Synthesis of Ferrocenyl-Based Unsymmetrical Azines via a Simple Reaction of Aldehydes with Ketone-Derived N-Tosyl Hydrazones and the Evaluation of the Extent of Conjugation in the Molecule

Abstract

We have designed and synthesized 1-substituted and 1,1′-disubstituted ferrocene-based unsymmetrical azines under metal-free conditions. The crystal structures of 3k, 5i, and 5g revealed that conjugative interactions between the ferrocene phenyl rings and the entire azine fragment exist. Furthermore, our electrochemical and optical analysis provided support for extended conjugation, which suggested a larger substituent effect in this system. Density functional theory calculations also supported the results. Thus, these results reflect a stronger conjugative interaction between the ferrocene phenyl rings and the entire azine fragment.

Pd(II)-Catalyzed Azine-Assisted Enantioselective Oxidative C–H/C–H Cross-Coupling of Ferrocenes with Various Heteroarenes

“…From the viewpoint of the atom and step economy, a strategy of this type would provide a promising future for rapid construction of chiral compounds and not need for preactivation of either coupling partners. , However, there is no report of the enantioselective C–H functionalizations of ferrocene utilizing azine as a directing group. Our group found a stronger conjugative interaction between the ferrocene phenyl rings and the entire azine fragment, and the structure containing “CNNC” can be used as multisignaling sensors to monitor Hg 2+ and Cu 2+ in an aqueous environment . Meanwhile, previous reports showed that azine can be used as an effective directing group to construct C–C, , C–S, and C–N , bonds via C–H activation.…”

“…General Procedure for the Synthesis of Substrates (1a− g). 36 Aryl aldehyde (53.1 mg, 0.5 mmol), ferrocenyl aldehyde-derived N-tosyl hydrazone (99.1 mg, 0.3 mmol), t BuOLi (22.0 mg, 0.3 mmol), and PPh 3 (131.2 mg, 0.5 mmol) were suspended in dioxane (5.0 mL) in a 25.0 mL Schlenk tube under nitrogen. The solution was stirred in a preheated oil bath at 90 °C for 16 h. Then, the reaction mixture was cooled to ambient temperature, diluted with 20.0 mL of CH 2 Cl 2 , and washed with brine (20.0 mL) and water (20.0 mL).…”

“…1 2-(1-Ferrocenylethylidene)-1-(4-methylbenzylidene)hydrazine 1b. 36 Red solid: the product was purified by column chromatography on silica gel (petroleum ether/ethyl acetate = 10/1) to afford the desired product. 1 H NMR (500 MHz, CDCl 3 ) δ 8.41 (s, 1H), 7.72 (d, 3 J = 7.2 Hz, 2H), 7.24 (d, 3 J = 7.4 Hz, 2H), 4.78 (s, 2H), 4.43 (3, 2H), 4.21 (s, 5H), 2.43 (s, 3H), 2.40 (s, 3H).…”

“…2-(1-Ferrocenylethylidene)-1-(4-methoxybenzylidene)hydrazine 1c. 36 Red solid: the product was purified by column chromatography on silica gel (petroleum ether/ethyl acetate = 10/1) to afford the desired product. 1 General Procedure for the Enantioselective Synthesis of Planar Chiral Ferrocene Derivatives.…”

“…34,35 However, there is no report of the enantioselective C−H functionalizations of ferrocene utilizing azine as a directing group. Our group found a stronger conjugative interaction between the ferrocene phenyl rings and the entire azine fragment, 36 and the structure containing "CNNC" can be used as multisignaling sensors to monitor Hg 2+ and Cu 2+ in an aqueous environment. 37 Meanwhile, previous reports showed that azine can be used as an effective directing group to construct C−C, 38,39 C− S, 40 and C−N 41,42 azines as a directing group in Pd(II)-catalyzed oxidative C−H/ C−H coupling reaction between ferrocenes and heteroarenes (Figure 1b).…”