Green chem.: Professor Wang Zhiyong's research group of the University of science and technology of China develops the diamine reaction of Styrene Catalyzed by iodine in aqueous phase

O-diamine groups are widely found in natural products and bioactive molecules The diamine reaction of olefins is the main method to synthesize these compounds At present, many progress has been made in the study of copper, palladium and other transition metal catalyzed diamine cyclization and intermolecular diamine reactions (scheme 1a-c) However, these synthesis methods often need to use stoichiometric reagents and organic solvents to react Therefore, it is of great significance to develop water-phase diamine reaction in line with the concept of green and sustainable development (source: Green chem.) recently, Professor Wang Zhiyong of University of science and technology of China has developed a diamine reaction of styrene in aqueous phase mediated by dodecyltrimethylammonium iodide (tmdai) / H 2O 2 Water is used as the reaction medium to avoid the use of organic solvents, and the only by-product is water, which has the characteristics of mild conditions and environmental protection Relevant research results were published on green chem (DOI: 10.1039 / c8gc01332b) First of all, the reaction conditions were screened by using 2-aminostyrene 1a and aniline 2A protected by p-toluenesulfonyl (TS) as model substrates (Table 1) The results show that the target product 3A (entry 12) can be obtained in 93% yield by using 20 mol% tmdai as catalyst, H 2O 2 as oxidant and water as reaction medium (source: Green chem.) then, the substrate applicability of the reaction was studied The results show that the reaction can proceed smoothly when the substituent of styrene is electron donor or electron acceptor In general, the electron donating groups such as methyl and butyl are favorable for the conversion, while the electron absorbing groups such as nitro, fluorine and chlorine atoms make the reaction yield slightly lower (Table 2) On the other hand, aniline substrate has a wide range of applications When aniline is replaced by halogen, methyl, butyl and methoxy, the reaction can proceed smoothly In addition, naphthylamine and aliphatic amine are also suitable for the conversion, but when the strong basic aliphatic amine is used as the substrate, phosphate should be added to the reaction system to control the reaction pH (scheme 2) (source: Green chem.) (source: Green chem.) further, the mechanism of the diamine reaction was studied (scheme 3) When the free radical inhibitor BHT was added to the reaction system, the reaction yield did not decrease significantly, and the free radical reaction mechanism (scheme 3a) was excluded When I 2 was substituted for H 2O 2 and tmdai, the reaction could not take place, which indicated that I 2 could not catalyze the reaction (scheme 3b) Styrene substrate 4 can not react under standard conditions, indicating that the NH part is very important for the reaction (scheme 3C) In addition, the kinetic isotope effect experiments of 1A / D - 1A and 2A have been carried out It is confirmed that the determination step of the reaction does not involve the hybrid process of olefin carbon from SP 2 to sp 3, that is to say, the reaction does not involve the electrophilic addition process of amino pair double bond (Scheme 3D) In addition, when olefin 5 is used as the substrate, the reaction can not take place, which shows that the conjugation of double bond and benzene ring is necessary (scheme 3e) (source: Green chem.) finally, the author proposed the mechanism of the reaction (scheme 4) I - is oxidized to IO by H 2O 2 - which reacts with 1a to obtain intermediate a; a further loses I - to obtain transition state B; imine attacks carbon positive ion to obtain transition state C; C reacts with aniline to obtain target product 3a and releases a molecule H 2O (source: Green chem.) conclusion: Professor Wang Zhiyong's research group of University of science and technology of China has developed a tmai / H 2O 2-mediated diamine reaction of styrene in aqueous phase The reaction conditions are mild, the substrate range is wide, no need to use organic solvents and transition metal catalysts, and the only by-product is water.