Absolute stereochemistry chiral auxiliary based methods

Methods to control the absolute stereochemistry of the products obtained from the cyclocondensation reaction have also been developed. The use of both chiral auxiliary based methods and chiral catalysts have been investigated. The first and most straightforward method of controlling absolute stereochemistry is the use of a chiral and optically pure aldehyde. All of the methodology developed for the control of relative stereochemistry can then be directly applied to give optically pure cyclocondensation products. In many cases, however, the synthesis of optically pure aldehydes is difficult (if not impossible) due to their tendency to undergo racemization under the reaction conditions. This method also suffers from the fact that only chiral aldehydes can be used in the cyclocondensation reaction to get optically pure products simple and readily available achiral aldehydes can not be used. 

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