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Tetracyclic skeletons combining an imidazo[1,2-a]pyridine moiety with a quinoline framework such as pyrido[2',1':2,3]imidazo[4,5-b]quinoline are stimulating increasing interests since they are close isosteres of a series of powerful antiproliferative compounds. In this paper, we report a novel methodology for the synthesis of pyrido[2',1':2,3]imidazo[4,5-c]quinolines through one-pot sequential reactions of commercially available or readily obtainable 2-aminopyridines, 2-bromophenacyl bromides, aqueous ammonia, and aldehydes. Moreover, dihydropyrido[2',1':2,3]imidazo[4,5-c]quinolines could also be obtained in a similar manner by using various ketones as the substrates in place of aldehydes. Notably, the whole procedure combines condensation/amination/cyclization reactions in one pot to give complex compounds in a simple and practical manner. Compared with literature methods, the synthetic strategy reported herein has the advantages of readily available starting materials, structural diversity of products, good functional group tolerance, and obviation of step-by-step operations., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Pyrimido[4,5-b]quinolinones have attracted considerable interest from both chemical and medicinal scientists as these compounds display remarkable antimicrobial, anti-inflammatory, antitumor, antiallergy, analgesic, and antioxidant activities. The importance of pyrimido[4,5-b]quinolinones has stimulated enormous efforts to develop efficient methodologies for their synthesis. Herein, we disclose a novel synthetic protocol toward pyrimido[4,5-b]quinolin-4-ones through Cu(OAc)2 -catalyzed one-pot four-component reactions of 2-bromobenzaldehydes, aqueous ammonia, cyanoacetamides and aldehydes. The synthetic procedure combines amination/condensation/cyclization/dehydrogenation reactions in one pot, allowing synthesis of complex compounds in a simple and practical manner. Compared with literature procedures, the synthetic strategies developed herein showed advantages such as readily available and economically sustainable starting materials, structural diversity of products, good functional group tolerance, and a remarkably simple operation process., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

In the title compound, C13H10O3, the pyran-one and benzene rings are almost coplanar, making a dihedral angle of 1.9 (1)°. The cyclo-hexenone ring adopts an envelope conformation, with a methyl-ene C atom located at the flap and displaced by 0.639 (3) Å from the mean plane of the other five atoms. In the crystal, pairs of weak C-H⋯π inter-actions occur between inversion-related mol-ecules.

In the title compound, C(13)H(12)O(2), the dihedral angle between the pyran-one and phenyl rings is 57.55 (9)°. In the crystal, the mol-ecules are linked by π-π stacking inter-actions between the parallel pyran-one rings of neighboring mol-ecules with distances of 3.5778 (11) Å and 3.3871 (11) Å between the planes. C-H⋯O interactions also occur.

In the structure of the title compound, C(20)H(15)BrN(4)O·C(2)H(6)O, the hydrogenated pyridinone ring adopts an envelope conformation. The dihedral angle between the bromo-substituted phenyl ring and the pyrazole ring is 79.6 (1)°, and that between the non-substituted phenyl ring and the pyrazole ring is 51.2 (1)°. In the crystal structure, mol-ecules are linked via inter-molecular N-H⋯O and O-H⋯N hydrogen bonds. A short inter-molecular N⋯Br contact [3.213 (4) Å] is present in the crystal structure.

In the title compound, C(21)H(16)N(4)O(2), the dihedral angle between the meth-oxy-substituted benzene ring and the ring system formed by the pyridinone ring and the pyrazole ring is 57.4 (1)°, and that between the unsubstituted phenyl ring and the ring system is 135.6 (1)°. In the crystal structure, mol-ecules are linked together via inter-molecular N-H⋯O hydrogen bonds.

In the crystal structure of the title compound, C(20)H(16)ClN(5), the dihedral angle between the pyrazole ring and the phenyl ring is 54.7 (1)° and that between the pyrazole ring and the chloro-substituted phenyl ring is 72.4 (1)°. The methyl H atoms are disordered over two positions with site occupancy factors of ca 0.7 and 0.3. One amino H is disordered equally over two positions. In the crystal structure, the mol-ecules are linked via inter-molecular N-H⋯N hydrogen bonding.

The title compound, C(20)H(14)N(6)O(2), contains four rings. The dihedral angle between the pyridine ring and the pyrazole ring is 1.9 (1)°, i.e. almost coplanar, which gives rise to a conjugated structure. The dihedral angle between the nitro-substituted phenyl ring and the pyridine ring is 76.3 (1)° and that between the pyrazole ring and the non-substituted phenyl ring is 40.5 (1)°. In the crystal structure, symmetry-related mol-ecules are linked by N-H⋯O and C-H⋯N hydrogen bonds.