Rhodium(II)-catalyzed transannulation of 1-sulfonyl-1,2,3-triazoles with 2 H -azirines: a new method to dihydropyrazines

Synthesis of 1,2-Dihydropyrimidine-2-carboxylates via Regioselective Addition of Rhodium(II) Carbenoids to 2H-Azirine-2-carbaldimines

“…The formation of the 2-azabuta-1,3-diene fragment from the azirine moiety in reactions of aryl, alkyl and halogeno-substituted azirines, and azirine-2-carbaldehydes was previously reported . These reactions were assumed to occur via the formation and ring-opening of azirinium ylides . The problem that could arise here is a change of the reactive center in compound B from azirine nitrogen to the more nucleophilic imine nitrogen atom which can bind with the carbenoid to give azomethine ylide and then undesirable products of its transformation.…”

Palladium-Catalyzed C–N Bond Cleavage of 2H-Azirines for the Synthesis of Functionalized α-Amido Ketones

“…The metal-catalyzed conversion of 2 H -azirines has attracted considerable attention in modern organic synthesis to build highly complex molecular skeletons. − On the basis of their inherently high ring-strain energy, − 2 H -azirines undergo various ring expansion reactions, such as [3 + 2], − [3 + 3], − and [3 + 2 + 2] cycloaddition with unsaturated molecules, aza-Diels–Alder reactions, intramolecular rearrangements, and various nucleophilic addition reactions. − Among these events, three general models for the chemical bond cleavage of 2 H -azirines have been well-established: (i) heterolytic C–N single-bond-cleavage mode to generate vinyl nitrenoid intermediates, , (ii) transition-metal-assisted or visible-light-induced C–C cleavage mode to generate nitrile ylides, and (iii) simultaneous cleavage of both C–C and C–N mode to form carbenoid species (Scheme a). Compared with the prevalence of ring expansion via cycloaddition reactions, the exploration of new applications of 2 H -azirines is highly desirable.…”

Ultrasonic Methylation of Triethylammonium Thiolate as a Key Strategy for Synthesis of Tetrahydropyrazine‐Containing 2‐Oxindole Scaffold

“…The most common preparation method of pyrazines is dehydrogenation of 2,3‐dihydropyrazines obtained from the reaction between 1,2‐diamines and 1,2‐dicarbonyl compounds . Recently, other methods have been developed for the synthesis of pyrazines among which self‐coupling of β ‐amino alcohols via metal catalyzed dehydrogenation, Cu‐catalyzed electrocyclization of 1,4‐diazahexatriene, transannulation of 1‐sulfonyl‐1,2,3‐triazoles with 2 H ‐azirines catalyzed by Rh(II) and copper catalyzed oxidation using β ‐ketoalcohols and diamines can be mentioned.…”