1,2,3-Oxadiazoles

Click and Bio-Orthogonal Reactions with Mesoionic Compounds

“…Finally, one-pot strategies were developed, avoiding the isolation of the toxic nitroso-amine intermediate. , In 2019, an alternative method using mechano-chemistry was developed by the group of Lamaty . Interestingly, the sydnone core offers various postfunctionalization possibilities, which have been the topic of several works, including reviews (Scheme b). ,− Indeed, the proton in position C 4 possesses an acidic character and can be abstracted in the presence of different organometallic species. The intermediate sydnone anion can further react with a large variety of electrophiles or participate in metal-catalyzed cross-coupling reaction via transmetalation. ,− Among the possible functionalization, halogenation (typically achieved in the presence of N -halosuccinimides) is of particular interest, as 4-halo-sydnones are good substrates for cross-coupling reactions. − More recently, Moran discovered that direct arylation, alkenylation, and alkynylation could be performed with 4- H -sydnones. , Following this work, Suzuki couplings and oxidative Heck reactions were developed. , …”