Stereoelectronically Controlled Regioselective Allylation of Aldehyde Under Photoredox/Chromium Catalysis.

The formation of structurally defined α,γ-disubstituted allylmetallic intermediate which could undergo regioselective allylation with carbonyl compounds remains a formidable challenge in synthetic chemistry. Although regioselective in situ formation of α,γ-disubstituted allylchromium intermediate controlled by coordinative directing groups has been achieved, how to achieve high selectivity for reactions involving α,γ-disubstituted allylic chromium intermediates through electronic control has been elusive. In this study, we report a silyl-group-directed strategy that exploits the α-silicon effect to achieve exceptional regiocontrol (rr > 95:5) in the chromium-catalyzed radical-type allylation of aldehydes with α-silyl-substituted diene and Hantzsch ester under photoredox catalysis. The method establishes a paradigm of electronic steering mode for chromium catalysis, enabling the highly regioselective and diastereoselective synthesis of a wide variety of valuable alkenylsilane-containing homoallylic alcohols commencing from readily accessible α-silyl-substituted dienes. The three-component reactions display good substrate generality and broad functional group compatibility, and could be successfully applied in the post-functionalization of biologically active complex molecules. Moreover, the resulting alkenylsilane-containing homoallylic alcohols could be easily converted into other value-added organic molecules, and the preinstalled silyl substituent could be readily manipulated for straightforward access of diverse substituents (e.g., alkyl, aryl, alkenyl, and alkynyl), which are difficult to access by using documented methodologies.