Mechanistic Investigation on the Formation of Indolizines from 2-Enynylpyridines

Abstract

2,3,7-Trisubstituted indolizines were obtained from E- or Z-2-enynyl-4-substituted pyridines. The mechanistic pathway involves a base-catalyzed double-bond isomerization, if the E-isomer is the starting material, followed by a concerted pseudocoarctate cyclization.

Coarctate versus Pericyclic Reactivity in Naphthalene‐Fused Azo–Ene–Ynes: Synthesis of Benzocinnolines and Benzoisoindazoles

“…The reaction mixture was stirred at À78 8C for 30 min, then warmed to 0 8C and stirred for an additional hour. The reaction mixture was diluted with aqueous NH 4 Cl solution and extracted three times with EtOAc. The combined organics were washed with brine, dried (MgSO 4 ), and concentrated.…”

“…[1] In particular, we have been examining the dual reaction pathways of conjugated azoene-ynes (1, Scheme 1), [2] where under thermal conditions a pericyclic cyclization generates a new benzo-fused six-membered ring (2), or addition of a carbene stabilizer induces a coarctate cyclization [3,4] to form a new benzo-fused fivemembered ring (3). Through these methodologies, a variety of substituted cinnolines and isoindazoles, respectively, are available from simple anilines in high yields and in only a few steps.…”

3‐(Pyridin‐2‐yl)imidazo[1,5‐a]pyridine (Pyridylindolizine) as Ligand in Complexes of Transition and Main‐Group Metals

“…The readily available bis(dithiophosphate)s of Zn II [24] and Cd II can be used as starting materials for the preparation of heteroleptic complexes with N-donor ligands, [25] [M{S 2 P(OEt) 2 } 2 (Py-indz)], M = Zn (8) and Cd (9). As can be seen in Figure 5, cadmium complex 9 is, as expected, hexacoordinate, whereas Zn complex 8 is pentacoordinate in which the Py-indz ligand and one dithiophosphate ligand act as bidentate chelates, and the second dithiophosphate ligand acts as a monodentate chelate.…”

“…Previous methods based mainly on the cyclization of N-2-pyridylmethylamines were modestly efficient, [3] and other new routes were proposed on the basis of the acid-promoted condensation of dipyridylamines, [4] the oxidative condensation of aldehydes with 2-pyridylamines, [5,6] the aza-Wittig reaction on N-vinyl-substituted phosphazenes, [7] plex. [M{S 2 P(OEt) 2 } 2 (Py-indz)] M = Zn (8), Cd (9) have pentacoordinate and hexacoordinate structures, respectively. Octahedral tin complexes [SnL 4 (Py-indz)] L 4 = I 4 (10), Cl 3 Ph (11), and Cl 2 nBu 2 (12) have different behaviors in solution; whereas complex 10 is practically insoluble, complex 11 displays the expected pattern in its NMR spectrum, and complex 12 shows dynamic behavior.…”

“…or the cyclization of 2-enynylpyridines, [8] and coupling reactions to provide imidazo[1, 5-a]pyridine N-heterocyclic carbene precursors. [9] Shortly after the publication of our work in the preparation of Py-indz mediated by manganese, the preparation of substituted 1-pyridineimidazo[1,5-a]pyridine ligands was reported.…”