Scandium(III)‐Triflate‐Catalyzed Multicomponent Reactions for the Synthesis of Nitrogen Heterocycles

Photo-induced scandium-catalyzed biomimetic skeleton conversion of lathyrane to naturally rare eupholathone Euphorbia diterpenes

The naturally scarce eupholathone-type euphornin E (1) was efficiently prepared from abundant lathyrane-type Euphorbia factor L1via a visible-light-induced Sc(OTf)3-catalyzed tandem process. Eupholathones 2 and 3 were also smoothly obtained by changing the reaction solvent. This route provides a convenient method for easily constructing scarce eupholathone- from lathyrane-type Euphorbia diterpenes, and confirms the biogenetic relationship between them from a chemical standpoint. Notably, compound 1 exhibited good anti-HIV activity.

Substrate-Dependent Selectivity in Sc(OTf)3-Catalyzed Cyclization of Alkenoic Acids and N-Protected Alkenamides

Five- and six-membered ring lactones and lactams are ubiquitous frameworks in various natural and synthetic molecules and are key building blocks in organic synthesis. Catalytic addition of an O-H or N-H bond across an unactivated C–C double bond is an appealing approach to rapidly access such highly valuable N- and O-containing skeletons in a waste-free and 100% atom efficient process. Herein, we report, for the first time, the efficient and high-yield cyclization of δ/ε-alkenoic acids and N-protected δ-alkenamides catalyzedby practical and easily accessible Lewis acid scandium(III) triflate under thermal and microwave conditions. The selectivity outcome of the reaction of δ/ε-alkenoic acids was dependent on the substitution patterns of the backbone chain and alkene moiety, leading to the exclusive formation of either the corresponding γ/δ-lactones via an O-selective cyclization or the Friedel–Crafts-type product by C-selective cyclization. An uncommon and rarely disclosed O-selective cyclization occurred preferentially or exclusively when N-protected δ-alkenamides were engaged in the reaction. The atom selectivity of the cyclization was unambiguously confirmed by single crystal X-ray crystallography.

Minor bioactive indoles from kimchi mirror the regioselectivity in indole-3-carbinol oligomerization

Kimchi is a globally consumed food with diverse health-benefits, but the low-abundance bioactive compounds in kimchi remain largely neglected. Here we show that kimchi contains a family of low-abundance (0.5-1.6 μg/g, dried weight) high-order indole oligomers derived from indole-3-carbinol (I3C), a breakdown product released from cruciferous vegetables used for producing the traditional subsidiary food. The structure determination of such complex molecules was accomplished by synthesizing linear indole oligomers as standard materials followed by the LC-HR-MS analysis. One indole tetramer (LTe2) is substantially toxic to tumor MV4-11 (IC₅₀ = 1.94 μM) and THP-1 cells (IC₅₀ = 7.12 μM). Collectively, the work adds valuable information to the knowledge package about kimchi, and may inspire the generation of indole-based molecules, to which many drugs belong.

Multicomponent Assembly of Trisubstituted Imidazoles and Their Photochemical Cyclization into Fused Polyheterocyclic Scaffolds

A straightforward route to a large and diverse library of trisubstituted imidazoles was established via a three-component reaction of 2-oxoaldehydes, 1,3-dicarbonyl compounds, and acyclic nitrogen bis-nucleophiles. The obtained products were subsequently explored in a photochemical cyclization yielding a variety of imidazole-fused polycyclic compounds.

Catalytic Approaches to Multicomponent Reactions: A Critical Review and Perspectives on the Roles of Catalysis

In this review, we comprehensively describe catalyzed multicomponent reactions (MCRs) and the multiple roles of catalysis combined with key parameters to perform these transformations. Besides improving yields and shortening reaction times, catalysis is vital to achieving greener protocols and to furthering the MCR field of research. Considering that MCRs typically have two or more possible reaction pathways to explain the transformation, catalysis is essential for selecting a reaction route and avoiding byproduct formation. Key parameters, such as temperature, catalyst amounts and reagent quantities, were analyzed. Solvent effects, which are likely the most neglected topic in MCRs, as well as their combined roles with catalysis, are critically discussed. Stereocontrolled MCRs, rarely observed without the presence of a catalytic system, are also presented and discussed in this review. Perspectives on the use of catalytic systems for improved and greener MCRs are finally presented.

The Ugi three-component reaction and its variants

A broad variety of α-aminoamide-based compounds have been synthesized via the three-component version of the Ugi reaction (U-3CR) or by any of its variants (Ugi-Zhu-3CR, Orru-3CR, Ugi-4C-3CR, Ugi-Joullié-3CR, GBB-3CR, Ugi-Reissert-3CR, and so on).