Cross-coupling Strategy Research Articles

Random property enhancement of a 1D chaotic PRNG with finite precision implementation

The random-like behavior of chaotic systems make them perfect candidates for the core of numerous pseudo-random number generators. The coupling of two or more chaotic maps has been proven to increase the random property robustness of the generated sequences. However, these properties are also strongly influenced by the datatype implementation of these generators owing to the effect of the sensitivity to initial conditions. Hence, several factors must be considered concerning the hardware implementation of these coupled chaotic map-based generators. This paper first examines the effect of fixed-point precision implementation on the periodicity of a single skew tent map and the extension of this effect on the statistical properties of the generated sequence from coupled skew tent maps. Then, the effect on cross-coupled skew tent maps is discussed. Further, a modification to the cross-coupled scheme is presented; this achieves a reduction in the fixed-point fraction length required for generating a sequence suitable for cryptographic applications while expanding the dependency on the control parameters of the maps. The generated sequences from the proposed modification met all the applied statistical and correlation test requirements, demonstrating that they possess acceptable random properties and are suitable for cryptographic applications.

Synthesis of Poly(heteroarylenevinylene) Derivatives via Rhodium-Catalyzed Hydroarylation of Alkynes

Organic electronics has developed into a significant field of research and industry in the last decade. The progress has been enabled by the many advancements made in synthetic technologies, which allow for the design of a plethora of interesting material candidates. Poly(p-phenylenevinylene) derivatives (PPVs) are a particularly interesting class of polymers that were among the first to garner attention. However, due to their demanding syntheses, limited scope, and relative intolerance to heterocycles, PPVs have fallen out of popularity. New synthetic methods, such as direct C–H bond activation, have emerged that allow for the creation of polyheteroaromatics through the use of simpler starting materials than those used in traditional cross-coupling strategies. Here, we report an extension of a hydroarylation reaction to the synthesis of poly(heteroarylenevinylene) derivatives (PHAVs) containing various desirable heterocycles with Mn values ranging from 8 to 23 kDa without producing stoichiometric amounts of waste.

Well-Defined Palladium(II)-NHC Precatalysts for Cross-Coupling Reactions of Amides and Esters by Selective N-C/O-C Cleavage.

Transition-metal-catalyzed cross-coupling reactions represent a most powerful tool for the rapid construction of C-C and C-X bonds available to synthetic chemists. Recently, tremendous progress has been made in the burgeoning area of cross-coupling reactions of amides and esters enabled by regio- and chemoselective acyl C-X (X = N, O) cleavage using well-defined Pd(II)-NHC complexes. The use of N-heterocyclic carbenes as ligands in palladium-catalyzed cross-couplings permits reactions of amides and esters that were previously impossible using palladium or could be achieved only under harsh conditions. These reactions provide an attractive method to synthetic chemists to manipulate the traditionally inert amide and ester bonds with the broad cross-coupling generality inherent to palladium catalysis. Research in the area of cross-coupling of stable acyl electrophiles can be broadly categorized by the type of electrophile undergoing the cross-coupling. Recent studies have shown that cross-coupling of amides by transition-metal catalysis represents one of the most straightforward and wide-ranging ways of manipulating the classically inert amide bonds into generic acyl-metal intermediates that can be systematically exploited in cross-coupling reactions as a new paradigm in organic synthesis. The key to achieving high chemoselectivity of the process is control of amidic resonance (nN to πC═O* conjugation, rotation of ca. 15-20 kcal/mol in planar amides), enabling oxidative addition of the N-C amide bond to a metal in a rational and predictable manner. This mode of catalysis has been extended to C(acyl)-O cross-coupling reactions of aryl esters, where selective C-O bond cleavage is accomplished through a rational match of aryl ester electrophiles and nucleophilic metal catalysts. These two types of transition-metal-catalyzed cross-coupling reactions represent an attractive concept in synthetic chemistry because of the ubiquity of esters and amides as precursors in organic synthesis. Furthermore, the high stability of amides and esters provides unprecedented opportunities for orthogonal cross-coupling strategies in the presence of other electrophiles. In this Account, we highlight advances that have taken place in the past few years in the field of cross-coupling of amides and esters, focusing on both (1) the stereoelectronic properties of well-defined Pd(II)-NHC complexes that have been critical to realize this challenging cross-coupling manifold and (2) the role of the isomerization barrier of the acyl electrophiles undergoing the cross-coupling. In a broader sense, the chemistry described here provides a practical approach to functionalize common amide and ester functional groups in organic synthesis and establishes straightforward access to acyl-metal intermediates that enable nonconventional cross-coupling strategies.

Palladium-Catalyzed Thiomethylation via a Three-Component Cross-Coupling Strategy.

In this report, the combination of masked inorganic sulfur and dimethyl carbonate was designed to achieve thiomethylated cross coupling of aryl chlorides. Remarkably, this powerful strategy realized thiomethylation of nucleosides bearing unprotected ribose, chloride-containing pharmaceuticals with late-stage coupling, and herbicides possessing multiple heteroatoms and steric hindrance. Moreover, this protocol is practically amenable to multigram-scale synthesis with a lower catalysis loading and a higher yield.

Preparation of Structurally Diverse Compounds from the Natural Product Lycorine.

The synthesis of a 52-member compound collection from the natural product lycorine is reported, highlighted by divergent cross-coupling and substitution strategies and an unusual ring rearrangement induced by reaction with aryne intermediates.

Frontispiece: Diversifying Cross‐Coupling Strategies, Catalysts and Monomers for the Controlled Synthesis of Conjugated Polymers

Frontispiece: Diversifying Cross‐Coupling Strategies, Catalysts and Monomers for the Controlled Synthesis of Conjugated Polymers

Acyl and Decarbonylative Suzuki Coupling of N-Acetyl Amides: Electronic Tuning of Twisted, Acyclic Amides in Catalytic Carbon–Nitrogen Bond Cleavage

We report the Pd-catalyzed acyl and the Ni-catalyzed biaryl Suzuki–Miyaura cross-coupling of N-acetyl-amides with arylboronic acids by selective N–C(O) cleavage. Activation of the amide bond by N-acylation provides electronically destabilized, acyclic, nonplanar amide, which readily undergoes cross-coupling with a wide range of boronic acids to produce biaryl ketones or biaryls in a highly efficient manner. Most crucially, the presented results introduce N-acetyl-amides as reactive acyclic amides in the emerging manifold of transition-metal-catalyzed amide cross-coupling. The scope and origin of high selectivity are discussed. Mechanistic studies point to remodeling of amidic resonance and amide bond twist as selectivity determining features in a unified strategy for cross-coupling of acyclic amides. Structural studies, mechanistic investigations as well as beneficial effects of the N-acyl substitution on cross-coupling of amides are reported.

Bacterial Catabolism of Biphenyls: Synthesis and Evaluation of Analogues.

A series of alkylated 2,3-dihydroxybiphenyls has been prepared on the gram scale by using an effective Directed ortho Metalation-Suzuki-Miyaura cross-coupling strategy. These compounds have been used to investigate the substrate specificity of the meta-cleavage dioxygenase BphC, a key enzyme in the microbial catabolism of biphenyl. Isolation and characterization of the meta-cleavage products will allow further study of related processes, including the catabolism of lignin-derived biphenyls.

Transformations of Isonitriles with Bromoalkanes Using Photoredox Gold Catalysis.

Isonitriles have excellent electronic compatibility to react with free radicals. Recently, photoredox catalysis has emerged as a powerful tool for the construction of C-C bonds with few protocols for alkylative heterocycle synthesis through isonitrile addition. Herein, we describe the photocatalytic generation of alkyl radicals from unactivated bromoalkanes as part of an efficient cross-coupling strategy for the diversification of isonitriles using a dimeric gold(I) photoredox catalyst, [Au2(dppm)2]Cl2.

An Interrupted Pummerer/Nickel-Catalysed Cross-Coupling Sequence.

An interrupted Pummerer/nickel-catalysed cross-coupling strategy has been developed and used in the elaboration of styrenes. The operationally simple method can be carried out as a one-pot process, involves the direct formation of stable alkenyl sulfonium salt intermediates, utilises a commercially available sulfoxide, catalyst, and ligand, operates at ambient temperature, accommodates sp-, sp2 -, and sp3 -hybridised organozinc coupling partners, and delivers functionalised styrene products in high yields over two steps. An interrupted Pummerer/cyclisation approach has also been used to access carbo- and heterocyclic alkenyl sulfonium salts for cross-coupling.

Synthesis of pentafluorosulfanyl (SF5) containing aromatic amino acids

Herein, a series of aromatic pentafluorosulfanyl (SF5) containing amino acids are reported. A Negishi cross-coupling strategy utilising a catalyst system of Pd(dba)2 and SPhos afforded the aforementioned SF5 amino acids in yields between 32% and 42%. Two dipeptides utilising both the amine and carboxylic functionalities of the synthesised SF5 containing amino acids were prepared, demonstrating their compatibility with common amide/peptide coupling reagents and strategies.

N-PD cross-coupling synchronization control based on adjacent coupling error analysis

In order to improve the trajectory tracking precision and reduce the synchronization error of a 6-DOF lightweight robot, nonlinear proportion-deviation (N-PD) cross-coupling synchronization control strategy based on adjacent coupling error analysis is presented. The mathematical models of the robot, including kinematic model, dynamic model and spline trajectory planing, are established and verified. Since it is difficult to describe the real-time contour error of the robot for complex trajectory, the adjacent coupling error is analyzed to solve the problem. Combined with nonlinear control and coupling performance of the robot, N-PD cross-coupling synchronization controller is designed and validated by simulation analysis. A servo control experimental system which mainly consists of laser tracking system, the robot mechanical system and EtherCAT based servo control system is constructed. The synchronization error is significantly decreased and the maximum trajectory error is reduced from 0.33 mm to 0.1 mm. The effectiveness of the control algorithm is validated by the experimental results, thus the control strategy can improve the robot’s trajectory tracking precision significantly.

Nickel-Catalyzed Umpolung Arylation of Ambiphilic α-Bromoalkyl Boronic Esters.

A nickel-catalyzed reductive arylation of ambiphilic α-bromoalkyl boronic esters with aryl halides is described. This platform provides an unrecognized opportunity to promote the catalytic umpolung reactivity of ambiphilic reagents with aryl halides, thus unlocking a new cross-coupling strategy that complements existing methods for the preparation of densely functionalized alkyl-substituted organometallic reagents from simple and readily accessible precursors.

Tetrathiafulvalene-[2.2]paracyclophanes: Synthesis, crystal structures, and chiroptical properties.

Two racemic tetrathiafulvalene-[2.2]paracyclophane electron donors EDT-TTF-[2.2]paracyclophane 1 and (COOMe)2 -TTF-[2.2]paracyclophane 2 have been synthesized via the phosphite mediated cross coupling strategy. Chiral HPLC allowed the optical resolution of the (RP ) and (SP ) enantiomers for both compounds. Solid-state structures of (RP )-1 and (rac)-2 have been determined by single crystal X-ray analysis. Intermolecular π-π and S•••S interactions are disclosed in the packing. Single crystal X-ray analysis of (RP )-1 combined with experimental and theoretical circular dichroism spectra allowed the assignment of the absolute configuration of the enantiomers of 1 and 2.

Cascade One-Pot Method To Synthesize Isoquinolin-1(2H)-ones with α-Bromo Ketones and Benzamides via Pd-catalyzed C–H Activation

A cross-coupling strategy of palladium-catalyzed ortho-C-H bond activation and intramolecular addition of N-C annulation to synthesize isoquinolin-1(2H)-ones has been developed. A wide range of α-bromo ketones with different substituents proceeded smoothly in this reaction, and varieties of isoquinolin-1(2H)-one derivatives were obtained in moderate to good yields.

Synthesis of arylated chalcone derivatives via palladium cross-coupling reactions

A useful protocol for arylation of the olefin double bond of chalcones to afford tri- and tetra-substituted chalcone derivatives is reported. The protocol begins with the Heck reaction between chalcones and aryl iodides providing β-arylchalcones. This reaction tolerates various functional groups on both rings, as well as deactivated aryl iodides. The products are obtained in moderate to excellent yields and the (E)-β-arylchalcones (E:Z > 96:4) can be isolated via precipitation. Competitive Heck reactions pointed to a significant effect of ring one substituents on the reaction rate, while substituents on ring two have a much smaller effect. To access α,β-diarylchalcones, a sequential bromination-Suzuki cross coupling strategy was applied to the β-arylated compounds which afforded double arylated chalcone derivatives in 60–99% yield over two steps.

The synthesis of arylcyanamides: a copper-catalyzed consecutive desulfurization and C–N cross-coupling strategy

A one pot highly efficient and simple protocol for the construction of aromatic cyanamides from thioureaviadesulphurization/C–N cross coupling using a cheap, readily available and air stable copper source as a catalyst has been described.

Three-Dimensional Printing in Catalysis: Combining 3D Heterogeneous Copper and Palladium Catalysts for Multicatalytic Multicomponent Reactions

Two 3D-hybrid monolithic catalysts containing immobilized copper and palladium species on a silica support were synthesized by 3D printing and a subsequent surface functionalization protocol. The resulting 3D monoliths provided a structure with pore sizes around 300 μm, high mechanical strength, and easy catalyst recyclability. The devices were designed to perform heterogeneous multicatalytic multicomponent reactions (MMCRs) based on a copper alkyne–azide cycloaddition (CuAAC) + palladium catalyzed cross-coupling (PCCC) strategy, which allowed the rapid assembly of variously substituted 1,2,3-triazoles using a mixture of tBuOH/H2O as solvent. The reusable multicatalytic system developed in this work is an example of a practical miniaturized and compartmental heterogeneous 3D-printed metal catalyst to perform MMCRs for solution chemistry.

Expansion of the aromatic part of Cinchona alkaloids. Annulation of quinolines with phenoxazine motifs

An oxidative cross-coupling strategy for quinoline ring annulation in Cinchona alkaloids has been developed. Key-reaction optimization by changing oxidants and adjusting the nucleophilicity of the 2-aminophenols led to cupreine and cupreidine expanded with the phenoxazinone unit in 56–75% yield. The stereochemical integrity of the obtained alkaloid structures was confirmed by combined experimental and computed CD and NMR data. The conformational study revealed a fast equilibrium of the three conformers, differing in the orientation of the pyrido[a-3,2]phenoxazine moiety.

Regioselective Cascade Synthesis of Chloro-Substituted 6H-Benzo[c]chromenes via Benzannulation

Abstract A simple and efficient cascade synthesis was achieved to produce chloro substituted 9-phenyl-6H-benzo[c]chromenes under mild and additive-free reaction conditions via chlorination followed by benzannulation. This would be a green alternative approach to introduce a chlorine atom on poly hetero aromatic rings without use of other toxic and malodorous chlorinating agents. The core structure is a part of several biological active compounds, and this new protocol allows design of new polyheterocyclic frameworks using an alternative to traditional cross-coupling strategies.