Highly Enantioselective Intramolecular Cyclopropanation Reactions of N-Allylic-N-methyldiazoacetamides Catalyzed by Chiral Dirhodium(II) Carboxamidates

Abstract

Catalytic diazo decomposition of representative N-allylic-N-methyldiazoacetamides produced the corresponding intramolecular cyclopropanation products in good to excellent yields and with exceptional enantiocontrol. In the simplest case, with N-allyl-N-methyldiazoacetamide, catalysis by dirhodium(II) tetrakis[methyl 2-oxapyrrolidine-5(S)-carboxylate], Rh2(5(S)-MEPY)4, achieved the highest yield and enantioselectivity (93% ee). Dirhodium(II) tetrakis[methyl 2-oxo-1-(3-phenylpropanoyl)imidazolidin-4(S)-carboxylate], Rh2(4S)-MPPIM)4, was preferred for substituted N-allylic-N-methyldiazoacetamides from which 92−95% ee's were obtained in intramolecular cyclopropanation reactions (88−95% yields), even when the catalyst was employed in only 0.1 mol %. Competition with intramolecular dipolar cycloaddition was minimized with the use of N-methyldiazoacetamides relative to N-tert-butyldiazoacetamides.