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submitted on 21.01.2020 and posted on 22.01.2020by Yuji Naruse, Atsushi Takamori, Kenji Oda
For mechanism of
decarboxylation reaction, all textbooks show that the electron moves from the piC=O bond. However, the most donating bond orbital
in the carbonyl group should be the lone pair(s) on the oxygen. Thus, a picture of orbital theory with delocalization from a lone pair should be
more appropriate than that from the piC=O orbital. We confirmed our idea by theoretical
calculation. In the TS, if we use 2-substituted b-ketoacids,
the boat-form conformation should result in exclusively preferred generation of
E-enolates. Normally, decarboxylation
reaction performs in polar solvent, so that the resulting enols should be
transformed to the corresponding ketones by tautomerization. Suppose we use the
heteroatoms to obtain the enolate or enol ethers without tautomerization, it
would offer a diastereoselective enol(ate) synthesis with regioselectivity, since the C=C
double bond should always be introduced between two carbonyl groups. After
screening the heteroatoms by the theoretical
calculations, we found that boron is suitable for this purpose. We confirmed
our idea by theoretical calculations, offering a new boradecarboxylation
reaction to produce enolates diastereoselecitively and regioselectively.