藥物合成反應第四章縮合反應-wenkub
2023-06-10 18:21:15 本頁面
【正文】 es, terminal alkynes)。 (87%) ? 引入 CH2Cl后，可進一步轉化成其他官能團并增長碳鏈。 ? ② the reaction is usually carried out with a slight excess of the carbonyl pound (to ensure the plete consumption of the amine) in either protic or aprotic medium。+C H 2 C H 2 R( C 6 H 5 ) 3 P ( C 6 H 5 ) 3 P COR 39。 ? the stereoselectivity, Eor Zselectivity, is influenced by many factors: type of ylide, type of carbonyl pound, nature of solvent； ? The Wittig reaction has several important variants: HWE Reaction ? ① the phosphonate carbanions are more nucleophilic than the corresponding phosphorous ylides, so they readily react with practically all aldehydes and ketones under milder reaction conditions； ? ② the byproduct dialkyl phosphates are watersoluble, so it is much easier to separate them from the alkene products than from the waterinsoluble triphenylphosphine oxide. ? ③ high (E)selectivity for disubstituted alkenes under much milder conditions than normally used in Wittig reactions； ? ④ the (E)selectivity is maximized by increasing the size of the alkyl group of the R1 or R2 substituents ? ⑤ There are an important modifications of the HWE olefination: ? in the StillGennari modification R1=OCH2CF3 and the reaction affords (Z)olefins exclusively； ? for basesensitive substrates, the use of a metal salt (LiCl or NaI) and a weak amine base (., DBU) has proven effective to avoid epimerization. ? （ 4）應用 二 羰基 a位的亞甲基化反應 1. 活性亞甲基的亞甲基化 Knoevenagel 反應 （ 1）反應通式 ? （ 2）反應機理 （ 3）影響因素 ? ① the nature of the catalyst is important, usually primary, secondary, and tertiary amines and their corresponding ammonium salts, certain Lewis acids bined with a tertiary amine (., TiCl4/Et3N). ? ② the byproduct of the reaction is water and its removal from the reaction mixture by means of azeotropic distillation, the addition of molecular sieves, or other dehydrating agents shifts the equilibrium toward the formation of the product。 ? 2. 反應機理 ? 3. 影響因素 ? A
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