仲醇与酮加成.ppt

第十二章 醛酮 第三讲 和Grignard试剂加成 加成产物水解后生成醇。 也可以在分子内发生，合成环状化合物。 RMgX与镁相连的碳原子带负电荷，具有强亲核性，与醛、酮、酯发生加成反应，产物为醇。 与甲醛加成：伯醇 与其他醛加成：仲醇与酮加成：叔醇 * 例如：2-丁醇的合成： 3-甲基-3-己醇的合成： Wittig Reaction 醛或酮和磷叶立德(ylide)发生亲核加成后再消除，生成烯烃。 Georg Friedrich Karl Wittig (1897–1987) was born in Germany. He received a Ph.D. from the University of Marburg in 1926. He was a professor of chemistry at the Universities of Braunschweig, Freiberg, Tübingen, and Heidelberg, where he studied phosphorus containing organic compounds. He received the Nobel Prize in chemistry in 1979, sharing it with H.C. Brown Wittig Reaction 磷叶立德 Phosphorus Ylides ? 三苯基膦(triphenylphosphine)与无位阻的卤烷发生SN2反应制备。 ? 正丁基锂(Butyllithium) 脱除与磷相连的碳上的一氢。 Mechanism for Wittig This reaction is the best way to make a terminal alkene Stereoselectivity(立体选择性)of the Wittig reaction Ylides can be divided into two types: Stabilized ylides have a group, such as a carbonyl group, that can share the carbanion’s negative charge; unstabilized ylides do not have such a group. Stabilized ylides form primarily E isomers unstabilized ylides form primarily Z isomers The synthesis of β-carotene(胡罗卜素) from vitamin A is an important example of the use of the Wittig reaction in industry. Notice that the ylide is a stabilized ylide and the product has the E configuration at the reaction site. Problem 3 (3) 氮亲核试剂 醛或酮和氨及其衍生物加成时，所得到的产物往往不稳定，常进一步脱水生成含有碳氮双键的化合物。 ①和氨反应： 醛或酮和氨反应生成羟胺，羟胺很不稳定，脱水得到亚胺。 和伯胺反应： Schiff碱 醛或酮与伯胺的生成的羟胺，由于氨基上还有H而不稳定，马上脱水生成亚胺，称为Schiff碱。 脂肪族亚胺一般不稳定，容易分解；芳香族亚胺则较稳定。 Formation of Imines 氨或伯胺发生亲核加成，再消除脱水 C=O becomes C=N-R Addition of Primary Amines Formation of Imines imine（亚胺）称为Schiff碱 这是一个亲核加成－消除反应 反应体系中的 pH 必须严格控制 Loss of water is acid catalyzed, but acid destroys nucleophiles. nucleophilic addition–elimination reaction Dependence of the rate of the reaction of acetone with hydroxylamine on the pH of the reaction: a pH rate profile Optimum pH is around 4.5 亚胺的形成是可逆的：在酸性水溶液中，亚胺可水解回原来的醛或酮 烯胺的形成Formation of enamines Aldeh