Two New Types Of D-A Cyclopropanes:Synthesis,[3+2] Annulation With Aromatic Aldehydes And Applications To The Syntheses Of Furanolignans

This dissertation focuses on the syntheses of two new types of donor–acceptor?D–A?cyclopropanes,namely chiral?-butyrolactone fused cyclopropanes and oxazolidinone-containing 2,3-disubstituted cyclopropane-1,1-diesters,has developed their[3+2]annulations with aromatic aldehydes respectively and using this as the lynchpin reaction has fulfilled the syntheses of several furanolignans.A three-step way to a series of new chiral?-butyrolactone fused cyclopropanes from enals and bromomalonate in moderate yields has been established by using a known organocatalytic asymmetric Michael addition-intramolecular alkylation sequence as key step.Under the optimized reaction conditions,namely 2.5 mol%of Sc?OTf?₃ as catalyst in 2.0 mL of 1,2-DCE at 40°C,the enantiospecific[3+2]annulation of such cyclopropanes with aromatic aldehydes proceeded well to provide a facile access to a series of chiral furanolignan derivatives bearing multiple contiguous stereogenic centers in good-to-excellent yields,exclusive diastereo-selectivities and excellent enantiopurities under mild reaction conditions.Elaboration work on the product of this reaction delivers stereoisomeric analogues of?+?-virgatusin in three steps.A new Michael addition/intramolecular alkylation sequence of?Z?-3-?2-bromo-3-arylacryloyl?oxazolidin-2-ones and malonates was developed.By a simple switch of the reaction conditions including the base promoter,solvent and reaction temperature,both the cis and trans isomers of a new series of oxazolidinone-containing2,3-disubstituted cyclopropane-1,1-diesters were obtained in good-to-excellent yields and with excellent diastereoselectivity.Using the AlCl₃-promoted[3+2]annulation of such cyclopropanes with veraldehyde or piperonal as the key step,diastereoselective syntheses of?±?-urinaligran and a stereoisomer of?±?-virgatusin have been achieved in four steps with 37.3%and 38.6%total yields respectively.All the new compounds have been fully characterized by ¹H,¹³C NMR,high resolution mass spectrometry?HRMS?and the configuration assignments of representative compounds have been confirmed by single crystal X-ray crystallographic analysis.