Recent Developments in the Use of Catalytic Asymmetric Ammonium Enolates in Chemical Synthesis

Facile and Convenient One-Pot Process for the Synthesis of Spirooxindole Derivatives in High Optical Purity Using (−)-(S)-Brevicolline as an Organocatalyst

“…At this point, the distinguishing features of the active species inducing chirality are not understood. However, we believe that the induced chirality is due to the intermolecular cycloaddition involving hydrogen-bonding interactions of the CN group with chiral N-methylpyrrolidinyl core as well as keto-enol tautomerism equilibrium via the interaction with the NH group [18]. This creates a chiral pocket which influences the selectivity of β-dicarbonyl group transfer from acetylacetone/ethyl 3-oxobutanoate to isatylidene malononitrile derivatives.…”

Organocatalytic Conjugate Addition in Stereoselective Synthesis

“…[16][17][18] Brønsted bases such as tertiary amines are known to activate carbonyl nucleophiles by deprotonation resulting in chiral ion pairs. 19 These two modes of action can be used separately or combined together in a bifunctional activation mode, resulting in extremely well-defined and reactive transition states (Scheme 11.2, eq 3). 20,21 Another mechanistic hypothesis for this dual activation involves enol formation by activation by the thiourea and electrophile activation by H-bond formation.…”

Isothiourea‐Mediated One‐Pot Synthesis of Functionalized Pyridines

“…[2] Despite many recent advances, novel methods for the synthesis of highly functionalized pyridines in a selective and high yielding manner from accessible starting materials remains an important goal within the synthetic community. [3] Following the demonstration by Romo and co-workers of generating ammonium enolates [4] from carboxylic acids, [5] we have shown that isothioureas [6,7] catalyze the intermolecular Michael addition/lactonization/lactamization of arylacetic acids and electron-deficient Michael acceptors. [8] To expand this mode of activation, we questioned whether this methodology could be used to access functionalized pyridines.…”