Studies On Organic Lewis Base-Catalyzed Carbon-Carbon Bond Forming Reactions

This dissertation mainly focuses on organic Lewis base-catalyzed carbon-carbon bond forming reactions including phosphine-catalyzed [3+2]cycloaddition reactions of allenes with imines and tertiary amine-catalyzed cascade/tandem multi-component reactions involving two different activated olefins as substrates.In search for some superior nucleophilic phosphine organocatalysts with both strong nucleophilicty and air-stability, a readily available and cage-like trialkylphosphine 1,3,5-triaza-7-phosphaadamantane (PTA) was further explored as an air-stable and highly nucleophilic catalyst. It was found that PTA could efficiently mediate the [3+2] cylcoaddtion reaction ofγ-substituted allenoates with N-tosylimines, showing comparable efficiency to that of the most often used but extremely air-sensitive tributylphosphine catalyst. It has been proven that PTA can be used as a convenient and versatile alternative for air-sensitive trialkylphosphine nucleophilic organocatalysts. Also regarding tertiary phosphine catalysis, it was disclosed in this dissertation that a nucleophilic phosphine-promoted [3+2] cycloaddition of electron-deficient allenes with N-(thio)phosphoryl imines could readily give the corresponding dihydropyrrole derivatives in moderate to good yields with good diastereoselectivity. Through an acidic methanolysis of the P-N bond, the first example of synthesis of free amine 3-pyrrolines has been successfully achieved by a new route of the [3+2] cycloaddition of allenes with N-(thio)phosphoryl imines. Organocatalytic cascade/tandem multi-component reactions, possessing some favorable inherent merits such as the high synthetic efficiency and more green chemistry factors, have recently attracted much extensive research interest from synthetic chemists. In this dissertation, organic Lewis base-catalyzed cascade multi-component reactions involving two different activated olefins have been specifically explored. A highly diastereoselective tertiary amine-catalyzed three-component annulation reaction via a Michael-Michael-Henry reaction sequence between nitromathane, doubly activated alkenes andα,β-unsaturated carbonyl compounds has been realized, which provides a new and efficient method for synthesizing both polysubstituted cyclohexanes and some bicyclic frameworks with a hydroxyl functionality positioned at the bridgehead carbon. A tentative mechanism for this annulation is proposed. The experimental results implied that this annulation reaction proceeds through a higher-order cascade mode comprising two intermolecular Michael addition reactions and one intramolecular Henry reaction. Also, the asymmetric version of this reaction has been initially explored. Efficient C-C bond construction and implementation of diverse functionalities are two crucial aspects in organic synthesis. For the purpose of developing new and highly efficient methods for construction of carbon-carbon and carbon-heteroatom bonds, organic Lewis base-catalyzed three-component tandem reactions between two different activated alkenes and heteroatom pronucleophiles have been investigated. As a result, Et3N-catalyzed three-component tandem reactions between doubly activated alkenes,α,β-unsaturated carbonyl compounds and oxygen-or phosphrus-containing pronucleophile were successfully realized. Through a single operation, this kind of tandem/cascade reaction highly efficiently achieves a sequential construction of both carbon-carbon and carbon-heteroatom bonds. These reactions also provide simple, efficient and new approaches for the synthesis of multiply functionalized organic compounds containing carbon-heteroatom functionality. The asymmetric organocatalytic three-component tandem reaction of alcohol, phenyl vinyl ketone and phenylmethylidenemalononitrile was preliminarily explored by using chiral tertiary amines and some encouraging results have been obtained.