Investigation On The Conversion Of Boronic Acid Group In Arylboronic Acids To Cyano Group And Phenolic Hydroxyl Group

Conversion of boronic acid group to other groups is often encountered in the multi-step synthesis of organic molecules, thus it is of academic and practical significance tosearch for new methods for conversion of boronic acid group in arylboronic acids tocyano group and phenolic hydroxyl group. At present, the conversion of boronic acidgroup to cyano group has been reported in previous literature where NaCN, KCN,Zn（CN）₂, CuCN and Me₃SiCN are used as the cyanating agent. Among thesecompounds, KCN and NaCN are highly poisonous. Zn（CN）₂, CuCN and Me₃SiCN areboth more expensive and moderate poisonous. As a result, it is of practical significanceto search for the inexpensive and lower poisonous cyanating agents.Being compared with the above-mentioned cyanating agents, K₄[Fe（CN）₆] is non-toxic and commercially available. In the present thesis, the conversion of boronic acidgroup in arylboronic acids to cyano group was actualized with K₄[Fe（CN）₆] as thecyanating agent. In addition, we developed a method for the conversion of boronic acidgroup in arylboronic acids to phenolic hydroxyl group. The details about the results ofour investigation are as follows:1. The conversion of boronic acid group in arylboronic acids to cyano group wasdeveloped with K₄[Fe（CN）₆] as the cyanating agent in combination with coppersalts/palladium salts as the catalyst system. Firstly, the catalytic effectivenesses of aseries of copper salts and palladium salts were demonstrated, and it was found thePd（OAc）₂/Cu（OAc）₂system was optimal. Then we optimized the reaction conditionsincluding temperature, solvent, additive etc, and the found optimal conditions wasfollows:30mol%Cu（OAc）₂,1mol%Pd（OAc）₂,50mol%K₄Fe（CN）₆,1equ. KOH,1equ. I2,1.5mL DMSO,120℃-180℃,6-24h.Under the optimal condition, a series ofarylboronic acids were cyanated in36%-90%yields. According to the rule forconservation of charge, the present conversion is an oxidative coupling reaction where the presence of oxidants is required. Surprisingly, only zerovalent iodine is effectiveamong the screened oxidants, which urge us to gain insight into the reaction pathway.Aryl iodide was found to be present throughout the reaction, revealing that the presentreaction involves iodination and cyanation step.2. The conversion of boronic acid group in arylboronic acids to phenolic hydroxylgroup was actualized with copper salts as the catalyst and water as the solvent. Weoptimized the reaction conditions such as catalyst, ligand, solvent and reactiontemperature etc, and a better result was obtained under the reaction conditions20mol%CuSO₄·5H₂O,30mol%TMEDA,3equ. KOH,5-6mL H₂O, and10-15h. The reactioncould be smoothly performed in room temperature, which provides a mild and effectivemethod for conversion of boronic acid group to phenolic hydroxyl group.