α-Phenylthioaldehydes for the effective generation of acyl azolium and azolium enolate intermediates.

Autor: Ewing PMDA; EaStCHEM, School of Chemistry, University of St Andrews St Andrews, Fife KY16 9ST UK ads10@st-andrews.ac.uk eli.zysman-colman@st-andrews.ac.uk.; EaStCHEM, School of Chemistry, University of Edinburgh EH9 3JF UK., Majhi PK; EaStCHEM, School of Chemistry, University of St Andrews St Andrews, Fife KY16 9ST UK ads10@st-andrews.ac.uk eli.zysman-colman@st-andrews.ac.uk., Prentice C; EaStCHEM, School of Chemistry, University of St Andrews St Andrews, Fife KY16 9ST UK ads10@st-andrews.ac.uk eli.zysman-colman@st-andrews.ac.uk., Young CM; EaStCHEM, School of Chemistry, University of St Andrews St Andrews, Fife KY16 9ST UK ads10@st-andrews.ac.uk eli.zysman-colman@st-andrews.ac.uk., van Rees K; EaStCHEM, School of Chemistry, University of Edinburgh EH9 3JF UK., Arnold PL; Dept of Chemistry, University of California Berkeley CA 94720 USA pla@berkeley.edu.; Chemical Sciences Division, Lawrence Berkeley National Laboratory Berkeley CA 94720 USA., Zysman-Colman E; EaStCHEM, School of Chemistry, University of St Andrews St Andrews, Fife KY16 9ST UK ads10@st-andrews.ac.uk eli.zysman-colman@st-andrews.ac.uk., Smith AD; EaStCHEM, School of Chemistry, University of St Andrews St Andrews, Fife KY16 9ST UK ads10@st-andrews.ac.uk eli.zysman-colman@st-andrews.ac.uk.
Jazyk: angličtina
Zdroj: Chemical science [Chem Sci] 2024 May 14; Vol. 15 (24), pp. 9369-9375. Date of Electronic Publication: 2024 May 14 (Print Publication: 2024).
DOI: 10.1039/d3sc06879j
Abstrakt: α-Phenylthioaldehydes are readily prepared using a simple multi-step procedure and herein are introduced as a new precursor for the NHC-catalysed generation of acyl azolium and azolium enolate intermediates that are of widespread synthetic interest and utility. Treatment of α-phenylthioaldehydes with an NHC precatalyst and base produces an efficient redox rearrangement via a Breslow intermediate, elimination of thiophenolate, and subsequent rebound addition to the generated acyl azolium to give the corresponding thiol ester. In the presence of an external alcohol, competition between redox rearrangement and redox esterification can be controlled through judicious choice of the N -aryl substituent within the NHC precatalyst and the base used in the reaction. With NEt 3 as base, NHCs bearing electron-withdrawing ( N -C 6 F 5 or N -C 6 H 2 Cl 3 ) substituents favour redox rearrangement, while triazolium precatalysts with electron-rich N -aryl substituents ( N -Ph, N -Mes) result in preferential redox esterification. Using DBU, redox esterification is preferred due to transesterification of the initially formed thiol ester product. Additionally, α-phenylthioaldehyde-derived azolium enolates have been used in enantioselective formal [4 + 2]-cycloaddition reactions to access dihydropyridinone heterocycles with high enantioselectivity (up to >95 : 5 dr, 98 : 2 er).
Competing Interests: There are no conflicts to declare.
(This journal is © The Royal Society of Chemistry.)
Databáze: MEDLINE
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