Intermolecular carbometallation

The intermolecular carbometallation reaction catalyzed by transition metals from groups 8 to 11 has been fully investigated during the last decade. Many examples have been reported in the literature concerning different metals in order to create C-C bonds. Overview of this powerful method will be given as exhaustively as possible and carbometallation reactions will be classified according to unsaturated systems. 

Trost reported the synthesis of 1,4-dienes with ruthenium catalysis through regioselective carbometallation of alkynes with alkenes.51 Di- and trisubstituted olefins can also be obtained with arylboronic acids through an intermolecular process under rhodium,30 52 55 nickel,56 and palladium catalysis.57 Recently, Larock has reported an efficient palladium-catalyzed route for the preparation of tetrasubstituted olefins.58,59... 

The vinyl metal intermediate arising from intermolecular nucleophilic addition of an oxygen nucleophile to a metal-alkyne complex has been harnessed for further transformations prior to protonation. An example is the ruthenium-catalyzed benzannulation of 1,5-enedyines that occurs through a tandem sequence involving hydroalk-oxylation, carbometallation, and protonation (Equation (82)).293... 

Scheme 2.48. Intermolecular and intramolecular carbometalation of alkynes with copper-zinc reagents.

Intermolecular carbometallations are typically accomplished with organolithiums however, dia-stereocontrolled intramolecular carbometallation can be attained with appropriate Grignard reagents, as exemplified in Scheme 88, the suprafacial and 5-exo-trig closure of ( )-6-bromo-3-methyl-1 -trimethylsi-lyl-1-hexene (267) to fraru-l-methyl-2-(trimethylsilyl)methylcyclopentane (268).203... 

Vicinal Difunctionalization of Alkenes and Acetylenes via Intermolecular Carbometallation 225... 

Cyclic amino-carbenes, in molybdenum carbonyls, 5, 457 Cyclic bis(phosphine) dichlorides, with iron carbonyls, 6, 48 Cyclic carbenes, as gold atom ligands, 2, 289 Cyclic carbometallation, zirconium complexes, 10, 276 Cyclic carbozirconation characteristics, 10, 276 intermolecular reactions, 10, 278 intramolecular reactions, 10, 278 Cyclic dinuclear ylides, and gold , 2, 276 Cyclic 1,2-diols, intramolecular coupling to, 11, 51 Cyclic enones, diastereoselective cuprate additions, 9, 515 Cyclic esters, ring-opening polymerization, via lanthanide catalysis, 4, 145 Cyclic ethers... 

An interesting sequence based on an intermolecular Michael addition and a subsequent transition metal-catalyzed carbocyclization was recently explored. Much of the development of this strategy relies on recent studies related to the intramolecular carbometalation reaction of stabilized carbanions bearing an unactivated alkynyl group. Several transition metal complexes such as Cu [52], Pd [53], Ti [54], Zn [55], Co [56] and Sn [57] have been reported to catalyze this reaction (Scheme 17). 

This chapter is intended to highlight recent results in the fields of intra- and intermolecular carbometallation, but we will concentrate only on the chemistry of lithium and zinc derivatives. Although the Group IV metallocene-mediated reductive cyclizations of enynes [36] and dienes [36], and the use of transition metals of Group VIII, as well as the more recent development of the organolanthanide chemistry [37] followed by selective reaction with different electrophiles [36], represent an important methodology for the construction of polysubstituted carbocycles, they will not be addressed here. 

The addition of an organometallic to an unactivated olefin is generally difficult to control since such an addition may lead to polymerization of the olefin unless the final organometallic adduct is stabilized, or has a structural modification. Thus, no general reaction for the intermolecular carbometallation of alkenes is known, although since the last review concerning this topic [3], many relevant papers have appeared. 

Scheme 8.86 Intermolecular carbometallation and subsequent cyclization of o-alkynylaniline derivatives [500].

An interesting sequential reaction, consisting of an intermolecular alkene carbometallation and subsequent intermolecular alkyne cross-coupling, has been reported (Scheme 8.87) [601]. Starting from an immobihzed tropane framework 459, stoichiometric carbopalladation yields a stable organopalladium intermediate, which in the presence of copper(I) iodide undergoes coupling with an added terminal acetylene. 

Scheme 10.38 Protocol for the copper-catalyzed directed intermolecular carbometallation of...

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