Hypervalent Iodine Mediated Chemoselective Iodination of Alkynes

Total Synthesis of Icumazole A Using a Modified Cadiot-Chodkiewicz Coupling

The first total synthesis of myxobacteria metabolite icumazole A (1) is reported. Key steps in the route include an organocatalyzed asymmetric self-aldol reaction followed by an acetate aldol reaction to form the stereotriad present in the oxazole moiety, an intramolecular Diels-Alder reaction to form the isochromanone, and an acetylide addition and selective methylation. The final steps involved a high-yielding modified Cadiot-Chodkiewicz coupling and stereoselective reduction to secure the Z,Z-diene and afford 1.

Development of On-DNA Thiophene Synthesis for DEL Construction

Thiophene and its substituted derivatives are a highly important class of heterocyclic compounds, with noteworthy applications in pharmaceutical ingredients. In this study, we leverage the unique reactivity of alkynes to generate thiophenes on-DNA, using a cascade iodination, Cadiot-Chodkiewicz coupling and heterocyclization. This approach, tackling on-DNA thiophene synthesis for the first time, generates diverse, and unprecedented structural and chemical features, which could be significant motifs in DEL screening as molecular recognition agents for drug discovery.

Co-operative halogen bonds and nonconventional sp-C-H...O hydrogen bonds in 1:1 cocrystals formed between diethynylpyridines and N-halosuccinimides

The rapid evaporation of 1:1 solutions of diethynylpyridines and N-halosuccinimides, that react together to form haloalkynes, led to the isolation of unreacted 1:1 cocrystals of the two components. The 1:1 cocrystal formed between 2,6-diethynylpyridine and N-iodosuccinimide (C₄H₄INO₂·C₉H₅N) contains an N-iodosuccinimide-pyridine I...N halogen bond and two terminal alkyne-succinimide carbonyl C-H...O hydrogen bonds. The three-dimensional extended structure features interwoven double-stranded supramolecular polymers that are interconnected through halogen bonds. The cocrystal formed between 3,5-diethynylpyridine and N-iodosuccinimide (C₄H₄INO₂·C₉H₅N) also features an I...N halogen bond and two C-H...O hydrogen bonds. However, the components form essentially planar double-stranded one-dimensional zigzag supramolecular polymers. The cocrystal formed between 3,5-diethynylpyridine and N-bromosuccinimide (C₄H₄BrNO₂·C₉H₅N) is isomorphous to the cocrystal formed between 3,5-diethynylpyridine and N-iodosuccinimide, with a Br...N halogen bond instead of an I...N halogen bond.

Hypervalent Iodine-Mediated Chemoselective Bromination of Terminal Alkynes

Practical approaches for chemoselective mono-bromination, di-bromination, and tetra-bromination of terminal alkynes to generate 1-bromoalkynes, 1,2-dibromoalkenes, α,α-dibromoketones, and 1,1,2,2-tetrabromoalkanes based on efficient oxidative brominations mediated by a hypervalent iodine reagent have been developed. Chemoselective bromination can be realized under mild conditions by altering the bromine source. The tetrabutylammonium bromide (TBAB)/(diacetoxyiodo)benzene (PIDA) system is specific for mono-bromination to provide 1-bromoalkynes, while the NaBr/PIDA system is selective toward di-bromination to achieve 1,2-dibromoalkenes. When a certain amount of water was added to the NaBr/PIDA system, a different di-bromination product, α,α-dibromo ketones, was generated. Tetra-bromination of terminal alkynes provides an efficient protocol for the synthesis of 1,1,2,2-tetrabromoalkanes in a system with an excess loading of NaBr/PIDA in one pot. This bromination affords good yields (up to 99%) with excellent chemoselectivity (up to 100%). These methods can be applied to the efficient chemoselective synthesis of bromide derivatives, intermediates, and related biologically active compounds.

Hypervalent Iodine-Mediated Diastereoselective α-Acetoxylation of Cyclic Ketones

A binary hybrid system comprising a hypervalent iodine(III) reagent and BF₃•OEt₂ Lewis acid was found to be effective for the diastereoselective α-acetoxylation of cyclic ketones. In this hybrid system, BF₃•OEt₂ Lewis acid allowed the activation of the hypervalent iodine(III) reagent and cyclic ketones for smooth α-acetoxylation reaction, achieving high diastereoselectivity. This hypervalent iodine-mediated α-acetoxylation of the cyclic ketone reaction plausibly undergoes an S_N2 substitution mechanism via an α-C-bound hypervalent iodine intermediate. The diastereoselectivity of the reaction mainly originates from thermodynamic control.

Efficient synthesis of 1-iodoalkynes via Al2O3 mediated reaction of terminal alkynes and N-iodosuccinimide

Iodination of terminal alkynes using N-iodosuccinimide (NIS) in the presence of γ-Al₂O₃ was developed to afford 1-iodoalkynes with good to excellent yields (up to 99%). This described approach featured excellent chemoselectivity, good functional group tolerance, and utilization of an inexpensive catalyst.

An efficient Al₂O₃-mediated direct iodination of terminal alkynes was developed to afford 1-iodoalkynes.

Concise and Gram-Scale Total Synthesis of Lansiumamides A and B and Alatamide

The total synthesis of potent anti-obesity lansiumamide B was accomplished in four steps using commercially available materials. The synthetic strategy, featured with copper-catalyzed Buchwald coupling, is concise, convergent, practical and can be carried out on a one-gram scale. This approach could give either Z- or E-configured enamide moiety in natural products with absolute stereocontrol and was applied in the total synthesis of natural products.

(E)-Di-iodination of Alkynes Using Dried Dowex H+/NaI Approach

We investigated the usefulness of the dried Dowex H⁺/NaI approach for the selective di-iodination of alkynes. The Dowex H⁺/NaI approach selectively produces only (E)-di-iodinated products; it is very straightforward and nontoxic. The utilization of 2-propanol as a solvent in the reactions can be considered as a "green" approach and the method maybe extended to radio-iodination. The method allows access to highly important building blocks. An initial example of the di-iodination and esterification in the same one-pot reaction is also presented.

Iodine–DMSO-promoted divergent reactivities of arylacetylenes

An unprecedented set of efficient, economical, atom-economic and exceedingly selective I₂–DMSO-promoted methods is described for the generation of different structures.

Chemoselective Preparation of 1-Iodoalkynes, 1,2-Diiodoalkenes, and 1,1,2-Triiodoalkenes Based on the Oxidative Iodination of Terminal Alkynes

We present the chemoselective synthesis of 1-(iodoethynyl)-4-methylbenzene, 1-(1,2-diiodovinyl)-4-methylbenzene, and 1-methyl-4-(1,2,2-triiodovinyl)benzene as representative examples for the practical chemoselective preparation of 1-iodoalkynes, 1,2-diiodoalkenes, and 1,1,2-triiodoalkenes from the chemoselective iodination of terminal alkynes mediated by hypervalent-iodine reagents. The chemoselectivity was confirmed by using p-tolylethyne as a model substrate to screen a variety of iodine sources and/or the hypervalent-iodine reagents. A combination of tetrabutylammonium iodide (TBAI) and (diacetoxyiodo)benzene (PIDA) selectively generates 1-iodoalkynes, while a combination of KI and PIDA generates 1,2-diiodoalkenes. A one-pot synthesis based on both TBAI-PIDA and KI-PIDA yields the corresponding 1,1,2-triiodoalkenes. These protocols were subsequently applied to the synthesis of synthetically important aromatic and aliphatic 1-iodoalkynes, 1,2-diiodoalkenes, and 1,1,2-triiodoalkenes, which were obtained in good yield with excellent chemoselectivity.

Chemoselective and stereospecific iodination of alkynes using sulfonium iodate(i) salt

The sulfonium iodate(i) electrophilc reagent efficiently promoted the stereodivergent iodination of alkynes. The chemoselective iodination was effectively realized by switching the solvent system to access the 1-iodoalkyne and (E)-vicinal-diiodoalkenes.