Asymmetric Aza‐Morita–Baylis–Hillman‐Type Reactions: The Highly Enantioselective Reaction between Unmodified α,β‐ Unsaturated Aldehydes and <i>N</i>‐Acylimines by Organo‐co‐catalysis

Abstract

Abstract The highly enantioselective organo‐co‐catalytic aza‐Morita–Baylis–Hillman (MBH)‐type reaction between N ‐carbamate‐protected imines and α,β‐unsaturated aldehydes has been developed. The organic co‐catalytic system of proline and 1,4‐diazabicyclo[2.2.2]octane (DABCO) enables the asymmetric synthesis of the corresponding N ‐Boc‐ and N ‐Cbz‐protected β‐amino‐α‐alkylidene‐aldehydes in good to high yields and up to 99% ee . In the case of aza‐MBH‐type addition of enals to phenylprop‐2‐ene‐1‐imines, the co‐catalytic reaction exhibits excellent 1,2‐selectivity. The organo‐co‐catalytic aza‐MBH‐type reaction can also be performed by the direct highly enantioselective addition of α,β‐unsaturated aldehydes to bench‐stable N ‐carbamate‐protected α‐amidosulfones to give the corresponding β‐amino‐α‐alkylidene‐aldehydes with up to 99% ee . The organo‐co‐catalytic aza‐MBH‐type reaction is also an expeditious entry to nearly enantiomerically pure β‐amino‐α‐alkylidene‐amino acids and β‐amino‐α‐alkylidene‐lactams (99% ee ). The mechanism and stereochemistry of the chiral amine and DABCO co‐catalyzed aza‐MBH‐type reaction are also discussed.