Synlett最新文献

C-Aryl glycosides have attracted considerable interest as biologically active natural products and as O-aryl glycoside mimetics in drug discovery. Here, we describe a straightforward synthesis of C-aryl glycosides by photoredox/Ni dual-catalyzed reductive cross-coupling between glycosyl bromides and aryl bromides. This methodology enables a highly α-stereoselective synthesis of C-aryl glucosides, galactosides, and mannosides.

A triazine-based reagent, 2-hydroperoxy-4,6-dimorpholino-1,3,5-triazine (Triazox-II), was developed for alkene epoxidation. This reagent can be prepared from inexpensive starting materials (cyanuric chloride and morpholine) on a 15 mmol scale in two steps with 54% overall yield and isolated as a pure, bench-stable solid with low sensitivity to impact and friction. Triazox-II exhibited higher solubility in chlorinated solvents than the previously reported reagent Triazox. Epoxidation using Triazox-II was conducted in various solvents, with a preference for CH₂Cl₂ at 0.5 M concentration, resulting in epoxides in 83–94% yield. The reaction was conducted under mild conditions owing to the low acidity of the reaction coproduct.

Natural products containing highly oxygenated furanofuranone fragments are known for their potent biological activity, but also for their challenging total synthesis. In this study, the synthesis of five novel dephenylated (–)-goniofufurone analogues was completed and their cytotoxic activity against eight malignant and one normal human cell line was evaluated. Compared with previous syntheses of similar analogues, the synthesis was carried out starting from l-xylose, resulting in improved yields and a reduced number of synthetic steps for three divergent intermediates.

Numerous reports invoke Cu^III–F intermediates engaging in oxidative cross-couplings mediated by low/mid-valent copper and formal sources of ‘F⁺’ oxidants. These elusive and typically instable Cu^III fluorides have been rarely characterized or spectroscopically identified, making their existence and participation within catalytic cycles somehow questionable. We have authenticated a stable organocopper(III) fluoride that undergoes C_sp–CF₃ bond formation upon addition of silyl-capped alkynes following a 2 e^– Cu^III/Cu^I redox shuttle. This finding strongly supports the intermediacy of Cu^III fluorides in C–C coupling. We review herein the state of the art about well-defined Cu^III fluorides enabling cross-coupling reactions.

1 Introduction

2 Brief History of Coupling-Competent Cu^III Fluorides

3 Design of an Isolable – yet Reactive – Organocopper(III) Fluoride

4 Alkyne Trifluoromethylation: Scope and Mechanism

5 Extension to Aryl–CF₃ and C–Heteroatom Couplings

6 Summary and Outlook

We herein developed a base-promoted cyclization reaction between N-acyl benzotriazoles and p-toluenesulfonylmethyl isocyanide (TosMIC) to afford 4,5-disubstituted oxazoles. In the presence of 3 equiv of K₃PO₄, the two readily available starting materials reacted in N,N-dimethylformamide at 80 °C to give 28 examples of 4-tosyl-5-aryl, -alkyl, or -alkenyl-substituted oxazoles in moderate to high yields.

Indium(III) triflate was found to be an efficient metal catalyst for the electrophilic substitution reaction of substituted indoles with various isatins or aryl aldehydes in acetonitrile solvent to afford the corresponding 3,3-diaryloxindoles or bis(indol-3-yl)methanes, respectively, in high yields at room temperature. This new procedure has remarkable features such as experimental simplicity, high conversions, good to excellent yields, short reaction times, and simple workup procedures

The selective construction of two C(sp³)–C(sp³) bonds through trimolecular cross-coupling of unactivated alkenes remains one of the most difficult challenges in organic synthesis. Despite previous advances in metal-catalyzed coupling for the dicarbofunctionalization of alkenes, dialkylation is still problematic due to the instability of the requisite metal–alkyl intermediate, which undergoes facile β-hydride elimination or protodemetalation. Recently, our group was successful in developing a bimolecular homolytic substitution (S_H2) strategy that circumvents metal–alkyl side reactions and accomplishes the challenging cross-coupling of metal–alkyl intermediates with alkyl radicals in the absence of a directing auxiliary, permitting a highly regioselective dialkylation of unactivated alkenes.

1 Introduction

2 Nickel-Catalyzed Dicarbofunctionalization of Unactivated Alkenes

3 Nickel-Catalyzed Dialkylation of Unactivated Alkenes

4 Conclusions and Perspectives

We report a practical scalable synthesis of the natural product (±)-tylophorine by using an operationally simple protecting-group-free route from readily accessible starting materials. Synthesis of a cyclic N-acetyl diester compound through cyclization, followed by two key steps (decarboxylation and a Clemmensen reduction), provides access to the target molecule.

Carbohydrates and their conjugates play important roles in life activities and drug development. Our group was committed to the general and effective glycosylation methods and their application in chemical biology using unsaturated glycosyl donors. In the past five years, we have reported several synthetic strategies with high stereoselectivity and milder conditions compared with previous works. In particular, high chemo-/regio- and stereoselective O-glycosylation, C-glycosylation and S-glycosylation could be achieved via palladium catalysis under open-air conditions at room temperature. In this Account, we will introduce our research progress in constructing four types of glycosides.

1 Introduction

2 Stereoselective Synthesis of O-Glycosides

3 Stereoselective Synthesis of C-Glycosides

4 Stereoselective Synthesis of N-Glycosides

5 Stereoselective Synthesis of S-Glycosides

6 Conclusion

A new heterogeneous polymeric disulfonimide was very easily synthesized from simple commercially available reagents. The new cost-effective catalytic material exhibited a tremendously enhanced reactivity in a benchmark Mukaiyama aldol reaction via silicon Lewis acid activation when compared with common acidic resins. Moreover, the reported polymeric disulfonimide exhibits outstanding robustness, as confirmed by its good thermal stability and excellent recyclability.