Glycosylamines as Auxiliaries in Stereoselective Syntheses of Chiral Amino Compounds

4 Glycosylamines as Auxiliaries in Stereoselective Syntheses of Chiral Amino Compounds 

Heiko Tietgen, Martin Schultz-Kukula and Horst Kunz 

Although carbohydrates are cheap and readily available chiral compounds, their application in stereoselective synthesis was for a long time limited to ex-chiral-pool syntheses [3]. They have been considered too complex compared to other chiral auxiliaries, for example a-pinene in borane-chemistry [4] or BINAP-derivatives in reduction chemistry [5]. However, it has been shown during the past few years that carbohydrates can be successfully applied as stereodifferentiating tools in many different reaction types such as aldol- [6], hydrogenation- [7], carbonyl addition- [8], Michael- [9], Diels-Alder- [10], hetero-Diels-Alder [11], and rearrangement reactions [12]. 

In many cases, the substrate to be subjected to asymmetric conversion is coupled to the carbohydrate via the anomeric position. For the synthesis of amino compounds, the substrate is linked to the carbohydrate as a derivative of a glycosyl-amine. After completion of the asymmetric synthesis the product can be detached from the carbohydrate auxiliary by acidic hydrolysis. In most cases auxiliary and product can be separated by extraction or recrystallization techniques, and the carbohydrate auxiliary readily regenerated from its recovered detachment derivative. 

The higher steric demand of carbohydrate templates containing the pivaloyl ester usually results in a higher stereoselectivity in their reactions compared to those of the acetyl-protected analogues [13]. 

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