Study On Synthesis Of Lactones Via C-O Bond Construction

C-O bonds are widely present in organic compounds,and therefore the construction of C-O bonds is an important method for the synthesis of oxygenates.Recently,the transition metal catalyzed construction of C-O bonds has been greatly advanced.Because of transition metal catalysis's efficiency,it attracted more and more attention from chemists.However,the traditional method has certain limitations for complex oxygenates.Herein,it is necessary to explore multiple-step tandem construction of C-O bond for these complex compounds.Lactone structures are widely used in modern chemical synthesis industries and exist in many natural products.Thus,it is essential to develop synthetic method for lactones.This paper is about the efficient multi-step tandem construction of C-O bond to construct lactone structures.The specific work is divided into the following aspects:1.Detrifluoroacetylative cascade reactions of bicyclic fluoro-enolates with ortho-phthalaldehydeThe development of new asymmetric methods for preparation of chiral fluorine-containing compounds is in extremely high demand in many areas of chemical research and industry.Herein,we describe a new cascade reaction approach,exemplified by the reactions of,in situ generated fluoro-enolates,with orthophthalaldehyde.The reactions proceed through the sequence of detrifluoroacetylation,aldol addition,intramolecular cyclization and oxidation,under convenient conditions with synthetically attractive stereochemical outcome and good structural generality.We demonstrate that these cascade reactions can be performed in catalytic asymmetric mode affording diastereomerically pure products with up to 86%ee.2.Catalytic enantioselective detrifluoroacetylative cascade aldol-cyclization of ?-fluoroenolates with 2-formylbenzoate.The first asymmetric catalytic aldol-cyclization reaction of detrifluoroacetylatively in situ generated enolates with methyl 2-formylbenzoate is reported.This reaction tolerates a wide range of substrates,affording fluorinated quaternary stereogenic ?,?-dialkyl/cyclo-alkyl-?-ketoesters with good yields,high diastereo-(94%de)and enantioselectivity(96%ee)at room temperature.3.Photoredox-Catalyzed Cascade Difluoroalkylation and Intramolecular Cyclization for Construction of Fluorinated ?-ButyrolactonesA cascade visible-light photocatalytic difluoroalkylation and intramolecular cyclization reaction has been developed for the synthesis of difluoroalkylated oxygen heterocycles.The reaction was carried out under very mild conditions,affording fluorinated isobenzofuran-l-ones,lactone,and cyclic ethers with up to 97%chemical yields.Furthermore,several types of bromofluoroalkane precursors bearing ester,keto,amido,and phosphate groups could all work very well in this reaction,which provides an easy method for the preparation of functionalized difluoroalkylated oxygen heterocycles.4.Access to Alkyl-Substituted Lactone via Photoredox-Catalyzed Alkylation/Lactonization of Unsaturated Carboxylic AcidsAn efficient photoredox-catalyzed alkylation/lactonization reaction of unsaturated carboxylic acids by using alkyl N-hydroxyphthalimide esters as alkylation reagents has been developed.Varieties of redox-active esters derived from aliphatic carboxylic acids were proved viable in this method,affording alkyl substituted lactones in moderate to good yields.This redoxneutral procedure features mild conditions and operational simplicity,which provides a new strategy for the synthesis of alkyl substituted lactones.