Description: The Heck Reaction is a means of forming C-C bonds between alkenyl or aryl halides and alkenes, using a palladium catalyst.
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what is the advantage and disadvantage of heck reaction?
Regioselectivity is a disadvantage.
The Suzuki is generally the cross coupling of choice because boronic acids/esters are generally easy to prepare and are non-toxic.
The knock against the Stille is that it employs organotin compounds, which are toxic. One tries to avoid using it if necessary. On the other hand, it’s super-mild, which can be useful when you’re dealing with a very complex molecule with base-sensitive functional groups.
Straight up Heck reactions are less common since the specific site where the reaction happens on the alkene isn’t dictated by the presence of a group that transmetallates (unlike the Stille / Suzuki). The Heck is OK in simple cases and especially good in many intramolecular situations but the lack of complete predicability can be an issue.
I meant between the Heck, Suzuki, and Stille
Of the three, which is more favored and why?
You mean the starting palladium compounds? It doesn’t matter *too* much. For any given reaction one is seeking to optimize, the choice of Pd precatalyst is an important (but by no means the most important) variable to look into, but that’s not something I’m going to get into too deeply here.
One thing about Pd(PPh3)4 is that for a long time the commercially available stuff was really bad from a *certain* provider (*cough* Aldrich). I’m not sure if that’s still the case. Pd(2)dba(3) has a huge molecular weight so you have to weigh out quite a bit to get a reasonable catalyst loading. Pd(OAc)2 is a simple and cheap Pd precatalyst.
The product of triethylamine ligation of Pd(OAc)2 in the image link to the mechanism of Pd(0) formation from triethylamine and Pd(OAc)2 is missing an ethyl group. This makes the illustration of the beta hydride elimination a little more confusing in my opinion.
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