Lithium aqua complexes

Quite a number of asymmetric thiol conjugate addition reactions are known [84], but previous examples of enantioselective thiol conjugate additions were based on the activation of thiol nucleophiles by use of chiral base catalysts such as amino alcohols [85], the lithium thiolate complex of amino bisether [86], and a lanthanide tris(binaphthoxide) [87]. No examples have been reported for the enantioselective thiol conjugate additions through the activation of acceptors by the aid of chiral Lewis acid catalysts. We therefore focussed on the potential of J ,J -DBFOX/ Ph aqua complex catalysts as highly tolerant chiral Lewis acid catalyst in thiol conjugate addition reactions. 

Hatano, M. Ikeno, T Miyamoto, T Ishihara, K. Chiral lithium binaphtho-late aqua complex as a highly effective asymmetric catalyst for cyanohydrin synthesis. J. Am. Chem. Soc. 2005,127, 10116-10111. 

Solid lithium carbonate is slowly added to a stirred solution containing 2 g of the [M(N5)(OH2)]3+ salt in 20 mL of water until a pH of 8-8.5 is attained. The amount of water taken is entirely dependent on the solubility of the aqua complex. It is best to start with a completely saturated solution. Approximately 2 g per 20 mL is close to the limit of saturation of the aqua complexes used. 

In an alternative procedure, a filtered 10% aqueous lithium hydroxide solution is added to the aqua complex solution until the pH 8-8.5 range is reached. Then carbon dioxide is bubbled slowly through the solution, the pH being maintained by occasional dropwise additions of the lithium hydroxide solution. 

Mono- or di-lithium salts of (7 )-BINOL give high yields and good ees in cyanations of aromatic aldehydes.262 Formation of an aqua (or alcohol) complex of the catalyst gives higher and reversed ee, and non-linear effects in some cases. 

MoOPH [pronounced moof and more correctly oxidoperoxymolybdenum(aqua)-(hexa-methylphosphoric triamide)] is a molybdenum peroxide complex 245 that hydroxylates lithium enolates.39... 

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