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

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 beta-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.