Palladium-catalyzed oxidative arylation of chromones via a double C–H activation: an expedient approach to flavones

A palladium-catalyzed oxidative arylation of chromones was examined. A regioselective 2-arylation of chromone was carried out via a double C–H activation process. The procedure provided an expedient approach for the preparation of flavone derivatives.     

A powerful approach to alkoxy radical-mediated remote C(sp~3)–H bonds functionalization

正The activation of inert C(sp~3)–H bonds with control of reactivity and selectivity is one of the central topics in chemical sciences.In this context,alkoxy radical-mediated 1,5-hydrogen atom transfer allows the regioselective transfor-     

Des3PI: a fragment-based approach to design cyclic peptides targeting protein–protein interactions

Journal of Computer-Aided Molecular Design - Protein–protein interactions (PPIs) play crucial roles in many cellular processes and their deregulation often leads to cellular dysfunctions. One...     

Silver mediated direct C–H arylation of 3-bromoisothiazole-5-carbonitrile

Palladium catalyzed direct C–H arylation of 3-bromoisothiazole-5-carbonitrile with aryl/hetaryl iodides in the presence of AgF gave 13 4-aryl/hetaryl-3-bromoisothiazole-5-carbonitriles. The scope of this arylation was investigated and explanations for the limitations proposed. 3-Bromoisothiazole-5-carboxamide was isolated as a side-product, and its formation was attributed to Ag⁺-catalyzed hydration of the C-5 nitrile. The analogous phenylation of 3-chloroisothiazole-5-carbonitrile and 3-bromoisothiazole-4-carboxamide gave 3-chloro-4-phenylisothiazole-5-carbonitrile and 3-bromo-5-phenylisothiazole-4-carboxamide in 83 and 64% yields, respectively.     

Copper-catalysed approach to spirocyclic oxindoles via a direct C–H,Ar-H functionalisation

A practical and efficient entry to spirocyclic oxindoles from readily accessible anilide precursors, using only catalytic amounts of an inexpensive copper salt together with air as the sole re-oxidant, is described. In addition to providing access to a broad range of spiro-oxindole products, the utility of this method is demonstrated in a formal synthesis of the natural product, horsfiline.     

Photocatalytic decarboxylative alkylations of C(sp~3)–H and C(sp~2)–H bonds enabled by ammonium iodide in amide solvent

A simple ammonium iodide salt in amide solvent catalyzes regioselective decarboxylative alkylation of C(sp~3)-H bonds of Naryl glycine derivatives, of C(sp~2)-H bond of heteroarenes, and cascade radical addition to unsaturated bond followed by intramolecular addition to arene, with a broad scope of N-hydroxyphthalimide derived redox active esters under visible light irradiation. The reactions are suggested to proceed through photoactivation of a transiently assembled chromophore from electron-deficient phthalimide moiety and iodide anion through an anion-π interaction in solvent cage followed by diffusion to generate solvated free radical species to react with C-H substrates. The simplicity, practicality, and broad substrate scope of this method highlight the synthetic power of photocatalysis through transiently assembled chromophore, and will hopefully inspire further developments of low cost photocatalysis based on various non-covalent interactions, which are prevalent in supramolecular chemistry and biosystems, for sustainable organic synthesis.     

All-at-once arrangement of both oxygen atoms of dioxygen into aliphatic C(sp~3)–C(sp~3) bonds for hydroxyketone difunctionalization

Both β-and γ-hydroxyketone structures are important units in biologically active molecules, synthetic drugs and fine chemicals.Although there are some routes available for their manufacture from pre-functionalized groups on one or two matrix molecule(s),the approaches to simply and simultaneously deposit two oxygen atoms from dioxygen into two specific C(sp~3) positions of pure saturated hydrocarbons have rarely succeeded because they are involved in the targeted activation of three inert C–H σ bonds all at once. Here, we show that a TiO_2-CH_3CN photocatalytic suspension system enables the insertion of dioxygen into one C(sp~3)–C(sp~3) bond of strained cycloparaffin derivatives, by which difunctionalized hydroxyketone products are obtained in a one-pot reaction. With the cleavage event to release strain as the directional driving force, as-designed photocatalytic reaction systems show 21 examples of β-hydroxyketone products with 31%–76% isolated yields for three-membered ring derivatives and 5 examples of γ-hydroxyketone products with 30%–63% isolated yields for four-membered ring substrates.~(18)O isotopic labeling experiments using ~(18)O_2, Ti~(18)O_2 and intentionally added H_2~(18)O, respectively, indicated that both oxygen atoms of hydroxyketone products were exclusively from dioxygen, suggesting a previously unknown H+/TiO_2-e-catalyzed arrangement pathway of the hydroperoxide intermediate to convert dioxygen into hydroxyketone units.     

The 3-substitution of naphthalene-1,2-diones with boronic acids: a C–H functionalization approach to novel spirooxazine photochromics

The addition of alkyl and aryl boronic acids to naphthalene-1,2-diones in the presence of an excess of ammonium persulfate and catalytic silver nitrate to yield 3-functionalized naphthalene-1,2-diones is reported. The products of these reactions were then further processed to yield the corresponding novel spirooxazine photochromic dyes.     

Copper-catalyzed C–N coupling/C–H functionalization: A tandem approach to azole-fused quinazoline derivatives

A Cu-catalyzed tandem synthesis of azole-fused pyrimido[1,2-c]quinazolines and imidazo[1,2-c]quinazolines has been developed. The reaction is based on a C–N cross-coupling/C–H functionalization reaction of 2-(2-bromophenyl)-1,4,5,6-tetrahydropyrimidines with azoles. A variety of the desired polycyclic products were obtained in moderate to excellent yields.     

Palladium-catalyzed oxidative C–H bond coupling of indoles and benzaldehydes: a new approach to the synthesis of 3-benzoylindoles

A palladium-catalyzed dehydrogenative acylation of indoles using easily accessible aldehydes as the acyl source is described. This reaction provides a new approach for the synthesis of 3-acylindoles.     

Regioselective introduction of vinyl trifluoromethylthioether to remote unactivated C(sp~3)–H bonds via radical translocation cascade

Described herein is an efficient protocol for the regioselective introduction of a vinyl trifluoromethylthioether to remote unactivated C(sp~3)–H bonds. The cascade process involves the vinyl radical-mediated 1,5-hydrogen atom transfer(HAT) and remote vinyl migration. During the transformation, inert C–H and C–C bonds are consecutively cleaved under mild conditions.The reaction features good functional group tolerance, broad substrate scope, and high regio-/stereo-selectivity.     

Palladium-catalyzed C–H arylation using aryltrifluoroborates in conjunction with a MnIII oxidant under mild conditions

This paper describes the development of a mild Pd-catalyzed C–H arylation reaction using potassium aryltrifluoroborates in conjunction with Mn(OAc)₃ as the oxidant. The scope of this transformation is explored with a variety of different aryltrifluoroborates and arylpyridine substrates. Preliminary mechanistic studies suggest that the reaction proceeds via a high-valent Pd mechanism with C–H activation occurring at or before the rate determining step.     

Rapid access to diverse α-carbolines through sequential transition metal catalyzed amination and direct C–H arylation

An efficient sequence of Pd catalyzed amination and direct C–H arylation for a synthesis of pharmacologically important α-carbolines is described. The outstanding feature in the synthetic sequence is that a combination of DBU and 2-(dicyclohexylphosphino)biphenyl (DCHPB) plays a critical role to not only enhance the reactivity but also suppress hydrodehalogenation in the direct C–H arylation step. The reaction protocol provides α-carbolines with various substituents including base-sensitive ester and ketone moieties in moderate to excellent yields. Moreover, combination with Cu catalyzed amination further enhanced the versatility of the α-carboline synthesis.     

Iron-catalyzed C(sp)–H functionalization of methyl azaarenes with α-oxoesters: a facile approach to lactic acid derivatives

A highly efficient method for the C(sp³)–H functionalization of methyl azaarenes to α-oxoesters in the presence of iron(II) acetate as an inexpensive, nontoxic catalyst with moderate-to-excellent yields has been developed. This transformation represents a facile approach to medicinally important lactic acid derivatives.     

Ruthenium(II)-catalyzed C(3)–H arylation of furan moiety in fuberidazole derivatives

An efficient selective C(3)–H arylation of furan ring in 2-(furan-2-yl)benzimidazoles, derivatives of fuberidazole fungicide, with aryl bromides catalyzed by [RuCl₂(cymene)]₂/ pivalic acid system has been accomplished. High selectivity of the process may be accounted for by the action of benzimidazol-2-yl substituent as the directing group.     

Combinatorial–computational–chemoinformatics (C3) approach to finding and analyzing low-energy tautomers

Finding the most stable tautomer or a set of low-energy tautomers of molecules is critical in many aspects of molecular modelling or virtual screening experiments. Enumeration of low-energy tautomers of neutral molecules in the gas-phase or typical solvents can be performed by applying available organic chemistry knowledge. This kind of enumeration is implemented in a number of software packages and it is relatively reliable. However, in esoteric cases such as charged molecules in uncommon, non-aqueous solvents there is simply not enough available knowledge to make reliable predictions of low energy tautomers. Over the last few years we have been developing an approach to address the latter problem and we successfully applied it to discover the most stable anionic tautomers of nucleic acid bases that might be involved in the process of DNA damage by low-energy electrons and in charge transfer through DNA. The approach involves three steps: (1) combinatorial generation of a library of tautomers, (2) energy-based screening of the library using electronic structure methods, and (3) analysis of the information generated in step (2). In steps 1–3 we employ combinatorial, computational and chemoinformatics techniques, respectively. Therefore, this hybrid approach is named “Combinatorial*Computational*Chemoinformatics”, or just abbreviated as C³ (or C-cube) approach. This article summarizes our developments and most interesting methodological aspects of the C³ approach. It can serve as an example how to identify the most stable tautomers of molecular systems for which common chemical knowledge had not been sufficient to make definite predictions.     

Metal-free sequential dual oxidative amination of C(sp3)–H bonds: A direct approach to benzothiadiazine 1,1-dioxide derivatives

An efficient and metal-free Di-tert-butyl peroxide (DTBP)-promoted dual oxidative amination annulation of 2-amino arylsulfonamide with methylarene has been developed. This protocol provides straightforward access to benzothiadiazine 1,1-dioxide derivatives without using prefunctionalized substrates in good to excellent yields with good functional group tolerance.     

Carbon–hydrogen (C–H) bond activation at PdIV: a Frontier in C–H functionalization catalysis

The direct functionalization of carbon–hydrogen (C–H) bonds has emerged as a versatile strategy for the synthesis and derivatization of organic molecules. Among the methods for C–H bond activation, catalytic processes that utilize a Pd^II/Pd^IV redox cycle are increasingly common. The C–H activation step in most of these catalytic cycles is thought to occur at a Pd^II centre. However, a number of recent reports have suggested the feasibility of C–H cleavage occurring at Pd^IV complexes. Importantly, these latter processes often result in complementary reactivity and selectivity relative to analogous transformations at Pd^II. This mini review highlights proposed examples of C–H activation at Pd^IV centres. Applications of this transformation in catalysis as well as mechanistic details obtained from stoichiometric model studies are discussed. Furthermore, challenges and future perspectives for the field are reviewed.     

Studies towards the total synthesis of altohyrtin A: a convergent approach to the C38–C51 carbon framework

The first pyranose-based approach to the F ring (C38–C43) of altohyrtin A 1 together with a synthetic approach to the C44–C51 chloro diene unit of 1 is described.