Transition-Metal-Free Synthesis of 2-Substituted Benzothiazoles from Nitrobenzenes, Methylheteroaryl Compounds, and Elemental Sulfur, Based on Nitro-Methyl Redox-Neutral Cyclization.

Greener and more sustainable chemical processes are required to address increasing environmental pollution and depletion of natural resources. This paper aims to develop greener and more sustainable modern synthetic chemical processes using redox-neutral cyclization. Redox-neutral cyclization has been shown to promote the efficient synthesis of 2-substituted benzothiazoles from easily available nitrobenzenes, methyl-heteroaryl compounds, and elemental sulfur in the absence of transition-metal catalysts. The 2-substituted benzothiazoles were obtained in reasonable yields through the sulfuration of electron-deficient C-H bonds with elemental sulfur. This synthetic methodology also affords a high atom economy without the use of any external oxidizing and/or reducing reagents.

Transition-Metal-Free and Oxidant-Free Cross-Coupling of Arylhydrazines with Disulfides: Base-Promoted Synthesis of Unsymmetrical Aryl Sulfides.

A novel synthesis of unsymmetrical aryl sulfides, which requires no transition metal catalyst and no oxidant, was developed. This base-promoted cross-coupling reaction proceeded using arylhydrazines and 1 equiv amount of disulfides under inert gas conditions to afford the unsymmetrical aryl sulfides in good yields.

A probable hydrogen-bonded Meisenheimer complex: an unusually high S(N)Ar reactivity of nitroaniline derivatives with hydroxide ion in aqueous media.

Observations show that nitroanilines exhibit an unusually high S(N)Ar reactivity with OH(-) in aqueous media in reactions that produce nitrophenols. S(N)Ar reaction of 4-nitroaniline (2a) in aqueous NaOH for 16 h yields 4-nitrophenol (4a) quantitatively, whereas a similar reaction of 4-nitrochlorobenzene (1a) gave 4a in 2% yield together with recovered 1a in 97%, suggesting that the leaving ability of the NH(2) group far surpasses that of Cl under these conditions. An essential feature of S(N)Ar reactions of nitroanilines is probably that the NH(2) leaving group participates in a hydrogen-bonding interaction with H(2)O. Density functional theory (DFT) calculations for a set of 4-nitroaniline, OH(-), and H(2)O suggest a possible formation of a Meisenheimer complex stabilized by hydrogen-bonding interactions and a six-membered ring structure. The results obtained here contrast with conventional S(N)Ar reactivity profiles in which nitroanilines are nearly unreactive with nucleophiles in organic solvents.

Contrasting intermolecular and intramolecular exciplex formation of a 1,4-dicyano-2-methylnaphthalene-N,N-dimethyl-p-toluidine dyad.

An intramolecular exciplex is formed upon excitation of the cyclohexane solution of the 1,4-dicyano-2-methylnaphthalene-N,N-dimethyl-p-toluidine dyad, but little if any intramolecular CT complex exists in the ground state of this substance in solution. In contrast, in the crystalline state, the dyad forms an intermolecular mixed-stack CT complex in the ground state and an intermolecular exciplex when it is photoexcited.