Unexpected Beneficial Effect of ortho-Substituents on the (S)-Proline-Catalyzed Asymmetric Aldol Reaction of Acetone with Aromatic Aldehydes

Abstract

An intriguing effect of electronegative 2,6-substituents on the stereochemical outcome of (S)-proline-catalyzed aldol reactions between benzaldehyde derivatives and acetone is reported. Remarkably high enantioselectivities can be achieved with such substrates

Biocatalytic Asymmetric Michael Additions of Nitromethane to α,β-Unsaturated Aldehydes via Enzyme-bound Iminium Ion Intermediates

“…Notably, the consequence of ortho -substituents on the stereochemical outcome of organo- and biocatalytic reactions with aromatic aldol and Michael acceptor substrates has been observed before. 2d,8…”

One-Pot Synthesis of Multiarylated Benzophenones via [3 + 2 + 1] Benzannulation of Ketones, Alkynes, and α,β-Unsaturated Carbonyls

“…Acidically diverse proton sources (benzoic acid, phenol, and n -propanol) were less effective for the present reaction than aliphatic acid (Table , entries 4–6). Some secondary amines and amino acids are known to catalyze the reaction between ketone enolate and some electrophiles by forming the enamine intermediate. The diethylamine, pyrrolidine, and l -proline additives were ineffective (Table , entries 7–9) and water was unsuitable as a proton source, although the yield was improved from that of no additive (Table , entry 10).…”