Huaming Sun

Ethanol promoted titanocene Lewis acid catalyzed synthesis of quinazoline derivatives

An efficient catalytic system involving in situ activation of kinetically inert titanocene dichloride with alcoholic solvent for the synthesis of quinazoline derivatives was developed. 1 mol% Cp2TiCl2 at 30 °C afforded 17 examples of quinazoline derivatives with yields of 95–98% in 7–12 minutes. Mechanistic experiments using in situ NMR and HRMS established that the coordination of ethanol to the titanocene moiety released the catalytic species [Cp2Ti(OCH2CH3)2].

Polyelectrolyte Brønsted acid catalyzed three-component Mannich reactions accelerated by emulsion

An effective polyelectrolyte Bronsted acid (polyacrylic acid) catalyzed three-component Mannich reaction accelerated by emulsion has been developed. The results demonstrated that the polyacrylic acid (PAA) provided the best catalytic activity in water because of the formation of emulsions during the reaction. This newly developed simple catalyst could be recycled at least five times without any loss of activity.

N-Donor ligand activation of titanocene for the Biginelli reaction via the imine mechanism

The remarkable activation of stable titanocene dichloride (Cp2TiCl2) was achieved using N-donor ligand urea in an alcoholic solvent, leading to the formation of a Ti(IV) species [(MeO)2Ti(NHCONH2)]+, the existence of which was verified by ESI-MS, ESI-MS/MS, and NMR. Catalyzed by the newly formed Ti(IV) species, a myriad of 3,4-dihydropyrimidin-2-(1H)-ones were produced via a three-component Biginelli reaction. Further mechanistic investigation indicated that the Biginelli reaction had taken place via the imine route.

Triple zirconocene/brønsted acid/CuO cooperative and relay catalysis system for tandem Mannich addition/C–C formative cyclization/oxidation

A new triple cooperative and relay catalysis system featuring the Mannich addition followed by C–C construction and oxydehydrogenation is described. The zirconocene dichloride and trimellitic acid synergic catalysis triggered the Mannich addition and C–C bond construction reactions, while CuO allowed relay catalysis for oxydehydrogenation. This novel strategy demonstrated superior activity for the synthesis of substituted quinolines from commercially available anilines, aldehydes and ketones. The corresponding substituted quinolines were synthesized with 32 examples in 90–96% yields under mild reaction conditions. A novel zirconocene–Bronsted acid complex, generated in situ and acting as an active catalyst, was validated from the mechanistic studies.

Sigma-spacer regulated thiophenyl triazine conjugates: synthesis and crystal, electronic and luminescent properties

A water-accelerated Pd catalyzed Suzuki–Miyaura cross-coupling reaction was developed for the synthesis of thiophenyl triazine conjugates (TTCs). The compounds (2a–2e and 3a–3e) with five σ-spacers were obtained and fully characterized. The X-ray analysis of 2a, 2d, and 3d found that the length of the intermolecular H bond was 3.465(3) A and the π–π interactions ranged from 3.6538(2)–3.9519(1) A. Five σ-spacers of TTCs had an effect on their emissions from blue (363 nm) to yellow (530 nm) whilst 2- and 3-thiophenyl chromophores finely tune the emission from 530 to 504 nm. The DFT computation showed the TTCs had low HOMO (−6.8 eV) and LUMO (−2.5 eV) energy and high triplet energy (ET, 2.4 eV). The energy level and gap of TTCs were regularly modulated by the σ-spacer.

Synthesis of air-stable mixed bis-carboxylate titanocene complexes and their catalytic behaviors in cross-aldol and Mannich reactions

AbstractnTunable organometallic Lewis acid catalysts were developed by combining salicylic acid (H2-Sal) with benzoic acid (H-Ben), 4-fluorobenzoic acid (H-BenF) and 3-thiophenic acid (H-Th), as coligands for mixed bis-carboxylate titanocene complexes. Three air-stable complexes [Cp2Ti(η1-HSal)(η1-Ben)] (1), [Cp2Ti(η1-HSal)(η1-BenF)] (2) and [Cp2Ti[η1-HSal][(η1-Th)] (3) were prepared in high yields by the reaction of salicylato titanocene chelate with carboxylate ligands. The mixed bis-carboxylate titanocene complexes were fully characterized by physicochemical and spectroscopic methods. Single-crystal X-ray diffraction studies revealed Ti–O(H-Sal) bond distances in 1, 2 and 3 of 1.972(3), 1.9245(18) and 1.912(5)xa0Å, respectively, while the bond distances involving the coligands of 1, 2 and 3 are 1.908(3)xa0Å (Ti–OBen), 1.9296(19)xa0Å (Ti–OBenF) and 1.945(5)xa0Å (Ti–OTh), respectively. These bis-carboxylate titanocene complexes showed satisfactory activities and selectivities in Mannich and cross-aldol reactions. Notably, complex 3 bearing the labile thiophene carboxylate ligand gave high yields with a diastereomer ratio (d.r.) as high as 1:99 for the direct Mannich reactions of benzaldehyde, cyclohexanone and aniline. In cross-aldol reaction of benzaldehyde and cyclohexanone, 1 and 2 successfully catalyzed the formation of double-aldol products in up to 99xa0% yield.