Zhu C, Liu J, Mai BK, Himo F, Bäckvall JE. Efficient Stereoselective Carbocyclization to
cis-1,4-Disubstituted Heterocycles Enabled by Dual Pd/Electron Transfer Mediator (ETM) Catalysis.
J Am Chem Soc 2020;
142:5751-5759. [PMID:
32101690 PMCID:
PMC7307908 DOI:
10.1021/jacs.9b13700]
[Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
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An efficient Pd/ETM
(ETM = electron transfer mediator)-cocatalyzed
stereoselective oxidative carbocyclization of dienallenes under aerobic
oxidation conditions has been developed to afford six-membered heterocycles.
The use of a bifunctional cobalt complex [Co(salophen)-HQ] as hybrid
ETM gave a faster aerobic oxidation than the use of separated ETMs,
indicating that intramolecular electron transfer between the hydroquinone
unit and the oxidized metal macrocycle occurs. In this way, a class
of important cis-1,4-disubstituted six-membered heterocycles,
including dihydropyran and tetrahydropyridine derivatives were obtained
in high diastereoselectivity with good functional group compatibility.
The experimental and computational (DFT) studies reveal that the pendent
olefin does not only act as an indispensable element for the initial
allene attack involving allenic C(sp3)–H
bond cleavage, but it also induces a face-selective reaction of the
olefin of the allylic group, leading to a highly diastereoselective
formation of the product. Finally, the deuterium kinetic isotope effects
measured suggest that the initial allenic C(sp3)–H bond cleavage is the rate-limiting step, which
was supported by DFT calculations.
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