Preparation And Application Of Heteroatom Substituted Cyclopropane Carboxylates

Cyclopropane, possessing the smallest carbon ring, can be observed in many natural products, and it has many unique reacitvities. This thesis focus on the synthesis of funcitionalized cyclopropane carboxylates and their further conversions, and it contains the following four chapters:1. a brief review on the preparation of functionalized cyclopropane,2. catalytic diastereo-and enantiocontrolled preparation of cis-β-fluorocyclopropane carboxylates,3. enantioselective preparation and desilylation of cis-β-silylcyclopropane carboxylates; and 4. asymmetric transfer hydrogenation of β-azidocyclopropane carboxylates.In Chapter one, we reviewed the preparation of functionalized cyclopropanes, and it could be divided into the following four parts:halo cyclopropanes, oxygen substituted cyclopropanes, nitrogen substituted cyclopropanes and silyl cyclopropanes.In Chapter two, we developed a catalytic diastereo-and enantiocontrolled preparation of cis-β*-fluorocyclopropane carboxylates through the Rh-catalyzed cyclopropanation of alkenyl fluorides with diazoarylacetates. A series of substrates were prepared, and Rh2(S-DOSP)4 and benzyl diazoarylacetates were found to be beneficial to the cyclopropanation with high diastereoselectivity. Thirteen cis-βfluorocyclopropane carboxylates were prepared in hexane at 0℃ with good to excellent yields. The enantiomeric excess was up to 97%, and the diastereomer ratio was up to 95:5.In Chapter three, we carried the research on the enantioselective preparation of βsilyl cyclopropane carboxylates and desilylation of the resulting silyl cyclopropane carboxylates. We observed that the Rh2(S·PTAD)4-catalyzed cyclopropanation of a-silyl styrenes with aryldiazoacetates could give the desired silyl cyclopropane carboxylates with excellent control of diastereo-and enantioselectivity (ee up to 99%, dr up to 99:1), and 23 cis-β-silyl cyclopropane carboxylates were prepared. The silyl group and ester group are observed to face to the same orientations. Further desilylation of the resulting βsilyl cyclopropane carboxylates afforded the rare and optically active cis-cyclopropane carboxylates.In Chapter four, we reported the asymmetric transfer hydrogenation of racemic β-azidocyclopropane carboxylates, affording a range of enantioenriched y-lactones. The Ru-TsDPEN was found to be a good catalyst for the reduction of β-azidocyclopropane carboxylates at 60℃ with the wet HCO2H/Et3N azeotrope. Eleven lactones were prepared through a four-step sequence of azide reduction/cyclopropane ring cleavage/ketone transfer hydrogenation/lactonization. The enantiocontrol and efficiency of the conversion were addressed, and the enantiomericexcess of the lactones was up to 94%, as the yield was up to 77%.