Enantioselective Approaches to 3,4-Annulated Indoles Using Organocatalytic Domino Reactions

Organocatalytic domino reactions of 4-substituted indoles are summarized in this account. Two reactions have been developed, one with enals, activated by secondary amine catalysts via iminium ions, and one with nitroethene, using a phosphoric acid catalyst. Both reactions required solving the challenge posed by the very low nucleo­philicity of the indole substrates, which bear an electron-withdrawing Michael acceptor at C4. DFT calculations were used to shed light on the unique reaction pathway followed by the phosphoric acid catalyzed transformation, wherein a bicoordinated nitronic acid intermediate was found to evolve preferentially through an intramolecular nitro-Michael reaction, instead of the common tautomerization pathway. These reactions provide new and efficient entries to 3,4-ring-fused indoles in dia­stereo- and enantioenriched form. In more detail, the structures obtained feature a 1,3,4,5-tetrahydrobenzo[cd]indole core, which is present in the structural framework of ergot alkaloids. Indeed, the preparation of an intermediate previously used in ergot alkaloid (6,7-secoagroclavine) synthesis was possible from one of the catalytic adducts.1 Introduction2 Reactions of 4-Substituted Indoles with α,β-Unsaturated Aldehydes Catalyzed by Secondary Amines3 Reactions of 4-Substituted Indoles with Nitroethene Catalyzed by Brønsted Acids4 Conclusion

The Salts of Nitronic acid as CO2-Corrosion Inhibitors

The salts of nitronic acids were obtained by nitration of higher olefins, both normal and isomeric structure in the presence of aqueous alkali. The resulting salts (Na+, K+, NH4+), were tested in CO2 -media as a corrosion inhibitor. The results showed that, the protective effect of the linear nitronated olefins increases by increasing the number of carbon atoms. This is due to the fact that because of the branched structure of the compounds, it is much more difficult to form a dense protective layer on the metal surface. 20% solutions of nitronated ethanolamine in isopropyl alcohol was synthesized and tested as corrosion inhibitor in carbon dioxide environments. The results showed that diethanolamine nitron based on a mixture of normal olefins C16-C18 at a concentration of 50 ppm has a high protective effect of 99.69%.