Studies On The Electrophilic Addition Reactions Of Carbocations With Methylenecyclopropanes Or Allenes

The formation of carbon-carbon bonds, an efficient pathway to construct complex skeletons, is one of the most important reactions in organic synthesis. The electrophilic addition reactions with carbocations as electrophiles are efficient strategies to form carbon-carbon bonds. Normally, the electrophilic protocols are attractive due to the high efficiency of carbon-carbon bonds formation, excellent regio-and stereoselectivity and mild reaction conditions.Methylenecyclopropanes (MCPs), bearing both a cyclopropane unit and a C=C double bond, are highly strained but readily accessible molecules. An attractive but often troublesome feature of MCPs is their multi-forms of reactivity leading to the formation of a variety of different products. In the past decades, mounting attention has been paid to the electrophilic addition reactions of MCPs; however, examples utilizing carbocations as electrophiles are very rare. Thus, the exploration of the electrophilic addition of various carbocations to MCPs with controlling of the regio-and stereoselectivity is meaningful and challenging in organic synthesis. On the other hand, allenes are a class of compounds possessing propadiene units with high reactivity, which can also take part in the electrophilic reaction with carbocations. In this thesis, the electrophilic addition reactions of1,3-diarylallylic carbocations, diarylmethyl carbocations, propynyl carbocations to MCPs or allenes were disclosed, constructing new carbon-carbon bonds under mild reaction conditions and furnishing useful molecular skeletons. We have developed the following reactions:Firstly,1,3-diarylpropenes were introduced as the precursor of carbocations. In the presence of2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ),1,3-diarylallylic carbocations could be formed in situ and react with MCPs. Proximal cleavage occurred and the resulting intermediate would be attracted by H2O to afford homoallylic alcohol derivatives. In the presence of ZnCl2, the above-mentioned intermediate would be attacked by Cl-, leading to homoallylic chloride derivatives. Secondly, we introduced a hydroxyl group into MCPs as the intramolecular nucleophile. When (2-arylidenecyclopropyl)methanols were employed to react with1,3-diarylallylic carbocations,3-oxabicyclo[3.1.0]hexanes were generated with good regio-and stereoselectivity via electrophilic addition/intramolecular cyclization. On the other hand, when2-cyclopropylidene-2-arylethanols were introduced, the electrophilic addition/ring enlargement/vinyl group migration/intramolecular cyclization sequence gave stereo-specified product3-oxabicyclo[3.2.0]heptanes.Thirdly, we realized the first example of the electrophilic addition of allenes and1,3-diarylallylic carbocations, diarylmethyl carbocations and propynyl carbocations. Stereodefined allylic halorides could be generated by introducing1-aryl allenes. With the employment of1,1-disubstituted allenes, Friedel-Crafts cyclization reaction could occur to furnish indene derivatives with excellent regio-and stereoselectivity.Finally, we developed the electrophilic additions of NXS with1-cyclopropylallenes. Two functional groups were introduced simultaneously to give2,6-difunctional-1,3-hexadienes stereoselectively, which are useful synthetic motifs in the construction of complex structures.