Investigation of reactions of Aryl Triazene/Diazene and their application for synthesis of Arylboronic esters and Diazaheterocycles

Abstract

1-Aryltriazene and 1,2-diaryldiazene are important organic compounds not only for their biological or physical activities, but also for their synthetic applications. They are widely used as building block in heterocycle synthesis and coupling reactions for containing the unique N=N double bond. Thus the author started a research on these two kind of interesting compounds. In this Ph.D thesis, an investigation of the reaction of 1-aryltriazenes and 1,2-diaryldiazenes and their applications in organic synthesis is described. 1-Aryltriazenes are traditionally used as an equiverlant of aryldiazonium salt in the presence of a Brønsted or Lewis acid and could be applied to various nucleophilic substitution reactions, such as halogenation, hydroxylation and hydrogenation. However, there are no known reports about the carbon−metal bond formation in this kind of transformation, for example, creating a carbon−boron bond. At first the author focused on the reactivity of 1aryltriazenes toward boron reagents. The author found 1-aryltriazene could be converted into the corresponding arylboronic ester via the deaminoborylation with B 2 pin 2 mediated by BF 3 •OEt 2. This method provides a facile transition-metal-free access to a variety of arylboronic esters, especially the electron-rich ones in moderate to good yield. 1-Aryltriazenes could be readily prepared from the corresponding arylamine in high yield and well tolerated under various conditions. Moreover, polymer-bonded 1-aryltriazenes have been extensively used in solid-supported synthesis. Thus this method is potentially useful in multistep synthesis and combinatorial chemistry. which R 1 and R 2 can be an alkyl, aryl or hydrogen group. 1-Aryltriazenes have been proved to be useful reagents since their discovery. The synthetic applications of 1aryltriazene were developed mainly on the basis of dediazoniation transformations before 1950s. Recently, 1-aryltriazenes were recognized as a versatile tool which was widely used in organic synthesis, combinatorial chemistry, organometallic chemistry, polymer synthesis, etc. 1 1-Aryltriazenes 1-4 can be easily prepared from readily available arylamines 1-1 which was diazotized with NaNO 2 and acid (e.g. HBF 4 , HCl) to form the diazonium salt 1-2, and then treated with primary or secondary amines in presence of base at-15-0 °C to afford corresponding 1-aryltirazene in high yield (Scheme 1-2). Alternatively the diazonium salt intermediate could also be prepared by treating arylamines with t BuONO and a strong Lewis acid like BF 3 •OEt 2. Scheme 1-2. Preparation of 1-aryltriazene In addition to their use as synthetic building block, 1-aryltriazenes can be used as linker in solid-phase organic synthesis which is an important tool in combinatorial chemistry. 2 The synthesis of the solid-supported 1-aryltriazene 1-6 and 1-8 usually includes two approaches: reaction of a solid-supported amine with free diazonium ion 3 or a solidsupported diazonium ion with free amines 4 (Scheme 1-3). 10 Scheme 1-12. Recently, the Haley group successfull...