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.

The Construction of Molecular Complexity from Functionalized Alkylidenecyclopropanes (FACPs)

“…The breakthrough in the Rh I ‐catalyzed reactions of the FACPs 6 with unsaturated systems, such as alkenes, alkynes, carbon monoxide, and allenes, with the simultaneous cleavage of the distal C−C bond of the alkylidenecyclopropanes was demonstrated by the group of Evans, furnishing the complex ring systems 8 , 9 , 10 , and 11 . Notably, the key Rh III ‐cycle intermediate 7 through a trimethylenemethane (TMM)‐like transition state was isolated and confirmed by X‐ray crystallography, which strongly demonstrated the reaction process (Scheme ) …”

Rhodium‐Catalyzed [(3+2)+2] Carbocyclization of Alkynylidenecyclopropanes with Substituted Allenes: Stereoselective Construction of Tri‐ and Tetrasubstituted Exocyclic Olefins

“…1].H ence, the ability to readily access the bicyclo [5.4.0]undecane ring system, which is also present in an umber of important bioactive natural products,significantly expands the synthetic utility of this process. [16] Hence,t he Scheme 2. [16] Hence,t he Scheme 2.…”

“…[8,9] Nevertheless,r hodium-catalyzed higher-order carbocyclizations with exogenous allenes have an umber of inherent challenges.F or instance,c onjugated allenes are generally required since unactivated allenes are either unreactive or provide mixtures of constitutional isomers.M oreover,t he products from distal insertion are formed with poor geometrical control irrespective of the type of substituent on the allene.I na ddition, monosubstituted allenes are either unreactive or provide proximal insertion, thereby making this achallenging problem. [15][16][17] Interestingly,t he analogous process with cationic complexes also provided 3a as the major adduct, albeit in significantly lower yield (entries 2a nd 3). Additionally,t his process provides arare example of ahighly selective distal carbometalation of am ono-or 1,1-disubstituted allene in am etalcatalyzed cycloaddition reaction.…”

Oxygenation of Simple Olefins through Selective Allylic C−C Bond Cleavage: A Direct Approach to Cinnamyl Aldehydes

“…[3] Allyl groups have acted as important skeletons in organic synthesis. [4] In addition to considerable numbers of allylic CÀHb ond functionalization reactions, [5] cleaving the corresponding allylic C À Cbond is gaining increased interest and developing rapidly.T he obstacle of the allylic C À Cbond cleavage lies in the mismatch of the HOMO/LUMO orbitals of the nonpolar allylic s-bonds with the frontier orbitals of catalysts or reagents.T he known allylic CÀCb ond cleavage reactions usually rely on specific or functionalized substrates (Scheme 1a), including:1 )vinylcyclopropanes A,w hich are easily activated by releasing the ring strain, [6] 2) homoallylic alcohols B with an OH group to assist in intramolecular chelation of transition metals, [7] and 3) allylic derivatives C bearing electron-withdraw groups in order to polarize the allylic CÀC bond. [8] To the best of our knowledge,a llylic CÀC s-bond cleavage of unfunctionalized olefins remains an unsolved challenge.D eveloping ag eneral allylic C À Cb ond cleavage with wide substrate scope is thus highly desirable and would promote the straightforward application of easily accessible olefins.…”

“…(3)-(6)]. U nder standard conditions,[ D]-3a was converted into [D]-5a in 50 %y ield, with the deuterium located at the C=Cd ouble bond rather than the aldehyde [Eq.(3)].…”