Dianion chemistry

Looking back on the history of ketone dianion chemistry, one soon notices that dianion species, derived from / -keto esters, have been in continuous steady use in organic synthesis3,4, as shown in Scheme 2. Thus, ethyl acetoacetate can be converted to the corresponding ketone o a -chainon via consecutive proton abstraction reactions. The resulting dienolate anion reacts with a variety of alkyl halides to give products, resulting from exclusive attack at the terminal enolate anions. 

For a review, see C. M. Thompson, Dianion Chemistry in Organic Synthesis, CRC Press, Boca Raton, 1994. 

A sequential lithiation-alkylation based on the dianion chemistry was utilized in an efficient synthesis of (—)-mesembrine (Scheme 175 <1998TL8979>. 

N. L. Holy, Chem. Rev., 74, 243 (1974) review of metal aromatic radical anion and dianion chemistry. 

A general synthetic route toward the marine metabolite eunicellin diterpenes was developed by G.A. Molander and co-workers.The power of this method was demonstrated by the completion of the asymmetric total synthesis of deacetoxyalcyonin acetate. A tricyclic (3-keto ester intermediate was methylated in the y-position with complete diastereoselectivity using dianion chemistry and the crude product was subjected to the Krapcho decarboxylation. This was one of the rare cases when the transformation did not only remove the methoxycarbonyl group, but at the same time epimerized the newly formed stereocenter to yield a separable mixture of methyl ketones. 

Molander reported formation of [3.2.1] and [3.3.1] oxabicydic compounds by applying Trost s trimethylenemethane dianion chemistry with dicarbonyl substrates, Eq. 47 [76]. The inherent symmetry of the dianion limits this methodology to those compounds with relatively simple and symmetrical structures. 

Deprotonation of porphyrins is possible with strong bases (e.g., sodium hydride) in pyridine or other polar, nonprotic solvents (not shown) (Falk, 1964). The corresponding sodium salts are formed, which produce similar two-banded visible spectra as the diprotonated dications. Little is known about the dianion chemistry. They cannot, however, be oxidized to dehydroporphyrins with only 16 7C-electrons in the inner conjugation pathway. Such a porphyrin would be antiaromatic and appear as a triplet state. It has not been detected so far. 

Reactions of Methylenephosphoranes.- A recent review of dianion chemistry includes a number of references to P-ketophosphonate 1,3-dianions and their use in synthesis.20... 

The application of dianion chemistry in synthesis is not confined to 7-alkylation of p-dicarbonyl compounds. Dianions derived from p-keto sulfoxides can be alkylated at the 7 -carbon atom. Nitroalkanes can be deprotonated twice in the a-position to give dianions 7. In contrast to the monoanions, the dianions 7 give C-alkylated products in good yield (1.19). ... 

Fig. 4 Bicyclosilanes obtained using oligosilanyl dianion chemistry...

Although redox processes are sometimes observed in metathetical reactions with metal halides, the pyramidal dianion [Te(NtBu)3] has a rich coordination chemistry (Scheme 10.8). For example, the reaction... 

Imidazole is characterized mainly by the T) (N) coordination mode, where N is the nitrogen atom of the pyridine type. The rare coordination modes are T) - (jt-) realized in the ruthenium complexes, I-ti (C,N)- in organoruthenium and organoosmium chemistry. Imidazolium salts and stable 1,3-disubsti-tuted imidazol-2-ylidenes give a vast group of mono-, bis-, and tris-carbene complexes characterized by stability and prominent catalytic activity. Benzimidazole follows the same trends. Biimidazoles and bibenzimidazoles are ligands as the neutral molecules, mono- and dianions. A variety of the coordination situations is, therefore, broad, but there are practically no deviations from the expected classical trends for the mono-, di-, and polynuclear A -complexes. 

R. B. Bates. Dianions and Polyanions in Comprehensive Carhanion Chemistry, E. Buncel, T. Durst, Eds.. Vol. 5A, Chapter 1, pp 1-53, Elsevier. Amsterdam 1980. 

The chemistry of polysulfide dianions is closely related to that of the radical-monoanions S since both types of anions are in equilibrium with each other in solution and in high-temperature melts, e.g. ... 

With the exception of a brief report of a dimethylaluminum complex [5], the coordination chemistry of the monomeric anion in (4) has not been investigated. By contrast, Stahl and co-workers have carried out extensive studies of both main group element and transition-metal complexes of the chelating dianion in the cube (7), which have been summarized in a recent review [9]. A noteworthy feature of the ligand behaviour of this N,N chelating dianion is the additional in-... 

Walter, M. and Hakkinen, H. (2006) A hollow tetrahedral cage of hexadecagold dianion provides a robust backbone for a tuneable sub-nanometer oxidation and reduction agent via endohedral doping. Physical Chemistry Chemical Physics, 8, 5407-5411. 

Chan, M.C.-W. and Che, C.-M. (1998) Application of 2,6-diphenylpyridine as a tridentate [C N C] dianionic ligand in organogold(III) chemistry. Structural and spectroscopic properties of mono- and binuclear transmetalated gold(III) complexes. Organometallics, 17, 3505-3511. 

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