Synlett

Two diaryl derivatives of 1,1,4,4-tetracyanobuta-1,3-diene were synthesized for use as colorimetric ion sensors in aqueous media. The key synthetic step involved a [2+2]-cycloaddition/retro-cycloaddition between an electron-rich diarylethyne and electron-deficient tetracyanoethene. The compound bearing two sulfonamide groups showed good selectivity toward hydrogen sulfide ion, with a detection limit of 15.5 μM. The use of this sensor for the quantitative analysis of hydrogen sulfide ion in water samples was successfully demonstrated.

The synthesis and characterization of a novel class of pillar[4]arene[1]thioarenes (P[4]A[1]SMe) are reported. An oxidation–thionation strategy was used to replace a single dialkoxybenzene panel in the parent pillar[5]arene. 1H NMR spectroscopic titration experiments, supported by density functional theory computational studies, revealed that P[4]A[1]SMe show starkly modulated host–guest binding properties for electron-deficient aliphatic guests.

A novel method has been developed for the synthesis of 1,5-disubstituted tetrazoles from nitrones by using bis(p-nitrophenyl) phosphorazidate in the presence of 4-(dimethylamino)pyridine. By this approach, various nitrones were converted into the corresponding tetrazoles. This method permits the preparation of 1,5-disubstituted tetrazoles without the need for toxic or explosive reagents.

Appropriately substituted 1,1′-bi-2-naphthols (BINOLs) are demonstrated as effective photoacid catalysts for promoting the acetalization of enol ethers with alcohols under irradiation with visible light. The reactions proceed efficiently with a wide range of substrates under mild, near neutral conditions.

An efficient synthetic method for coumarin derivatives was developed using a dual organocatalytic reaction. A combination of p-toluenesulfonic acid monohydrate and piperidine was found to efficiently catalyze the cyclization between salicylaldehydes and alkynoic esters to give various coumarin derivatives in good yield and high selectivity. Mechanistic and kinetic data suggested that the conjugate addition between piperidine and alkynoic esters played a crucial role in the reaction mechanism.

A new and simple method for preparing 2-arylindole derivatives under transition-metal-free conditions has been developed. When N-(2-methyl-3-nitrophenyl)acetamide was treated with 2-fluorobenzaldehydes in the presence of Cs2CO3 in DMF at 60 °C, the desired indoles were typically obtained in moderate to good yields (up to 83%). When other aniline substrates were employed, only a Knoevenagel condensation occurred, giving the corresponding diarylethenes in moderate to excellent yields.

Most chiral secondary amine catalysts are usually synthesized from chiral amino acids and their derivatives. On the other hand, amine catalysts based on a binaphthyl backbone have previously been developed, and show unique chemo- and stereoselectivity in several asymmetric reactions. However, in spite of their utility, the applications of binaphthyl-based amines in asymmetric reactions are still rare due to their synthetic inefficiency. In this context, we have designed amine catalysts possessing a phenylcyclopropane scaffold as a novel chiral motif. These novel catalysts can be synthesized easily and construct a similar chiral environment to that of binaphthyl-based amine catalysts. In addition, a phenylcyclopropane-based amino sulfonamide is found to be an effective catalyst for syn-selective Mannich reactions and conjugate additions using alkynyl Z-ketimines.1 Introduction2 Design and Synthesis of Novel Chiral Secondary Amine Catalysts3 Performance Evaluation of Phenylcyclopropane-Based Amine Catalysts4 Development of Asymmetric Reactions Catalyzed by a Novel Chiral Amino Sulfonamide5 Conclusions

The strategy of embedding coordinative functional group into the starting material is frequently employed to enhance reactivity and enantioselectivity in various asymmetric catalytic reactions other than enantioselective hydrocarbonylation. Recent progress in palladium-catalyzed asymmetric hydrocarbonylation with this strategy for the synthesis of chiral heterocycles was highlighted. The merits of the innate coordinative functional group not only enhance the reactivity and boost the multiple selectivity, but also facilitates the synthesis of chiral heterocycles.1 Introduction2 Challenges in Pd-Catalyzed Asymmetric Hydrocarbonylation3 Pd-Catalyzed Asymmetric Hydrocarbonylation for the Synthesis of Chiral Heterocycles4 Summary and Outlook

The hydrogenolysis of iodoarenes using a silicon nanoarray palladium catalyst under microwave irradiation was investigated. When triethanolamine was used as the sacrificial reductant, the reaction proceeded via reductive deiodination under an aerobic atmosphere even without the presence of the explosive hydrogen gas, affording the corresponding hydrogen-substituted arenes in high yields. No reaction occurred in the absence of microwaves, indicating a noticeable microwave effect.

Solubility is a crucial encumbrance for the synthesis of squaramides through nucleophilic substitution of squaric acid. The reactions must be performed in an aqueous medium since squaric acid is insoluble in virtually all organic solvents. The scope of amine nucleophiles was consequently restricted to those amines soluble in water. Owing to remarkable solvating ability of ionic liquid, reactions of squaric acid with a variety of structurally diverse amine nucleophiles were achieved. Interestingly, a catalyst-free reaction in 1-butyl-3-methylimidazolium chloride or [bmim]Cl could produce squaramides up to 99% yield. With the same efficacies, [bmim]Cl could be reused for at least three cycles. The catalyst-free, ionic liquid mediated approach expanded the reactant scope and offered a simple, efficient, and environmentally friendly synthesis of squaramides.