Metal-Free Cascade [4 + 1] Cyclization Access to 4-Aryl-NH-1,2,3-triazoles from N-Tosylhydrazones and Sodium Azide.

A molecular iodine-mediated coupling cyclization reaction for the synthesis of 4-aryl-NH-1,2,3-triazoles has been developed from N-tosylhydrazones and sodium azide. This metal-free cascade [4 + 1] cyclization reaction could rapidly synthesize valuable compounds via a sequential C-N and N-N bond formation. Mechanistic studies demostrate that the nitrogen atoms of the 1,2,3-triazoles are not entirely from sodium azide.

A cascade oxidation/[4 + 1] annulation of sulfonium salts for synthesis of polyfunctional furans: DMSO as one carbon source.

A novel DMSO-involved cascade reaction of stabilized sulfonium salts has been established for direct construction of polyfunctional furans. This one-pot sequential reaction involving in situ generated α-methylene sulfonium salts was followed by [4 + 1] annulation with sulfur ylides. Notably, DMSO plays a very important role in this transformation, not only as a solvent but also as one carbon source.

TFA-Mediated DMSO-Participant Sequential Oxidation/1,3-Dipolar Cycloaddition Cascade of Pyridinium Ylides for the Assembly of Indolizines.

A trifluoroacetic acid (TFA)-mediated cascade oxidation/1,3-dipolar cycloaddition reaction of stabilized pyridinium salts with dimethyl sulfoxide (DMSO) has been developed in the presence of K2S2O8 and trimethylethylenediamine (TMEDA). In this transition-metal-free reaction, DMSO acts as a one-carbon source, thus providing a convenient method for the efficient and direct synthesis of various indolizine derivatives.