Thianthrenium-Enabled Chromium-Catalyzed Deuterated Alkyl Addition to Aldehydes via a Photoactive Electron Donor–Acceptor Complex

Abstract

The Nozaki–Hiyama–Kishi reaction offers effective and reliable strategies for the preparation of alcohols via carbon–carbon bond formation. Typical methods usually require stoichiometric amounts of chromium salts, co-transition metals, and auxiliary reagents, which limits their practical application in industrial chemistry. To mitigate these limitations, substantial efforts have been made to develop chromium-catalytic approaches. However, an excess of metal reductants or expensive photocatalysts played essential roles during the catalytic cycles. Here, we present a photoactive electron donor–acceptor (EDA) complex-induced chromium-catalyzed route, accomplishing alkyl addition to aldehydes without the requirement of metal reductants or photocatalysts. Furthermore, on the basis of the pH-dependent site-selective hydrogen isotope exchange of alkyl thianthrenium salts, a range of β-deuterated secondary alcohols could be prepared with high efficiency and excellent deuterium incorporation. Mechanistic studies revealed that the photoinduced intramolecular single-electron transfer of the EDA complex happened to provide alkyl radicals that are captured by Cr(II) species to facilitate the subsequent carbon–carbon bond formation. Meanwhile, the excited Hantzsch ester could act as a terminal reductant for the turnover of the chromium catalyst.