Palladium/Copper-Catalyzed Aerobic Oxidative C–H Carbonylation for the Synthesis of o-Aminobenzoates

Pd(II)-catalyzed cascade annulation of N-substituted anilines with CO, NH4OAc and aldehydes to N1-substituted 2,3-dihydroquinazolin-4(1H)-ones

A facile and direct approach to N1-substituted 2,3-dihydroquinazolin-4(1H)-ones has been developed via Pd(II)-catalyzed one-pot cascade annulation of N-substituted anilines with CO, NH4OAc and aldehydes, and it features an intrinsic directing strategy, cheap and easily obtainable raw materials, low cost, high step economy and efficiency, broad substrate scope and good product diversity. This protocol has been successfully applied to the synthesis of glycozolone A and gram-level experiments. Based on the control experiments and the literature, the reaction mechanism was proposed.

Electrochemical Oxidative Carbonylation of NH-Sulfoximines

The electrochemical synthesis of N-aroylsulfoximines features the use of tetra-n-butylammonium iodide (TBAI) as the medium and a broad substrate scope, thus affording a wide range of N-aroylated sulfoximines in moderate to good yields. The advantages of this electrochemical strategy are augmented by mild reaction conditions that are external oxidant-free, ligand-free, and easy to scale up to gram scale. Both the control experiments and the mechanistic studies revealed that the whole electrochemical process proceeded through a palladium (II/IV/II) catalytic cycle.

Palladium-Catalyzed Carbonylations: Application in Complex Natural Product Total Synthesis and Recent Developments

Carbon monoxide is a cheap and abundant C1 building block that can be readily incorporated into organic molecules to rapidly build structural complexity. In this Perspective, we outline several recent (since 2015) examples of palladium-catalyzed carbonylations in streamlining complex natural product total synthesis and highlight the strategic importance of these carbonylation reactions in the corresponding synthesis. The selected examples include spinosyn A, callyspongiolide, perseanol, schizozygane alkaloids, cephanolides, and bisdehydroneostemoninine and related stemona alkaloids. We also provide our perspective about the recent advancements and future developments of palladium-catalyzed carbonylations.

Transition-Metal-Catalyzed Directing Group Assisted (Hetero)aryl C-H Functionalization: Construction of C-C/C-Heteroatom Bonds

Transition-metal-catalyzed C-H functionalization is one of the fascinating scientific fronts in organic synthesis for the formation of conjugated arenes and has emerged as a benchmark to revolutionize the synthetic enterprise since past decades. In this realm, chelation-guided functionalization of C-H bonds using an exogenous directing group has received considerable attention recently for the expedient regioselective construction of C-C and C-heteroatom bonds as an efficient and sustainable alternative. This article outlines our contribution towards a wide variety of transformations that have been achieved by the directed C-H functionalization through the fine tuning of catalytic systems.

Pd-Catalyzed sp3 C-H alkoxycarbonylation of 8-methylquinolines using Mo(CO)6 as a CO surrogate

A Pd(ii)-catalyzed three-component sp³ C-H alkoxycarbonylation of 8-methylquinonlines (8-MQs) with alcohols is accomplished using the colorless crystalline Mo(CO)₆ as a CO source. The protocol is compatible with a wide range of 8-MQs and alcohols, furnishing the carbonylated adducts in moderate to good yields. The substrate scope, functional group tolerance and natural product mutation are the important practical features.

Synthesis of indolo- and pyrrolo[1,2-a]quinoxalinones through a palladium-catalyzed oxidative carbonylation of the C2 position of indole

A methodology that involves the Pd-catalyzed direct C(sp2)–H bond carbonylation of the C₂ position of indole has been introduced for the synthesis of indolo[1,2-a]quinoxalin-6(5H)-ones.

Ligand Promoted, Palladium-Catalyzed C(sp2)-H Arylation of Free Primary 2-Phenylethylamines

A mono- N-protected amino acid (MPAA) ligand promoted, Pd(II)-catalyzed C(sp²)-H arylation of free primary 2-phenylethylamines using the native NH₂ as the directing group has been achieved. This method is compatible with challenging simple primary 2-phenylethylamines bearing α-hydrogen atoms. Application of this protocol in the direct structure modification of the drug molecule amphetamine is also demonstrated.

Palladium catalyzed carbonylative annulation of the C(sp2)-H bond of N,1-diaryl-1H-tetrazol-5-amines and N,4-diaryl-4H-triazol-3-amines to quinazolinones

Pd(ii) catalyzed direct C-H carbonylative annulation of N,1-diaryl-1H-tetrazol-5-amines and N,4-diaryl-4H-1,2,4-triazol-3-amines gave the corresponding triazole and tetrazole fused quinazolinones in good yields. This methodology offers a convenient method for the synthesis of these important heterocyclic scaffolds in a highly atom economical process. On the mechanistic aspect weakly nucleophilic triazole and tetrazole moieties function as both directing as well as intramolecular nucleophiles. The catalytically active C-H activated intermediate dimeric Pd complex was isolated and characterized which on exposure to CO gas gave the corresponding tetrazole fused quinazolinone derivative. On the basis of isolation of the intermediate and observed kinetic isotope effects, a mechanism has been proposed for the C-H activated direct carbonylative annulation reaction.

Palladium(II)-Catalyzed C(sp2)-H Carbonylation of Sterically Hindered Amines with Carbon Monoxide

A palladium-catalyzed, amine-directed C(sp²)-H carbonylation of α,α-disubstituted benzylamine under 1 atm of CO for the facile synthesis of sterically hindered benzolactam has been developed. The key to success is the use of 2,2,6,6-tetramethyl-1-piperidinyloxy as the crucial sole oxidant. The synthetic utility of this transformation has been demonstrated by the first concise synthesis of the natural product spiropachysin-20-one.

Pd-Catalyzed C(sp2)-H carbonylation of 2-benzylpyridines for the synthesis of pyridoisoquinolinones

An efficient synthesis of pyridoisoquinolinones, through Pd-catalyzed carbonylative annulation of 2-benzylpyridines, has been developed. The pyridinyl moiety in the substrate acts as both a directing group and an internal nucleophile for sp² C-H activation and pyridocarbonylation. The ready availability of 2-benzylpyridines as well as the operational practicality makes this transformation potentially useful for the synthesis of analogues of protoberberine alkaloids.

Efficient palladium-catalyzed C(sp2)–H activation towards the synthesis of fluorenes

A newly developed palladium-catalyzed direct arylation via C–H activation adopting diphenylmethane type reactants for the synthesis of fluorene derivatives.

Pd-catalyzed aminocarbonylation of alkynes with amines using Co2(CO)8 as a carbonyl source

A facile protocol for aminocarbonylation of alkynes with amines at room temperature was developed using a metal carbonyl source.

Oxalyl amide assisted palladium-catalyzed synthesis of pyrrolidones via carbonylation of γ-C(sp3)-H bonds of aliphatic amine substrates

The first Pd-catalyzed regioselective γ-carbonylation of oxalyl amide protected aliphatic amines with carbon monoxide leading to synthesis of pyrrolidones has been developed. Both γ-methyl and cyclopropyl methylene C-H bonds are well activated to obtain the corresponding pyrrolidones in moderate to excellent yields. The role of 3-(trifluoromethyl)benzoic acid as an additive is critical as it helps in stabilizing the palladium intermediate formed during the catalytic cycle. The reaction scope is extended to benzylamine and allyl amine derivatives, thereby affording the corresponding products in good to excellent yields.

Beyond conventional routes, an unprecedented metal-free chemoselective synthesis of anthranilate esters via a multicomponent reaction (MCR) strategy

A hitherto unreported route for the synthesis of anthranilate esters is demonstrated using 2-nitrobenzaldehyde, malonitrile and an alcohol or amine via a metal and oxidant free multicomponent reaction (MCR) strategy.