Iodine‐Catalyzed Diels‐Alder Reactions

Iodine-Catalyzed Carbonyl-Alkyne Metathesis Reactions

The reaction between aldehydes or ketones and alkynes-the carbonyl-alkyne metathesis-constitutes a very useful strategy for the synthesis of α,β-unsaturated carbonyls. We now demonstrate that iodine is a highly efficient catalyst for both the intra- and intermolecular metathesis reaction in very small concentrations (0.1-1 mol %). Our protocol outperforms other catalytic systems, is operationally very simple, cheap, metal-free, and tolerates a large variety of functional groups (e. g., -CN, -CO2Me, -Br, -OH) at very low catalyst loadings. We can furthermore show that iodine-catalyzed carbonyl-alkyne metatheses can be combined with other iodine-catalyzed reactions in one-pot procedures to afford larger and more complex molecular structures. Finally, our mechanistic studies indicate that the iodonium ion is the active catalyst under the reaction conditions.

Halogen Bond Catalysis: A Physical Chemistry Perspective

As important noncovalent interactions, halogen bonds have been widely used in material science, supramolecular chemistry, medicinal chemistry, organocatalysis, and other fields. In the past 15 years, halogen bond catalysis has become a developed field in organocatalysis for the catalysts' advantages of being environmentally friendly, inexpensive, and recyclable. Halogen bonds can induce various organic reactions, and halogen bond catalysis has become a powerful alternative to the fully explored hydrogen bond catalysis. From a physical chemistry view, this perspective provides an overview of the latest progress and key examples of halogen bond catalysis via activation of the lone pair systems of organic functional group, π systems, and metal complexes. The research progresses in halogen bond catalysis by our group were also introduced.

Iodine-Catalyzed Claisen-Rearrangements of Allyl Aryl Ethers and Subsequent Iodocyclizations

Iodine can be considered as the simplest halogen-bond donor. Previous investigations have revealed its remarkable catalytic effect in various reactions. The catalytic activity of iodine can often even compete with that of traditional Lewis acids. So far, iodine was typically used to activate carbonyl derivatives like Michael acceptors. We now demonstrate that iodine can also be used to activate allyl aryl ethers in Claisen rearrangements. The formed ortho-allylic phenols rapidly undergo iodocyclizations to afford dihydrobenzofurans, which are important building blocks for medicinal applications. A comparison with different catalysts further highlights the potential of iodine catalysis for this reaction. Computational and mechanistic investigations provide deeper insights into the underlying non-covalent interactions and their role for the catalysis.

Oxa-Nazarov Cyclization-Michael Addition Sequence for the Rapid Construction of Dihydrofuranones

The Nazarov cyclization has been established as a powerful tool in constructing cyclopentenone skeletons. In sharp contrast, oxa-Nazarov cyclization that affords dihydrofuranones, a new type of product, has been less explored. In this work, we report the I2-catalyzed oxa-Nazarov cyclization-Michael addition cascade between vinyl α-diketones and enones. The protocol allows access to a range of functionalized dihydrofuranones with good to high yields, and diverse further transformations on the products have been achieved. Furthermore, the mechanistic studies reveal that the 1,2-hydride shift occurs simultaneously during the dihydrofuranone formation.

Synthesis of functionalized 1-aminoisoquinolines through cascade three-component reaction of ortho-alkynylbenzaldoximes, 2H-azirines, and electrophiles

We have developed a new three-component approach using ortho-alkynylbenzaldoximes involving the formation of a cyclic nitrone in the presence of Br₂ or ICl for the synthesis of 1-aminoisoquinolines via cascade 6-endo-cyclization, 1,3-dipolar cycloaddition reaction with 2H-azirines, and ring-opening reaction sequences. The broad range of structurally diverse products, good to high yields, high atom-economy and high bond-formation efficiency make this method an attractive alternative for the synthesis of 1-aminoisoquinolines.

N-Heterocyclic Iod(az)olium Salts - Potent Halogen-Bond Donors in Organocatalysis

This article describes the application of N-heterocyclic iod(az)olium salts (NHISs) as highly reactive organocatalysts. A variety of mono- and dicationic NHISs are described and utilized as potent XB-donors in halogen-bond catalysis. They were benchmarked in seven diverse test reactions in which the activation of carbon- and metal-chloride bonds as well as carbonyl and nitro groups was achieved. N-methylated dicationic NHISs rendered the highest reactivity in all investigated catalytic applications with reactivities even higher than all previously described monodentate XB-donors based on iodine(I) and (III) and the strong Lewis acid BF3 .