3 years ago

Mechanistic Study on Platinum-Catalyzed Domino Reaction of Benziodoxole and Pyrrole Homopropargylic Ethers for Indole Synthesis

Mechanistic Study on Platinum-Catalyzed Domino Reaction of Benziodoxole and Pyrrole Homopropargylic Ethers for Indole Synthesis
Yuxia Liu, Yuan-Ye Jiang, Xiaoping Man, Siwei Bi
Benzene ring functionalization provides useful alternatives to access indole derivatives and has received much attention in recent years. In this work, the mechanism of Pt(II)-catalyzed cyclization/alkynylation of benziodoxole with pyrrole homopropargylic ethers to generate C5-alkenylated indole derivatives has been studied with the aid of density functional theory (DFT) calculations. We found that five-membered-ring cyclization/six-membered-ring cyclization is competitive in the formation of an indole skeleton. The following aromatization stage prefers the reaction sequence bicarbonate-assisted deprotonation at the C3a position, H2CO3-promoted methoxy elimination at the C7 position, and bicarbonate-assisted deprotonation at the C6 position. In the last alkynylation stage, the oxidative substitution mechanism assisted by H2CO3 is found to be favored over the previously proposed 1,2-iodo shift and oxidative addition. The overall rate-determining step is oxidative substitution. Additionally, an interesting substituent effect on chemoselectivity was investigated. The electronic and steric effects caused by methyl result in reverse chemoselectivity.

Publisher URL: http://dx.doi.org/10.1021/acs.organomet.7b00338

DOI: 10.1021/acs.organomet.7b00338

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