Carbanions cycloalkyl

So far, the formation of cyclic alkoxyallenes bearing an exocydic or endocyclic allenyl unit has been less developed. Several examples with this structural feature are described as unstable compounds or highly reactive intermediates [32-35]. However, in the 1990s, Lavoisier-Gallo and Rodriguez demonstrated a useful one-pot protocol for the synthesis of 2-vinylidenedihydrofurans such as 29 involving a tandem C-O cycloalkylation of stabilized carbanion intermediates 28 as crucial step (Scheme 8.10) [36, 37]. 

The Michael reaction can also be applied to the formation of cyclopropanic systems. Thus, Michael addition of phosphonate carbanions, generated by electrochemical technique or by thal-lium(I) ethoxide in refluxing THF, to a,p-unsaturated nitriles provides a convenient preparation of substituted 2-cyanocyclopropylphosphonates via a tandem Michael addition-cycloalkylation sequence (Scheme 6.25). - - ... 

In addition to the presented Sjj/Michael transformations, a twofold domino Sn/Sn cycloalkylation of stabilized carbanions from cyclic P-ketoesters with 1,4-dibromobut-2-yne yielding annulated 2-vinyHdenehydrofurans has been reported... 

The synthesis of azo-compounds via condensation of perfluorinated w-nitrosoalkanecarboxylic acids or esters with amines was mentioned earlier [item (vi), p. 231]. An alternative method to the AtNHj-RfNO condensation for the preparation of azo-compounds of the type AtNiNRf (Rf = perfluoro-alkyl or -cycloalkyl) has now been discovered, viz. trapping of peifluoro-carbanions (from perfluoro-olefins + caesium or potassium fluoride) with arenediazonium salts (see Scheme 36). ... 

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