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Hydrogen-bond-directed catalysis: Faster, regioselective and cleaner Heck arylation of electron-rich olefins in alcohols
被引:59
作者:
Hyder, Zeynab
[1
]
Ruan, Jiwu
[1
]
Xiao, Jianliang
[1
]
机构:
[1] Univ Liverpool, Dept Chem, Liverpool Ctr Mat & Catalysis, Liverpool L69 7ZD, Merseyside, England
基金:
英国工程与自然科学研究理事会;
关键词:
alcohols;
Heck reaction;
hydrogen bonds;
palladium catalysis;
regioselectivity;
D O I:
10.1002/chem.200800411
中图分类号:
O6 [化学];
学科分类号:
0703 ;
摘要:
A general method for the regioselective Heck reaction of electron-rich olefins is presented. Fast, highly regioselective Pd-catalysed alpha-arylation of electron-rich olefins, vinyl ethers (1a-d), hydroxyl, vinyl ethers (1e,f), enamides (1g,h) and a substituted vinyl ether (1i) has been accomplished with a diverse range of aryl bromides (2a-r), for the first time, in cheap, green and easily available alcohols with no need for any halide scavengers or salt additives. The reaction proceeds with high efficiency, leading exclusively to the a-products, in 2-propanol and particularly in ethylene glycol. In the latter, the arylation can be catalysed at a palladium loading of 0.1 mol% and finish in as short a time as 0.5 h. The remarkable performance of the alcohol solvents in promoting a regiocontrol is attributed to their hydrogen-bond-donating capability, which is believed to facilitate the dissociation of halide anions from Pd-II, and hence, the generation of a key ionic Pd-II-olefin intermediate responsible for the alpha product. This belief is further strengthened by the study of a benchmark arylation reaction in 21 different solvents. The study revealed that exclusive alpha-regioselective arylation takes place in almost all of the protic solvents, and there is a rough correlation between the alpha-arylation rates and the solvent parameter E-T(N). The method is simpler, cleaner and more general than those established thus far.
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页码:5555 / 5566
页数:12
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