Study On The Organocatalytic Asymmetric [4+2] Annulations Via Enol/dienol Intermediates

Since the seminal work pioneered by List,MacMillan and Jacobsen groups,organocatalysis has become the third pillar in the realm of asymmetric catalysis.Over the past decade,fruitful achievements hace beem reached concerning the development of new activation modes,new catalysis,novel reaction design and catalysis-based natural products synthesis.As a continuing program to our group's study in organocatalyzed efficient and green transformations toward functionalized molecules,this thesis mainly centered on the following three chapters.Chapter 1: The [4+2] cycloaddition reaction is a powerful strategy for the formation of carbon-carbon bonds in organic synthesis,which allows facile,stereospecific entry into six-membered ring systems.Many different versions of the Diels-Alder reaction were elaborated,including intramolecular [4+2] cycloadditions,hetero Diels-Alder reactions,pressure-accelerated Diels-Alder reactions,Lewis acid accelerated Diels-Alder reactions,and organocatalyzed asymmetric Diels-Alder reaction.The recent progress in [4+2] cycloaddition reaction,especially in organocatalyzed [4+2] cycloaddition reactions will be reviewed in this chapter.Chapter 2: HOMO-raising non-covalent nucleophilic activation of ?-phenyl aldehydes was achieved via a chiral enol intermediate using Corey guanidine catalyst.This activation enables the first inverse-electron-demand aza-hetero-Diels-Alder(IEDDA)reaction of phenyl aldehydes with 1-aza dienes,delivering synthetically intriguing complex chiral molecules.This chemistry provides a complementary knowledge to the well-established covalent aminocatalysis and aldehyde activation.Chapter 3: In summary,we have uncovered a stereodivergent all-carbon [4+2]-cyclization of ?,?-unsaturated aldehydes and nitroolefins toward the asymmetric synthesis of cyclohexenes with four contiguous stereocenters in high yields with high to excellent enantioselectivities.The chiral dienolate complexes were generated in situ from ?,?-unsaturated aldehydes in a noncovalent activation mode using bifunctional Br?nsted base catalysts.Diastereodivergent control of the products was achieved by introducing a bulky indane scaffold as a second steric control element to the catalyst.By simple use of two pairs of catalysts and their(pseudo)enantiomers,four isomers were selectively obtained out of 16 possible stereoisomers.The synthetical potentials of the current protocol were demonstrated by the derivatization of the products toward synthetically useful substituted 2-aminocyclohexanols and axially chiral biaryls which can find more applications as chiral ligands or catalysts.Further investigation of this new catalytic concept is underway in our laboratory.