Here, we report the method for copper-catalyzed N-arylation of diverse oxadiazolones by diaryliodonium salts under mild conditions in high yields (up to 92%) using available CuI as a catalyst. The developed method allows utilizing both symmetric and unsymmetric diaryliodonium salts bearing auxiliary groups such as 2,4,6-trimethoxyphenyl (TMP). We found that the steric effects in aryl moieties determined the chemoselectivity of N-and O-arylation of the 1,2,4-oxadiazol-5(4H)-ones. Mesityl-substituted diaryliodonium salts demonstrated the high potential as a selective arylation reagent. The structural study suggests that steric accessibility of N-atom in 1,2,4-oxadiazol-5(4H)-ones impact to arylation with sterically hindered diaryliodonium salts. The synthetic application of proposed method was also demonstrated on selective arylation of 1,3,4-oxadiazol-2(3H)-ones and 1,2,4-oxadiazole-5-thiol.
Five
new copper(I) complexescomposed of the paired dibenzohalolium
and [CuL2]− (L = 1,2,4-oxadiazolate)
counterions in which O,O-atoms of the anion are simultaneously linked
to the halogen atomwere generated and isolated as the solid
via the three-component reaction between [Cu(MeCN)4](BF4), sodium 1,2,4-oxadiazolates, and dibenzohalolium triflates
(or trifluoroacetates). This reaction is different from the previously
reported CuI-catalyzed arylation of 1,2,4-oxadiazolones
by diaryliodonium salts. Inspection of the solid-state X-ray structures
of the complexes revealed the strong three-center X···O,O
(X = Br, I) halogen bonding occurred between the oxadiazolate moieties
and dibenzohalolium cation. According to performed theoretical calculations,
this noncovalent interaction (or noncovalent chelation) was recognized
as the main force in the stabilization of the copper(I) complexes.
An explanation for the different behavior of complexes, which provide
either chelate or nonchelate binding, is based on the occurrence of
additional −CH3···π interactions,
which were also quantified.
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