Cyclization Reactions Of 3-cyclopropylideneprop-2-en-1-ones

Allenes,featured by two cumulated C=C bonds,of which two ?-orbitals are perpendicular to each other,have shown a wide variety of unique reactivity.Their reaction behavior where the reactivity is spread over three contiguous carbon atoms has been successfully applied to the field of the synthesis of natural products,pharmaceuticals,dyes,polymers,etc.On the other hand,cyclization reactions are highly valuable for the modular construction of advanced cyclic molecules through the mutual addition of unsaturated bonds.In particular,the cyclization of allenes,providing an attractive strategy for the building various heterocycles with high efficient and atomic economy,have received considerable attention.However,the development of milder and environmentally benign cyclization reaction of allenes with complete controlled regio-and stereoselectivity remains a grand challenge.The 3-cyclopropylideneprop-2-en-1-ones,which contain the highly strained cyclopropyl ring and carbonyl group adjacent to the two ends of cumulated double bonds,are a class of thermally stable,yet activated allenic derivatives.In this dissertation,we mainly studied intermolecular or intramolecular cyclization reactions of 3-cyclopropylideneprop-2-en-1-ones under transition metals or metal-free conditions,which provide efficient entry to valuable polysubstituted furans and indanones.This thesis contains two parts:Part I: We have developed a gold-catalyzed cascade cycloisomerization/ring-opening reaction of 3-cyclopropylideneprop-2-en-1-ones with a wide variety of alcohols or ketones.This reaction involves an unprecedented1,2-gold carbene transfer to provide regioselective and modular access to tri-or tetra-substituted furans in moderate to high yields.The mechanism has also been well investigated by controlled experiments.Part II: We have disclosed a catalyst-free Nazarov cyclization of allenyl ketones under thermal condition.Various densely functionalized 2,3-dihydroindanones or indenones are readily produced in moderate to excellent yields.The resulting substituted 2,3-dihydroindanones can be conveniently converted into valuableconjugated benzofulvene building blocks.