Isothiourea-Catalyzed Enantioselective Michael Addition of Malonates to α,ß-Unsaturated Aryl Esters.

ABSTRACT

An enantioselective Michael addition of malonates to α,ß-unsaturated para-nitrophenyl esters was achieved using the Lewis basic isothiourea HyperBTM, giving excellent levels of product enantioselectivity (up to >991 enantiomeric ratio) in good yields and with complete regioselectivity (>201 regioselectivity ratio) in the presence of alternative (phenyl ketone and ethyl ester) Michael acceptors. Density functional theory calculations indicate that N-acylation is rate-limiting. This constitutes a rare example of a highly enantioselective addition of simple, readily available malonates to α,ß-unsaturated esters.