α‑Functionalization of 2‑Vinylpyridines via a Chiral Phosphine Catalyzed Enantioselective Cross Rauhut–Currier Reaction

Herein, 2-vinylpyridines as a new type of electron-poor system for the asymmetric cross Rauhut–Currier reaction are reported. 2-Vinylpyridines are chemo- and enantioselectively activated by a newly designed chiral phosphine catalyst. The new reaction provides a powerful synthetic tool for accessing structurally diverse, highly valued chiral pyridine building blocks in good yields and with high enantioselectivities. Preliminary mechanistic studies reveal that two NH protons in the catalyst are critical for the synergistic activation of the substrates and governing the stereoselectivity of this reaction

Effect of transition metal ions on the thermal degradation of chitosan

<p>Chitosan–transition metal compounds with Mn²⁺, Co²⁺, Ni²⁺, Zn²⁺, and Cd²⁺ were obtained containing 0–4.0% weight fraction of metal ions. The microstructure of these compounds was determined, and the effect of the metal ions on the thermal degradation of chitosan in nitrogen was studied. The results showed that the second thermal degradation of chitosan was significantly affected by the metal ion species. The temperature of maximal weight loss rate was dependent on the content of the metal ion, with a higher metallic ion concentration sample presenting a lower temperature, and also the metal ion species, which decreased in the order Cd²⁺ > Ni²⁺ > Mn²⁺ > Co²⁺ > Zn²⁺. However, the weight loss, which decreased with an increasing weight fraction of the metal ion, was not proportional to the initial metal concentration in the compound. The activation energies of the second thermal degradation of the compounds were calculated and compared.</p