Procedures for Stereochemical Analysis

Even two chiral centers (in C1S or Clg methyl-branched carbonyl compounds, cf. Fig. 12) can be determined simultaneously with high accuracy ( 0.3%) by GC analysis of acetals 34 and 35 (n= 1) derived from C2-symmetric tartrate esters. Laboratory-made 80- to 100-meter capillary columns were used in the original work [76, 77]. Recently we have shown [78] that this methodology can be applied routinely by using commercially available reagents [79] and GC columns [80]. It has to be pointed out that up to now this protocol is the only one that is capable of accomplishing such an analysis. 

At the end of the synthesis, the outcome of enantioselective reactions can be checked by the full stereochemical characterization of the final product 3. The chromatographic separation of all eight stereoisomers of 3, that is the concurrent determination of all three chiral centers [81, 82], is in principle based on the separation of enantiomers by HPLC on a chiral phase and separation of diastereoi-somers on an achiral GC column. While also in this case special laboratory-made columns were used in the original procedure [82] for both HPLC and GC separation steps, analyses are done today routinely on the stable and easy-to-prepare methyl ether derivative 36 with the use of commercial columns [80, 83], 

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