Controlling the α/γ‐Reactivity of Vinylogous Ketone Enolates in Organocatalytic Enantioselective Michael Reactions. Issue 30 (20th June 2017) - Iriarte, Igor
Abstract: The first regio‐, diastereo‐, and enantioselective direct Michael reaction of β, γ‐unsaturated ketones with nitroolefins is enabled by Brønsted base/hydrogen‐bonding bifunctional catalysis. A squaramide‐substituted tertiary amine catalyzes the reaction of a broad range of β, γ‐unsaturated ketones to proceed at the α‐site exclusively, giving rise to adducts with two consecutive tertiary carbon stereocenters in diastereomeric ratios of up to >20:1 and enantioselectivities generally in the 90–98 % ee range. Abstract : Direct with a switch : Most catalytic reactions with vinylogous enolate equivalents generated in situ proceed through the γ‐carbon atom (conjugation preserved). It is now shown that a bifunctional tertiary amine/hydrogen‐bonding catalyst can be used for highly diastereo‐ and enantioselective α‐additions of β, γ‐unsaturated ketones to nitroolefins.