Condensation of 4-hydroxy-2-thiazolines with 1,2-phenylenediamine as a novel effective route to thiazolo[3,4-a]quinoxalines

Thiazolo[3,4-a]quinoxalin-4-ones were prepared in two steps starting from methyl phenylchloropyruvate using a new strategy for the construction of the ring system. A key step in this new method involves the reaction of 4-hydroxytetrahydrothiazoles with 1,2-phenylendiamines

Acid-Catalyzed Rearrangements of 3-Aryloxirane-2-Carboxamides: Novel DFT Mechanistic Insights

Efficient synthesis of 3-arylquinolin-2(1H)-ones and N-(2-carboxyaryl)-oxalamides from protic acid-catalyzed rearrangements of 3-aryloxirane-2-carboxamides was achieved recently but not well understood. In contrast to the classical Meinwald rearrangement, extensive DFT calculations reveal that the proximal aryl and amide groups have strong synergetic effects to control the amide-aided and aryl-directed oxirane-opening and further rearrangement sequences. The ortho-nitro substituent of the proximal aryl is directly involved in a nucleophilic oxirane ring-opening, the amide C=O is an important proton shuttle for facile H-shifts, while the N-aryl may act as a potential ring-closing site via Friedel-Crafts alkylation. The mechanistic insights are useful for rational design of novel synthesis by changing the aryl and amide functional groups proximal to the oxirane ring

Reaction for the Synthesis of Benzimidazol-2-ones, Imidazo[5,4‑<i>b</i>]‑, and Imidazo[4,5‑<i>c</i>]pyridin-2-ones via the Rearrangement of Quinoxalin-2-ones and Their Aza Analogues When Exposed to Enamines

A synthetically useful protocol has been developed for the preparation of highly functionalized <i>N</i>-pyrrolylbenzimidazol-2-ones. The reaction of variously substituted 3-aroyl- and 3-alkanoylquinoxalin-2­(1<i>H</i>)-ones with commercially available enamines in acetic acid results in a rapid rearrangement and formation of <i>N</i>-pyrrolylbenzimidazol-2-ones in modest to excellent yields. The key step of the rearrangement involves the novel ring contraction of 3-aroyl- and 3-alkanoylquinoxalin-2­(1<i>H</i>)-ones with enamines. In this case, the atom of carbon which is displaced from the pyrazine ring of quinoxalin-2­(1<i>H</i>)-one becomes the fourth carbon atom of the newly formed pyrrole ring. The method is applicable for the aza analogues of quinoxalin-2­(1<i>H</i>)-ones

Rearrangement of Quinoxalin-2-ones When Exposed to Enamines Generated in Situ from Ketones and Ammonium Acetate: Method for the Synthesis of 1‑(Pyrrolyl)benzimidazolones

The reaction of 3-benzoylquinoxalin-2­(1<i>H</i>)-ones with enamines (generated in situ from ammonium acetate and the corresponding methylaryl­(hetaryl)­ketones) proceeds smoothly to give the corresponding substituted 1-(pyrrolyl)­benzimidazolone derivatives in moderate yields through the novel rearrangement of 3-benzoylquinoxalin-2­(1<i>H</i>)-ones involving a dual cleavage of the C3N4 and C2-C3 bonds under mild conditions