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Controlling Selectivity in Cross-Couplings of Dihalo(hetero)arenes

http://neufeldt-chemistry.com/group/


Abstract:Pd-catalyzed cross-coupling reactions are among the most powerful transformations in organic synthesis. Nevertheless, controlling selectivity can be problematic whenemploying substrates with more than one (pseudo)halide. Two such challenges are discussed in this presentation. Overfunctionalization is one challenge: it can be difficult to control even withcarefully tuned stoichiometry. We have investigated the mechanistic origin of ligand effects on controlling between mono- versus diarylation in Suzuki cross-couplings. Ligand sterics influence thecompetition between two pathways: a bimolecular mechanism for dissociation of the mono-coupled product from Pd versus a second oxidative addition event. Our studies provide insight into strategies tominimize (or maximize) polyfunctionalization in cross-coupling reactions. This presentation will also describe another selectivity challenge that arises with dihalogenated heteroarenes. Mostdihaloheteroanes undergo cross-coupling reactions with a strong preference for breaking one C–halide bond over the other. For a few such substrates, catalyst-controlled approaches have been describedthat enable inversion of the conventional site selectivity. However, 2,4-dihalopyrimidines are particularly resistant to change: they always undergo cross-coupling at C4, and SNAr reactions also tendto favor that site. We recently developed a method to preferentially cross-couple at the C2 position of 2,4-dihalopyrimidines. The selectivity is surprising, and preliminary mechanistic investigationsuggests that C—X cleavage does not take place through a traditional oxidative addition mechanism.

Building character means to strengthen and incorporate virtues such as kindness to develop self-reliance and how to set boundaries.

Start off your semester with a good plan in place! This one-hour workshop discusses easy-to-apply strategies for overcoming the procrastinatory tendencies that impede a healthy work-life balance.Reasonable time-management tips will be offered to restore a sense of control as well as methods for mitigating the anxiety, fatigue, or strain seeded by successive all-nighters. Lastly, triagetactics for particularly daunting circumstances will be covered.

This workshop will be held over Zoom:
https://uvic.zoom.us/j/97389771497
(*no passcode)

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Join us for "Sacred Steps", a transformative program that invites you to embark on a journey of self-discovery through walking meditation, barefoot walking, and nature walks. Immerse yourself inthe beauty of Finnerty Gardens, Mystic Vale, and other enchanting locations around the campus.

Yoga is a mind and body practice. Yoga for meditation combines physical postures, breathing techniques, and relaxation. Yoga involves movement, meditation, and breathing techniques to promotemental & physical well-being.