Studies on selective cleavages of small membered cyclic ethers with $SmI_2$

Abstract

The usefulness of $SmI_2$ as a versatile reagent in organic synthesis has been demonstrated by its widespread application for reduction of various functional groups, as well as its mediation of a range of promoting numerous synthetic transformations for the construction of complex organic compounds. The development of novel sequential reactions mediated by $SmI_2$ with high degree of stereo- and chemoselectivity has been described. A new and convenient method of iodination with samariumiodide complex has been developed. The present reaction provides an efficient method for the synthesis of iodohydrins in a regio- and stereoselective manner. This reaction was applied to the specific transformation of 2``,3``-anhydropurine nucleosides into 3``-deoxypurine nucleoside analogues including a natural product of cordycepin. A novel method of generating γ -lactones mediated by $SmI_2$ has been developed under mild conditions in high chemical yields. Tandem epoxide opening-cyclization reactions provided the construction of cis-fused bicyclic γ -lactones, spiro γ -lactones and $\alpha$ -methylene-γ-lactone derivatives. It has been found that epoxides cleaved to iodohydrins with catalytic amount of samariumiodide complex in a regio- and stereoselective manner. This reaction was also applied to the polymer-supported Sm reagent mediated transformation of epoxides into the iodohydrins. A novel method for tandem epoxide opening-iodocyclization reaction has been developed using catalytic amount of samariumiodide complex under neutral and mild conditions. Propiolate esters reacted with ketones in the presence of $SmI_2$ and t-BuOH to afford 4-hydroxy-(E)-2-alkenoic acid derivatives in moderate to good yields under mild reaction conditions. Acylative cleavages of cyclic ethers (3- to 5-membered rings) by chelation control between samarium and ether oxygen afforded functionalized acylated iodide compounds in high chemical yields with high regioselectivity. Treatment o...