Nontransferable ligands

In these reactions one equivalent of chiral azaenolate remains unused. This can be overcome when a mixed azaenol cuprate 9 is employed with an acetylide as nontransferable ligand or when a mixed azaenol dimethylzincate 10 is used. Higher diastereoselectivities are achieved with zincates than with copper azaenolates and with (li ,2S )-2-methoxy-1,2-diphenylethanamine as auxiliary231. 

A nontransferable ligand is used to advantage in the above spiroannulation, and is generally important when a highly valued ligand must be transferred. In the synthesis of a steroid nucleus, the nucleophilic addition of a cuprate to enone (51) was one of two key steps (equation 56).117 A good yield of the 3-alky lated product was obtained, and a high stereochemical preference was reported as well. 

The use of a 2-thienyl group as a nontransferable ligand in lower order cuprates has been described, H. Malmberg, M. Nilsson and C. Ullenius, Tetrahedron Lett., 1982, 23, 3823. 

Mixed homocuprates.7 Mixed cuprates (1) in which the nontransferable ligand is an a-sulfonyl carbanion are easily prepared from dimethyl sulfone or methyl phenyl sulfone (equation I), and are effective for conjugate addition to enones and for a synthesis of ketones from acid chlorides. 

An alternative to the use of the 2-thienyl group as a nontransferable ligand in h.o. cyanocuprates is the anion of DMSO (1) efficient alkylation of primary iodides at -78 °C... 

New heterocuprates (2-4), with a diphenylphosphino, di(terr)butylphosphino or dicy-clohexylamino nontransferable ligands, are reported to alkylate primary alkyl iodides. 

LO cuprate = A lower order cuprate HO cuprate = A higher order cuprate Rr = A residual or nontransferable ligand R/ = A transferable hgand hfa = Hexafluoroacetylacetone acac = Acetylacetonate EWG = Electron-withdrawing group TfO = Trifluoromethylsulfonyloxy (triflate). 

Posner has also studied the effect of various other nontransferable ligands in the process. It was concluded that phenylthio was equivalent to r-butoxide as a nontransferable ligand, but phenoxy, dimethyl-amino and r-butylthio were inferior (equations 63 and 64). 

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