I want to synthesis the benzofuran by larock reaction, but it always fails.
In my case, I used an iodine compound, NaHCO3, (Pph3)PdCl2, LiCl, internal alkyne compound and DMF as a solvent at 110oC reaction.
The first time, I used a condenser.
NaHCO3 at this temp production H2O reflux, and the reaction only produces a 3 % yield.
Now, I don't know how to fix this problem.
Should I change the base or not use a condenser? are there any other kind suggestions that can help me fix this problem?
I referenced these articles for synthesis.
http://www.pubfacts.com/fulltext_frame.php?PMID=22669348&title=Synthesis%20of%20anti-HIV%20lithospermic%20acid%20by%20two%20diverse%20strategies.
Article Synthesis of anti-HIV lithospermic acid by two diverse strategies
Are you reproducing the reaction exactly, or are you doing a variation? If the yield is only 3%; what happens to the rest of it? Do you see a lot of "tarring"? Have you tried adding a spatula of catalyst after eg. 3 hrs? Perhaps you can try to substitute (PPh)4Pd as catalyst; that's generally more efficient.
There are apparently a lot of ways to make benzofurans, Personally, I hadn't seen this decarboxylative method before; perhaps some other procedure is more reliable? You may find some alternative routes here: http://www.organic-chemistry.org/synthesis/heterocycles/furans/benzo[b]furans.shtm
The method reported will be extremely sensitive to electronic factors. Both the electron poor alkyne and the aldehyde adjacent to the iodine in their substrate act strongly in favour of product formation.
Mechanistically the reaction most likely occurs via a Michael type addition to the alkyne followed by an intramolecular Heck reaction.
As suggested above, tetrakis is worth trying, potentially you could also change metals to something more alkynophilic such as a Au(I) catalyst. A catalytic quantity of CuI or a silver salt can aid the oxidative addition across the Aryl-Iodide bond.
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