Study On The Synthesis Of Methanol - Promoted Arylamine To Aromatic Boronic Acid And Its Esters

Arylboronic acids and arylboronates are useful reaction intermediates, which are widely used in transition metal catalyzed C-C, C-N, C-O and C-S bond formation reactions. They also have the characteristics of low toxicity and high stability. So the development of methodology to synthesise arylboronic acids and arylboronates has attracted great attention. Traditional methods for the synthesis of arylboronic acids or arylboronates involve the use of Grignard reagents and lithium reagents. Catalytic borylation reactions, with Palladium, Copper, Rhodium, Iridium or Ruthenium catalysts, emerged as greener options in recent years.Arylamines are inexpensive and easily available starting materials; which can be obtained by nitration of aromatic compounds followed by reduction. Aromatic amine can be converted to various other functional groups by sandmeyer reaction. The construction of C-B bond from aryl amines or aryl diazonium salts has attracted much attention and seen great development.Despite the progresses, C-B bond formation reactions still have the following disadvantages:the use of expensive transition metal, high reaction temperature, and the need to use dangerous peroxide. To solve the problems above, this thesis describes a methanol-promoted coupling of arylamine with diboron compounds to prepare arylboronic acids and arylboronates. Aryl amines, which are cheap and easily available, were used as substrates. The reaction proceeded in the absence of a catalyst and under room temperature. Good yields were obtained for various substrates with different functional groups.The effect of reaction time, temperature, solvents and the moler ratio of reactants were studied first.The molar ratio of reactants and sovlents are the most importment factors affecting the reaction yield. Optimum reaction conditions were established starting from arylamines via a one-pot two step process. The first step converted arylamines to aryldiazonium salts under the following conditions:arylamine (0.5mmol), methanol (1mL), hydrochloric (3M,0.5mL), sodium nitrite (0.035g), H2O (0.5mL),0-5℃,30min; In the second step, diboron reagent (1.5mmol) and additional methanol (1mL) were added to transform aryl diazo salts into arylboronic acids or arylboronates.An effective and green methanol-promoted coupling of arylamine with diboron compounds at room temperature has been developed under metal-free conditions. This protocol could be applyed to the synthesis of arylboronic acids utilizing arylamine and tetrahydroxydiboron B2(OH)4as boron source. This borylation process has the following features:(1), Arylamines are inexpensive and easily achieved starting materials;(2), The borylation showed good tolerance to various functional groups on the aryl amines;(3), Sodium nitrite is used as diazotization agent;(4), The reaction is carried out at the room temperature without the use of catalyst.