Chemo- and stereoselectivity in the ring-openingreaction of epoxides with a reagent prepared from allylmagnesium halide and chlorotitanium triphenoxide is described. It has been proven that the allylating reagent can also be used for the reaction of epoxides bearing a tert-butyl ester, amide, or acetal moiety, and that the epoxide cleavage regioselectively takes place at the more substituted carbon
Asymmetric reduction of ethyl α-chloroacetoacetate (3) with Baker's yeast followed by treatment with sodium ethoxide afforded a mixture of ethyl (2R,3S)-( 8) and (2S,3S)-2,3-epoxybutanoate (9) (8/9, 85:15), which could be converted into the optically pure methyl (2R,3S)-2,3-epoxybutanoate (25) via one recrystallization of the brucine salt of the diastereomeric mixture of the corresponding epoxy acid.
Abstract. Kinetic data for the epoxidation of a series of α,β-unsaturated esters, 2-10, by dimethyldioxirane in dried acetone are reported. These epoxidations are less sensitive to steric effects and occur with lower k2 values than those for simple alkenes. Relative reactivity could be modeled based on a spiro transition state mechanism. The density function calculations were in good agreement with
Regioselective AlPO<sub>4</sub>–Al<sub>2</sub>O<sub>3</sub>Promoted Ring-Opening of 2,3-Epoxy Esters
作者:Juan Riego、Antonio Costa、José Manuel Saa
DOI:10.1246/cl.1986.1565
日期:1986.9.5
Synthetic AlPO4–Al2O3 promotes regioselective ring-opening of 2,3-epoxy esters by some oxygen and sulphur nucleophiles. Ritter type ring-opening with acetonitrile allowed the regioselective introduction of the acetamido group.