1,3-dipolar cycloaddition of nitrones to free and coordinated nitriles: Routes to control the synthesis of 2,3-dihydro-1,2,4-oxadiazoles

Microwave‐Assisted 1,3‐Dipolar Cycloaddition: an Eco‐Friendly Approach to Five‐Membered Heterocycles

“…However, coordination of a nitrile to a metal center, usually Pd II or Pt II , has been used to improve the 1,3-dipolar cycloaddition. [50] One example of a set of reactions between nitrones and uncoordinated nitriles under mi- Scheme 17. crowave irradiation conditions is known. [50,51] C,N-Diphenylnitrone reacts with NCCO 2 Et under microwave irradiation conditions to afford the corresponding oxadiazole in 39 % yield.…”

“…[50] One example of a set of reactions between nitrones and uncoordinated nitriles under mi- Scheme 17. crowave irradiation conditions is known. [50,51] C,N-Diphenylnitrone reacts with NCCO 2 Et under microwave irradiation conditions to afford the corresponding oxadiazole in 39 % yield. Under conventional thermal conditions the same compound could only be obtained in 4 % yield.…”

Interplay between nitronates and nitriles accomplished in a PtIV-mediated reaction

“…RCN and RNC species, toward coupling [1] or cycloaddition (CA) [2] and this topic has been surveyed by some of us [1a-d,2a-d,f-h] and others [1e-m,2e]. Our experimental [2b-d,2f-h] and theoretical [3] results demonstrate that the coordination of RCN to platinum centers dramatically enhances the reactivity of the nitriles toward dipoles of both allyl- (e.g., open chain A and cyclic nitrones B [2b-d,2h]; Fig.…”

“…2; IUPAC [4] name: 4-(4-methoxy-phenyl)-6,6-dimethyl-5,6-dihidro-4H- [1,2] oxazin-2-oxide) with EtCN in trans-[PtCl 4 (EtCN) 2 ] insofar as it was previously demonstrated that the ligation of nitriles to a Pt IV center ought to provide even a higher activation effect upon cycloaddition in comparison with the introduction of such powerful electron-acceptor group R as CF 3 to RCN [3]. To our knowledge, this report covers the first example of any reaction between a nitronate and a nitrile and it makes known that the interaction becomes possible in a metal-mediated reaction.…”

“…2 ]. Hence, the elemental analyses and HRESI + -MS support only the composition of 2 and its structure should be verified by physicochemical methods.…”