The Cycloaddition of the Benzimidazolium Ylides with Alkynes: New Mechanistic Insights

Abstract

New insights concerning the reaction mechanism in the cycloaddition reaction of benzimidazolium ylides to activated alkynes are presented. The proposed pathway leading both to 2-(1H-pyrrol-1-yl)anilines and to pyrrolo[1,2-a]quinoxalin-4(5H)-ones involves an opening of the imidazole ring from the cycloaddition product, followed by a nucleophilic attack of the aminic nitrogen to a proximal carbonyl group and the elimination of a leaving group. The mechanistic considerations are fully supported by experimental data, including the XRD resolved structure of the key reaction intermediate.

Ultrasound assisted synthesis of hybrid quinoline-imidazole derivatives: a green synthetic approach

“…Initially, the dihydro-benzopyrrolo-imidazolo quinoline derivatives 5a-i are formed via the Huisgen [3 + 2] cycloaddition of ylides 4a-i (canonical structure B) to DMAD. As in related cases, [41][42][43][44][45] the initial cycloaddition is followed by an oxidative dehydrogenation of the dihydro-structure 5, leading to more thermodynamically stable compounds: the aromatized benzopyrrolo-imidazolo quinoline compounds 6a-i. The formation of the dihydro-pyrroloquinoxaline quinoline compounds 7a-i could be explained via the following reaction mechanism (Scheme 2): aer the initial Huisgen [3 + 2] cycloadditions which lead to the type I dihydro-benzopyrroloimidazolo derivatives, a ring opening of the imidazole cycle occurs simultaneously with a prototropic rearrangement, with the formation of a type II pyrroloaniline derivative.…”

“…In order to achieve our goal, we decided to use our expertise in cycloimmonium ylides chemistry, [35][36][37][38][39][40][41] with the Huisgen [3 + 2] dipolar cycloaddition reactions of ylides to dipolarophiles with triple bonds (activated alkynes) being our choice. In this regard, Scheme 1 Synthesis of hybrid quinoline imidazolium salts 3a-i and 3 0 a-i.…”

Fluorescent Azasteroids through Ultrasound Assisted Cycloaddition Reactions

“…Our group has presented in previous work several studies on the synthesis of azine derivatives and their biological activities [ 29 , 30 , 31 , 32 , 33 , 34 ]. A special focusing was paid to the dipolar cycloaddition reactions of azinium ylides with various dipolarophiles in order to obtain new compounds with blue-fluorescent properties.…”

Hybrid Pyridine Bis-Anthracene-Imidazolium Salt: NMR Studies on Zn-Acetate Complexation

“…Considering our experience in the field of the synthesis of hybrid compounds with imidazole/benzimidazole, pyridine and anthracene units [2,[6][7][8][9][10][11], and our previous experience in the area of cycloimonium ylides [12][13][14][15][16][17][18][19][20][21][22], we decided to synthesize a novel hybrid pyridine bis-anthracene-imidazolium salt, and also to study its complexation to Zn acetate by NMR.…”