Lithium halocarbenoids alkylation

An interesting application of lithium halocarbenoids at temperatures above —80 °C involving substitution of halogen by alkylanions (cf. Scheme 1) and subsequent alkylation of the resulting carbanion has been reported by Duhamel59) (reaction sequence (54)). 

Villieras and coworkers have contributed a considerable number of synthetic methods employing lithium halocarbenoids. An early example was the alkylation of dibromomethyllithium and higher homologs (Scheme 15). The anion (15) is easily generated from 1,1-dibromoalkanes by deprotonation with LDA in THF at low temperature. Alkenes can then be generated simply by treating the products with Bu"Li in EtjO, Alkylation of dichloromethyllithium with primary alkyl halides followed by reaction of the dichloroalkanes with Bu"Li represents a method for the preparation of 1 -alkynes. ... 

Cyclopropylidenelithium halocarbenoids are easily prepared by halogen-lithium exchange of the di-bromocyclopropanes, and they undergo a variety of synthetically useful reactions including alkylation. A recent report by Hiyama et al. for example, describes the synthesis of alkyl-substituted 2-cyclohept-enones (Scheme 16). 

---