Synthesis Of Heterohelicenes-like Compounds

Helicenes are a class of aromatic compounds with helical structure composed of at least four aromatic(hetero)rings fused in the ortho position,and their applications in the fields of asymmetric catalysis,material science and biomedicine have been widely concerned.At present,the methods that can be used to synthesize helicenes mainly include photocatalytic cyclization,Diels-Alder reaction,Friedel-Crafts reaction,and transition metal-involved cyclization reaction.Common helicene molecules can be divided into carbon helicenes containing only carbon atoms in the molecule and heterohelicenes containing heteroatoms in the molecule.The introduction of heteroatoms can increase the potential application value of helical compounds.As a special type of helical molecule,there are relatively few reports on the synthesis of heterohelicenes.In this thesis,we designed and synthesized novel substrates with high reactivity and multiple reaction sites,achieved the synthesis of heterohelicene-like compounds through intramolecular cyclization.Firstly,we designed and synthesized a class of diacetyl substituted naphthol derivatives.With toluene as the solvent,Vinylidene ortho-Quinone Methides(VQMs)intermediates were formed in the presence of electrophilic reagents,and then carried out intramolecular oxa [4+2] cycloaddition reaction to synthesize mono-heterohelicene compounds.With this strategy,we obtained a series of racemic mono-heterohelicene compounds in 72%-95% yields.On this basis,we introduced chiral catalysts to expect the asymmetric synthesis of chiral mono-heterohelicene compounds through VQM intermediates.After the screening of catalysts,reaction solvents,concentrations and other conditions,it is shown that the chiral catalyst had limited affection on the enantioselectivity of the reaction.In order to synthesize heterohelicene-like compounds with high enantioselectivities,we further modified the structure of substance and synthesized tetra-alkynyl substituted naphthol derivatives as the reaction substrate.By using NBP as the electrophilic reagent,cinchona base derived squaramide as organocatalyst,three pairs of chiral tetra-heterohelicene analogs were obtained with excellent enantioselectivities(87%-96% ee)and good yields(32%-54%).The development of this strategy provides an efficient preparation method for the synthesis of heterohelicenes,and lays a certain foundation for the application and development of chiral heterohelicenes.