The Isolation and Characterization of a Rhodacycle Intermediate Implicated in Metal‐Catalyzed Reactions of Alkylidenecyclopropanes

Abstract

The isolation and characterization of a rhodacycle intermediate implicated in rhodium‐catalyzed reactions of alkylidenecyclopropanes (ACPs) is described. The structure of the metallacycle was unambiguously determined by X‐ray crystallography and is catalytically competent in the rhodium‐catalyzed carbocyclization and ene‐cycloisomerization reactions of ACPs. This work represents a rare example of the isolation of a metallacycle in a metal‐catalyzed higher‐order carbocyclization reaction and thereby provides important insight into the ligand requirements for the insertion of π‐components. Furthermore, it serves as a convenient synthon for the development of challenging higher‐order carbocyclization reactions, as exemplified by the reaction with an activated allene.

Catalytic C–C Bond Activations via Oxidative Addition to Transition Metals

“…Regio- and diastereoselective intermolecular rhodium-catalyzed [3 + 2+2]-carbocyclization reactions of ACPs 87 with activated alkynes for the construction of the bicycloheptadienes 92 were reported (Scheme a) . The proposed mechanism is supported by the isolation and characterization of rhodacyclic intermediates . Carbon- and heteroatom-tethered ACPs 87 bearing mono- or disubstituted alkynes are tolerated in the reation.…”

Recent Methodologies That Exploit C–C Single-Bond Cleavage of Strained Ring Systems by Transition Metal Complexes

“…Subsequent studies succeeded in isolating and characterizing neutral rhodium complexes related to 27; these underwent insertion of alkynes and CO and were also shown to be catalytically competent. 44 By employing these isolable metallacycles as a starting point, (3 + 2 + 2) cycloadditions involving exogenous allenes were demonstrated, and this led to a catalytic protocol (Scheme 9). 45 The approach enables the preparation of challenging seven-membered rings bearing allene-derived triand tetrasubstituted exocyclic olefins; the geometry of this unit is controlled by preferential syn-carbometalation of the less hindered face of the terminal allene π-bond.…”