Development of Boron-Based Reactions and Reagents for Organic Synthesis

Abstract

New boron-based reactions utilizing boron reagents such as silylboranes, cyanoboranes, alkynylboranes, chloroboranes, and aminoboranes are described. They involve transition metal-catalyzed silaboration, cyanoboration, and alkynylboration, which allow efficient synthesis of functionalized organoboron compounds. The application to the catalytic asymmetric silaboration is also demonstrated. Another mode of boron-element addition reaction has been shown by transmetalative carboboration of alkynes, in which the activation of the boron-halogen bonds and the supply of the organic fragment from organometallic reagents are involved as key elementary steps. In addition to those new catalytic reactions for boron-carbon bond formation, we have also utilized amino borane as new iminium ion generators in non-acidic Strecker-type reaction, Mannich reaction, reductive amination, and Ugi reaction. A protective group for the boronyl group in Suzuki-Miyaura cross-coupling was established and used as a temporary mask in iterative synthesis of oligoarenes.