Investigation On Nitrogen Oxide Species-catalyzed Aerobic Iodination Of Arenes

Aromatic iodides are extensively used in the organic synthesis, and are used for thesynthesis of various biologically active compounds. Thus the synthetic methods foriodoarenes have attracted signiifcant attention. Aryl iodides can be synthesized viamany methods, e.g. iodo-deboronation of arylboron compounds, halogen-exchange ofaryl halides or the Sandmeyer reaction from aromatic amines. In contrast, electrophiliciodination of aromatic compounds seems to be a more attractive alternative to thesynthesis of aryl iodides due to the use of readily available substrates. Different fromchlorine and bromine, iodine is less reactive towards most aromatic compounds, thusthe electrophilic iodination requires the presence of the more reactive species with apronounced1+character. One of the most effective solutions to this situation is the useof iodonium equivalents (1+)，e.g. A^-iodosuccinimide^, A-iodosaccharin, iodinemonochloride and10Ac. Another effective solution is the oxidative activation strategywhere the electrophilic I+-type species is generated from oxidation of iodine sources byoxidizing reagent systemsThe use of molecular oxygen as the oxidant is a still desirable goal fromenvironmental and economic perspectives. In this thesis, it was found that the nitrogenoxide species was effective to catalyze iodination of aromatic compounds in airatmosphere, and a mild and atom-economic method was developed for the synthesis ofthe iodoarenes. The main content of the investigation are as follows:1. The iodination of aromatic compounds was performed with nitrogen dioxide asthe catalyst, molecular iodine as the iodide reagent in air atmosphere at temperature of60?80。C. Firstly, anisole was used as a model substrate to investigate the effect of theiodine loading, catalyst, temperature, reaction time and solvent on the reaction.According to the reaction results under different reaction conditions, it was found thatthe best result was obtained in the case of0.5equiv. I2,6.5mol%of NO2,5h，acetonitrile as the solvent and air atmosphere. Subsequently, the present NCh-catalyzediodination method was applied to other substrates. When the mono-substituted benzenes containing alkyl groups were employed as the substrates, all the iodination reactionsproceeded efficiently with high yields and high para-selectivities. Surprisingly，thephenyl rings with other activated groups were converted into the desired products inpoor yields. Although the present method was limited to the iodination of the benzeneswith alkyl group, it was compatible with various groups including alkyl, ester group,nitro group, halogen-substituted groups. Among the tested disubstituted benzenes，ortho-and meta-substituted alkoxybenzenes were found to be good substrates for theiodination. Even the alkoxybenzene with a deactivated substituent was iodinated inmoderate yield. In addition, the regioselectivity was excellent and the iodination of thetested disubstituted benzenes selectively occurred at the para-position with regard toalkoxy group. Preliminary mechanistic investigation suggests that the resulting NO+seems to be the real catalytic species.2. Based on the above results, it was also found that the reaction could proceedeffectively in the presence of nitronium tetralfuoroborate (NOBF4). Then the reactionconditions were optimized, and the best result was obtained in the case of0.5equiv. I2，10mol%of nitronium tetrafluoroborate,5h，acetonitrile as the solvent and airatmosphere. A series of alkoxy substituted benzenes and benzyloxybenzenes wereiodinated in satisfactory yields.