Recent Developments in Enantioselective Gold(I) Catalysis

Recent Developments in Enantioselective Gold(I) Catalysis -...

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Unformatted text preview: Click to edit Master subtitle style 4/9/10 Recent Developments in Enantioselective Gold(I) Catalysis Based on Ross A. Wildenhoefer (not McMurry) Presented By Avi Novick 11 4/9/10 Contents-The Main Points-Introduction-Body:- Addition of Carbon Nucleophiles to Alkynes. - Enantioselective ∏ Activation of Allenes.- Addition of Carbon Nucleophiles to Allenes.- Carbon-Heteroatom bond formation.- Hydrofunctionilization with Chiral Anions.- Cyclopropanation of Vinyl Arenes.- Conclusions and Outlook. 22 4/9/10 The main points: ① Over the past ten years, the use of gold(I) complexes to drive reactions has become more popular. Using this method has led to some useful carbon-carbon and carbon-heteroatom bond forming techniques. ② Even more recently, using gold(I) for enantioselective catalysis has become more popular now that the gold(I) has become more controllable. The problem before (which still exists to a lesser extent) was that gold(I) forms a dual linear coordinate complex- making enantioselectivity very hard obviously. The most notable of the enantioselectivities is hydrofunctionilization of allenes. 33 4/9/10 Introduction: As mentioned before, gold(I) catalysis for organic transformations has become common. For example: ● The use of cationic gold(I)-phosphine complexes is the main type of catalyst used in these transformations. ● The use of these complexes are particularly helpful for metathesis (the transfer of alkene and alkyne bonds) which can also lead to cycloisomerization. ● Also useful for hydrofunctionilization of allenes, alkenes and alkynes with carbon heteroatom nucleophiles. A heteroatom is something like this: THF All this is, is a carbon molecule with something else on it o 44 4/9/10 ● A common transformation is the pi-bond activation towards nucleophilic attack. Gold (I) is very good at doing this. For example, the [AuL]+ fragment is highly carbophilic, which allows the molecule being acted on to become electrophilic and susceptible to nucleophilic attack. Graphically: Au A u Nu: Au Nu H3O H Nu This is [AuL] ● Gold (I) is a soft metal , meaning that it is NOT oxophilic . Had it been oxophilic- it would be considered a hard metal. Meaning, gold(I) is not used to extract or exchange oxygen centers in organic compounds. What this means for the graphic reaction above is that if we react AuL+ with something like H20 we do not get AuO + HL. WHO CARES? Actually, we do. The whole point of this presentation is to show you that gold(I) can be used for enantioselectivity- so the first step is being chemoselective . 55 4/9/10 ● An advantage to using Gold(I): Some redox reactions (reactions in the presence of oxygen) may be deleterious ....
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Recent Developments in Enantioselective Gold(I) Catalysis -...

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