Formal and standard ruthenium-catalyzed [2 + 2 + 2] cycloaddition reaction of 1,6-diynes to alkenes: a mechanistic density functional study

The Journal of Organic Chemistry
Jesús A VarelaCarlos Saa

Abstract

"Formal" and standard Ru(II)-catalyzed [2 + 2 + 2] cycloaddition of 1,6-diynes 1 to alkenes gave bicyclic 1,3-cyclohexadienes in relatively good yields. The neutral Ru(II) catalyst was formed in situ by mixing equimolecular amounts of [Cp*Ru(CH3CN)3]PF6 and Et4NCl. Two isomeric bicyclic 1,3-cyclohexadienes 3 and 8 were obtained depending on the cyclic or acyclic nature of the alkene partner. Mechanistic studies on the Ru catalytic cycle revealed a clue for this difference: (a) when acyclic alkenes were used, linear coupling of 1,6-diynes with alkenes was observed giving 1,3,5-trienes 6 as the only initial reaction products, which after a thermal disrotatory 6e-pi electrocyclization led to the final 1,3-cyclohexadienes 3 as probed by NMR studies. This cascade process behaved as a formal Ru-catalyzed [2 + 2 + 2] cycloaddition. (b) With cyclic alkenes, the standard Ru-catalyzed [2 + 2 + 2] cycloaddition occurred, giving the bicyclic 1,3-cyclohexadienes 8 as reaction products. A complete catalytic cycle for the formal and standard Ru-catalyzed [2 + 2 + 2] cycloaddition of acetylene and cyclic and acyclic alkenes with the Cp*RuCl fragment has been proposed and discussed based on DFT/B3LYP calculations. The most likely mechanism for ...Continue Reading

References

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Jun 20, 2002·Journal of the American Chemical Society·Barry M Trost, Anthony B Pinkerton
Oct 2, 2003·Journal of the American Chemical Society·Yoshihiko YamamotoKenji Itoh
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Jun 29, 2006·Journal of the American Chemical Society·Vincent GandonCorinne Aubert
Jul 20, 2006·Journal of the American Chemical Society·Jesús A VarelaCarlos Saa
Jun 26, 2007·Journal of the American Chemical Society·Nicolas AgenetCorinne Aubert

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Citations

Feb 27, 2016·Chemistry : a European Journal·Gema Domínguez, Javier Pérez-Castells
Mar 25, 2011·Chemical Society Reviews·Gema Domínguez, Javier Pérez-Castells
Sep 4, 2008·Chemistry : a European Journal·Silvia García-RubínCarlos Saá
Feb 13, 2021·Chemical Reviews·Rosalie S DoerksenMichael J Krische
Oct 2, 2008·Journal of the American Chemical Society·Matthew CarnesColin Nuckolls
Feb 5, 2015·The Journal of Organic Chemistry·Silvia AlvarezJavier Pérez-Castells

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