Asymmetric Preparation And Transformation Of The Cyclopropylboronates

In this paper,a series of cyclopropylboronates were prepared by asymmetric cyclopropanation of vinyl boronates and diazoarylacetates and preliminary investigation was conducted on the further conversion of the cyclopropylboronates.The thesis is divided into the following three chapters:1.a brief review on the preparation of cyclopropylboronates;2.catalytic diastereo-and enantiocontrolled preparation of cyclopropylboronates;3.Study on the conversion of the cyclopropylboronates.In the first chapter,a literature review of the currently reported strategies for the cyclopropylboronates synthesis is carried out,and in particular,we focused on the asymmetric preparation of the cyclopropylboronates.It was discussed from the following five parts:Simmons-Smith type cyclopropanations;reaction of allylic carbonates or phosphonates with diboron derivatives;the hydroboration of cyclopropenes;the asymmetric boronation of cyclopropanes and the carbene reaction.In the second chapter,we developed a catalytic diastereo-and enantiocontrolled preparation of cyclopropylboronates through the Rh-catalyzed cyclopropanation of ?-vinyl boronates with diazoarylacetates.A series of substrates were prepared,and Rh2(S-PTTL)4 was found to be the best catalyst,21 kinds of cyclopropylboronates were prepared in hexane at 5? with good to excellent yields.The enantiomeric excess was up to 99%,and the diastereomer ratio was up to 99:1 with only a single isomer obtained.Futher substrate scopes show that:the cyclopropanation reaction can obtain both diastereo-and enantiocontrolled product with ?-boryl styrenes and ?-diazoarylacetates at the above catalytic system,while the reaction between ethyl diazoacetate and vinyl boronates cannot be proceed effectively.Based on the experimental results,the mechanism of stereochemical control of the reaction system was preliminarily discussed.In the third chapter,the studies on the conversion of the cyclopropylboronates were carried out.Take Methyl(1S,2R)-1,2-diphenyl-2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)cyclopropane-1-carboxylate 3aa as the template substrate,we tried the C-B bond transformations and coupling reaction,however,no positive results were obtained.The oxidation of Methyl(1S,2R)-1,2-diphenyl-2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)cyclopropane-1-carboxylate 3aa under the hydrogen peroxide gave a ring-opening product 4-oxo-2,4-diphenylbutanoic acid 4aa with a yield of 91%,and this method provides a new practical method for the synthesis of 1,4-dicarbonyl compounds.In addition,the conversion of the cyclopropylboronates to halo-containing trifluoroborates substituted cyclopropane obtained the target product methyl(IS,2R)-1,2-diphenyl-2-(trifluoro-14-boraneyl)cyclopropane-1-carboxylate potassium salt 5aa in 86%yield.This reaction provides a raw material for the subsequent C-B bond transformations study.