musings on music and life

August 27, 2013

enantioselective alkene dibromination

Filed under: Chemistry — Tags: — sankirnam @ 10:39 am

The chiral functionalization of alkenes has been a hot topic for a while in organic chemistry. K. B. Sharpless (Scripps) received the Nobel Prize in 2001 for his eponymous reactions – asymmetric epoxidation (AE), asymmetric dihydroxylation (AD), and asymmetric aminohydroxylation (AA). These were groundbreaking in that they were robust, reproducible, and predictable; the desired enantiomer could be easily synthesized by using the appropriate chiral ligand. Although tremendous progress has been made since then in asymmetric catalysis (especially in the area of asymmetric organocatalysis), there has not been any new reactions developed for the enantioselective difunctionaliztion of olefins since the work of Sharpless.

Nicolaou published a paper in 2011 revealing his efforts in developing a enantioselective dichlorination reaction of allylic alcohols, but theĀ ee‘s obtained were only moderate. This is understandable since the intermediate involves a halonium ion, which has a tendency to racemize. That being said, I came across this paper in JACS last week. The corresponding author is an assistant professor at Stanford and it appears that this is his first publication as a faculty; he’s gotten his career off to a good start! By revisiting Sharpless’s titanium catalysis and combining that with Seebach’s TADDOL ligands, he was able to come up with a catalytic system for enantioselective olefinĀ dibromination! The kicker is that he also used a dibromomalonate as the bromine source. He mentions that that particular compound has not seen much use as a bromination reagent in the literature; it just goes to show that thoroughly reading the literature can yield big benefits.

I’m keeping my eyes peeled for more cool publications from this group…

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