A Straightforward Procedure for the [2+2+2] Cycloaddition of Enediynes

Abstract

Enediynes undergo intramolecular [2 + 2 + 2] cycloaddition in the presence of cobalt(II) iodide (CoI 2 ), manganese and an N-heterocyclic carbene (IPr) generated in situ from the corresponding imidazolium salt and butyllithium (BuLi). Polycyclic cyclohexadienes are obtained selectively. This new method represents an interesting alternative to those employing air-sensitive cyclopentadi-Moreover, the N-heterocyclic carbene can be used catalytically, which is a significant improvement compared to the corresponding phosphine-based system which requires an excess of ligand.

Catalytic Version of Enediyne Cobalt‐Mediated Cycloaddition and Selective Access to Unusual Bicyclic Trienes

“…As an alternative to [Co(Cp)(L) 2 ] catalysts, we recently demonstrated that simpler and easier to handle systems consisting of CoX 2 /L/Mn could mediate the [2+2+2] cycloaddition of enediynes in an efficient manner 5. Lastly, replacement of the initial phosphine ligand L with catalytic amounts of N‐heterocyclic carbene (NHC) furnished a competitive system even if the need of a stoichiometric amount of cobalt salt is still necessary 6…”

“…[5] Lastly, replacement of the initial phosphine ligand L with catalytic amounts of Nheterocyclic carbene (NHC) furnished a competitive system even if the need of a stoichiometric amount of cobalt salt is still necessary. [6] Recently, a new reaction pathway was highlighted by both Saµ and our group during the study of the cycloaddition of a,w-diynes with alkenes by using ruthenium and cobalt complexes, respectively, as the catalyst for the cyclohexadiene formation. Depending on the cyclic or acyclic nature of the alkene partner Saµ et al obtained two different cyclohexadiene regioisomers, both formed from a classic ruthenacycloheptadiene intermediate.…”

Transition metal-catalyzed [2 + 2 + 2] cycloaddition of nitrogen-linked 1,6-diynes: a straightforward route to fused pyrrolidine systems

“…42 Co/Mncatalyzed intramolecular [2 + 2 + 2] cycloaddition of enediynes 63, provided unsaturated isoindolines 64 instead (Scheme 24b). 43 2.2.3. Chiral isoindolines.…”

Cobalt-Catalysed Bond Formation Reactions; Part 2

“…The intramolecular version of this type of [2+2+2] cycloaddition from an enediyne led to considerably better yields and the diastereoselective formation of tricyclic products, such as 148 (Scheme 79). 284 The strategy for the construction of tricyclic adducts derived by an intramolecular [2+2+2] cycloaddition from an enediyne was applied by Mulzer in the key step of the synthesis of pasteurestins A and B. The tricyclic intermediates, 149 and 150, were formed in acceptable yields, although the diastereoselectivity was not sufficiently controlled by the remote stereogenic centre.…”