Homoenolate Aryl coupling

A very practical route to zinc homoenolate involves reduction of 3-iodoesters with zinc/copper couple in the presence of a polar solvent, e.g. DMF, DMA [49] Eq. (51). The nature of the species obtained in this approach is not well-defined, but appears to be essentially the same as the one obtained along the siloxycyclo-propane route. Acylation, arylation, and vinylation reactions have been reported. 

Subsequently, with the newly developed sterically bulky chiral triazolium salt precatalyst, the Rovis group disclosed a homoenolate Michael addition reaction of enals to nitroalkenes that delivers complementary syw stereoselectivity and allows coupling with aliphatic nitroalkenes. Bulky substituents in the ortho ortho position of the Al-aryl ring of the NHC are crucial for the success of this reaction as it would shift product distribution toward the desired nitro ester by partially bloeking the aeyl anion position (Scheme 7.64). 

One particular aspect of this chemistry is in the preparation of zinc homoenolates prepared from P-iodoesters (Scheme 2.33). This chemistry becomes particularly significant with p-iodoesters 2.95 derived from the amino acid serine 2.94. These are useful for the synthesis of novel amino acids by Negishi coupling with aryl and acyl halides (Scheme 2.34). Coupling of a complex peptidyl aryl iodide 2.98 with a zinc reagent 2.99 of this type was a late step in a synthesis of a cyclic tripeptide and aminopeptidase inhibitor OF494-III 2.100 (Scheme 2.35). ... 

Siloxycyclopropane Cleavage. Siloxycyclopropanes undergo C-C bond cleavage and coupling to aryl triflates (eq 27) and acid chlorides (eq 28) in the presence of (1) and a phosphine or phosphite ligand. In this fashion, the siloxycyclopropanes serve as synthetically useful homoenolate anions. 

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