Construction of linear-fused tricyclopentanoids by intramolecular [6 + 2] cycloadditions of fulvenes with enamines

An overview of the cycloaddition chemistry of fulvenes and emerging applications

“…This unusual reactivity is hypothesised to be due to an increased electron density in the 6-aminofulvene π-system [96], which would increase the nucleophilic character, and stabilise the fulvene system (see dipolar forms in Scheme 1). Similar results have been observed by other groups [32,96,124,203].…”

“…The synthesis of the listed organic molecules (Table 3) is generally successful, with high yields in almost all cases. However, some of these synthetic pathways are multistep [124], hence require optimisation for viability and large-scale production.…”

The Game of Electrons: Organocatalytic Higher‐Order Cycloadditions Involving Fulvene‐ and Tropone‐Derived Systems

“…In 2011, Hayashi reported an intramolecular [6+2]‐cycloaddition reaction of fulvenes 3 substituted at the exocyclic 6‐position with a δ‐formylalkyl group (Scheme ) . The contribution was inspired by a previous report by Wu and Houk, who reported a similar reactivity employing stoichiometric amount of achiral secondary amine . The [6+2]‐cycloaddition was realized in the presence of diphenylprolinol silyl ether 4 a as the catalyst allowing for the activation of 3 through the formation of enamine 6 .…”

“…[13] The contribution was inspired by ap revious report by Wu and Houk,w ho reported as imilarr eactivity employing stoichiometric amount of achiral secondary amine. [14] The [6+ +2]-cycloaddition was realizedi nt he presence of diphenylprolinol silyl ether 4a as the catalysta llowing for the activation of 3 through the formation of enamine 6.I nt his structureb oth the triene (fulvene system)a nd trienophile (enamine double bond) motifs are incorporated. Authorso btained 11 useful linear triquinane derivatives 5 in an enantio-and diastereoselective manner.T he reactionw as applicable with different substituents at the 6-position with good yields and stereoselectivity.A uthorsa lso per-Scheme4.New terminology of reactantsf or higher-order cycloadditions.…”

Diarylprolinol Silyl Ethers: Development and Application As Organocatalysts

“…Compared to the well-established [4þ2] cycloaddition reactions, very few [6þ2] cycloaddition reactions are known [43]. Although a racemic version of this intramolecular [6þ2] cycloaddition reaction (and its reaction mechanism) has been demonstrated by the Houk group [44], an asymmetric catalytic version of this chemistry had not been previously reported. When a linear substrate 53 was exposed to a catalytic amount of 9, a [6þ2] cycloaddition reaction proceeded to afford the tricyclic compound 54 [45].…”