| Research Abstract |
This research has been conducted in order to develop synthetically useful new carbon-carbon bond forming reactions based on theoretical design of organometallic reagent, which often exists as a cluster in solution. As an example of the c-C bond forming reaction with an organometallic cluster, we examined the addition of allylzinc chloride to vinyl Grignard reagent, which was first reported by Gaudemar in 1971 and has been developed by Normant and co-workers to be a synthetically useful reaction. We revealed, for the first time, that the formation of a Zn/Mg organometallic aggregate functions as a key intermediate to facilitate the addition reaction, and the formation of organozinc aggregate resulted in the stabilization of product to make the whole process thermodynamically favored one. In the course of our continuing study on the organometallic cluster reaction, we found that the vinyl boron substrate can be exploited as a reactive carbometalation acceptor. The mechanistic detail of the addition of allylzine reagent to vinylboronate was studied by using the DFT calculations. The reaction starts with the formation of σ-complex, in which zinc atom is bound to one of the two oxygens of boronic and ester. Two distinct reaction pathways, "bora-Claisen" pathway and "zincio-ene" pathway, were obtained as in the addition of allylzine reagent to vinyl boronate. In contrast to the allyizincation reaction, the addition of zincioenamine to vinylboronate proceeds via concerted six-membered chair and boat transitiion states. Low activation energy was required to effect the addition via the boat transition state, indicating high reactivity of the zincioenamine toward an olefinic double bond. Thus, the addition of zincioenamine to a simple alkene, such as 1-octene and allylbenzene, was examined and was proved to be a facile reaction under certain conditiions.
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