Synthesis and Transformations of Functionalized Benzosiloxaboroles

The synthesis and characterization of a series of fluorinated benzosiloxaboroles bearing synthetically useful formyl and cyano groups is reported. These compounds have been obtained by multistep syntheses starting with simple halogenated benzenes. The general synthetic protocol was based on the generation of ortho-boronated aryldimethylsilanes which undergo dehydrogenative cyclization upon hydrolytic workup due to activation of the Si-H bond by the adjacent boronic group. In some cases the synergy of adjacent boron-and silicon-based functionalities resulted in an unexpected hydrosilylation of the CHO group under mild aqueous conditions. The reduction of a benzosiloxaborole derivative bearing the formyl group at the ortho position with respect to the boron atom resulted in a structural transformation reflecting the higher stability of the carboxaborole heterocycle with respect to its silicon counterpart. Thus, a unique heterocyclic system featuring a central 10-membered ring comprising two borasiloxane linkages was isolated.