Suárez Rosa M, Pérez Sestelo José, Sarandeses Luis A
Departamento de Química Fundamental Universidade da Coruña 15071 A Coruña, Spain.
Chemistry. 2003 Sep 5;9(17):4179-87. doi: 10.1002/chem.200304790.
The stereoselectivity of the ultrasonically induced zinc--copper conjugate addition of iodides to chiral alpha,beta-unsaturated carbonyl systems under aqueous conditions was studied. Alkyl iodides add diastereoselectively to methylenedioxolanone 1 and methyleneoxazolidinone 2 to afford the 1,4-addition products in good yields (38-95 %) and with high diastereomeric excess (44-90 % de). The 1,4-addition to chiral gamma,delta-dioxolanyl-alpha,beta-unsaturated esters 3-5 also proceeds with good yields (51-99 %). The diastereoselectivity is dependent on the geometry of the olefin: the Z isomer 3 gives high diastereoselectivity, while the reactions with the E isomer 4 are nonstereoselective. The reaction proceeds with excellent chemoselectivity and allows the use of iodides bearing ester, hydroxy, and amino groups. Since the 1,4-addition products can be readily hydrolyzed, this methodology constitutes a novel entry for the enantioselective synthesis of alpha- and gamma-hydroxy acids and alpha-amino acids in aqueous media. The results obtained support the radical mechanism proposed by Luche, and represent one of the few examples of a radical stereoselective conjugate addition in aqueous medium.
研究了在水相条件下超声诱导碘化物对手性α,β-不饱和羰基体系进行锌-铜共轭加成反应的立体选择性。烷基碘化物非对映选择性地加成到亚甲基二氧戊环酮1和亚甲基恶唑烷酮2上，以良好的产率（38 - 95%）得到1,4-加成产物，且具有高的非对映体过量（44 - 90% de）。对手性γ,δ-二氧戊环基-α,β-不饱和酯3 - 5的1,4-加成反应也能以良好的产率（51 - 99%）进行。非对映选择性取决于烯烃的几何构型：Z异构体3具有高非对映选择性，而与E异构体4的反应是非立体选择性的。该反应具有优异的化学选择性，并且允许使用带有酯基、羟基和氨基的碘化物。由于1,4-加成产物可以很容易地水解，这种方法构成了在水介质中对映选择性合成α-和γ-羟基酸以及α-氨基酸的一种新途径。所获得的结果支持了Luche提出的自由基机理，并且是水相中自由基立体选择性共轭加成的少数例子之一。
