Copper(I)-Catalyzed 1,3-Dipolar Cycloaddition of Ketonitrones to Dialkylcyanamides: A Step toward Sustainable Generation of 2,3-Dihydro-1,2,4-oxadiazoles

Abstract

Cu I -catalyzed cycloaddition (CA) of the ketonitrones, Ph 2 C=N + (R′)O – (R′ = Me, CH 2 Ph), to the disubstituted cyanamides, NCNR 2 (R = Me 2 , Et 2 , (CH 2 ) 4 , (CH 2 ) 5 , (CH 2 ) 4 O, C 9 H 10 , (CH 2 Ph) 2 , Ph(Me)), gives the corresponding 5-amino-substituted 2,3-dihydro-1,2,4-oxadiazoles (15 examples) in good to moderate yields. The reaction proceeds under mild conditions (CH 2 Cl 2 , RT or 45 °C) and requires 10 mol % of [Cu(NCMe) 4 ](BF 4 ) as the catalyst. The somewhat reduced yields are due to the individual properties of 2,3-dihydro-1,2,4-oxadiazoles, which easily undergo ring opening via N—O bond splitting. Results of density functional theory calculations reveal that the CA of ketonitrones to Cu I -bound cyanamides is a concerted process, and the copper-catalyzed reaction is controlled by the predominant contribution of the HOMO dipole –LUMO dipolarophile interaction (group I by Sustmann’s classification). The metal-involving process is much more asynchronous and profitable from both kinetic and thermodynamic viewpoints than the hypothetical metal-free reaction.

A novel family of homoleptic copper(i) complexes featuring disubstituted cyanamides: a combined synthetic, structural, and theoretical study

“…orbital, charge, and vibrational frequencies analysis, were also conduced in this work and the obtained data provide a further insight into the mechanism of Cu I -catalyzed 1,3-dipolar cycloaddition of ketonitrones to cyanamides (Scheme 1). 2 All these results are given in the following sections.…”

“…Recently we reported on the Cu I -catalyzed 1,3-dipolar cycloaddition of ketonitrones, Ph 2 CQN + (R 0 )O À , to cyanamides, NCNRR 0 , 1 that gives corresponding 5-amino-substituted 2,3dihydro-1,2,4-oxadiazoles (Scheme 1). 2 The reaction proceeds under mild conditions and requires 10 mol% of [Cu(NCMe) 4 ](BF 4 ) as the catalyst. This synthesis exemplifies the first catalytic system for the generation of less explored metal-free 2,3-dihydro-1,2,4oxadiazoles.…”

“…These complexes could be interesting as precursors for the substitution chemistry and also as potential intermediates in copper-involving catalytic reactions of cyanamides. 2,5 A theoretical comparative study of the nature of Cu-N coordination bonds in homoleptic nitrile-and dialkylcyanamide copper(I) complexes and a comparison of the electrophilic activation of NCR and NCNRR 0 species, viz. orbital, charge, and vibrational frequencies analysis, were also conduced in this work and the obtained data provide a further insight into the mechanism of Cu I -catalyzed 1,3-dipolar cycloaddition of ketonitrones to cyanamides (Scheme 1).…”

Cyclometalated Iridium(III) Complexes Featuring Disubstituted Cyanamides

“…Transition metal dialkylcyanamide complexes attract significant attention for the past decades due to structural features of NCNAlk 2 ligands, which is differ from those of conventional nitrile ligands NCR (R=Alk, Ar) . Moreover, coordinated dialkylcyanamides exhibit excitingly different reaction behavior as compared to the conventional nitrile ligands, and metal‐involving reactions of NCNR 2 ’s allow the atom‐economic synthesis of aminosubstituted five‐membered heterocycles, e. g. 5‐amino‐1,2,4‐oxadiazoles,, 5‐amino‐2,3‐dihydro‐1,2,4‐oxadiazoles,, 5‐aminotetrazoles, 2‐amionooxazoles, 2‐aminoimidazolones, and 1,2,4‐oxadiazol‐5‐imines, and six‐membered heterocycles, e. g. aminopyridines, and aminopyrimidines …”

“…Owing our interest in the luminescent platinum group metal complexes (for our works in this field see) and coordination chemistry of cyanamides (for recent works see,, , ), we report herein the generation of a novel family of mono‐ and bis (dialkylcyanamide) cyclometalated iridium(III) complexes, viz. [IrCl(ppy) 2 (NCNR 2 )] and [IrCl(ppy) 2 (NCNR 2 ) 2 ](OTf) (ppy is 2‐phenylpyridinato‐ C 2 , N , OTf is CF 3 SO 3 ), and study of their photoluminescence in the solid state.…”