Related Experiment Video
Updated: Jan 26, 2026

Microwave-Assisted Preparation of 1-Aryl-1H-pyrazole-5-amines
Published on: June 23, 2019
Evaluating aryl esters as bench-stable C(1)-ammonium enolate precursors in catalytic, enantioselective Michael
Claire M Young1, James E Taylor, Andrew D Smith
1EaStCHEM, School of Chemistry, University of St Andrews, North Haugh, St Andrews KY16 9ST, UK. ads10@st-andrews.ac.uk.
Abstract:
An evaluation of a range of aryl, alkyl and vinyl esters as prospective C(1)-ammonium enolate precursors in enantioselective Michael addition-lactonisation processes with (E)-trifluoromethylenones using isothiourea catalysis is reported. Electron deficient aryl esters are required for reactivity, with 2,4,6-trichlorophenyl esters providing optimal product yields. Catalyst screening showed that tetramisole was the most effective isothiourea catalyst, giving the desired dihydropyranone product in excellent yield and stereoselectivity (up to 90 : 10 dr and 98 : 2 er). The scope and limitations of this process have been evaluated, with a range of diester products being generated after ring-opening with MeOH to give stereodefined dihydropyranones with excellent stereocontrol (10 examples, typically ∼90 : 10 dr and >95 : 5 er).
Related Concept Videos
Conjugate Addition of Enolates: Michael Addition
Cyclohexenones via Michael Addition and Aldol Condensation: The Robinson Annulation
Alkylation of β-Ketoester Enolates: Acetoacetic Ester Synthesis
Alkylation of β-Diester Enolates: Malonic Ester Synthesis
Types of Enols and Enolates
Reactivity of Enols

