The Studies Toward Some Annulation Reactions Based On The Chemistry Of Quinone Methides And Enamides

Transition metal-catalyzed asymmetric annulation reaction provides a very effective method for construction of chiral polycyclic skeleton.Over the past decades,it has been successfully used in the synthesis of nature products,functional materials,drug and bioactive molecules.Meanwhile,the development of an efficient asymmetric synthetic method for the quaternary carbon stereocenters that are ubiquitous in nature products has always been one of the important topics in organic chemistry.In this dissertation,three transition metal-catalytzed asymmetric annulation reactions have been developed on the basis of the chemistry of quinone methides and enamides,in which the construction of chiral quaternary stereocenters has been achieved.This thesis is mainly divided into the following three chapters.Chapter 1: The progress of the chemistry of ortho-quinone methides(o-QMs)in asymmetric catalysis and stereoselective aromatic Claisen rearrangement is reviewed.A novel palladium catalyzed asymmetric [4+5] annulation reaction of o-QMs with vinylethylene carbonates has been developed to construct chiral nine-memebered oxo-heterocycles in moderate yields and excellent enantioselectivities.Importantly,inspired by the intrinsic nature of the allylic aryl ether subunit embedded in above-mentioned [4+5] annulation adducts,an unprecedented tandem reaction featuring a unique asymmetric aromatic Claisen rearrangement followed by a subsequent aromatizing [3,1] C-to-O rearrangement is disclosed using silica gel as a heterogeneous promoter,leading to a new method for asymmetric creation of all-carbon quaternary stereocenter in chiral phenol-functionalized homoallylic alcohols.The present studies not only enrich the design and development of asymmetric catalytic methodologies related to the chemistry of ortho-quinone methides,but also provide a new perspective for exploring asymmetric aromatic Claisen rearrangement in organic chemistry.Chapter 2: Historical background of para-quinoallenes(p-QAs)is described.A novel palladium catalyzed asymmetric [2+4] annulation reaction of p-QAs with ?-methylidene-?-valerolactones has been developed to construct a series of [5.5]-spiro skeletons with chiral all-carbon quaternary stereocenters and allene units in excellent yields and enantioselectivities.This methodology explores chemical reactivity of p-QAs for the first time,and enriches the chemistry of p-QAs in asymmetric catalysis.Significantly,this asymmetric annulation reaction provides a new approach to the construction of multisubstituted [5.5]-spiro skeletons.Chapter 3: The progress of the annulation reactions of enamides is reviewed.A novel chiral gold-catalyzed asymmetric [2+3] annulation reaction of enamides with propargyl esters has been developed to construct the core framework of cephalotaxine with moderate yields and enantioselectivities.Although the present results are not satisfactory,this work has established the foundation for the effective asymmetric synthesis of cephalotaxine.