Chiral ferrocenylalkyl alcohols

The formation of a chiral carbocation by treatment of a chiral a-ferrocenylalkyl alcohol is stereoselective, without loss of chirality information. The same is true for the reaction of the cation with nucleophiles. An overall retention of the configuration for this S l process is observed. This was demonstrated experimentally by the construction of synthetic cycles in which the product is identical with the starting material and shows the same enantiomeric excess ee, Fig. 4-4) [30—34]. 

Kinetic resolution of ferrocene derivatives, mainly alcohols, had an important place during the early stage of stereochemical investigations of ferrocene derivatives. The reaction of (partially) resolved ferrocenylalkyl alcohols and amines with racemic 2-phenylbutyric acid anhydride (Korean s method) was the basis for the configurational assignment before the establishment of structures by X-ray crystallography [41]. There has been some debate on the reliability of the method [62, 63], and additional chirality information seems necessary for certainty. Recently, the kinetic resolution of 1-ferrocenylethanol by transesterification with vinyl acetate, catalyzed by a lipase from PseudomonasJluorescens, led to an enantiomeric excess of 90—96% of both enantiomers [64], opening new preparative aspects. 

We have tried here to incorporate the ferrocene moiety into amino alcohol catalysts and have synthesized the following four kinds of compounds (a) chiral ferrocenyl zincs bearing an aminoethanol auxiliary [12] (b) iV-(l-ferrocenylalkyl)-iV-alkylnorephedrines [13] (c) chiral polymers bearing iV-ferrocenylmethylephe-drine [14] and (d) chiral 1,2-disubstituted ferrocenyl amino alcohols (Fig. 3-2) [15-17]. 

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