Synthesis Of Benzofluorene Derivatives Via Cascade Michael Addition/benzannulation Reaction

This paper mainly includes the following two parts:Part?:(1)This part summarizes the application of polycyclic aromatic hydrocarbons;(2)It summarizes the application of benzofluorene compounds;(3)It summarizes the method for synthesizing benzofluorenes.The construction of ring skeletons is a central issue in synthetic chemistry.Benzofluorenes are important polycyclic aromatic compounds with many special properties,which endow them with broad potential applications in multiple fields,including material science and biological chemistry.These tetracyclic skeletons and related derivatives are also found widely in natural products.However,the methods for their synthesis,particularly for benzo[a]fluorenes,are very limited,only a handful of examples can be found in literatures up to now.Therefore,developing new methods for efficient assembly of these polycarbocycles from readily available materials is in high demand.Part ? : A study on the synthesis of benzofluorene derivatives via cascade Michael addition/benzannulation reaction:A cascade annulation method for constructing polycyclic aromatic compounds via the sequential Michael Addition/cycloaromatization reaction is described.This method allows two new C=C bonds and two rings to be furnished in a single operation.As our continued interest in the C-O/C=O bond functionalization reactions as well as in the development of practical methods to access polycarbocycles,we envisaged that the benzo[a]fluorene skeleton might be built-up from the styrene-linked cinnamaldehydes or chalcones via a cascade intramolecular Michael addition and benzannulation reaction;in this process the styrene moiety may act as a double nucleophile to react with the enal or enone segment which is activated by a catalyst.To our knowledge,direct employment of this sequential 1,4-or1,2-addition protocol to construct polycarbocycles is absent in the literature.In the experimental part,ortho-vinylcinnamaldehyde were selected as the template substrate for intramolecular cyclization reaction.The optimum conditions were obtained as follows:trifluoromethenic acid(10 mol%),iron trifluoromethesulfonic acid(10 mol%),a temperature of 80 °C and 1,2-dichloromethane as the solvent.Under the optimum conditions,a series of compounds in good to excellent yields were synthesized by using enaldehyde and ketene as substrates.The structure of the products were identified by nuclear magnetic resonance and high resolution mass spectrometry.