Photoinduced pinacol coupling of carbon-carbon bonds via triethoxysilane or Hantzsch Ester

Abstract

The photocatalytic reductive coupling of carbon-carbon bonds via pinacol coupling represents a significant transformation in organic synthesis chemistry. Several elegant studies have reported the use of metal or organic photocatalysts in this process, but these often lead to trace metal residues or involve intricate operational procedures. Herein, we report a photoinduced pinacol coupling of carbon-carbon bonds from ketones, achieved under photocatalyst-free conditions using triethoxysilane or Hantzsch ester as the reductant. In the model reaction employing benzophenone as substrate and triethoxysilane as the reductant, the corresponding pinacol product was obtained in 96 % yield under 370 nm LED light irradiation. Similarly, when Hantzsch ester served as the reductant, the pinacol product was obtained in 95 % yield under 423 nm LED light irradiation. The substrate scope demonstrated that six substrates yielded the corresponding products with yields ranging from 40 % to 96 %. Notably, when acetophenone, a substrate with minimal steric hindrance, was used under the established conditions, only 1-phenylethanol was produced. This work introduces two practical methods for the synthesis of carbon-carbon coupling intermediates through pinacol coupling of benzophenone-derived substrates, positioning these methodologies as promising candidates for various applications.