The Wurtz Reaction. Allylic and Related Couplings

Earlier we mentioned the Wurtz reaction as being one of the simplest approaches to the formation of C-C bonds. In this reaction, the alkyl halide serves as the electrophile (carbocation equivalent) and the organometallic derivative plays the role of the nucleophile (carbanion equivalent). We have also seen that this old reaction has recently become a feasible route for the creation of C-C bonds due 

Therefore if a target molecule contains an aromatic ring or a double or triple bond, it is useful to initiate a retrosynthetic analysis of such a structure by cleavage of the bonds at the benzylic, allylic, or propargylic positions, respectively. The aim is to arrive at the pair consisting of the stabilized cation and the required anion and then to analyse the comparative availability of the corresponding reagents.  

Either of these fragments can be regarded as a potential cation or anion. The formation of C-C bonds via the coupling of two allylic fragments is considered to be dependable and there are numerous and well-elaborated procedures to achieve this goal. This is the reason why so many isoprenoid syntheses are 

2 Carbonyl Compounds as Nucleophiles and Electrophiles. The Problem of Role Assignment and the Modern Image of the Classical Condensations of Carbonyl Compounds. The Wittig Reaction as a Method for the Controlled Synthesis of Alkenes 

Classic synthetic methods based upon the alkylation of enolates were therefore limited to cases where especially stable enolates could be generated. Usually )S-dicarbonyl compounds such as acetoacetic ester or malonic ester were used as precursors in these reactions. For example, alkylation of the stable enolate derived from malonic ester served as a routine and totally reliable method to achieve C2 chain elongation, as shown in the standard sequence below  

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