The Study On The Iodization Of Arylboronic Acids

Due to various applications of iodoarenes in organic synthesis, the syntheticmethods for iodoarenes draw chemists’ attention. Bromoarenes can be well preparedvia electrophilic substitution of aryl rings, while the direct iodination of arenes isdifficult to be performed. At present, a number of methods for the preparation ofiodoarenes have been reported. These include:（a） the use of strong oxidizing reagentsto activate the halogens,（b） the iodination of highly reactive and toxic aromaticmercury and thallium compounds,（c） the Sandmeyer reaction[1]where chlorine,bromine and iodine are regioselectively introduced to aryl rings via aryl diazoniumions under acidic condition.Compared with organic mercury and thallium compounds, arylboronic acids are oflow toxicity and easy of handling. In this thesis, iodination of arylboronic acids wasinvestigated with arylboronic acids as the main substrates, and a mild method wasdeveloped. The details about the results of our investigation are as follows:1. Conversion of arylboronic acids to iodoarenes was actualized with copper salts asthe catalyst and zerovalent iodine as the iodination reagent at room temperature.Firstly, iodination of was chosen as a model reaction to investigate the effect ofdifferent copper salts, solvent, reaction atmosphere, etc on the reaction. Afterscreening a a series of ligands, it was found that the best result was obtained in thecase of no ligand, and86%yield was obtained. Among the screened copper catalysts,Cu（NO₃）₂·3H₂O was the most effective. But Cu（OAc）₂·H₂O had high catalytic activityin the case of3,5-difluorophenylboronic acid. Different type of solvent had asignificative effect on the reaction. The reactions with acetonitrile, NMP and DMF asthe solvent gave the good results. Considering that the isolation handling of theproduct was easy in the case of low-boiling point solvent, we chose acetonitrile as thesolvent. In order to further demonstrate the scope of the present method, we test15arylboronic acids. The experimental results revealed that the reactions were able totolerate some functional groups such as alkyl, fluo, nitryl and alkoxy groups. The isolated yield of iodination products were up to85%.2. Based on the above results, we found that the reaction could proceed smoothly inabsence of copper catalyst. Then we optimized the reaction conditions, and the resultsshew that the used amount of I2was required to increase to2.5equv. to obtaingratifying yields. Subsequently the effect of several solvents was studied, and theresults revealed that the reaction in NMP and DMF provided the iodination products inhigh yields. Under the condition of no catalyst, a series of arylboronic acids weresmoothly iodinated and up to72%yield was obtained. However,3-aminobenzeneboronic acid and4-acetylphenylboronic acid trace amount of iodinationproduct was detected. The demonstrated optimal condition was that:1.0mmolphenylboronic acid,2.5mmol I2,0.8mL DMF, room temperature and6h.