Tandem Cyclopropanation/Ring-Closing Metathesis of Dienynes

Abstract

Certain dienynes give cyclorearrangement by tandem cyclopropanation/ring-closing alkene metathesis, triggered by either a ruthenium carbene or noncarbene ruthenium(II) precatalyst. The process represents a variation of enyne metathesis where presumed cyclopropyl carbene intermediates undergo a consecutive ring-closing metathesis. A mechanistic proposal is offered, and sequential use of catalysts provided a tandem ring-closing enyne/alkene metathesis product.

Gold(I)‐Catalyzed Intermolecular Cyclopropanation of Enynes with Alkenes: Trapping of Two Different Gold Carbenes

“…Alternatively, III may undergo a 1,2-shift (pathway b) to form a new gold carbene V, which gives double cleavage rearrangement diene VI after a-hydrogen elimination. The double cleavage rearrangement can also take place directly from intermediate II to give V. Strong evidence for the existence of metal carbenes of type II has been obtained by intramolecular trapping with alkenes in ruthenium-, [5] platinum-, [6,7] and gold-catalyzed reactions. [4a, 8] We have recently shown that the anti arrangement of the carbene and the cyclopropane accounts for the configuration observed in all these intramolecular processes.…”

Ruthenium-catalyzed allylation reaction in ionic liquid

“…Moreover, the use of the same counteranion as that of the catalyst is always preferable as it prevents anion metathesis between the solvent and the catalytic species, which can modify the catalytic properties of the initial precatalyst. Concerning the cation, an important criteria to consider is the possible oxidative addition to the metal centre as reported for nickel, platinum and palladium [21], and the possibility to generate diaminocarbenes via hydrogen abstraction [22], which can coordinate the metal centre as suggested in some ruthenium-catalyzed metathesis reactions [23,24]. The presence of the ethylate anion generated in situ from carbonate 1 during the catalytic process might favour the latter transformation.…”

Inside the black box — Perspectives on transformations in catalysis

“…It also represents an expansion of our perspective on tandem catalysis, beyond manipulation of the active site, to consideration of the ligand architecture and properties best suited to meeting the demands unique to each stage of catalysis, including those of robustness and lifetime. Beyond hydrogenation, this approach holds promise for improving catalyst efficiency in tandem metathesis-functionalization reactions, emerging applications of which include RCM-oxidation (45,46) and RCM-cyclopropanation (47,48) methodologies.…”