Alkene Synthesis: Activating Iodoniums

research highlights

ALKENE SYNTHESIS Activating iodoniums J. Am. Chem. Soc. 135, 5332–5335 (2013) © 2013 AAAS Tetrasubstituted alkenes are found in a variety of biologically active natural compounds, drugs and functional materials, but methods for their synthesis are limited. Steric congestion around the double bond Welcome to the club is problematic for the classic Wittig-type Twitter’s new #chemclub aims to help you reactions in terms of both substrate scope find exciting chemistry to read. and stereoselectivity. There has been much recent interest in the use of metal catalysts A weekly laboratory journal club is a great to activate alkynes towards reaction with way to encourage researchers to read nucleophiles, however, a polarity-reversed the literature and share their enthusiasm process — activating a carbon electrophile for great pieces of chemistry. Writing at that can also be used to create synthetic drug- towards reaction with an alkyne — which Behind NMR Lines, Andrew Bissette found delivery systems. However, fabricating such looks reasonable on paper, has not received that he often caught wind of interesting extended three-dimensional structures with the same attention. Now, Matthew Gaunt papers via the watchful eyes of the a predetermined geometry requires control and co-workers from the University of chemistry crowd on Twitter. So he came over the interactions that drive assembly. Cambridge have reported a copper(i) up with an idea (http://go.nature.com/ Now, Derek Woolfson and co-workers at catalysed addition of diaryl- or vinyl(aryl) pHRRZI): why not form an online journal the University of Bristol, UK, have designed iodonium triflates to alkynes. club that draws attention to ‘cool papers’ peptides that self-assemble to form dimer Gaunt and co-workers have previously and spark some discussion? Thus began or trimer bundles, which themselves self- shown copper catalysts could activate #chemclub. assemble to form hollow peptide cages. diaryliodonium salts towards reaction with Chemists of the Twitterverse have The peptides are derived from sequences π-electron-rich nucleophiles such as indoles thrown themselves in with wild abandon. known to assemble into a coiled-coil or anilines and wondered if this could be Andrew posts weekly round-ups of the arrangement. One peptide was tailored extended to reaction with alkynes. It is best material, and the contributions so far to ensure that it self-assembles into a believed that the hypervalent iodine reagent range from the most cutting-edge total homotrimer. Adding peptides to the outside reacts with the copper catalyst to give a Cu(iii) syntheses (http://go.nature.com/v7UX4z) edges of the homotrimer — through complex, which then reacts with the alkyne to the dusty old classics of yesteryear disulfide bridges — enabled the formation to give a vinyl copper triflate intermediate. (http://go.nature.com/jmWc1Q). Anyone of hexamer peptide hubs. To create a larger Reductive elimination would then return can join in with #chemclub, so if you’re array, Woolfson and co-workers formed two the copper(i) catalyst and produce the vinyl reading a truly fascinating (or even slightly different hexamer hubs by adding two different triflate product. In general, disubstituted weird) paper, why not let the rest of us peptides to the outside of the homotrimer. alkynes react to produce Z-alkenes. And know about it? These additional peptides were designed to addition to unsymmetrical alkynes proceeds Meanwhile, JessTheChemist who dimerize with each other, therefore mixing with useful regioselectivity when the writes at The Organic Solution has these two hubs created a hexagonal array in substituents are sterically or electronically been wondering just how academically which homotrimers, at the vertices of the array, differentiated. Despite some potential pitfalls, interconnected the online chemistry are linked together by heterodimers. terminal alkynes and even acetylene itself community really is. Jess started out Naively, one might expect the hexagonal were also shown to be suitable substrates building her own chemistry ‘family tree’, array to form an extended planar structure, for the reaction. As yet, only a few examples but the project has since blossomed however, microscopy experiments showed are described involving transfer of an aryl and is still growing (http://go.nature. that spherical particles were formed. These group (rather than vinyl) from the iodonium com/7z3QXf). We’re encouraged to add particles were hollow with a unilamellar reagent — which may be due to the need to our own branches to the tree and who construction — rather than being solid or synthesize the iodine reagents, or perhaps to a knows where your branch might lead. formed with multiple walls — and Woolfson problem in controlling which of two groups is Perhaps even to the not-long-departed and co-workers called them self-assembled transferred to the copper catalyst. Maggie Thatcher? And on that note, cage-like particles or SAGEs. The driving The synthetic utility of the vinyl triflate Kat Day of The Chronicle Flask (http:// force behind the formation of their spherical products is unquestionable as they were then go.nature.com/v2a63E) tells us to cage structure is unclear; however, the shown to undergo a wide variety of palladium- ‘never mind the politics’, Thatcher will extended hexagonal array retains some catalysed cross-coupling reactions. Suzuki and always be one of those very famous flexibility, which enables it to bend and close Sonagashira couplings gave alkenes with four female chemists who ‘ignored the limits’ in on itself. Molecular dynamics simulations carbon substituents, and Buchwald–Hartwig (http://go.nature.com/togjya). Besides, also suggest that repulsion between positive type amination and Miyaura borylation gave once part of the club, always part of the charges at one end of the assembled peptides amido alkenes and alkenyl boronic esters, club, right? may contribute to the hexamer hubs adopting respectively, and all without loss of isomeric a more wedge-like shape. Forming SAGEs purity of the alkene. SD Written by Doctor Galactic, who blogs at also limits the number of unpartnered peptide www.doctorgalacticandthelabcoatcowboy. edges in the hexagonal array, and maximizes Written by Stuart Cantrill, Stephen Davey, wordpress.com the number of coiled-coil interactions. RJ Russell Johnson and Anne Pichon.

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