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 carbon...

The ten-membered fused ring of the title compound, C(12)H(10)N(2)O, is essentially planar in the two independent mol-ecules of the asymmetric unit (r.m.s. deviations = 0.012 and 0.015 Å).

The ten-membered fused ring system in the title compound, C(21)H(16)N(2)O(2), is planar (r.m.s. deviation = 0.03 Å). The phenyl substituent is aligned at 15.1 (1)° with respect to the mean plane through this system, whereas the phenyl ring of the benzyl substitutent is aligned at 84.4 (1)°.

In the title compound, C(11)H(9)BrN(2)O, the mol-ecules are linked into R(2) (2)(8) dimers by paired N-H⋯O hydrogen bonds and these dimers are further stacked into columns along the c axis by π-π inter-actions between pyrazinone rings [centroid-centroid distance = 3.544 Å; the dihedral angle between the planes of these rings is 7.51 (16)°]. The title compound is a precursor for agents with pote...

The phenyl substituents in both independent mol-ecules of the title compound, C(15)H(12)N(2)O, are twisted with respect to the quinoxaline system [dihedral angles = 19.3 (1) and 30.4 (1)°].

The title compound, C(10)H(8)ClNO, is almost planar (r.m.s. deviation for the 13 non-H atoms = 0.023 Å). In the crystal, inversion dimers linked by pairs of N-H⋯O hydrogen bonds generate R(2) (2)(8) rings. Weak aromatic π-π stacking inter-actions [centroid-centroid distance = 3.7622 (12) Å] also occur.

The asymmetric unit of the title compound, C(16)H(12)O(3), contains two crystallographically independent mol-ecules. The isochromene ring system is planar (maximum deviation 0.024 Å) and is oriented at dihedral angles of 2.63 (3) and 0.79 (3)° with respect to the methoxy-benzene rings in the two independent mol-ecules.