Heterogeneous Meerwein‐Ponndorf‐Verley–type Reduction of Aromatic Aldehydes Having Other Reducible Functional Groups over a TiO 2 Photocatalyst

Abstract Chemoselective reduction of benzaldehydes having other reducible functional groups without the use of a reducing agent such as metal hydrides is important because metal hydrides simultaneously produce a large amount of undesirable waste containing metal compounds. Here we report that a titanium(IV) oxide (TiO 2 ) photocatalyst is effective for heterogeneous Meerwein‐Ponndorf‐Verley (MPV)‐type reduction of various benzaldehydes having reducible functional groups to corresponding benzyl alcohols at room temperature under a metal‐free condition. We also investigated the effects of physical properties of TiO 2 samples on chemoselective reduction of p ‐chlorobenzaldehyde (CBAD) to p ‐chlorobenzyl alcohol (CBAO) and we observed a linear correlation between the amount of CBAD adsorbed and the rate of CBAO formation, suggesting that ability of TiO 2 for CBAD adsorption is one of the key factors for effective MPV‐type reduction of CBAD to CBAO.