Copper-Catalyzed Oxidative Synthesis of 3-Aryl-5-fluoroalkyl-1,3,4-oxadiazol-2(3H)-ones Using Perfluorocarboxylic Anhydride as a Reagent

A copper-catalyzed oxidative annulation of sydnones with perfluorocarboxylic anhydride for the synthesis of 3-aryl-5-fluoroalkyl-1,3,4-oxadiazol-2(3H)-ones is developed. A diverse array of 3-aryl-5-fluoroalkyl-1,3,4-oxadiazol-2(3H)-ones are prepared with good yields (>73 examples, yields up to 95%). The synthetic utility of the developed protocol was demonstrated by gram-scale synthesis, and the synthetic transformation to 1,2,4-triazol-3-one products. A mechanistic study suggests that the reaction proceeds via the extrusion of carbon dioxide to generate the hydrazide intermediate, which then undergoes intramolecular cyclization and oxidation.

Selective N-functionalization of Arylhydrazines with Primary Alcohols and Acids under PPh3/DDQ System

We present a PPh3/DDQ-mediated regiospecific selective N-functionalization of arylhydrazines with primary benzylic alcohols and aryl carboxylic acids for the synthesis of N1-benzyl arylhydrazines and N2-acyl arylhydrazines, respectively. This metal- and base-free approach features very short reaction times (about 10 min), broad substrate scope, good functional group tolerance, and mild reaction conditions. Furthermore, N1-benzlated products have also been successfully applied to the concise synthesis of N-substituted indoles and anticancer drug MDM2 inhibitor.

One-pot synthesis of 1,3,4-oxadiazol-2(3H)-ones with CO2 as a C1 synthon promoted by hypoiodite

A convenient and efficient route has been developed to synthesize 1,3,4-oxadiazol-2(3H)-ones from CO₂, hydrazines and aryl or aliphatic aldehydes. Promoted by hypoiodite (IO^-) generated in situ from KI and oxidant TBHP, the one-pot synthesis could proceed smoothly to afford the desired products in moderate to high yields. Mechanism studies revealed that nitrile imine was an important intermediate in this transformation. Notably, a commercial herbicide Oxadiazon could be successfully synthesized by this route.

Annulation Reactions of In-Situ-Generated N-(Het)aroyldiazenes with Isothiocyanates Leading to 2-Imino-1,3,4-oxadiazolines

A novel annulation reaction of N-(het)aroyldiazenes and isothiocyanates has been established. This transformation involves a sequential cyclization and desulfurization/intramolecular rearrangement to produce 2-imino-1,3,4-oxadiazolines. The less-stable N-(het)aroyldiazenes can be conveniently generated in situ by I₂-mediated oxidation of hydrazides, which allows a one-pot synthesis of the products directly from readily accessible hydrazide and isothiocyanate substrates. This operationally simple synthetic process requires no use of malodorous isocyanides and can be conveniently conducted on a gram scale.

KI-catalyzed reactions of aryl hydrazines with α-oxocarboxylic acids in the presence of CO2: access to 1,3,4-oxadiazol-2(3H)-ones

A novel KI-catalyzed synthesis of 1,3,4-oxadiazol-2(3H)-ones from aryl hydrazines, α-oxocarboxylic acids and CO₂ was reported.

A metal-free and mild approach to 1,3,4-oxadiazol-2(3H)-ones via oxidative C–C bond cleavage using molecular oxygen

A metal-free aerobic oxidative C–C bond cleavage reaction for the synthesis of 1,3,4-oxadiazol-2(3H)-ones is described.