The efficient synthesis of three-membered rings via photo- and electrochemical strategies

Three-membered rings, such as epoxides, aziridines, oxaziridines, cyclopropenes, vinyloxaziridines, and azirines, are recognized as crucial pharmacophores and building blocks in organic chemistry and drug discovery. Despite the significant advances in the synthesis of these rings through photo/electrochemical methods over the past decade, there has currently been no focused discussion and updated overviews on this topic. Therefore, we presented this review article on the efficient synthesis of three-membered rings using photo- and electrochemical strategies, covering the literature since 2015. In this study, a conceptual overview and detailed discussions were provided to illustrate the advancement of this field. Moreover, a brief discussion outlines the current challenges and opportunities in synthesizing the three-membered rings using these strategies.

Electrochemical Iodine-Mediated Oxidation of Enamino-Esters to 2H-Azirine-2-Carboxylates Supported by Design of Experiments

An electrochemical iodine-mediated transformation of enamino-esters for the synthesis of 2H-azirine-2-carboxylates is presented. In addition, a thermic conversion of azirines to 4-carboxy-oxazoles in quantitative yield without purification was described. Both classes 2H-azirines-2-carboxylates and the 4-carboxy-oxazoles are substructures in natural products and therefore are of considerable interest for synthetic and pharmaceutical chemists. The optimization was not performed in a conventional manner with a one-factor-at-a-time process but with a Design of Experiments (DoE) approach. Beside a broad substrate scope the reaction was also employed to a robustness screen, a sensitivity assessment, and complemented with mechanistic considerations from cyclic voltammetry experiments.

Bifunctional squaramide catalyzed stereoselective Mannich reaction of α-azido ketones with isatin-derived ketimines

Bifunctional squaramide catalyzed asymmetric Mannich reaction of alpha-azido ketones and isatin derived ketiminines were established for the first time with high stereoselectivity. Adducts are valuable synthons for optically active heterocycles.

Visible light triggered photo-decomposition of vinyl azides to (E)-stilbene derivatives via 1,2-acyl migration

An efficient photocatalyst-free visible light assisted synthetic route to various (E)-stilbene derivatives was developed. The reaction proceeds through a denitrogenative photo-decomposition of vinyl azides into 2H-azirines followed by neighboring amino group assisted ring opening, 1,2-acyl migration and enolization. The photochemical reaction offers light harvesting without any photocatalyst to access a wide variety of substituted (E)-stilbenes in moderate to high yields.

First total synthesis of the only known 2-isopropyliden-2H-benzofuran-3-one isolated from V. luetzelburgii

The first total synthesis of the unique isopropyliden-2H-benzofuran-3-one, isolated from Verbesina luetzelburgii, is reported in racemic and a chiral form.

Reactivities of vinyl azides and their recent applications in nitrogen heterocycle synthesis

Nitrogen heterocycles are abundant in natural products and pharmaceuticals. An emerging interest among synthetic chemists is to apply vinyl azides as a pivotal three-atom synthon for the construction of structurally complex and diverse N-heterocyclic skeletons. The unique features of the azide group connected to an alkene moiety permit vinyl azides to function as electrophiles, nucleophiles, or radical acceptors; their access to diverse reaction pathways provides great opportunities to generate highly reactive intermediates with often unusual or unconventional reactivities. This tutorial review will systematically illustrate the reactivities of vinyl azides and describe recent breakthroughs in the development of new transformations that create N-heterocycles.

Selective synthesis of substituted pyrrole-2-phosphine oxides and -phosphonates from 2H-azirines and enolates from acetyl acetates and malonates

A simple and efficient selective synthesis of 1H-pyrrole-2-phosphine oxides 3 and -phosphonates 7 by addition of enolates derived from acetyl acetates to 2H-azirinylphosphine oxide 1 and -phosphonate 6 is reported. Nucleophilic addition of enolates derived from diethyl malonate to 2H-azirines 1 and 6 led to the formation of functionalized 2-hydroxy-1H-pyrrole-5-phosphine oxide 9 and -phosphonate 10, while vinylogous α-aminoalkylphosphine oxides 14 and -phosphonate 15 may be obtained from azirines and the enolate derived from diethyl 2-phenylmalonate. Ring closure of vinylogous derivatives 14 and 15 in the presence of base led to the formation of 1,5-dihydro-3-pyrrolin-2-ones containing a phosphine oxide 17 or a phosphonate group 18.