STEREOCHEMICAL CONTROL IN RADICAL REACTIONS BY COMPLEXATION WITH LEWIS ACIDS

在Ln(Fod)_3存在下，α-溴-β-硅氧基酯的自由基烯丙化反应的立体选择性受到显著影响。在α-溴-β-硅氧基丁二酸酯的烯丙化反应中，需要化学计量的Lewis酸[Eu(Fod)_3或La(Fod)_3]来最大化立体选择性。而在α-溴-β-硅氧基丁酸酯与alpha-bromo-beta-silyloxy-beta-phenylpropanoate酯的反应中，Eu(FOD)_3对酯基的配位作用是催化的。在Lewis酸存在下，β-手性β-烷氧基-α-溴甲醛二甲缩醛和相应的烷氧基溴的非对映选择性显著提高。氢化反应用的MgI_2)。

Stereoselectivity in the radical-mediated allylation of alpha-bromo-beta-silyloxy esters yielding alpha-allyl-beta-silyloxy esters was remarkably affected when the reaction was conducted in the presence of Ln(fod)_3. In the allylation of alpha-bromo-beta-silyloxysuccinate esters affording preferentially syn diastereomers through the chelated trasition states was required stoichiometric amount of the Lewis acid [Eu(fod)_3 or La(fod)_3] to maximize the stereoselectivities, whereas in the reaction of alpha-bromo-beta-silyloxybutanoateesters and alpha-bromo-beta-silyloxy-beta-phenylpropanoate ester the effect induced by the coordination of Eu(fod)_3 to the ester group was catalytic.Diastereoselectivity in the radical mediated allylation and deuteration reactions of beta-chiral beta-alkoxy-alpha-bromoaldehyde dimethyl acetals and a related alkoxy bromide were remarkably enhanced when the reactions were conducted in the presence of Lewis acid (MgBr_2-OEt_2 for allylation ; MgI_2 for deuteration).