Microwave-Assisted Cu-Catalyzed Diaryletherification for Facile Synthesis of Bioactive Prenylated Diresorcinols.

Prenylated diresorcinols exhibit various bioactivities, including cytotoxic, antibacterial, and antifungal activities. Therefore, establishing facile and efficient synthetic routes for prenylated diresorcinols facilitates their development as chemical probes or drugs with a novel mode of action. In this study, microwave-assisted copper catalysis was explored as a cost-effective and environmentally friendly method for the cross-coupling of sterically hindered ortho-prenylated phenols and aryl halides to produce bioactive prenylated diresorcinols, diorcinol I and leotiomycene B. Notable advantages of microwave-assisted catalysis include not only operational simplicity and rapid heating but also shorter reaction times and higher chemical yields. In addition, highly regioselective prenylation of phenol was achieved for the preparation of ortho-prenyl phenol via directed lithiation and subsequent alkylation. This study provides valuable insights for the preparation of other bioactive prenylated diresorcinols. Furthermore, considering that prenylated benzenoids are biosynthetic precursors of various polycyclic natural products, this synthetic route could be expanded to more complex bioactive compounds possessing diaryl ethers.

Unexpected Rearrangement of N-Allyl-2-phenyl-4,5-Dihydrooxazole-4-Carboxamides to Construct Aza-Quaternary Carbon Centers.

The unexpected rearrangement of N-allyl-2-phenyl-4,5-dihydrooxazole-4-carboxamides in the presence of LiHMDS has been found. The key features are: (1) the net reaction consisted of 1,3-migration of the N-allyl group, (2) the rearrangement produced a congested aza-quaternary carbon center, (3) both cyclic and acyclic substrates underwent the unexpected rearrangement to afford products in moderate to high yields, and (4) the reaction seemed to be highly stereoselective. In addition, a plausible mechanism has been discussed.

Increase in convective extreme El Niño events in a CO2 removal scenario.

Convective extreme El Niño (CEE) events, characterized by strong convective events in the eastern Pacific, are known to have a direct link to anomalous climate conditions worldwide, and it has been reported that CEE will occur more frequently under greenhouse warming. Here, using a set of CO2 ramp-up and ramp-down ensemble experiments, we show that frequency and maximum intensity of CEE events increase further in the ramp-down period from the ramp-up period. These changes in CEE are associated with the southward shift of the intertropical convergence zone and intensified nonlinear rainfall response to sea surface temperature change in the ramp-down period. The increasing frequency of CEE has substantial impacts on regional abnormal events and contributed considerably to regional mean climate changes to the CO2 forcings.