Carbene from organolithium compounds

Chromium carbene complexes like 13, which are called Fischer carbene complexes, can conveniently be prepared from chromium hexacarbonyl 11 and an organolithium compound 12, followed by an O-alkylation step ... 

J-Oxygen-functionalised sp3 organolithium compounds react with alkenyl-carbene complexes to generate the corresponding cyclic carbene complexes in a formal [3+3] process (see Sect. 2.8.1). In those cases where the organolithium derivative contains a double bond in an appropriate position, tricyclic ether derivatives are the only products isolated. These compounds derive from an intramolecular cyclopropanation of the corresponding cyclic carbene complex intermediate [89] (Scheme 83). 

A further synthetic approach to carbon-metal double bonds is based on the acid-catalyzed abstraction of alkoxy groups from a-alkoxyalkyl complexes [436 -439] (Figure 3.11). These carbene complex precursors can be prepared from alk-oxycarbene complexes (Fischer-type carbene complexes) either by reduction with borohydrides or alanates [23,55,63,104,439-445] or by addition of organolithium compounds (nucleophilic addition to the carbene carbon atom) [391,446-452]. 

The synthetic applications of acyllithiums, generated by reaction of organolithium compounds with carbon monoxide, by treatment with electrophiles started when Nudelman and coworkers found that phenyllithium reacted with carbon monoxide in the presence of alkyl bromides to yield diphenylalkylcarbinols24,27. a-Hydroxy-a-phenylacetophenone was also obtained resulting from the dimerization of the carbene intermediate of type 3. In the absence of electrophiles a,a-diphenylacetophenone was obtained in 94% yield, attributed to the dimerization of the corresponding aroyl anion radical28. 

Table 1. Arylcyclopropanes from Alkenes and Carbenes, Generated from Arylhalomethane or Aryldihalomethane with Organolithium Compounds... 

The three-component reaction of lithiated [bis(phenylsulfanyl)methyl]trimethylsilane, phenyloxirane, and an alkene takes an interesting reaction pathway. Obviously the oxirane serves as a trapping reagent for lithium benzenethiolate, which results from a-elimination of the initially formed organolithium compound. The generated phenylsulfanyl(trimethylsilyl) carbene (4) adds stereoselectively to various alkenes. In all cases the sterically less crowded Z-isomer cyclopropane 5 is formed. 

The exact formulation of the reactive intermediate in a-elimination reactions using organolithium compounds as bases has been difficult. Apart from the free carbene, various carbenoids are possible, including the a-haloorganolithium formed on metalation, and carbene-lithium halide complexes of various degrees of association. In the case of the dichlorocarbene-trichloromethyllithium equilibrium, the... 

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