Reaction of hydroxyamide-functionalized azolium salt with Ag2O: Three different transformations

Abstract

We report three different transformations in the reaction of the hydroxyamide-functionalized azolium chloride 1 with Ag2O. These transformations were controlled by the N-substituent at the azolium ring of 1. Treatment of 1c (R = Me, alkyl) with Ag2O afforded the corresponding monodentate NHC-Ag (NHC represents N-heterocyclic carbene) complex, 6c, in 95% yield. In contrast, the reaction of 1b (R = Ph, aryl) with Ag2O yielded the corresponding 2-hydroxyoxazolidine-substituted azolium hydroxide, 7b, in 90% yield. In this transformation, perhaps the cyclization of the hydroxyamide moiety of 1b to 2-hydroxyoxazolidine occurred under the influence of the hydroxide counter anion. Several aryl-substituted azolium chlorides, 1d-f, were also converted into the corresponding cyclization products, 7d-f. However, the reaction of 1h (R = 2,4,6-Me3C6H2, aryl) with Ag2O afforded the corresponding NHC-Ag complex, 6h, in 93% yield, whereas the reaction of 1i (R = 4-MeOC6H4, aryl) with Ag2O provided a mixture of 6i and 7i in 56% and 32% yields, respectively. Moreover, the reaction of azolium chloride, 1j (R = 2,6-iPr2C6H3, aryl), which has a more sterically hindered substituent at the ortho-position of the aryl side-arm, was investigated. Treatment of 1j with Ag2O gave unexpected urea derivative, 8j, in 99% yield.