Studies On The Nucleophilic Addition Reactions Of Electron-deficient Allenes

Much attention has been paid to allenes chemistry due to their unique structures and reactivates in organic synthesis. Based on the results from our group on the nucleophilic addition reactions of electron-deficient allenes, my dissertation mainly focus on the conjugate addition reactions of Grignard reagents/organozinc reagents and2,3-allenoates with diversified substituents, as well as design of new reaction pathways for the reaction intermediates. Besides, intramolecular nucleophilic additions of electron-deficient allenes derivative from2,3-allenoic acids and benzynes have also been studied.The whole dissertation can be divided into three parts:Part1:Addition reactions of2,3-allenoates with Grignard reagents(1) FeCl3·6H2O catalyzed conjugate addition reaction of2,3-allenoates with Grignard reagentsIron catalyzed conjugate addition reaction of2,3-allenoates with Grignard reagents were continuously studied based on the research of Dr. Zhan Lu and FeCl3·6H2O was shown to be an efficient catalyst. β,γ-Alkenoates were obtained in good to excellent yields with high regio-and stereoselectivity and primary, secondary and tertiary alkyl, vinylic or aromatic groups may be introduced by using the readily available Grignard reagents. Compared with Fe(acac)3used in our previous reports, FeCl3·6H2O is slightly higher yielding, more readily available and extremely cheap, which is suitable for scale-up.(2) Synthesis of polysubstituted a-methoxycarbonyl allylsilanes and vinyl silyl ketenesStereodefined a-methoxycarbonyl allylsilanes were synthesized via Fe(acac)3catalyzed conjugate addition of Grignard reagents with2-trimethylsilyl-2,3-allenoates in good to excellent yields. The products could be used as allylation reagents to afford polysubstituted a,p-alkenoates with various electrophiles. Controllable regiospecific desilylations were also developed to afford α,β-alkenoates and P,y-alkenoates, respectively. Furthermore, altering the reaction conditions, the1,3(2)-dienolate intermediates could undergo elimination reaction to afford vinyl silyl ketene products. Applications of these products for the synthesis of stereodefined α-acyl substituted allylsilanes, stereodefined1,3-diene, and polysubstituted phenols have also been demonstrated.Part Ⅱ:Addition/cyclizations of2,3-allenoates with organozinc reagents(1) Addition/cyclizations of4-aryl-2,3-allenoates and organozinc reagentsDiversified poly-substituted a-naphthols have been efficiently constructed via a tandem reaction of4-aryl-2,3-allenoates and organozinc reagents in moderate to excellent yields. Some of the products may undergo a couple of sequential coupling reactions to afford polysubstituted naphthalenes.(2) Addition/cyclizations of4-alkyl-2,3-allenoates and organozinc reagentsThe reaction of4-alkyl-2,3-allenoates and organozinc reagents could afford polysubstituted cyclobutenones via a tandem conjugate addition/cyclic1,2-addition/elimination process. An application to the synthesis of stereodefined β,γ-unsaturated enones in the presence of organolithium reagents has been demonstrated.Part Ⅲ:Intramolecular nucleophilic additions of electron-deficient allene species.Chromone derivatives could be obtained from the reaction of2,3-allenoic acids with benzynes in moderate to excellent yields under mild conditions, involving intramolecular nucleophilic addition of electron-deficient allene intermediate as the key step. This protocol allows the diversity due to the substituent-loading capability of2,3-allenoic acids as well as benzynes.