Bifuctional Amino-Squaramides Catalyzed Asymmetric Synthesis Of Spiro-3,4-Dihydropyrans

3,4-Dihydropyransare important structural motifs in a myriad of biologically interesting natural products and pharmaceutical targets; they also serve as versatile building blocks in organic synthesis. Accordingly, asymmetric transformations enabling expeditious and stereoselective construction of dihydropyran derivatives are of particular importance in organic synthesis. This dissertation demonstrates the cyclization ofβ-oxo aldehydes withβ,γ-unsaturated a-keto ester which was carried by utilizing squaramide organocatalyst. This procedure provided a promising approach to a variety of spiro-3,4-dihydropyrans bearing three continues quateranery and tertiary stereocenters in moderate to good yield with high stereoselectivities. On that basis, we have developed an intramolecular Oxo-Michael reaction using phase transfer catalyst. The dissertation is consisted of three chapters.In the first chapter, we summarized the synthetic methods of3,4-dihydropyrans as well as their current research and trends, respectively. Then we discuss various general methods that involve the generation of spirocyclic centers. Moreover, we describe here the development and successful demonstration of a new family of H-bonding catalysts based on the squaramide catalophore.In the second chapter, we investigated the domino Michael/hemiacetalization reaction of cyclic β-oxo aldehydes withβ,γ-unsaturated a-keto ester in the presence of squaramide, obtained the complex of spiro-dihydropyran architectures, which containing three continuous chiral centers. To our delight, good yields as well as high diastereo-and enatioselectivities was observed, even the catalyst loading was reduced to3mol%.In the third chapter, we explored an intramolecular Oxo-Michael reaction using phase transfer catalyst, to afford spirocyclic compound in excellent yield, based on previous experimental results.