Study On The Conjugate Addition And Annulation Of P-Quinone Methides

Para-Quinone methides are a class of benzoquinone derivatives consisting of cyclohexenones and extra-cyclic double bonds.The alkyne-substituted para-quinone methides and light-derived para-quinone methides are less reported so far,In this thesis,two new synthetic methodology based on the conjugate addition and conjugate addition mediated annulations of para-quinone methides are developed,which provides efficient pathway to a series of indole derivatives containing chiral quaternary carbon and indeno[2,1-c]chromene skeletons.Three main parts of this thesis are descried as follows.Part Ⅰ: In the first part of this thesis,conjugate additions and conjugate addition mediated annulations of para-quinone methides are reviewed.Part Ⅱ: A series of indole derivatives containing chiral quaternary carbon structures were synthesized via visible-light-promoted three-component reactions of benzoquinones,arylalkynes and 2,3-disubstituted indoles.First,the arylalkyne and benzoquinone undergo visible-light-promoted-[2+2]-cycloaddition to produce spirooxetene,which is unstable and is transformed into the more stable p-quinone methide,which is a stronger electrophilic and can more easily react with the C6 position of 2,3-disubstituted indoles to give the product.This work achieves remote stereoselective control of the conjugate addition of 2,3-substituted indoles at the C6-position to para-quinone methides intermediates for the first time.Part Ⅲ: A series of tetracyclic indeno[2,1-c]chromene skeletons were efficiently synthesized based on 1,8-conjugate addition/cyclization/ rearrangement tandem reactions of alkynyl-substituted para-quinone methides with 2-vinylphenols.The Lewis acids catalyzed dehydration of propargyl alcohol to form the para-quinone methides intermediate.and subsequent 1,8-addition/cyclization/rearrangement to yield the tetracyclic product.Conjugate addition of para-quinone methides and 2-vinylphenol at the C8 position gives intermediate ortho-quinone methides,followed by intramolecular [4+2]-cyclization to produce[3,1,1]-bridged ring III,which is very unstable.The ring-opening of cyclobutane gives ortho-quinone methides cation,followed by intramolecular Friedel-Crafts-type cyclization gives,and migration of the double bond gives the final indeno[2,1-c]chromene product.The present tandem annulation methodology provides an alternative method for synthesis of indeno[2,1-c]chromenes.