Stereoisomerically Pure Trisubstituted Vinylaluminum Reagents and their Utility in Copper‐Catalyzed Enantioselective Synthesis of 1,4‐Dienes Containing Z or E Alkenes

Abstract

Catalytic enantioselective addition of vinyl groups to C-based electrophiles constitutes a versatile class of C–C bond forming processes.[1–3] We recently reported that vinylaluminum reagents, generated through reactions of alkyl- or alkenyl-substituted terminal alkynes with commercially available and inexpensive diisobutylaluminum hydride (dibal-H), can be used in site- and enantioselective Cu-catalyzed allylic alkylations.[4] The above protocol, however, suffers from two notable deficiencies. First, cis vinylmetals cannot be accessed (>98% trans product formed due to syn addition of Al–H to terminal alkynes). Second, aryl-substituted vinylaluminums cannot be utilized since the corresponding hydroaluminations are inefficient.[5] Herein, we present solutions to the above shortcomings through efficient, site- and stereoselective preparation of vinylaluminum reagents by reactions of Si-substituted alkynes with dibal-H. The vinylmetals can be used in situ in site- and enantioselective Cu-catalyzed allylic alkylations.[6] Enantiomerically enriched vinylsilanes are proto-desilylated with trifluoroacetic acid (TFA), affording the derived Z or E alkenes typically as a single stereoisomer in up to >99:1 enantiomeric ratio (e.r.).