안자리 알카인을 이용한 3-methoxy-1, 6-enyne의 금 촉매 고리이성질화 반응 연구
- 안자리 알카인을 이용한 3-methoxy-1, 6-enyne의 금 촉매 고리이성질화 반응 연구
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- In organic synthesis, developing new method to make chemical bond is one of the most important issues. Besides of classical method, the method using catalyst can solve the problems since it needs only small amount of catalyst. Many transition metal elements show catalytic activity. Among them, catalytic reactions using palladium (Pd), platinum (Pt), ruthenium (Ru) have been studied.
Gold was considered as noble metal, which showed no chemical activity. However, in 1980s, it is known that gold can catalyze oxidation of CO. In 2000s, moreover, the alkyne coordinating ability of gold was found and examined by relativistic effect. Nowadays, gold(I) catalysis is considered as one of the most powerful strategies to make diversity in the reaction method.
There are some specialties of gold such as alkynophilicty, reactivity of weak nucleophiles, free from oxidation-reduction. Because of these specialties, gold(I) catalysis coupled with various nucleophiles has been developed.
However, it shows some limitations in application to diverse alkynes. Generally, gold(I) catalysis shows totally different result from terminal and internal alkyne because of its cis-addition feature. Internal alkyne and terminal alkyne show lager difference with exo-mode addition than endo-mode addition in gold(I) catalysis. Generally, internal alkyne shows endo-selectivity and low activity in reaction including exo-mode addition.
The reactivity and selectivity in gold(I) catalyzed cycloisomerization of 3-methoxy-1,6-enyne with internal alkyne was envisioned in this study.
Beside of methyl and SePh group, CO2Me group substituted alkyne shows high reactivity in the cycloisomerization. When the side product was depressed by addition of 2,6-DBP, the yield of the cycloisomerization with CO2Me group substituted alkyne was comparable to that of terminal one.
Encouraged by this result, the stereochemistry of CO2Me substituted alkyne was also confirmed. After the cycloisomerization which forms two sterogenic centers, the only one stereoisomer was obtained. To confirm the stereochemistry of the product, the known compound, whose structure was confirmed by X-ray crystallography, was synthesized by hydration and decarboxylation. The two compounds are identical and also matched with the structure by theoretical prospect.
The scope of the CO2Me was expanded to various substrates. Similar result to terminal alkyne was given with substrate generated from tertiary alcohol. On contrary, the reaction with substrate generated from secondary alcohol showed different behavior and it was hard to generalize. The possible explanation for this behavior was also suggested. The further studies on the mechanism and application were on progress.
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