Synthesis Of 1,3,5-conjugated Trienes And 1,4-dithiines(diselenins) Through The Base Promoted Difunctionalization Reaction Of Alkynones

1,3,5-conjugated trienes and 1,4-dithiines（diselenins）are widely used in pharmaceutical chemistry,biochemistry,organic synthesis,material science and other fields.Developing new methods for the synthesis of these compounds has important scientific significance.Generally,the preparation of these compounds requires the use of transition-metal catalysts,which is costly and poses environmental pollution issues.Therefore,the development of efficient transition-metal-free methods to synthesize these compounds by constructing carbon-carbon bonds and carbon-sulfur（selenium）bonds has attracted widespread interest among researchers.Due to the conjugated structure,alkynones are considered to be highly reactive molecules and are regarded as important organic building blocks.The purpose of this dissertation aims to explore new methods for the synthesis of 1,3,5-conjugated trienes and 1,4-dithiines（diselenins）by the difunctionalization of alkynones to construct carbon-carbon bonds and carbon-sulfur（selenium）bonds under the alkaline condition,including the following two parts:1)Base-promoted synthesis of 1,3,5-conjugated trienes with high regioselectivityUsing alkynones and allyl carbonyl compounds as substrates,we realized the insertion of alkynes into carbon-carbonσ-bonds of allyl carbonyl compounds in the presence of Cs₂CO₃.Twenty-five functionalized 1,3,5-conjugated trienes were synthesized in 38%to 87%yields.Further cyclized chromone derivatives could be obtained when ortho-halide-substituted alkynones or allyl carbonyl compounds participated in the reaction.This methodology has the advantages of good economy of atoms and mild conditions,complex molecules such as pyrrole and conjugated tetraene can be constructed rapidly by product transformation.2)Base-promoted synthesis of 1,4-dithiins and 1,4-diselenins with high regioselectivityIn the presence of K₂CO₃,the difunctionalization of alkynones was developed using cheap and readily available elemental sulfur（selenium）as the starting material with the advantages of mild conditions and simple operation.The reaction which improved the problem of poor selectivity in literature could construct two carbon-sulfur or carbon-selenium bonds at the same time.Twenty-one functionalized 1,4-dithiins and1,4-diselenins were obtained with high regioselectivity（up to 12:1）and good yields（up to 95%）.The reaction could take place smoothly no matter whether there were electron-withdrawing substituents or electron-donating substituents on the benzene ring of alkynones.It was worth noting that alkynones with alkyl substituents at the triple bond termini could obtain a single isomer.Olefination structure can be obtained by product’s Wittig reaction and heterocyclic compounds such as polysubstituted thiophene could be delivered by other subsequent transformation of the product.