Super-electrophilic 10π Heteroaromatics. New Mechanistic and Synthetic Applications

"The Sulfur Dance" Around Arenes and Heteroarenes - the Reversible Nature of Nucleophilic Aromatic Substitutions

We disclose the features of a category of reversible nucleophilic aromatic substitutions in view of their significance and generality in dynamic aromatic chemistry. Exchange of sulfur components surrounding arenes and heteroarenes may occur at 25 °C, in a process that one may call a "sulfur dance". These SN Ar systems present their own features, apart from common reversible reactions utilized in dynamic covalent chemistry (DCC). By varying conditions, covalent dynamics may operate to provide libraries of thiaarenes with some selectivity, or conversion of a hexa(thio)benzene asterisk into another one. The reversible nature of SN Ar is confirmed by three methods: a convergence of the products distribution in reversible SN Ar systems, a related product redistribution between two per(thio)benzenes by using a thiolate promoter, and from kinetic/thermodynamic data. A four-component dynamic covalent system further illustrates the thermodynamically-driven formation of a thiacalix[2]arene[2]pyrimidine by sulfur component exchanges. This work stimulates the implementation of reversible SN Ar in aromatic chemistry and in DCC.

Mechanisms of nitric oxide generation in living systems

In modern chemical and biochemical studies, special attention is paid to molecular systems capable of generating nitric oxide (NO), which is one of the most important signalling molecules in the body and can trigger a whole cascade of reactions. Despite the importance of this molecule, the mechanisms of its formation in living organisms remain a subject of debate. This review combines the most important methods of releasing NO from endogenous and exogenous sources. The history of endogenous NO donors dates back more than 150 years, since the synthesis of nitroglycerin, which remains the standard vasodilator today, even though it is known that it and many other similar compounds lead to the development of a nitrate tolerance. Particular awareness is devoted to the mechanisms of NO formation without the participation of enzymes, since these methods are most important for creating exogenous sources of NO as drugs. The study of NO formation methods is centred on both the creation of new NO donors and understanding the mechanisms of tolerance to them.

A snapshot of inorganic Janovsky complex analogues featuring a nucleophilic boron center

The addition of phenyl lithium (PhLi) to an aromatic 1,3,2,5-diazadiborinine (1) afforded isolable ionic species 2, which can be deemed as an inorganic analogue of a Janovsky complex.

New electron-donor and -acceptor architectures from benzofurazans and sym-triaminobenzenes: intermediates, products and an unusual nitro group shift

New all-conjugated C-C coupling products bearing both an electron-poor and an electron-rich aromatic moiety have been obtained from the reaction between sym-triaminobenzene derivatives and a series of isomeric chloro-nitrobenzofurazans. The reactions occur under mild reaction conditions, and in some cases a different behaviour depending on the presence, or not, of triethylamine was observed. From 1,3,5-tris(N-morpholinyl)benzene and 5-chloro-4-nitrobenzofurazan in the presence of triethylamine an unexpected product derived from the shift of the nitro group from C-4 to C-5 of the electrophile and bearing the nucleophile at position 4 was obtained. Moreover, from the coupling between 1,3,5-tris(N-pyrrolidinyl)benzene and 4-chloro-7-nitrobenzofurazan a highly stable Wheland intermediate was isolated.

The α-effect in the SNAr reaction of 1-(4-nitrophenoxy)-2,4-dinitrobenzene with anionic nucleophiles: effects of solvation and polarizability on the α-effect

A kinetic study on SNAr reactions of 1-(4-nitrophenoxy)-2,4-dinitrobenzene (1a) with various anionic nucleophiles in 80 mol% water – 20 mol% DMSO at 25.0 °C is reported. The Brønsted-type plot for the reaction of 1a with a series of substituted phenoxides and HOO− results in an excellent linear correlation with βnuc = 1.17. However, OH− exhibits dramatic negative deviation from the Brønsted-type plot, while N3−, C6H5S−, and butane-2,3-dione monoximate (Ox−) deviate positively from linearity. HOO− is 680-fold more reactive than OH− but does not exhibit the α-effect. In contrast, Ox− is 166-fold more reactive than isobasic 4-Cl−C6H4O− and exhibits the α-effect. Differential solvation effects have been suggested to be responsible for the α-effect in this study, i.e., Ox− exhibits the α-effect, since it is 5.7 kcal/mol less strongly solvated than 4-Cl−C6H4O− in the reaction medium, while HOO− does not show the α-effect due to a strong requirement for partial desolvation before nucleophilic attack. The highly enhanced reactivity of polarizable N3− and C6H5S− and extremely decreased reactivity of nonpolarizable OH− are in accord with the hard–soft acid and base principle.