Some Applications Of Organoselenium Reagents In Organic Synthesis

The development of multi-component reactions and combinatorial chemistry enhances the efficiency of synthesis of diversified compounds, thus producing less wastes. As a result, these two new approaches have been shown with many applications in modern organic chemistry. Selenium is discovered to be an essential element for mammalian life. At the meantime, organoselenium reagents are wildly used in organic synthesis.Based on the unique reactivities of organoselenium reagents, we have established several methods to prepare target molecules which may have potential biological or medicinal activities in a straightforward and efficient way.This dissertation mainly includes two parts:PartⅠ——The application of solution-phase organoselenium reagents in multi-component reactions1. A novel three-component reaction of lithium selenolates with 1-(1-alkynyl) cyclopropyl ketones and electrophiles was developed. In this reaction, initially the lithium selenolates attack the 1-(1-alkynyl)cyclopropyl ketones to open the cyclopropane rings, then electrophiles were used to capture the formed carboanions to furnish the corresponding products. By changing the electrophiles, we can obtain (E)-4-alken-1,3-diketones,1,2-allenic ketones, furans, and fluorine substituted 1-alkynyl ketones, respectively.2.2-Furylaldehydes, amines,2-(phenylselenyl)acrylic acids, and isocyanides were used to perform a Ugi-type four-component condensation reaction. Then at room temperature or under reflux, the corresponding products underwent a further Diels-Alder cycloaddition reaction. Promoted by BF3·OEt2, sequential oxygen bridge opening, phenylselenyl elimination, and aromatization of the Diels-Alder products finally gave the highly substituted isoindolinones.PartⅡ——The application of resin-bound organoselenium reagents in solid-phase organic synthesis1. The polystyrene-supported a-seleno-β-amino esters were used to react with a-functionalized acids to form the corresponding amide resins. According to the differences of functional group on the acids, six and seven-membered rings were formed respectively. After cleavage from the resins, we could prepare three libraries of 2-pyridones,1,4-diazepines, and 1,4-oxazepines. It should be noted that when natural a-amino acids were used, optically pure 1,4-diazepines would be given as the expected products.2. The resin-bound a-seleno methyl acrylates were used to undergo 1,3-dipolar cycloaddition with azomethine ylides to furnish polystyrene-supported pyrrolidine-substituted selenide resins. Then further reactions took places on these resins to construct the hydantoin and 2,5-diketopiperazine rings. After oxidation and elimination of the selenides, the corresponding 3-pyrrolines, 3-pyrroline-fused hydantoins, and 3-pyrroline-fused 2,5-diketopiperazines were released from the resins in moderate yields and good purities.