[Show abstract][Hide abstract] ABSTRACT: Fluorinated methoxy arenes are emerging as important motifs in both agrochemicals and pharmaceuticals. A novel technique for the synthesis of monofluoromethoxy arenes through the direct fluorodecarboxylation of carboxylic acids was developed that uses photosensitizers and N-fluorobenzenesulfonimide (NFSI). Utilization of the oxidatively mild fluorine transfer agent NFSI enabled the synthesis of fluoromethyl ethers that were previously inaccessible with decarboxylative fluorinations performed with Selectfluor. Mechanistic studies are consistent with the photosensitizer effecting oxidation of the aryloxyacetic acid.
Preview · Article · Feb 2015 · European Journal of Organic Chemistry
[Show abstract][Hide abstract] ABSTRACT: Radical relay cyclizations initiated by alkoxy radicals are a powerful tool for the rapid construction of substituted tetrahydrofurans. The scope of these relay cyclizations has been dramatically increased with the development of two strategies that utilize an oxygen atom in the substrate to accelerate the desired hydrogen atom transfer (HAT) over competing pathways. This has enabled a chemoselective 1,6-HAT over a competing 1,5-HAT. Furthermore, this allows for a chemoselective 1,5-HAT over competing direct cyclizations and beta-fragmentations. Oxygen-atom incorporation leads to a general increase in cyclization diastereoselectivity over carbon analogs. This chemoselective relay cyclization strategy was utilized in the improved synthesis of the tetrahydrofuran fragment in (-)-amphidinolide K.
No preview · Article · Dec 2014 · The Journal of Organic Chemistry
[Show abstract][Hide abstract] ABSTRACT: Coming to light: The title reaction simply requires an aqueous alkaline solution of Selectfluor and light. The method is inexpensive and effective for a wide range of neutral and electron-poor 2-aryloxy and 2-aryl acetic acids to provide fluoromethyl ethers and benzyl fluorides, respectively. The mechanism most likely proceeds through an initial aryl excitation with a subsequent single-electron transfer.
No preview · Article · Oct 2012 · Angewandte Chemie International Edition
[Show abstract][Hide abstract] ABSTRACT: The development of new synthetic technologies for the selective fluorination of organic compounds has increased with the escalating importance of fluorine-containing pharmaceuticals. Traditional methods potentially applicable to drug synthesis rely on the use of ionic forms of fluorine (F(-) or F(+)). Radical methods, while potentially attractive as a complementary approach, are hindered by a paucity of safe sources of atomic fluorine (F(•)). A new approach to alkyl fluorination has been developed that utilizes the reagent N-fluorobenzenesulfonimide as a fluorine transfer agent to alkyl radicals. This approach is successful for a broad range of alkyl radicals, including primary, secondary, tertiary, benzylic, and heteroatom-stabilized radicals. Furthermore, calculations reveal that fluorine-containing ionic reagents are likely candidates for further expansion of this approach to polar reaction media. The use of these reagents in alkyl radical fluorination has the potential to enable powerful new transformations that otherwise would take multiple synthetic steps.
Full-text · Article · Mar 2012 · Journal of the American Chemical Society
[Show abstract][Hide abstract] ABSTRACT: This study examines the chemoselectivity of alkoxy radical cyclizations onto silyl enol ethers compared to competing cyclizations, 1,5-hydrogen atom transfers (1,5-HATs), and β-fragmentations. Cyclization onto silyl enol ethers in a 5-exo mode is greatly preferred over cyclization onto a terminal alkene. The selectivity decreases when any alkyl substitution is present on the competing alkene radical acceptor. Alkoxy radical 5-exo cyclizations displayed excellent chemoselectivity over competing β-fragmentations. Alkoxy radical 5-exo cyclizations onto silyl enol ether also outcompeted 1,5-HATs, even for activated benzylic hydrogen atoms. In tetrahydropyran synthesis, where 1,5-HAT has plagued alkoxy radical cyclization methodologies, 6-exo cyclizations were the dominant mode of reactivity. β-Fragmentation still remains a challenge for tetrahydropyran synthesis when an aryl group is present in the β position.
No preview · Article · Aug 2011 · The Journal of Organic Chemistry
[Show abstract][Hide abstract] ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
[Show abstract][Hide abstract] ABSTRACT: An efficient method for the rapid construction of carbo- and heterocycles has been developed using radical relay cyclizations initiated by alkoxy radicals. Linear substrates were cyclized to form a wide range of cyclopentane, pyrrolidine, tetrahydropyran, and tetrahydrofuran derivatives in excellent yields. This methodology was utilized as a key step in the synthesis of the tetrahydrofuran fragment in (-)-amphidinolide K.