高等有机化学亲电加成反应.pptx

1第四章第四章 亲电加成反应亲电加成反应2（1）亲电加成）亲电加成(electrophilic addition)（2）亲核加成）亲核加成(nucleophilic addition)（3）自由基加成）自由基加成(radical addition)（4）环加成）环加成(cycloaddition)碳碳重键碳碳重键(multiple bonds)的加成反应的加成反应3一、碳一、碳-碳双键的亲电加成反应碳双键的亲电加成反应n 烯烃活泼的原因：烯烃活泼的原因：电子受核束缚力小，电子受核束缚力小，容易极化。容易极化。41.烯烃的亲电加成反应历程烯烃的亲电加成反应历程5Mechanism（1）involves prior dissociation of the electrophile and implies that a carbocation is generated that is free of the counterion Y-at its formation.（1）Prior dissociation of electrophile and formation of carbocation intermediate6（2）Formation of carbocation ion pair from alkene and electrophile.7Mechanism（2）also involves a carbocation intermediate,but it is generated in the presence of an anion and exists initially as an ion pair.Depending on the mutual reactivity of the two ions,they might or might not become free of one another before combining to give product.8（3）Formation a bridged carbonic intermediate from alkene and electrophile.9Mechanism（3）leads to a bridged intermediate that undergoes addition by a second step in which the ring is opened by a nucleophile.Mechanism（3）implies stereospecific anti addition.Mechanisms（1）,（2）and（3）are all AdE2 reactions:they are bimolecular electrophilic additions.10（4）Concerted addition of electrophile and nucleophile in a termolecular reaction11Mechanism（4）is a process that has been observed for several electrophilic additions and implies concerted transfer of the electrophilic and nucleophilic components of the reagent from two separate molecules.It is a termolecular electrophilic addition,AdE3,a mechanism that implies formation of a complex between one molecule of the reagent and the reactant and also is expected to result in anti addition.12 碳正离子历程碳正离子历程v=k isopropeneHCl（2）双分子历程）双分子历程13 生成结构稳定的碳正离子中间体生成结构稳定的碳正离子中间体n碳正离子中间体的碳正离子中间体的AdE2历程历程的条件的条件叔碳正离子中间体、苄基型碳正离子叔碳正离子中间体、苄基型碳正离子14 通常不具有立体选择性通常不具有立体选择性15 有时有重排产物出现有时有重排产物出现重排产物的出现可作为经碳正离子重排产物的出现可作为经碳正离子中间体历程的证据之一中间体历程的证据之一16 鎓型离子历程鎓型离子历程立体化学为立体化学为反式加成反式加成17“Bromine with two bonds and a positive charge?In a three-membered ring?In 1937,two Columbia chemists proposed just such a species as an intermediate in the reaction of ethylene with bromine.They were right.”18n 溴鎓离子具有八隅体结构，碳正离子为溴鎓离子具有八隅体结构，碳正离子为六电子体，前者比后者稳定。六电子体，前者比后者稳定。Br2,I2,IN3,RSCl or ArSCl,Hg(OCOCH3)2亲电试剂的原子半径要足够大亲电试剂的原子半径要足够大思考：思考：为什么形成溴鎓离子而不是碳正离子？为什么形成溴鎓离子而不是碳正离子？哪些哪些亲电试剂与烯烃可形成鎓型离子中间体？亲电试剂与烯烃可形成鎓型离子中间体？19 鎓离子存在的直接证据？鎓离子存在的直接证据？Biadamantylidene bronomium20（3）三分子历程（）三分子历程（AdE3）n 某些某些非共轭烯烃非共轭烯烃与与HX加成按加成按AdE3历程进行。历程进行。n 立体化学通常为立体化学通常为反式加成反式加成21complex22232.烯烃亲电加成反应的立体化学烯烃亲电加成反应的立体化学（1）反式加成（）反式加成（Antiaddition）24n AdE2：涉及环状鎓离子的形成：涉及环状鎓离子的形成反反式式加加成成25反式加成反式加成26反式加成反式加成27n AdE3：一分子烯烃和一分子烯烃与：一分子烯烃和一分子烯烃与HX形形成的络合物反应。成的络合物反应。反式加成反式加成28（2）顺式加成（）顺式加成（synaddition）碳碳双键与苯基共轭的烯烃碳碳双键与苯基共轭的烯烃和和HX的加成反的加成反应主要给出顺式加成产物应主要给出顺式加成产物29Ion pairOwing to the greater stability of the benzylic carbocations formed in these reactions,concerted attack by halide ion is not required for protonation.30对比立体选择性对比立体选择性31顺式加成顺式加成p硼烷与烯烃的加成为硼烷与烯烃的加成为顺式加成顺式加成32（3）无立体选择性的加成）无立体选择性的加成33实例实例1：l 解释双键碳原子上解释双键碳原子上连有苯基的烯烃与溴连有苯基的烯烃与溴加加成时，顺式加成产物增多。如：溴与反成时，顺式加成产物增多。如：溴与反-1-苯苯基丙烯反应所得反、顺式加成产物之比为基丙烯反应所得反、顺式加成产物之比为88:12；当双键碳原子所连的苯基上有给电子；当双键碳原子所连的苯基上有给电子基团时，顺式加成产物的比例也明显升高。基团时，顺式加成产物的比例也明显升高。34反式反式加成加成产物产物（88%）顺式顺式加成加成产物产物（12%）35反式反式加成加成产物产物（63%）顺式顺式加成加成产物产物（37%）36l 某些芳烃与卤素加成，主要生成顺式加成某些芳烃与卤素加成，主要生成顺式加成产物。产物。（35%）（10%）实例实例2：37提示：提示：38邻基参与邻基参与（注意）（注意）当双键邻位有带未共用电子对的基团存当双键邻位有带未共用电子对的基团存在时，该基团会对碳正离子中间体进行亲在时，该基团会对碳正离子中间体进行亲核进攻。核进攻。39例如：例如：40对比：对比：4142 某些某些五、六元环状内酯或环醚五、六元环状内酯或环醚的形成也和的形成也和邻基参与有关。邻基参与有关。43443.烯烃烯烃亲电加成反应的活性亲电加成反应的活性（1）烯烃结构对加成速率的影响）烯烃结构对加成速率的影响45结论：结论：Z为推电子基，使双键电子云密度增为推电子基，使双键电子云密度增加；稳定碳正离子中间体，降低活化能加；稳定碳正离子中间体，降低活化能46结论：结论：Z为吸电子基，使双键电子云密度为吸电子基，使双键电子云密度降低；使碳正离子中间体更不稳定，增加降低；使碳正离子中间体更不稳定，增加活化能活化能47Z为强吸电子基时为强吸电子基时，烯烃不发生亲电加成，烯烃不发生亲电加成反应，反应，发生亲核加成反应！发生亲核加成反应！4849（2）亲电试剂）亲电试剂对加成速率的影响对加成速率的影响 对于特定烯烃，卤化氢的加成速率与对于特定烯烃，卤化氢的加成速率与酸性强弱一致。酸性强弱一致。HI HBr HCl HF 对于特定烯烃，混合卤素的加成速率对于特定烯烃，混合卤素的加成速率与其异裂难易程度相符与其异裂难易程度相符ICl IBr I2504.烯烃亲电加成反应的定向规律烯烃亲电加成反应的定向规律n 区域选择性影响因素：区域选择性影响因素：电子效应，空间电子效应，空间效应。效应。51（1）电子效应）电子效应52n“Markovnikov 规则规则”？n“围绕碳正离子的围绕碳正离子的-C C单键旋转，当带单键旋转，当带正电荷碳原子的正电荷碳原子的p轨道轴和轨道轴和-C H键的键的 轨道轴在同一平面时，轨道轴在同一平面时，这两个轨道可发生这两个轨道可发生部分重叠，部分重叠，使部分正电荷分散到甲基上，使部分正电荷分散到甲基上，起稳定碳正离子的作用，这种现象称超共起稳定碳正离子的作用，这种现象称超共轭作用轭作用”。53n 对含对含强吸电子基团强吸电子基团的烯烃与的烯烃与不对称亲电试剂不对称亲电试剂的加成，从表面上看是反马氏规则的。的加成，从表面上看是反马氏规则的。54n 也适用于苯乙烯类与卤化氢等不对称试剂的也适用于苯乙烯类与卤化氢等不对称试剂的加成的区域选择性，加成的区域选择性，且当苯环上连有强吸电且当苯环上连有强吸电子基时，其区域选择性与吸电子基和双键碳子基时，其区域选择性与吸电子基和双键碳原子直接相连时相似。原子直接相连时相似。55（2）立体效应）立体效应56二、炔烃和丙二烯类的亲电加成反应二、炔烃和丙二烯类的亲电加成反应1.炔烃炔烃的亲电加成的亲电加成57p Since alkynes have type orbitals,it is not surprising that there is a good deal of similarity to the reactivity of alkenes.p The fundamental questions about additions to alkynes include the following:How reactive are alkynes in comparison with alkenes?What is the stereochemistry of additions to alkynes?58 What is the regiochemistry of additions to alkynes?The important role of bridged ions in addition reactions of alkenes raises the question of whether similar species are involved with alkynes,where the ring includes a double bond and bridged intermediates and would be expected to be substantially more strained.59p The basic mechansims that are considered to be involved in electrophilic additions to alkynes:vinyl cationsyn+antiAdE260 This mechanism involves a discrete vinyl cation.In general,this reaction will lead to a mixture of the two stereoisomeric addition products.61Bridged intermediateBridged intermediateAdE3AdE262 Mechanisms B and C depict bridged intermediates formed without or with participation of a second electrophilic molecule.They should lead to anti addition.63 Mechanism D is a termolecular process that would be expected to be a stereospecific anti addition.AdE364 In general,alkynes are somewhat less reactive than alkenes toward many electrophiles.A major reason for this difference in reactivity is the substantially higer energy of the vinyl cation intermediate that is formed by an electrophilic attack on an alkyne.p Reactivity65 For additions that proceed through bridged intermediates,the alkynes are also less reactive because of additional strain in the intermediate.p Reactivity66p Example 1.Hydrohalogenation Aryl-substituted acetylenes give mainly the syn addition product.vinyl cation(as ion pair)67 Alkyl-substituted acetylenes can react with HCl by either the AdE3 or the AdE2 mechanism,depending on the reactant structure and the reaction conditions.The stereochemistry is anti addition.68antiThe presence of Br-greatly accelerates the reaction69p Example 2.Halogenation of alkynesDisubstituted(internal)anti702.丙二烯类丙二烯类的亲电加成的亲电加成（注意）（注意）alleneallylic carbocation?vinyl carbocation71p The kinetically favored protonation at a sp2 carbon leads to the vinyl cation intermediate.p The reason is stereoelectronic:the allene structure is nonplanar,so that a protonation of the center carbon leads to a twisted structure that lacks of allylic conjugation.+72+中间过程缺乏烯丙基型碳正离子的共轭中间过程缺乏烯丙基型碳正离子的共轭73（1）丙二烯与卤化氢）丙二烯与卤化氢加成时，主要生成加成时，主要生成卤素卤素加到中间碳原子上加到中间碳原子上的产物的产物.主产物主产物74（2）丙二烯与卤素和汞离子）丙二烯与卤素和汞离子可形成桥状离子可形成桥状离子中间体，亲核试剂一般进攻其烯丙位。中间体，亲核试剂一般进攻其烯丙位。753.共轭二烯共轭二烯的亲电加成反应的亲电加成反应761,2-779.3 9.3 共轭二烯的亲电加成反应共轭二烯的亲电加成反应78低温，动力学控制（考察中间体的稳定性），主要生成1,2-加成产物；高温，热力学控制（考察产物的稳定性），主要生成1,4-加成产物。在同样的反应条件下，高温加热两异构体可得相同含量的混合物卤素和共轭多烯加成也可生成多种加成产物799.4 9.4 亲电加成反应在有机合成中的应用亲电加成反应在有机合成中的应用形成CX键、CO键、CN键、CC键等1.CX键的形成加X2，HX，HOX2.CO键的形成加H2O，醇，羧酸3.CN键的形成加NOCl，NO2Cl804.CC键的形成加RX，RCOCl81习题：习题：（1）比较下列化合物与）比较下列化合物与HCl反应的反应活性：反应的反应活性：（2）比较下列化合物与）比较下列化合物与Br2反应的反应活性：反应的反应活性：（3）完成下列反应方程式：）完成下列反应方程式：