1,3-Dipolar Cycloaddition of Nitrile Imine with Carbon Dioxide: Access to 1,3,4-Oxadiazole-2(3H)-ones.

Efficient synthesis of 1,3,4-oxadiazole-2(3H)-one was achieved by CsF/18-crown-6 mediated 1,3-dipolar cycloaddition of nitrile imine and 2.0 MPa of CO2. CsF/18-crown-6 played a key role in enhancing the reactivity of CO2 as a 1,3-dipolarophile. The practical utility of this transition-metal-free approach to 1,3,4-oxadiazole-2(3H)-one is highlighted by the convenient synthesis of a commercial herbicide Oxadiazon and a MAO B inhibitor.

Access to α-Arylglycines by Umpolung Carboxylation of Aromatic Imines with Carbon Dioxide.

A straightforward and transition-metal-free approach for the efficient synthesis of α-arylglycine derivatives from aromatic imines and carbon dioxide was enabled by an umpolung carboxylation reaction. Various substituted diphenylmethimines underwent the carboxylation smoothly with carbon dioxide in the presence of potassium tert-butoxide and 18-crown-6 to give the corresponding carboxylated products in good to high yields. Besides the enhancement of the solubility of potassium tert-butoxide in THF, 18-crown-6 also plays key roles in suppressing the reverse protonation or 1, 3-proton shift isomerization as well as by stabilizing the carboxylated intermediate.

Silver(I)-catalyzed carboxylation of arylboronic esters with CO2.

A variety of arylboronic esters were efficiently carboxylated with CO(2) using a simple AgOAc/PPh(3) catalyst, affording the corresponding carboxylic acids in good yield. This simple and efficient silver(i) catalytic system showed wide functional group compatibility.

Structure elucidation and antioxidant activity of a novel polysaccharide isolated from Tricholoma matsutake.

In this study, structural features of Tricholoma matsutake polysaccharide (TMP-A) were investigated by a combination of infrared (IR) spectra, gas chromatography-mass spectrometry (GC-MS), nuclear magnetic resonance (NMR) spectroscopy. The results indicated that TMP-A had a backbone of 1,4-beta-d-glucopyranose residue which branches at O-6 based on the experimental results. The branches were mainly composed of an (1-->3)-alpha-d-galactopyranose residue, and terminated with alpha-d-xylopyranose residue. The antioxidant activity of TMP-A was evaluated with several biochemical methods, including DPPH(-) radical scavenging, hydrogen peroxide scavenging, superoxide anion radical scavenging. The results indicated that TMP-A showed strong antioxidant. In the in vitro antioxidant assay by MTT method, TMP-A could attenuate PC12 cell damage significantly caused by hydrogen peroxide.