Study On Ring Opening Reactions Of Donor-acceptor Cyclopropanes With Two Vicinal Acceptors

The vicinal electron-donating group and electron-withdrawing group in donoracceptor cyclopropanes reduce the ring opening energy barrier of cyclopropane,which makes them as highly reactive three-carbon synthons.Currently,most donor-acceptor cyclopropanes for ring opening reactions have two geminal acceptors,while those with two vicinal acceptors is less studied.In this thesis,two different ring opening patterns of donor-acceptor cyclopropanes with two vicinal acceptors have been established,providing new methods for the construction of 3-/5-ylidenebutenolides and 2-pyrones.1.TfOH-promoted ring-opening/aryl shift rearrangement to 3-and 5-ylidenebutenolides.The convenient synthesis of 3-and 5-ylidenebutenolides was realized through the ring opening reaction of cis-2-acylcyclopropane-1-carboxylates.Under the action of TfOH,the synergistic activation of cyclopropane produces a highly strained bicyclic oxocarbenium ion intermediate which undergo the ring-opening/aryl shift/deprotonation cascade process to form the 3-or 5-ylidenebutenolides.On the other hand,the corresponding trans cyclopropane isomers are difficult to form such intermediates,so that similar reactions cannot occur under the same conditions.2.Facile synthesis of polysubstituted 2-pyrones via TfOH-mediated ring expansion of 2-acylcyclopropane-1-carboxylates.A simple method for the synthesis of polysubstituted 2-pyranone from 2-acylcyclopropane-1-carboxylates mediated by TfOH was realized.In this reaction,the strong donor aryl stabilizes the 1,3-dipolar formed in the ring opening process,which is very important for guiding the C-C bond breaking of the donor-acceptor cyclopropane,and then forms 2-pyranone compounds by lactonization.