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Review
. 2022 Nov 17;27(22):7990.
doi: 10.3390/molecules27227990.

A Review on Generation and Reactivity of the N-Heterocyclic Carbene-Bound Alkynyl Acyl Azolium Intermediates

Ziyang Dong  1 , Chengming Jiang  1 , Changgui Zhao  1
Affiliations
Review

A Review on Generation and Reactivity of the N-Heterocyclic Carbene-Bound Alkynyl Acyl Azolium Intermediates

Ziyang Dong et al. Molecules. .

Abstract

N-heterocyclic carbene (NHC) has been widely used as an organocatalyst for both umpolung and non-umpolung chemistry. Previous works mainly focus on species including Breslow intermediate, azolium enolate intermediate, homoenolate intermediate, alkenyl acyl azolium intermediate, etc. Notably, the NHC-bound alkynyl acyl azolium has emerged as an effective intermediate to access functionalized cyclic molecular skeleton until very recently. In this review, we summarized the generation and reactivity of the NHC-bound alkynyl acyl azolium intermediates, which covers the efforts and advances in the synthesis of achiral and axially chiral cyclic scaffolds via the NHC-bound alkynyl acyl azolium intermediates. In particular, the mechanism related to this intermediate is discussed in detail.

Keywords: N-heterocyclic carbene; alkynyl acyl azolium; annulation; intermediate; mechanism.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Scheme 1
Scheme 1
N-heterocyclic carbene (NHC)-bound acyl azoliums (A), generation and reactivity of the alkynyl acyl azoliums (B), and the main challenges to explore the concerning reactivity of alkynyl acyl azoliums (C).
Scheme 2
Scheme 2
Overview of NHC structures discussed in this review.
Scheme 3
Scheme 3
NHC-catalyzed [3 + 3] atroposelective annulation of ynals and 1,3-diones.
Scheme 4
Scheme 4
Mechanism of the NHC-catalyzed [3 + 3] atroposelective annulation of ynals and 1,3-diones.
Scheme 5
Scheme 5
NHC-catalyzed [3 + 3] atroposelective annulation of ynal and pyrrol-4-one.
Scheme 6
Scheme 6
NHC-catalyzed [3 + 3] annulation of activation of alkynoic acid ester and N-Ts imine.
Scheme 7
Scheme 7
NHC-catalyzed [3 + 3] annulation of ynals and N-Ts 2-aminoacrylates.
Scheme 8
Scheme 8
NHC-catalyzed formal [2 + 3] annulation of the activation of alkynoic acid esters and amidomalonates.
Scheme 9
Scheme 9
NHC-catalyzed formal [3 + 3] annulation of ynals and amidines.
Scheme 10
Scheme 10
NHC-catalyzed [3 + 3] annulation of the in situ activation of alkynyl acids and 2-mercaptobenzimidazoles.
Scheme 11
Scheme 11
[3 + 3] annulation of alkynyl acyl azolium intermediates and 3-oxo indolin-2-ide or 3-imino benzofuran-2-ide.
Scheme 12
Scheme 12
Catalytic atroposelective formal [3 + 3] annulation between alkynyl acyl azolium intermediate and 2-sulfonamidoindolines.
Scheme 13
Scheme 13
NHC-catalyzed atroposelective [3 + 3] annulation of ynals and thioureas.
Scheme 14
Scheme 14
NHC-catalyzed atroposelective [3 + 2] annulation of ynals and urazoles.
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