed by palladium-catalysed aminocarbonylation. 4-Iodoacetophenone was used as starting material to prepare to 1’,4-diiodostyrene, which underwent several aminocarbonylation reactions, using in situ formed palladium-phosphine catalysts and various biologically relevant amines as N-nucleophiles such as, amino acid esters, nortropine, and aminoandrostane derivatives. By exploring the remarkable difference in reactivity between the iodoalkene and iodoarene functionalities, the aminocarbonylation of the iodoalkene moiety was carried first with high chemoselectivity, followed by sequential transformation of the iodoarene functionality into the corresponding carboxamide using a different nucleophile. This approach allowed us to obtain a range of otherwise challenging chiral dicarboxamides, in moderate to high isolated yields through highly chemoselective reactions.

Synthesis of a 3,7-Disubstituted Isothiazolo[4,3-b]pyridine as a Potential Inhibitor of Cyclin G-Associated Kinase.

Disubstituted isothiazolo[4,3-b]pyridines are known inhibitors of cyclin G-associated kinase. Since 3-substituted-7-aryl-isothiazolo[4,3-b]pyridines remain elusive, a strategy was established to prepare this chemotype, starting from 2,4-dichloro-3-nitropyridine. Selective C-4 arylation using ligand-free Suzuki-Miyaura coupling and palladium-catalyzed aminocarbonylation functioned as key steps in the synthesis. The 3-N-morpholinyl-7-(3,4-dimethoxyphenyl)-isothiazolo[4,3-b]pyridine was completely devoid of GAK affinity, in contrast to its 3,5- and 3,6-disubstituted congeners. Molecular modeling was applied to rationalize its inactivity as a GAK ligand.

Synthesis of Chroman-2,4-diones via Ring-Opening/Ring-Closing Reaction Involving Palladium-Catalyzed Intramolecular Aryloxycarbonylation.

Palladium-catalyzed aminocarbonylation of 3-iodochromone was studied in the presence of primary and secondary amines using atmospheric pressure of carbon monoxide as a carbonyl source. This procedure successfully provided a library of chromone-3-carboxamides and 3-substituted chroman-2,4-diones in 40 to 92% isolated yields. The reaction proceeded via highly chemoselective aminocarbonylation (up to 100%) in the presence of secondary amines by using monodentate or bidentate phosphine ligands. The tendency of 3-iodochromone substrate to undergo ANRORC rearrangement with N-nucleophiles was crucial to shift the reaction toward an unprecedented chemoselective carbonylative transformation, where a late-stage carbonyl insertion is favored concomitantly to the last ring-closure step. The proposed aza-Michael addition/ring-opening/intramolecular aryloxycarbonylation sequence showed compatibility, uniquely, to primary amines when XantPhos was used as a ligand. The solid-state structures of chromone-3-carboxamide (2a) and chroman-2,4-dione (3s) were undoubtedly established by single-crystal XRD analysis. A catalytic cycle was proposed to rationalize the formation of the two types of carbonylated compounds.

Photoinduced CO-releasing molecule (photoCORM) as an in situ CO surrogate for palladium-catalysed aminocarbonylation.

Herein, we show that a photoCORM behaves as a highly substrate-tolerant, photoactivable in situ CO surrogate, allowing the synthesis of variously functionalised amides including the biologically active compound Moclobemide by Pd-catalysed aminocarbonylation between aryl iodides and amines under mild conditions. This work should bring about a useful input to the field of carbonylative transformations.

Selective Synthesis of (Z)- and (E)-β-Fluoro-α,β-Unsaturated Amides Using Palladium-Catalyzed Aminocarbonylation.

The selective synthesis of (Z)- and (E)-β-fluoro-α,β-unsaturated amides via the palladium-catalyzed aminocarbonylation of 1-fluoro-2,2-diiodovinylarenes is described in the present study. Using {Pd(allyl)Cl}2 as a catalyst and DBU as a base in DMF, the primary product is (Z)-isomers. Conversely, the use of a Xantphos ligand along with {Pd(allyl)Cl}2 and Et3N as the bases in 1,4-dioxane leads to the selective formation of (E)-isomers. Notably, 1-fluoro-2,2-diiodovinylarenes with various substituents on the phenyl ring react with various secondary amines, producing the corresponding (Z)-isomeric amides with a high yield and selectivity. In contrast, (E)-isomeric amides exhibit lower yields and restricted applicability.

Carboxamide formation in less favoured positions: Facile synthesis of 7-carboxamidochenodeoxycholanic acid derivatives

The sterically highly un-favoured position-7 of a steroidal skeleton was functionalised in a reaction sequence of conventional synthetic reactions and palladium-catalysed aminocarbonylation. The synthesis was based on the use of chenodeoxycholanic acid as starting material, which was transformed to 24-carboxamide, followed by oxidation of 7-hydroxy group. The resulting 7-oxo functionality was converted to the corresponding iodoalkene by the Barton's method. The 7-iodo-6-ene functionality underwent high-yielding aminocarbonylation in the presence of palladium-phosphine in situ catalysts and various amines as N-nucleophiles. The new 7-carboxamido compounds were obtained in good isolated yields, via highly chemoselective reactions, under relatively mild conditions.

Alkyl Levulinates and 2-Methyltetrahydrofuran: Possible Biomass-Based Solvents in Palladium-Catalyzed Aminocarbonylation

In this research, ethyl levulinate, methyl levulinate, and 2-methyltetrahydrofuran as bio-derived hemicellulose-based solvents were applied as green alternatives in palladium-catalyzed aminocarbonylation reactions. Iodobenzene and morpholine were used in optimization reactions under different conditions, such as temperatures, pressures, and ligands. It was shown that the XantPhos ligand had a great influence on conversion (98%) and chemoselectivity (100% carboxamide), compared with the monodentate PPh3. Following this study, the optimized conditions were used to extend the scope of substrates with nineteen candidates (various para-, ortho-, and meta-substituted iodobenzene derivatives and iodo-heteroarenes), as well as eight different amine nucleophiles.

Palladium-Catalyzed Aminocarbonylation of Isoquinolines Utilizing Chloroform-COware Chemistry.

The carbonyl group forms an integral part of several drug molecules and materials; hence, synthesis of carbonylated compounds remains an intriguing area of research for synthetic and medicinal chemists. Handling toxic CO gas has several limitations; thus, using safe and effective techniques for in or ex situ generation of carbon monoxide from nontoxic and cheap precursors is highly desirable. Among several precursors that have been explored for the generation of CO gas, chloroform can prove to be a promising CO surrogate due to its cost-effectiveness and ready availability. However, the one-pot chloroform-based carbonylation reaction requires strong basic conditions for hydrolysis of chloroform that may affect functional group tolerability of substrates and scale-up reactions. These limitations can be overcome by a two-chamber reactor (COware) that can be utilized for ex situ CO generation through hydrolysis of chloroform in one chamber and facilitating safe carbonylation reactions in another chamber under mild conditions. The versatility of this "Chloroform-COware" technique is explored through palladium-catalyzed aminocarbonylation of medicinally relevant heterocyclic cores, viz., isoquinoline and quinoline.

Palladium-Catalyzed Aminocarbonylation of (Hetero)aryl Iodides with α-Amino Acid Esters as Nucleophiles.

We report palladium-catalyzed aminocarbonylation of (hetero)aryl iodides with α-amino acid esters as nucleophiles. The synthesized N-capped α-amino acids are biologically important building blocks. The mild conditions provide products with high enantioselectivity at 80 °C in 35 min. The reactions are performed under air in a sealed vessel using chloroform as an in situ CO source. For the first time, regioselective carbonylation of histidine is also presented.

A general synthesis of aromatic amides via palladium-catalyzed direct aminocarbonylation of aryl chlorides

Aryl amines made easy by palladium-catalyzed aminocarbonylation of aryl chlorides.

Highly Selective Synthesis of 6-Glyoxylamidoquinoline Derivatives via Palladium-Catalyzed Aminocarbonylation.

The aminocarbonylation of 6-iodoquinoline has been investigated in the presence of large series of amine nucleophiles, providing an efficient synthetic route for producing various quinoline-6-carboxamide and quinoline-6-glyoxylamide derivatives. It was shown, after detailed optimization study, that the formation of amides and ketoamides is strongly influenced by the reaction conditions. Performing the reactions at 40 bar of carbon monoxide pressure in the presence of Pd(OAc)2/2 PPh3, the corresponding 2-ketocarboxamides were formed as major products (up to 63%). When the monodentate triphenylphosphine was replaced by the bidentate XantPhos, the quinoline-6-carboxamide derivatives were synthesized almost exclusively under atmospheric conditions (up to 98%). The isolation and characterization of the new carbonylated products of various structures were also accomplished. Furthermore, the structure of three new mono- and double-carbonylated compounds were unambiguously established by using a single-crystal XRD study.

Palladium-catalyzed carbonylative synthesis of 3-arylquinolin-2(1H)-ones from benzyl chlorides and o-nitrobenzaldehydes

• A general and straightforward palladium-catalyzed aminocarbonylation procedure of benzyl chlorides have been developed. • o- nitrobenzaldehydes have been used as stable nitrogen sources for the synthesis of 3-arylquinolin-2(1 H )-ones. • Mo(CO) 6 has been used both as CO precursor and reductant. A palladium-catalyzed carbonylative cyclization of benzyl chlorides with o- nitrobenzaldehydes has been developed for the synthesis of 3-arylquinolin-2(1 H )-ones. Mo(CO) 6 played a dual role as both a CO surrogate and a reductant in this carbonylative transformation.

An Expedient Approach to Pyrazolo[3,4-b]pyridine-3-carboxamides via Palladium-Catalyzed Aminocarbonylation

AbstractPyrazolo[3,4-b]pyridine is a privileged scaffold found in many small drug molecules that possess a wide range of pharmacological properties. Efforts to further develop and exploit synthetic methodologies that permit the functionalization of this heterocyclic moiety warrant investigation. To this end, a series of novel 1,3-disubstituted pyrazolo[3,4-b]pyridine-3-carboxamide derivatives have been prepared by introducing the 3-carboxamide moiety using palladium-catalyzed aminocarbonylation methodology and employing CO gas generated ex situ using a two-chamber reactor (COware®). The functional group tolerance of this optimized aminocarbonylation protocol is highlighted through the synthesis of a range of diversely substituted C-3 carbox­amide pyrazolo[3,4-b]pyridines in excellent yields of up to 99%.

Palladium-Catalyzed Domino Aminocarbonylation of Alkynols: Direct and Selective Synthesis of Itaconimides.

The first direct and selective synthesis of substituted itaconimdes by palladium-catalyzed aminocarbonylation of alkynols is reported. Key to the success of this transformation is the use of a novel catalyst system involving ligand L11 and appropriate reaction conditions. In the protocol here presented, easily available propargylic alcohols react with N-nucleophiles including aryl- and alkylamines as well as aryl hydrazines to provide a broad variety of interesting heterocycles with high catalyst activity and excellent selectivity. The synthetic utility of the protocol is demonstrated in the synthesis of natural product 11 with aminocarbonylation as the key step. Mechanistic studies and control experiments reveal the crucial role of the hydroxyl group in the substrate for the control of selectivity.

Synthesis of N-picolylcarboxamides in aminocarbonylation

Palladium-catalysed aminocarbonylation of iodocamphene and steroidal iodoalkenes was carried out in the presence of 2-, 3- and 4-picolylamine, as well as secondary amines possessing 1-picolyl substituent. In general, primary picolylamines require less than 2 h to achieve practically complete conversion. The secondary amines proved to be less reactive, requiring 6–24 h depending on the substrate structure. The corresponding carboxamides were isolated in moderate to excellent yields. The synthesis of α,β-unsaturated carboxamides is based on the synthesis of iodoalkene substrates from enolizable ketones. • Facile synthesis of unsaturated carboxamides in palladium-catalysed aminocarbonylation. • High-yielding functionalization of camphene and steroidal skeletons. • The use of easily available, reactive iodoalkene substrates.

Selective Synthesis of N-Acylnortropane Derivatives in Palladium-Catalysed Aminocarbonylation.

The aminocarbonylation of various alkenyl and (hetero)aryl iodides was carried out using tropane-based amines of biological importance, such as 8-azabicyclo[3.2.1]octan-3-one (nortropinone) and 3α-hydroxy-8-azabicyclo[3.2.1]octane (nortropine) as N-nucleophile. Using iodoalkenes, the two nucleophiles were selectively converted to the corresponding amide in the presence of Pd(OAc)2/2 PPh3 catalysts. In the presence of several iodo(hetero)arenes, the application of the bidentate Xantphos was necessary to produce the target compounds selectively. The new carboxamides of varied structure, formed in palladium-catalyzed aminocarbonylation reactions, were isolated and fully characterized. In this way, a novel synthetic method has been developed for the producing of N-acylnortropane derivatives of biological importance.

Synthesis of novel pregnane-based 20-carboxamides via palladium-catalysed aminocarbonylation

20-Carboxamidopregnene derivatives, such as 3β-acetoxy-5α-pregn-20-ene-20-carboxamides and 5α-pregn-20-ene-20-carboxamides were synthesized from the widely accessible 3β-acetoxy-pregn-5,16-dien-20-one (PDA) using selective hydrogenation, hydrazine and iodoalkene formation, as well as palladium-catalysed aminocarbonylation. The 20-iodo-20-ene derivatives, obtained from the corresponding 20-keto derivatives via their hydrazones, served as substrates. 23 new 20-carboxamides were obtained using various N-nucleophiles ranging from simple primary amines to α-amino acid esters. The novelty of this methodology lies in the application of facile, moderate or high-yielding reactions to obtain otherwise hardly accessible steroidal 20-carboxamides of pharmaceutical importance. In other words, instead of the enzymatic or synthetic degradation of e.g., sterols or cholanic acids, functionalization of the basic skeleton (a ‘building-up’ approach) was used.

Palladium-catalyzed aminocarbonylation of aryl iodides with amines: efficient access to bidentate amide directing groups

A new route to bidentate amide directing groups has been developed via the palladium(II)-catalyzed aminocarbonylation. Under atmospheric carbon monoxide pressure, using commercially available aryl iodides and aromatic amine derivatives as substrates, the three-component reaction proceeded smoothly to give the desired products in moderate-to-excellent yields with good functional-group compatibility.

Sequential catalytic carbonylation reactions for sustainable synthesis of biologically relevant entities

The sustainable synthesis of highly functionalised formylcarboxamide compounds with biological relevance is reported through a sequential aminocarbonylation/hydroformylation approach. The optimisation of palladium-catalysed aminocarbonylation of iodoaromatic substrates, using allylamine as nucleophile was first performed, with molybdenum hexacarbonyl as alternative CO source versus gaseous carbon monoxide. The combination of microwave irradiation with molybdenum hexacarbonyl allowed to selectively prepare a set of N-heterocyclic-based allylcarboxamides. Subsequent rhodium-catalysed hydroformylation of the allylcarboxamide intermediates led to the preparation of new pyridine, pyrazoline and chalcone derivatives containing both carboxamide and formyl moieties.