Synthesis and applications of rhodacyclopentanones derived from C–C bond activation

Abstract

Rhodacyclopentanones, an "sp(3)-rich" class of metallacycle, underpin an emerging range of catalytic methodologies for the direct generation of complex scaffolds. This review highlights strategies for accessing rhodacyclopentanones (and related species) by C-C bond activation of cyclobutanones or cyclopropanes. The scope and mechanism of methodologies that exploit these activation modes is outlined.

RhI‐Catalyzed Carbonylative [3+1] Construction of Cyclobutenones via C−C σ‐Bond Activation of Cyclopropenes

“…The reason for the regio‐divergent formation of C is not clear at this moment. The different Lewis basicity of directing group (X=C or SO) may account for the divergent oxidative addition . The selective migratory insertion of CO to the sp 2 carbon‐rhodium bond produces the key rhodacyclopentenone complex D while at the same time releasing of the strain energy of cyclopropene moiety.…”

Modular Access to Eight‐Membered N‐Heterocycles by Directed Carbonylative C−C Bond Activation of Aminocyclopropanes

“…In conclusion, we demonstrate the first examples of "capture-collapse" heterocyclizations that provide eight-membered rings.O ur strategy hinges on the tandem exploitation of strain relief and metallabicycle templating to overcome the usual enthalpic and entropic barriers associated with medium-sized ring closures.Significantly,this is achieved within the context of as tep-and atom-economical reaction design that is also well-suited to the introduction of stereodefined substituents.T hese studies add to ag rowing body of processes that exploit catalytic CÀCb ond cleavage of small rings to enable the synthesis of medium-sized rings. [8] The present method is unusual in the flexibility and stereocontrol that it allows.…”

“…[6,7] Under carbonylative conditions,c arbonyl-directed CÀCb ond activation of aminocyclopropanes 1 by Rh I catalysts leads to rhodacyclopentanones I. [8] From here, dissociation of the directing group enables metalation of ap endant nucleophile by the Rh III center to form 5,5metallabicyclic intermediate II ("capture") in advance of CÀ Nu bond-forming reductive elimination and protodemetalation ("collapse") to the targets." Capture-collapse" heterocyclizations of this type are,i np rinciple,w ell-suited to the synthesis of medium-sized rings (8-to 11-membered) because the templating effect of the metallabicycle and the release of the cyclopropane ring strain address the kinetic and thermodynamic impediments typical of conventional medium-sized ring closures.…”

“Cut and Sew” Transformations via Transition-Metal-Catalyzed Carbon–Carbon Bond Activation

“…26 Although different TMs have been extensively studied towards the activation of cyclopropane derivatives, their utilization in a “cut and sew” transformation was less-commonly seen in literature, majorly due to the facile β-hydrogen elimination side reaction from the metallacyclobutane complex. 27 Narasaka and coworkers in 1999 reported the first rhodium-catalyzed carbonylative addition with a tethered cyclopropane and alkyne (Scheme 13). 28 Though the presence of CO suppressed side-reactions, the reactions proceeded more slowly under increased CO pressure.…”