Stereoselective Synthesis of Cyclic Ethers Using Vinylogous Sulfonates as Radical Acceptors: Effect ofE/ZGeometry and Temperature on Diastereoselectivity. by Evans Pa, Manangan T.
Treatment of the E-vinylogous sulfonates 1a−g with tris(trimethylsilyl)silane and triethylborane, in presence air, furnished cyclic ethers 2/3a−g good to excellent diastereoselectivity favoring cis-isomer 2. This study demonstrated level stereocontrol a 6-exo radical cyclization may be attributed type intermediate. Hence, modest selectivity obtained for 1e function acyl geometry (sp2) high inversion barrier (29 kcal/mol) as compared alkyl (1 vinyl (2.9 radicals. is consistent having an earlier transition state than corresponding The can improved dramatically using Z-vinylogous sulfonate (≥34:1; R = Ph) promote kinetic trapping s-trans rotamer I III, respectively (Figure 1). 5-exo reaction under nonreductive Keck-allylation condi…