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

Abstract The Nozaki-Hiyama-Kishi (NHK) reaction offers effective and reliable strategies for the preparation of alcohols via carbon-carbon bond formation. Typical methods usually require stoichiometric amount of chromium salts, co-transition metals and auxiliary reagents, which limits practical application in industrial chemistry. In order to mitigate these limitations, substantial efforts have been made to develop chromium-catalytic approaches. However, excess amount 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, based on the pH-dependent site-selective hydrogen isotope exchange (HIE) of alkyl thianthrenium salts, diversities of β-deuterated secondary alcohols could be prepared with high efficiency and excellent deuterium incorporation. Mechanistic studies revealed that the photo-induced intramolecular single electron transfer (SET) of EDA complex happened to provide alkyl radicals that are captured by Cr(II) species to facilitate the subsequent carbon-carbon formation. Meanwhile, the excited Hantzsch ester could act as the terminal reductant for the turnover of the chromium catalyst.