Visible-Light-Induced Acylative Pyridylation of Styrenes.

A visible-light-induced photocatalyst-free acylative pyridylation of styrenes with 4-acyl-1,4-dihydropyridines (DHPs) and 4-cyanopyridines has been described, featuring mild reaction conditions, a broad substrate scope, and good functional group tolerance. The reaction could also be performed under sunlight irradiation albeit with a slightly lower conversion. 4-Acyl-1,4-DHPs serve a dual role, acting as both a photoreductant to reduce the cyanopyridine to its radical anion intermediate and a radical precursor to produce the acyl radical.

Accessing -Alkylphenols via Iridium-Catalyzed Site-Specific Deoxygenation of Alcohols.

An iridium-catalyzed and phenol-directed deoxygenation of benzylic alcohols comes as an alternative access to 4-alkylphenols, featuring low catalyst loading (/ up to 20,000, TOF up to 12,400 h), high functionality compatibility, and excellent site-selectivity. The applications in late-stage modification of steroids and gram-scale total synthesis of a extract are highlighted. Mechanistically, the intermediacy of quinone methide controls the site-selectivity, and the formation of iridium hydride serves as the rate-limiting step.

Direct Regioselective C-H Cyanation of Purines.

A direct regioselective C-H cyanation of purines was developed through a sequential triflic anhydride activation, nucleophilic cyanation with TMSCN, followed by a process of base-mediated elimination of triflous acid (CFSOH). In most cases, the direct C-H cyanation occurred on the electron-rich imidazole motif of purines, affording 8-cyanated purine derivatives in moderate to excellent yields. Various functional groups, including allyl, alkynyl, ketone, ester, nitro et al.

Cross dehydrogenation coupling reaction of purine derivatives with thioethers.

A metal-free cross-dehydrogenation coupling method was established to synthesize N alkylated purine derivatives. Using PhI(OAc) as the oxidant, versatile thioethers were successfully employed as alkylation reagents. Under the optimized conditions, a variety of alkylated purine derivatives and other aromatic N-heterocycles were obtained in moderate to good yields.

Direct Bis-Alkyl Thiolation for Indoles with Sulfinothioates under Pummerer-Type Conditions.

A base-free bis-alkyl thiolation reaction of indoles with sulfinothioates under Pummerer-type conditions is described. Sulfinothioates, activated with 2,2,2-trifluoroacetic anhydride, are demonstrated to be an efficient thiolation reagent for wide applications. This approach enabled double C-H thiolation at the C2 and C3 of the indole in one pot.

Access to Deuterated Unnatural α-Amino Acids and Peptides by Photochemical Acyl Radical Addition.

A visible-light-enabled, photocatalyst-free conjugate addition reaction of dehydroamino acids is disclosed. Employing 4-acyl-1,4-dihydropyridines as both a radical reservoir and reductant, various β-acyl α-amino acids and their deuterated analogues were obtained in good results. Both late-stage peptide modification and stereoselective synthesis of chiral oxazolidinones are successfully achieved.

Visible-light-promoted photocatalyst-free alkylation and acylation of benzothiazoles.

Herein we report a protocol for the visible-light-mediated alkylation/acylation reaction of benzothiazoles. Alkyl/acyl substituted Hantzsch esters are easily prepared and rationally used as radical precursors. In the presence of BF3·Et2O and Na2S2O8, various benzothiazole derivatives were readily obtained in good yields.

Cross-Dehydrogenative Coupling of Azoarenes with Dialkyl Disulfides.

A catalyst-free cross-dehydrogenative coupling reaction of purines and some azoarenes with dialkyl disulfides has been developed. This procedure provided a novel strategy to construct unsymmetrical disulfides through the α-heterocyclic functionalization of symmetrical dialkyl disulfides. The S-S bond was successfully tolerated in this transformation.

Methanesulfinylation of Benzyl Halides with Dimethyl Sulfoxide.

A phenyltrimethylammonium tribromide-mediated nucleophilic substitution/oxygen transformation reaction of benzyl halides with DMSO has been developed. In this transition-metal-free reaction, DMSO acts as not only a solvent but also a "S(O)Me" source, thus providing a convenient method for the efficient and direct synthesis of various benzyl methyl sulfoxides.

Synthesis of Functionalized Thietanes via Electrophilic Carbenoid-Induced Ring Expansion of Thiiranes with Sulfonium Acylmethylides as Carbene Precursors.

Various functionalized thietanes were prepared from thiiranes via an electrophilic ring expansion with rhodium carbenoids as electrophiles generated from safe and readily accessible dimethylsulfonium acylmethylides. The reaction appears to proceed through electrophilic metallocarbenoid-induced activation of thiiranes, nucleophilic ring-opening of the activated thiiranes with dimethyl sulfide as a transient nucleophile, and nucleophilically intramolecular cyclization. The Umpolung from the nucleophilic ylides to the electrophilic carbenoids plays an important role in both the activation and ring opening of thiiranes and subsequent cyclization.

Regiospecific synthesis of polysubstituted furans with mono- to tricarboxylates from various sulfonium acylmethylides and acetylenic esters.

Polysubstituted furans were prepared in moderate to good yields from various sulfur ylides and alkyl acetylenic carboxylates. The direct reactions of dimethylsulfonium acylmethylides with dialkyl acetylenedicarboxylates afforded dialkyl furan-3,4-dicarboxylates through a tandem sequence of Michael addition, intramolecular nucleophilic addition, 4π ring opening, intramolecular Michael addition, and elimination. The method was extended to synthesize furan-3-carboxylate, -2,4-dicarboxylates, and -2,3,4-tricarboxylates as well.

Synthesis of α-heterosubstituted ketones through sulfur mediated difunctionalization of internal alkynes.

Synthesis of α-heterosubstituted ketones was achieved through sulfur mediated difunctionalization of internal alkynes in one pot. The reaction design involves: phenyl substituted internal alkyne attacking triflic anhydride activated diphenyl sulfoxide to give a sulfonium vinyl triflate intermediate, hydrolysis to give an α-sulfonium ketone, and then substitution with various nucleophiles. This method provides a unified route to access α-amino ketones, α-acyloxy ketones, α-thio ketones, α-halo ketones, α-hydroxy ketones, and related heterocyclic structures, in a rapid fashion.

Sulfur-Mediated Electrophilic Cyclization of Aryl-Substituted Internal Alkynes.

A sulfur-mediated electrophilic cyclization reaction of aryl-tethered internal alkynes has been developed. Triflic anhydride-activated sulfoxides induced the electrophilic cyclization and then demethylation with triethylamine in one pot, affording 3-sulfenyl-1,2-dihydronaphthalenes and related types of products in yields of ≤96%.

I/TBHP-Mediated tandem cyclization and oxidation reaction: Facile access to 2-substituted thiazoles and benzothiazoles.

The efficient synthesis of 2-substituted thiazoles and benzothiazoles has been accomplished employing readily available cysteine esters and 2-aminobenzenethiols as N and S sources. The reaction proceeds under an I2/TBHP system and involves a one-pot tandem cyclization and oxidation sequence. A diverse range of aldehydes is amenable for this transition-metal-free protocol, which provides an alternative method to rapidly access thiazole-containing molecules.

Stereochemistry and mechanistic insights in the [2 + 2 + 2] annulations of thioketenes and imines.

Stereochemical models and mechanistic insights are proposed for [2 + 2 + 2] annulations of thioketenes and imines on the basis of experimental and computational investigations. In the [2 + 2 + 2] annulations involving cyclic imines, the zwitterionic intermediates generated from monosubstituted thioketenes and the cyclic imines undergo a stepwise nucleophilic endo-addition/Si-face attack pathway with a second imines molecule, giving initially (2,4)-cis-(4,5)-cis-[2 + 2 + 2] annuladducts, which completely epimerize into the corresponding (2,4)-cis-(4,5)-trans-annuladducts under basic reaction conditions. The annuloselectivity of thio-Staudinger cycloadditions is dependent on the substituents of both thioketenes and imines.

Anti-Markovnikov rearrangement in sulfur mediated allylic C-H amination of olefins.

Cationic rearrangement reactions usually follow Markovnikov's rule to give more substituted carbocations as stable intermediates. During our study on sulfur mediated allylic C-H amination of olefins, very rare cases of anti-Markovnikov rearrangement from secondary carbocations toward primary carbocations or primary triflates were observed.

Purinyl N(3)-Directed Palladium-Catalyzed C-H Alkoxylation of N(9)-Arylpurines: A Late-Stage Strategy to Synthesize N(9)-(ortho-Alkoxyl)arylpurines.

A palladium-catalyzed alkoxylation of N(9)-arylpurines with primary or secondary alcohols has been developed successfully, which is a rare C-H activation reaction of polynitrogenated purines and offers a late-stage strategy to synthesize N(9)-(ortho-alkoxyl)arylpurines. Although there are more than four nitrogen atoms present in the purine moiety, the reaction can be effectively conducted by sterically blocking the N(1) site for catalyst coordination and first employing the purinyl N(3) atom as a directing group.

Copper-Catalyzed Intramolecular Alkoxylation of Purine Nucleosides: One-Step Synthesis of 5'-O,8-Cyclopurine Nucleosides.

A novel copper-catalyzed intramolecular dehydrogenative alkoxylation of purine nucleosides has been developed successfully, providing the 5'-O,8-cyclopurine nucleosides in one-step with a yield up to 90%. The method, which utilized an inexpensive CuCl catalyst and a di-tert-butyl peroxide (DTBP) oxidant was suitable in a broad substrate scope and proceeded well even in gram scale.

BF066, a novel dual target antiplatelet agent without significant bleeding.

In this study, we report BF066, a novel adenine derivative, inhibits platelet activation and thrombosis via the adenosine receptor (A(2A)) activation and phosphodiesterase (PDE) inhibition. BF066 inhibits platelet aggregation and ATP releasing induced by multiple platelet agonists in a dose-dependent manner. The inhibition of BF066 on ADP-induced aggregation is potentiated by adenosine and can be dramatically antagonized by the A(2A) antagonist SCH58261.

Synthesis of N6-alkyl(aryl)-2-alkyl(aryl)thioadenosines as antiplatelet agents.

A series of novel N(6)-alkyl(aryl)-2-alkyl(aryl)thioadenosines were synthesized, and their human antiplatelet aggregation activities were evaluated by the stimulation of adenosine 5'-diphosphate (ADP). Some of these compounds showed strong activity, among which compound 5b(11) displayed the highest activity with an IC(50) value of 29 ± 3 μM. Furthermore, five compounds were tested against arachidonic acid (AA)-induced human platelet aggregation.

BF061, a novel antiplatelet and antithrombotic agent targeting P2Y₁₂ receptor and phosphodiesterase.

The addition of phosphodiesterase (PDE) inhibitors has been reported to potentiate the antithrombotic effects of P2Y₁₂ antagonists without increasing bleeding risk. In this study, we report that a potent antiplatelet agent, 2-ethylthio-6-phenethylaminoadenosine (BF061), inhibits platelet activation and thrombosis via P2Y₁₂ antagonism and PDE inhibition. We explored the antiplatelet mechanism of BF061 by measuring cAMP, cGMP levels, PDE activity, and the interaction between ADP and P2Y₁₂ using atomic force microscopy.

3D-QSAR studies on a series of dihydroorotate dehydrogenase inhibitors: analogues of the active metabolite of leflunomide.

The active metabolite of the novel immunosuppressive agent leflunomide has been shown to inhibit the enzyme dihydroorotate dehydrogenase (DHODH). This enzyme catalyzes the fourth step in de novo pyrimidine biosynthesis. Self-organizing molecular field analysis (SOMFA), a simple three-dimensional quantitative structure-activity relationship (3D-QSAR) method is used to study the correlation between the molecular properties and the biological activities of a series of analogues of the active metabolite.

BF0801, a novel adenine derivative, inhibits platelet activation via phosphodiesterase inhibition and P2Y12 antagonism.

Though antiplatelet drugs are proven beneficial to patients with coronary heart disease and stroke, more effective and safer antiplatelet drugs are still needed. In this study we report the antiplatelet effects and mechanism of BF0801, a novel adenine derivative. BF0801 dramatically inhibited platelet aggregation and ATP release induced by ADP, 2MeSADP, AYPGKF, SFLLRN or convulxin without affecting shape change in vitro .