Transmetallation substitution reactions

In general, the syntheses of these complexes are achieved through (i) nucleophilic addition/substitution reactions of silver(i) fluoride or (ii) transmetallation reactions with other metal alkyl, alkenyl, and aryl complexes. 

Aside from substitution reactions on silicon, interesting reactivity on SCB-substituted methylstannane has been described <2005CC3047>. Upon treatment of the mixed SCB/stannane substrate with -BuLi, transmetallation predominates over ring-opening and ambiphilic SCB-methyllithium can be generated (product formed after quenching with electrophile was isolated in 50-60% yield, Scheme 64). 

The last electrophilic substitution reaction of a Grignard compound we want to consider is a transmetalation, namely one that leads to an arylboronic ester (Figure 5.45). Arylboronic esters or their hydrolysis products, the arylboronic acids, are valuable reagents in modem aro-... 

Whereas uncatalyzed substitution reactions of organozinc compounds are limited to very reactive electrophiles, metal-transmetallated organozinc compounds are able to perform substitution reactions on various electrophiles. In the case of conjugated electrophiles, these zinc copper reagents can follow a Sn2 or Sn2 mechanism. 

Louie, J., Hartwig, J. F. Transmetalation, Involving Organotin Aryl, Thiolate, and Amide Compounds. An Unusual Type of Dissociative Ligand Substitution Reaction. J. Am. Chem. Soc. 1995,117,11598-11599. 

One can imagine that the Sonogashira coupling proceeds by a catalytic cycle very similar to the Stille coupling. The transmetallation step of the Stille coupling is replaced with a ligand substitution reaction, in which a deprotonated alkyne displaces X- from the Pd(II) complex. The alkyne may be deprotonated by the Et3N that is present in the reaction mixture. 

To expand of the scope of electrophiles in the lithiation-substitution reaction, aldehydes were employed and a highly diastereoselective homoaldol methodology was developed [104]. After generation of lithiated 141 under the standard conditions, transmetallation with EtjAlCl or TiCl(Oi-Pr)3, and substitution with various aldehydes provided the homoaldol products with both high diastereo-and enantioselectivities (Scheme 48). 

The enantiodetermining step in the reaction was found to be an asymmetric substitution by transmetallation-substitution of the 2-trimethylstaimyl derivative. The vinyl heterocycles serve as useful precursors to fused bicyclic lactams through Boc deprotection, subsequent acylation and ring closing metathesis... 

The synthesis of aryllead triacetates has been well developed over the past 40 years [79]. There are two principle methods for the synthesis of aryllead triacetates direct plumbation and transmetallation. The simplest method is direct plumbation where an arene can be reacted directly with Pb(OAc>4 to form an aryllead triacetate by a highly selective electrophilic aromatic substitution reaction. Pb(OAc>4 can be reacted with 1,3,5-trimethoxybenzene (138) in CHCI3 at room temperature to generate 2,4,6-trimethoxyphenyllead triacetate (139) in 76 % yield (Scheme 4.35). Although this method is limited to electron rich arenes it is a remarkably selective reaction. 

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