Sequential kinetic resolution of C2-symmetric compounds as a key step in two-directional synthesis: structural requirements for efficient resolution of difuryl diols
作者:Michael Harding、Robert Hodgson、Adam Nelson
DOI:10.1039/b206478b
日期:2002.10.29
The C2-symmetrical diols (R*,R*)-1,4-difuran-2-yl-butane-1,4-diol 13 and (1R*,3S*,4S*,6R*)-3,4-bis(tert-butyldimethylsilyloxy)-1,6-difuran-2-yl-hexane-1,6-diol 26 were synthesised in a two-directional manner: the reductions of (3R*,4R*)-3,4-bis(tert-butyldimethylsilyloxy)-1,6-difuran-2-ylhexane-1,6-dione with DIBAL-H and Red-Al were remarkably 1,3syn selective, presumably as a result of reduction of chelates formed from the 3-silyloxy-1-(2-furyl)ketones. Sequential Sharpless kinetic resolutions of 13 and 26 were studied. The first step of the kinetic resolution of 26 was shown to proceed with an enantioselectivity factor of E
= 1.9, and sequential resolution yielded the doubly oxidised product in 43% yield and 43% ee; this compares favourably with the enantiomeric excess (24% ee at 43% completion) of a product derived from a similarly enantioselective conventional kinetic resolution. The structural features of C2-symmetric substrates which are required for efficient sequential kinetic resolution, and the relevance of these reactions in two-directional syntheses, are discussed.
(R*,R*)-1,4-二呋喃-2-基-丁烷-1,4-二醇 13 和 (1R*,3S*,4S*,6R*)-3,4-双(叔丁基二甲基硅氧基)-1,6-二呋喃-2-基-己烷-1,6-二醇 26 的 C2 对称二醇以双向方式合成:用 DIBAL-H 和 Red-Al 还原 (3R*,4R*)-3,4-双(叔丁基二甲基硅氧基)-1,6-二呋喃-2-基己烷-1,6-二酮时,1,3syn 具有显著的选择性,这可能是由于 3-硅氧基-1-(2-呋喃基)酮形成的螯合物被还原的结果。研究了 13 和 26 的 Sharpless 顺序动力学解析。结果表明,26 的第一步动力学解析的对映选择性系数为 E = 1.9,顺序解析产生的双氧化产物的收率为 43%,ee 为 43%;这与类似对映选择性的传统动力学解析产生的产物的对映过量(完成度为 43% 时的ee 为 24%)相比更为有利。本文讨论了高效顺序动力学解析所需的 C2 对称底物的结构特征,以及这些反应在双向合成中的相关性。