Selective functionalizations of arylboronic acids and studies on cationic intermediates

Abstract

Selective functionalizations of arylboronic acids were carried out to obtain the ipso-substituted products in all cases. Arylboronic acids were converted to aryl iodides and subsequently coupled to form symmetrical biaryls in one pot in good yields. Additionally, arylboronic acids were selectively converted to phenols. This methodology allows subsequent coupling to afford symmetrical diaryl ethers in one pot under mild conditions in good to excellent yields. Furthermore, arylboronic acids were nitrated using Crivello's reagent. The reaction gave mononitro- and dinitro-products at −35°C in acetonitrile for a variety of electronically and sterically different substrates in good yields.

Quantum chemical ab initio and Density Functional calculations were performed on trimethylsilyl-substituted norbornyl cations. For the substituted 2-norbomyl cation, the 3-exo-trimethylsilyl-2-norbornyl cation is the global minimum. This cation has a classical structure due to extensive stabilization by the β-silyl substituent. Transition states for the interconversion of the isomeric cations and the corresponding activation barriers were also computed. Additionally, higher-coordinated singlet XH₄⁺ and XH₆⁺ (X = B, Al and Ga) were calculated by Density Functional and Coupled Cluster methods. Their structures and energetics as well as their stabilities for deprotonation and dehydrogenation were also computed.