Synthesis and Reactions of Highly Strained 2,3‐Bridged 2H‐Azirines

Abstract

Take the strain: Despite extreme ring strain and reactivity, the heterocycles 2, which are easily obtained from azides 1 and detectable by NMR spectroscopy, can be converted stereoselectively by novel addition and cycloaddition reactions.

β‐Elimination of an aziridine to an allylic amine: a mechanistic study

“…Davis also noted that other N ‐tosyl aziridines can rearrange to vinylic amines; both processes are thought to begin with α‐deprotonation of the aziridine. Note that the highly strained bicyclic azirine that would form from aziridines 5 and 7 – 9 has only recently been detected spectroscopically, in situ , by Banert and Meier 27. Another possible decomposition pathway, reductive alkylation, was reported by O'Brien for aziridines treated with sec ‐butyl lithium;17 however, the likelihood of the bulky diisopropylamide exhibiting this reaction is low.…”

Domino reactions of 2H-azirines with acylketenes from furan-2,3-diones: Competition between the formation of ortho-fused and bridged heterocyclic systems

“…It was found that water [37], Brønsted [44,48] and Lewis acids [40–41 43] facilitate the formation of pyrazine derivatives. 2 H -Azirines undergo ring opening on electronic excitation to give nitrile ylides [50].…”

“…3 ) that the reaction involving dihydropyrazines 11 on the way to 4 and 5 could be quite competitive with the reaction leading to 3 , provided that a source of dihydropyrazines 11 is available. Formation of ‘dimer azirines’, dihydropyrazines [ 37 – 41 ], or products of their dehydrogenation, pyrazines [ 37 – 49 ] under different conditions is quite common. Moreover, everybody who works with 3-aryl-2 H -azirines faces the problem of their storage, because these compounds, both with unsubstituted and an electron-donor substituted benzene ring, fast transform into pyrazines, even when stored in a fridge.…”

“…Different mechanisms of dimerization were assumed, such as formation and dimerization of nitrile ylides [ 37 , 40 ], hydrolysis to α-aminoketenes followed by condensation [ 37 , 41 ], intermediate formation of metal complexes in the reaction mediated by metals [ 41 , 43 , 46 ]. It was found that water [ 37 ], Brønsted [ 44 , 48 ] and Lewis acids [ 40 – 41 43 ] facilitate the formation of pyrazine derivatives. 2 H -Azirines undergo ring opening on electronic excitation to give nitrile ylides [ 50 ].…”

Synthesis of carbazolones and 3-acetylindoles via oxidative C–N bond formation through PIFA-mediated annulation of 2-aryl enaminones

“…However, when the cyclic enaminone D was treated with PhI(OAc) 2 under identical conditions, the formation of the aromatic C-N bond occurred to give the carbazolone compound E. The corresponding 2Hazirine F was not formed due to its highly strained bridged-ring system. 11 This unexpected finding revealed a complementary route to the construction of the important carbazolone skeleton (Scheme 1).…”