Studies On The AllylSmBr Mediated "Ester-alkene" Cascade Coupling/Cyclization For The Synthesis Of Cyclopropanol Derivatives

Samarium(II)iodide has been widely used as a single electron transfer agent and a reducing agent for the reduction of functional groups and the formation of C-C bonds.However,reports on allylSmBr as a single electron transfer reagent are still few.To further study on the chemical properties of allylSmBr and develop new bivalent samarium reagents,the dissertation studied the use of additives to tune the reactivity of allylSmBr and developed the methods for the preparation of cyclopropanol derivatives using the allylSmBr/additives system.It is divided into two parts:In the first part,the synthesis of oxobicyclo[3.1.0]hexan-l-ols by allySmBr-promoted"ester-alkene" coupling/cyclization of a-allyloxy esters has been described.a-Allyloxy esters are readily available,however,the synthesis of oxobicyclo[3.1.0]hexan-l-ols by the known Kulinkovinch method has been unsuccessful by the substrates.By screening the proton source such as H2O,alcohols and organic acids,an optimized reaction condition was finally established and CH3SO3H was found to be the best co-additive.Promoted by allylSmBr/HMPA/CH3SO3H,a variety of oxobicyclo[3.1.0]hexan-l-ols were synthesized in moderate to good yields and also in good diastereoselectivity.The relative configuration of the oxobicyclo[3.1.0]hexan-l-ols has been confirmed by X-ray single-crystal diffraction and a rational explanation for the stereoselectivity has been provided.Besides,by control experiments and the detection of generation of propene,a new Sm(II)species,namely,CH3SO3SmBr,was proposed as the key reagent for the promotion of the reaction,which possess better reductive coupling ability than that of common Sm(II)reagents such as SMI2.Part 2 explored the feasibility of the "ester-alkene" coupling/cyclization of the esters of homoallylic alcohols for the synthesis of cyclopropanol derivatives.It has been found when allylSmBr,HMPA,samarium powder and TMSBr were used in the molar ratio of 0.3/1.2/3.3/1.0,the Sm(II)could be recycled and the the esters of homoallylic alcohols could be consumed gradually to afford the desired cyclopropanol derivatives in reasonable to moderate yields.The notable advantage of the method is the great reduction of dosage of HMPA(from 12 equiv.to 1.2 equiv.),thus making the reaction greener.However,it should be pointed out the yields of the desired products were unsatisfactory and the deprotection of the esters occurred to a significant extent.Therefore,more investigation has remained to be conducted to further develop the catalytic reaction into a practical useful synthetic method.In conclusion,the studies of the dissertation have broadened the applications of allylSmBr in organic synthesis and are helpful for further developing useful novel divalent samarium reagent.