Acetals from dimethyl tartrate

The (R)-(+)-chiral 1,4-diol 17b was easily prepared from L-(+)-dimethyl tartrate. Dimethyl tartrate was converted to the corresponding phenylethylidene derivative by treatment with 1,1-dimethoxy-l-phenylethane and cat. p-toluenesulfonic acid in refluxing benzene, followed by conversion to the diol 17b with excess phenylmagnesium bromide. The diol was purified by column chromatography on silica gel (hexane ethyl acetate =5 1), and recrystalization from a mixture of hexane and 2-propanol. 

Preparative Methods chiral titanates are usually prepared by mixing dichlorodiisopropoxytitanium and a chiral 1,4-diol in toluene. Other solvents such as ether and dichloromethane can also be employed. The alcohol exchange reaction takes place immediately at rt. Wherever necessary, liberated isopropyl alcohol is removed by azeotropic removal with toluene. The chiral 1,4-diols are prepared from dimethyl (or diethyl) tartrate by a two-step procedure comprising acetalization followed by the addition of an aryl Grignard reagent. ... 

Acetals derived from Dimethyl L-Tartrate react with Me2BBr to generate a-bromo ethers which react further with cuprate reagents to give optically active secondary alcohol derivatives (eq 14). The alcohols may be liberated by treatment with Samarium(II) Iodide or by a straightforward sequence of reactions (mesylation and elimination to form an enol ether followed by exposure to methoxide in refluxing methanol). Selectivity is enhanced by the... 

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