藥物合成反應(yīng)第四章縮合反應(yīng)-文庫吧資料
2025-06-01 18:21本頁面
【正文】 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(yīng)用 二 羰基 a位的亞甲基化反應(yīng) 1. 活性亞甲基的亞甲基化 Knoevenagel 反應(yīng) （ 1）反應(yīng)通式 ? （ 2）反應(yīng)機(jī)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。R 39。+C H 2 C H 2 R( C 6 H 5 ) 3 P ( C 6 H 5 ) 3 P COR 39。 ? 2) depending on the type and strength of the electronwithdrawing group (negative charge stabilizing group), the use of even relatively weak bases is possible (., NEt3)。 ? 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。nsted AcidCatalysis ? 4. Protonated Chiral Catalysis ? 5. ACDC ? 6. HBond Catalysis ? 7. PTC Trost, B. M. J. Am. Chem. , 128, 27782779. Proline catalysis Br248。 (87%) ? 引入 CH2Cl后，可進(jìn)一步轉(zhuǎn)化成其他官能團(tuán)并增長碳鏈。苯環(huán)上供電子基 ,有利于反應(yīng)進(jìn)行。 amines, terminal alkynes)。 ? 2) the reagents are usually thermodynamically stable but air and moisture sensitive and inpatible with acidi
職業(yè)教育相關(guān)推薦
鄂ICP備17016276號-1