Organocatalytic asymmetric transformations have recently attracted a great deal of attention from synthetic chemists as powerful and fascinating tools because of their mildness, high efficiencies, and environmentally friendly characteristics. In this laboratory, we have been interested in the use of this technique for the synthesis of biologically interesting natural products in optically active forms. In this presentation, our own synthetic approaches to biologically interesting natural products using organocatalytic asymmetric transformations will be discussed. The major topics are as follows: 1. Chiral diamine-catalyzed Robinson-type annulation: we have developed an unprecedented organocatalytic asymmetric synthesis of cyclohexenone derivatives with a quaternary carbon stereogenic center at the 4-position with complete control via chiral diamine/dicarboxylic acid-catalyzed Robinson-type annulation. 2. Formal synthesis of (+)-sporochnol A: the above methodology was successfully applied to the short synthesis of (+)-sporochnol A. 3. Formal synthesis of (-)-mesembrine: a new short synthesis of (-)-mesembrine was also achieved using the same synthetic strategy as above. 4. A practical synthesis of aminohydroxyacetone synthons: a new practical method for the synthesis of aminohydroxyacetone synthons has been developed, and their versatile utility in organocatalytic asymmetric aldol and Mannich reactions was exemplified by using a pyrrolidine-tetrazole organocatalyst. 5. Asymmetric synthesis of aza-sugars: the great utility of aminohydroxyacetone synthons obtained above was demonstrated by the short-cut synthesis of aza-sugars in an enantioselective manner.

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