Selective Synthesis of Sulfonamides and Sulfenamides from Sodium Sulfinates and Amines.

An effective method was explored for the selective synthesis of sulfonamides and sulfenamides using sodium sulfinates and amines as starting materials. This method offers mild reaction conditions, a broad substrate scope, high efficiency, and readily accessible materials, making it suitable and an alternative strategy for the preparation of a variety of biologically or pharmaceutically active compounds.

Cobalt/Salicylaldehyde-Enabled C-H Alkoxylation of Benzamides with Secondary Alcohols under Solvothermal Conditions.

C-O bond formation via C-H alkoxylation remains a challenge, especially coupling with a secondary alcohol, due to its low activity and sterically encumbered property. Here, we report a general and effective cobalt-catalyzed oxidative cross-coupling of benzamides with secondary alcohols via C-H alkoxylation reaction under solvothermal conditions, enabled by a salicylaldehyde/cobalt complex. The protocol features easy operation without additives, broad substrate scope, and excellent functional tolerance. The applicability is proven by the gram-scale synthesis and modification of natural products.

Salicylaldehyde-Cobalt(II)-Catalyzed C-H Alkoxylation of Indoles with Secondary Alcohols.

A straight and efficient protocol for the synthesis of hindered indole-ethers via C-H alkoxylation of indoles was developed by a cobalt-catalyzed cross-dehydrogenative coupling reaction with secondary alcohols. The selection of the salicylaldehyde-Co(II) catalyst enables the reaction to proceed under conditions without acid or base addition in the presence of limited alcohols. The protocol has broad substrate scope for both indole and secondary alcohols and exhibits good functional tolerance. The synthetic applications are proven by gram-scale reaction and further diversification of the product. Preliminary mechanistic investigations indicate that the activation of C-H bonds is not the rate-determining step of the reaction.

Construction of Bulky Ligand Libraries by Ru(II)-Catalyzed P(III)-Assisted ortho-C-H Secondary Alkylation.

Modification of commercially available biaryl monophosphine ligands via ruthenium(II)-catalyzed P(III)-directed-catalyzed ortho C-H secondary alkylation is described. The use of highly ring-strained norbornene as a secondary alkylating reagent is the key to this transformation. A series of highly bulky ligands with a norbornyl group were obtained in excellent yields. The modified ligands with secondary alkyl group outperformed common substituted phosphines in the Suzuki-Miyaura cross-coupling reaction at a ppm mole level of Pd catalyst.

Overcoming the limitations of directed C-H functionalizations of heterocycles.

In directed C-H activation reactions, any nitrogen or sulphur atoms present in heterocyclic substrates will coordinate strongly with metal catalysts. This coordination, which can lead to catalyst poisoning or C-H functionalization at an undesired position, limits the application of C-H activation reactions in heterocycle-based drug discovery, in which regard they have attracted much interest from pharmaceutical companies. Here we report a robust and synthetically useful method that overcomes the complications associated with performing C-H functionalization reactions on heterocycles. Our approach employs a simple N-methoxy amide group, which serves as both a directing group and an anionic ligand that promotes the in situ generation of the reactive PdX2 (X = ArCONOMe) species from a Pd(0) source using air as the sole oxidant. In this way, the PdX2 species is localized near the target C-H bond, avoiding interference from any nitrogen or sulphur atoms present in the heterocyclic substrates. This reaction overrides the conventional positional selectivity patterns observed with substrates containing strongly coordinating heteroatoms, including nitrogen, sulphur and phosphorus. Thus, this operationally simple aerobic reaction demonstrates that it is possible to bypass a fundamental limitation that has long plagued applications of directed C-H activation in medicinal chemistry.

Switchable Synthesis of Arylalkynes and Phthalides via Controllable Palladium-Catalyzed Alkynylation and Alkynylation-Annulation of Benzoic Acids with Bromoalkynes.

A ligand-promoted palladium(II)-catalyzed synthesis of arylalkynes and phthalides from benzoic acids and bromoalkynes via carboxylate-assisted ortho-C-H activation is reported. A series of phthalides with various functional groups are prepared via ortho-alkynylation and alkynylation-annulation. Moreover, the key ortho-alkynylated products are also obtained by controlling the reaction conditions. In addition, heteroaryl acids could react smoothly to form the corresponding alkynylation and cyclization products.

Tracking the Progress and Mechanism Study of a Solvothermal in Situ Domino N-Alkylation Reaction of Triethylamine and Ammonia Assisted by Ferrous Sulfate.

Atom economic in situ domino N-alkylation reactions of triethylamine/ammonia with 2-(hydroxymethyl)quinolin-8-ol (HL-OH) assisted by FeSO4·7H2O were realized under mild solvothermal conditions at 120 °C in acetonitrile. The resulting tripodal 2,2',2″-[nitrilotris(methylene)]tris(quinolin-8-ol) (H3L3-N) forms a linear trimer [Fe3(L3-N)2] (1). Electrospray ionization mass spectrometry of the reaction solution provides evidence for the intermediates of three steps, while crystallography and X-ray photoelectron spectroscopy characterize the trimer. Shortening the time of the reaction allowed for the organic intermediates to be isolated, which led to a proposed mechanism. The method provides a facile way to produce symmetric tertiary amine from widely used NEt3 and NH3. The results represent an example of the in situ Fe2+-catalyzed domino reaction in which Fe2+ is coordinated by the generated ligands and is involved in each step until the final cluster 1.

Pd-Catalyzed α-Selective C-H Functionalization of Olefins: En Route to 4-Imino-ß-Lactams.

Pd-catalyzed α-olefinic C-H activation of simple α,ß-unsaturated olefins has been developed. 4-imino-ß-lactam derivatives were readily synthesized via activation of α-olefinic C-H bonds with excellent cis stereoselectivity. A wide range of heterocycles at the ß-position are compatible with this reaction. The product of 4-imino-ß-lactam derivatives can be readily converted to 2-aminoquinoline which exists extensively in pharmaceutical drugs and natural products.

Divergent and Stereoselective Synthesis of ß-Silyl-α-Amino Acids through Palladium-Catalyzed Intermolecular Silylation of Unactivated Primary and Secondary C-H Bonds.

A general and practical PdII -catalyzed intermolecular silylation of primary and secondary C-H bonds of α-amino acids and simple aliphatic acids is reported. This method provides divergent and stereoselective access to a variety of optical pure ß-silyl-α-amino acids, which are useful for genetic technologies and proteomics. It can also be readily performed on a gram scale and the auxiliary can be easily removed with retention of configuration. The synthetic importance of this method is further demonstrated by the late-stage functionalization of biological small molecules, such as (-)-santonin and ß-cholic acid. Moreover, several key palladacycles were successfully isolated and characterized to elucidate the mechanism of this ß-C(sp3 )-H silylation process.

Copper/silver-mediated direct ortho-ethynylation of unactivated (hetero)aryl C-H bonds with terminal alkyne.

A copper/silver-mediated oxidative ortho-ethynylation of unactivated aryl C-H bonds with terminal alkyne has been developed. The reaction uses the removable PIP directing group and features broad substrate scope, high functional-group tolerance, and compatibility with a wide range of heterocycles, providing an efficient synthesis of aryl alkynes. This procedure highlights the potential of copper catalysts to promote unique, synthetically enabling C-H functionalization reactions that lie outside of the current scope of precious metal catalysis.

Ru(II)-catalyzed P(III)-assisted C8-alkylation of naphthphosphines.

We report a phosphine-directed ruthenium-catalyzed C8-selective alkylation of naphthalenes with alkenes. This protocol provides straightforward access to a large library of electron-rich C8-alkyl substituent 1-naphthphosphines, which outperformed common commercial phosphines and their precursors in the Pd-catalyzed Suzuki-Miyaura coupling of aryl bromides with alkylboronic acid.

Salicylaldehyde-Promoted Cobalt-Catalyzed C-H/N-H Annulation of Indolyl Amides with Alkynes: Direct Synthesis of a 5-HT3 Receptor Antagonist Analogue.

A cobalt-catalyzed annulation of the C(sp2)-H/N-H bond of indoloamides with alkynes assisted by 8-aminoquinoline is reported for the synthesis of six-membered indololactams. The use of salicylaldehyde as the ligand is crucial for this transformation. The protocol has a broad scope for both alkynes and indoles. Preparing an active Co complex illustrates that salicylaldehyde plays a key role in the C-H activation step. The synthetic applications are proven by the gram-scale reaction and one-step construction of the multicyclic 5-HT3 receptor antagonist.

Cooperative Ligand-Promoted P(III)-Directed Ruthenium-Catalyzed Remote Meta-C-H Alkylation of Tertiary Phosphines.

Herein, we disclose a ruthenium-catalyzed meta-selective C-H activation of phosphines by using intrinsic P(III) as a directing group. 2,2,6,6-Tetramethylheptane-3,5-dione acts as the ligand and exhibits an excellent performance in boosting the meta-alkylation. The protocol allows an efficient and straightforward synthesis of meta-alkylated tertiary phosphines. Several meta-alkylated phosphines were evaluated for Pd-catalyzed Suzuki coupling and found to be superior to commercially available ortho-substituted phosphines. The practicability of this methodology is further demonstrated by the synthesis of difunctionalized phosphines.

Synthesis of seven-membered lactones by regioselective and stereoselective iodolactonization of electron-deficient olefins.

A regio- and stereoselective iodolactonization of internal electron-deficient olefinic acids has been reported, which provides a straightforward access to a series of multi-functionalized seven-membered lactones containing two consecutive chiral centers. The ester substituents on the olefins played a key role in achieving high regioselectivity. This result was proved through experiments and DFT calculations.

Remote and Selective C(sp2)-H Olefination for Sequential Regioselective Linkage of Phenanthrenes.

Biphenylcarboxylic acid with two competing C(sp2)-H sites was designed for site selective C(sp2)-H functionalization by developing carboxylic acids assisted remote and selective olefination via 7-membered palladacycle. Mechanism investigation and DFT calculations reveal a kinetics-determined process, which could be utilized to explore a variety of remote site selectivity. The practicability of this method was highlighted by the precise construction of phenathrene under sequential site selectivity.

Late-Stage Modification of Tertiary Phosphines via Ruthenium(II)-Catalyzed C-H Alkylation.

Ru(II)-catalyzed direct alkylation of tertiary phosphines via hydroarylation of activated olefins promoted by mono-N-protected amino acid (MPAA) was achieved. This protocol provides a straightforward access to a large library of Buchwald-type bulky alkylated monophosphines from commercially available biaryl phosphine. Moreover, two ruthenacycle intermediates of tertiary phosphines via C-H bond cleavage were isolated to illustrate the mechanism of P(III)-directed C-H activation.

Carboxylate-Assisted Pd(II)-Catalyzed ortho-C-H and Remote C-H Activation: Economical Synthesis of Pyrano[4,3- b]Indol-1(5 H)-ones.

An original Pd(II)-catalyzed domino two C-H activations strategy has been designed to synthesize pyrano[4,3- b]indol-1(5 H)-one motifs from inexpensive and commercially available olefins and heteroaromatic acids by carboxylate-directed sequential ortho-C-H alkenylation and remote C-H lactonization. Importantly, this protocol overcomes the selectivity for carboxylic acids with acrylates of the conventional Michael addition-type process. Preliminary studies of mechanism indicate that both aryl and olefinlic C-H activations may participate in this catalytic system.

Smart pH-responsive polymeric micelles for programmed oral delivery of insulin.

The development of intelligent oral drug delivery carrier aiming at efficiently bring insulin to intestine is of great significance for diabetes mellitus therapy. In the present study, a series of amphiphilic pH-sensitive block copolymer poly(methyl methacrylate-co-methacrylicacid)-b-poly(2-amino ethyl methacrylate) [P(MMA-co-MAA)-b-PAEMA] was synthesized via activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) and further self-assembled into pH-responsive cationic polymeric micelles (PCPMs) for oral insulin delivery. The structure and molecular weight were confirmed by proton nuclear magnetic resonance (1H-NMR), Fourier transforming infrared spectrum (FT-IR) and gel permeation chromatography (GPC), respectively. The critical micelle concentration (CMC) values of these copolymers were measured by fluorescent probe method at pH 1.2 (8-15 µg/mL) and pH 7.4 (22-42 µg/mL), respectively, demonstrating high stability at acidic environment. A decrease in the particle size of PCPMs was associated with an increased pH at beginning, which reached around 200 nm at neutral pH, while the particle size increased obviously with pH increase, indicating the pH-sensitivity of PCPMs. The insulin was entrapped into the core of PCPMs (Ins-loaded PCPMs) with high loading efficiency via diafiltration method. The in vitro experiments show Ins-loaded PCPMs have low toxicity and exhibit pH-triggered release profile with remitted initial burst release. The results indicate that the PCPMs self-assembled from P(MMA-co-MAA)-b-PAEMA may be potential carriers for efficient oral delivery of insulin with controlled release property.

Ruthenium-Catalyzed Gram-Scale Preferential C-H Arylation of Tertiary Phosphine.

A general protocol for site-preferential mono-C-H arylation of tertiary phosphine ligands catalyzed by a ruthenium(II) complex was devised. This protocol gives access to a series of modified Buchwald-biaryl monophosphines on a gram scale in moderate to excellent yields. A catalytic cycle is proposed derived from knowledge of the intermediates observed by ESI-MS. Importantly, these monoarylated products could be further transformed into dibenzophosphole derivatives.

Facile synthesis of unnatural ß-germyl-α-amino amides via Pd(ii)-catalyzed primary and secondary C(sp3)-H bond germylation.

Pd(ii)-Catalyzed direct C(sp3)-H germylation of α-AA derivatives with the assistance of a bidentate auxiliary for the efficient synthesis of ß-germyl-α-amino amides is reported. This protocol features good generality for primary and secondary C-H bonds of aliphatic amides. Mechanistic studies show that a crucial five-membered palladacycle intermediate may play a key role in this process.