Dual Roles of Azide: Dearomative Dimerization of Furfuryl Azides.

A dearomative dimerization of furfuryl azides for the construction of furfuryl triazoles is developed. As a rare leaving group, azide is capable of initiating the generation of a furfuryl cation under the Lewis acid-catalyzed conditions, followed by reacting with the other azide to realize an intermolecular [3 + 2] cycloaddition/furan ring-opening cascade. By extending the reaction time, a fragmentation reaction of resulting furfuryl triazoles occurs to afford 1H-triazoles in high yield. Control studies demonstrated that key furfuryl cations also can be obtained from furfuryl triazoles. Furthermore, a chemoselective cross-cycloaddition can be achieved between furfuryl azides and a benzyl azide.

Manganese-Catalyzed Achmatowicz Rearrangement Using Green Oxidant H2O2.

Oxidation reactions have been extensively studied in the context of the transformations of biomass-derived furans. However, in contrast to the vast literature on utilizing the stoichiometric oxidants, such as m-CPBA and NBS, catalytic methods for the oxidative furan-recyclizations remain scarcely investigated. Given this, we report a means of manganese-catalyzed oxidations of furan with low loading, achieving the Achmatowicz rearrangement in the presence of hydrogen peroxide as an environmentally benign oxidant under mild conditions with wide functional group compatibility.

Ytterbium-Catalyzed Intramolecular [3 + 2] Cycloaddition based on Furan Dearomatization to Construct Fused Triazoles.

The 1,2,3-triazole-containing polycyclic architecture widely exists in a broad spectrum of synthetic bioactive molecules, and the development of expeditious methods to synthesize these skeletons remains a challenging task. In this work, the catalytic cyclization of biomass-derived 2-furylcarbinols with an azide to form fused triazoles is described. This approach takes advantage of a single catalyst Yb(OTf)3 and operates via a furfuryl-cation-induced intramolecular [3 + 2] cycloaddition/furan ring-opening cascade.

Furfuryl Cation Induced Cascade Formal [3 + 2] Cycloaddition/Double Ring-Opening/Chlorination: An Approach to Chlorine-Containing Complex Triazoles.

A TiCl4-promoted cascade formal [3 + 2] cycloaddition/double ring-opening/chlorination of 2-furylcyclobutanols with alkyl or aryl azides is described. This highly efficient transformation involves the formation/cleavage of several C-N, C-Cl, C-C, and C-O bonds in a single operation. It enables the quick construction of trisubstituted 1,2,3-triazoles with an ( E)-enone moiety and a 3-chloropropyl unit. The chlorinated products are readily transformed into other structurally diverse analogues.