hapter 6 Alkynes and Dienes Structure Alkynes sp-hybridized 6.1 Structure, Isomerism and Nomenclature( 结构, 异构和命名 ) Electronegativity( 电负性 ):sp>sp 2 >sp The acidity of the - bonds increases. The geometry at carbon is linear. The bond becomes shorter and stronger. Nomenclature ommon names 2 5 2 甲基乙炔 甲基乙基乙炔 乙烯基乙炔 IUPA names -ane -yne 1- 戊炔 2- 戊炔 - 甲基 -1- 丁炔 Isomerism 4,4- 二甲基 -2- 戊炔 4,4-dimethyl-2-pentyne 2 l 5- 甲基 -6- 氯 -2- 庚炔 6-chloro-5-methyl-2-heptyne (E)-- 戊烯 -1- 炔 (E)--penten-1-yne (Z)-,6- 庚二烯 -1- 炔 (Z)-,6-heptadien-1-yne Alkynyl groups( 炔基 ) 2 乙炔基 丙炔基 炔丙基 1- 丙炔基 2- 丙炔基 4- 乙烯基 -1- 庚烯 -5- 炔 4-vinyl-1-hepten-5-yne 1- 甲基 -2- 炔丙基环己烯 1- 甲基 -2-(2- 丙炔基 ) 环己烯 1-methyl-2-(2-propynyl)cyclohexene (E)-2- 己烯 -4- 炔 (E)-2-hexen-4-yne 1 2 4 5 6 7 5- 乙炔基 -1,,6- 庚三烯 5-ethynyl-1,,6-heptatriene l 1 4 顺 -1- 氯乙炔基 -4- 溴环己烷 cis-1-bromo-4-chloroethynylcyclohexane 1
6.2 Physical Properties( 物理性质 ) 6. eactions( 反应 ) 6..1 Acidity of terminal alkynes ( 末端炔烃的酸性 ) pk a = 25 pk a = 44 pk a = 50 - arbanion ( 碳负离子 ) onjugate base ( 共轭碱 ) a very weak acid( 很弱的酸 ) an exceptionally strong base( 非常强的碱 ) elative acidity( 相对酸性 ) F > S > > > > N 2 > = 2 > 2 Basicity of conjugate base ( 共轭碱的碱性 ) elative stability of anion ( 负离子的相对稳定性 ) N 2 N 4 - N Li 4 LiN 2 2 5 2 S 4 2 5 2 S 4-2 5 Na 2 2 5 Na A B - B A - (stronger acid) (stronger base) (weaker base) (weaker acid) Formation of metal alkynides ( 金属却化物的形成 ) NaN 2 liq. N : Na N LiN 2 liq. N : Li N n-buli Li n-bu Mg Mg : Na Addition to carbony compounds( 与羰基化合物的加成 ) carbony compounds( 羰基化合物 ) K 2 - press 2 2 / K press 2 - - 2 K -- Mechanism( 机理 ) B - - [Ag(N ) 2 ] Ag( 白 ) N - [u(n ) 2 ] u( 红棕 ) δ _ - - δ alogenation of terminal alkynes( 末端炔烃的卤代 ) - 2 6..2 eduction of alkynes ( 炔烃的还原 ) atalytic hydrogenation( 催化氢化 ) Lindlar s catalyst Pd-Pb/a 2 Pt Pt = 2 2 2 2 syn addition Metallic palladium deposited on calcium carbonate and is poisoned with lead acetate and quinoline Lindlar's catalyst quinoline eduction with Na or Li in liquid N ( 用金属钠或金属锂在液氨中还原 ) ( 2 ) 2 Mechanism ( 2 ) 2 1)Na / N (l), -78 o 2)N 4 l ( 2 ) 2 ( 2 ) 2 anti addition N 2 Na Na - Vinylic anion - adical anion ( 自由基负离子 ) N 2 Vinylic radical ( 乙烯基自由基 ) 2
eduction with LiAl4( 用氢化铝锂还原 ) LiAl 4 anti addition 6.. ydroboration( 硼氢化反应 ) B / TF B syn addition Anti-Markovnikov addition Tautomerism( 互变异构 ) 2 2 / - 氧化 Enol( 烯醇式 ) Keto( 酮式 ) ' 还原 ( 2 ) 5 B / TF ( 2 ) 5 B ( 2 ) 5 ' 6..4 Electrophilic addition( 亲电加成 ) E E A - 2 2 / - ( 2 ) 5 E A ( 2 ) 5 2 1) 活性 : 炔烃的亲电加成比烯烃困难, 并且可以与两分子试剂加成 ( 第二步的加成更困难 ), 如控制试剂用量则可以使反应停留在一分子加成产物上 2) 区域选择性 : 加成取向遵循马氏规则 ) 立体化学 : 大多是反式加成 EA E E A A Addition with ( 与卤化氢加成 ) gem-dihalide ( 偕二卤代物 ) eactivity of alkynes( 炔的活性 ) > > eactivity of hydrogen halides ( 卤化氢的活性 ) I > > l egioselectivity( 区域选择性 ) Markovnikov s rule( 马氏规则 ) gl 2 l 2 l 150~160 Stereochemistry( 立体化学 ) anti addition ( 反式加成 ) 2 5 I 2 5 I I I 2 5 I Peroxide effect( 过氧化物效应 ) Free radical addition( 自由基加成 ) n-bu peroxide peroxide n-bu= n-bu 2 Anti-Markovnikov addition ( 反马氏加成 ) Vic-dibromide ( 邻二溴代物 ) n-bu= n-bu= n-bu n-bu 2 Addition with 2 ( 与卤素加成 ) x 2 2 l l 2 l 2 Fel l l Fel 2 l 2 2 2 2 2 (1mol) 2 2 2 (1mol) 2 2 Stereochemistry( 立体化学 ) anti addition ( 反式加成 ) eactivity of halogens ( 卤素的活性 ) F 2 >l 2 > 2 >I 2
Addition with 2 ( 与水加成 ) 2 / g 2 egioselectivity( 区域选择性 ) Markovnikov s rule( 马氏规则 ) Enol to Keto (in Acid) Enol to Keto (in Base) 2 6..5 xidation of alkynes ( 炔烃的氧化 ) ' ' 1. 2. Ac 2 ' 2 1. KMn 4, - 2. 2 ' 2 6..6 Nuleophilic addition of alkynes ( 炔烃的亲核加成 ) N 2 =N ul base 2= 6..7 Polymerization of alkynes ( 炔烃的聚合 ) ul / N 4 l 2 2 u 2 l 500 2 = 6.4 Preparation of alkynes( 炔烃的制备 ) M base, - base, - 发生两次 E2 反应, 第二次更困难 Must be 1 alkyl halide δ δ- (the alkylating agent 烷基化试剂 ) ' _ ' Bimolecular nucleophilic substitution( 双分子亲核取代 ): S N 2 v = k[ 卤代烷 ] [ 金属炔化物 ] 6.4.1 Dehydrohalogenation of dihalides( 二卤代物脱卤化氢 ) NaN 2 2 2 mineral oil 110-160 o NaN 2 2 Na N 4l 2 2 2 NaN 2 2 mineral oil 2 110-160 o 2 2 K / alcohol NaN 2 / mineral oil heat 2 4
Migration of Triple Bond( 三键的迁移 ) Molten K or alcoholic K at 200 favors an internal alkyne. Sodium amide, NaN 2, at 150, followed by water, favors a terminal alkyne.( 熔融的氢氧化钾或者氢氧化钾醇溶液常使炔键移向链中, 而氨基钠使炔键移向链端 ) 6.4.2 Alkylation of metal alkynide ( 金属却化物的烷基化 ) NaN 2 liq. N : Na N LiN 2 liq. N : Li N n-buli Li n-bu base 2 2 2 base base 2 2 - Mg Mg δ δ- : Na M ' S N 2( 双分子亲核取代 ) Must be 1 alkyl halide (the alkylating agent 烷基化试剂 ) ' 2 - Na 2 2 2 Na S N 2 - ' '' 2 o Alkyl halide E2 ' '' - etrosynthetic Analysis( 逆合成分析 ) anti-addition 2 - Na I - Na I 1. NaN 2/liq. N 2. I 1. NaN 2/liq. N 2. I 1. Li,EtN 2 2. N 4 l TM onjugated dienes ( 共轭二烯烃 ) 共轭二烯烃 孤立二烯烃 累积二烯烃 5
2 1 2 6 4 1 5 1,-yclohexadiene 4 5 6 1,4-yclohexadiene 6.5 Structure and Physical Properties of onjugated Dienes ( 共轭二烯的结构和物理性质 ) 2 =-= 2 1,- 丁二烯 Allene not conjugated a b d e a b d e 2 2 rotate about 2 s-cis conformation s-trans conformation sp hybrid 6.5.1 π,π-conjugation(π,π- 共轭 ) 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2-2 2 6.5.2 The molecular orbital theory( 分子轨道理论 ) The Ms in the 1,-butene(1,- 丁二烯的分子轨道 ) Antibonding M 反键轨道 π π 4 Antibonding M 反键轨道 π π Bonding M 成键轨道 π π 2 Bonding M 成键轨道 π π 1 6
The Ms in the allyl system( 烯丙基体系 ) Allyl cation ( 烯丙基正离子 ) Allyl radical ( 烯丙基自由基 ) Allyl anion ( 烯丙基负离子 ) Antibonding M 反键轨道 π Nonbonding M 非键轨道 n Bonding M 成键轨道 π 6.6 eactions of onjugated Dienes( 共轭二烯的反应 ) 6.6.1 Aaddition with 2 or ( 与卤素或卤化氢加成 ) 2 == 2 2 == 2 2 15 o 2 60 o 2 = 2 2 = 2 (55%) (45%) 1,2-addition direct addition 1,4-addition conjugate addition 2 = 2 2 = 2 (1%) (99%) 1,2-addition 1,4-addition 80 o 2 2 2 40 o 2 (80%) (20%) 40 o 2 2 遵循马氏规则 (20%) (80%) Mechanism 2 2 2 2 2 2 2 2 1,2 Product 2 1,4 Product 2 2-80 o 40 o kinetic control or rate control ( 动力学控制或速率控制 ) 2 2 40 o (80%) (20%) 2 2 (20%) (80%) thermodynamic or equilibrium control ( 热力学控制或平衡控制 ) 2 7
Thermodynamic Versus Kinetic ontrol ( 热力学控制与动力学控制比较 ) The thermodynamic product is the most stable product ( 热力学产物是最稳定的产物 ). The thermodynamic product predominates when the reaction is reversible(thermodynamic control)( 当反应可逆时, 热力学产物占主导, 即反应受热力学控制 ). The kinetic product is the product that is formed most rapidly( 动力学产物生成得最快 ) The kinetic product predominates when the reaction is irreversible (kinetic control)( 当反应不可逆时, 动力学产物占主导, 即反应受动力学控制 ). igher temperature favors the formation of the thermodynamic product( 高温有利于热力学产物的生成 ). 6.6.2 Addition with 2 ( 与氢加成 ) 2 / Ni 1,2-addition 2 / Ni 2 =-= 2 1,4-addition 6.6. The Diels-Alder eaction 2 2 Synthetic method for preparing compounds containing a cyclohexene ring diene ( 二烯 ) Dienophile ( 亲二烯体 ) transition state cyclohexene ( 环己烯 ) tto Diels and Kurt Alder won the Nobel Prize for hemistry in 1950 for developing this reaction. N Morphine (M. Gates) holesterol (. B. Woodward) Prostaglandins F2a and E2 (E. J. orey) Vitamin B12 (A. Eschenmoser and. B. Woodward) Electrons flow from the M of the diene to the LUM of the dienophile. 2 ortisone (. B. Woodward) Me N Me 2 N Me Me Me Me eserpine (. B. Woodward) Influence of the structure of the reactants ( 反应物结构的影响 ) The diene must adopt the s-cis conformation in the transition state. Stereochemistry( 立体化学 ) syn addition( 顺式加成 ) stereospecific reaction( 立体专一反应 ) eaction is favored by electro-withdrawing groups (EWG) in the dienophile and electron-donating groups in the diene. N N N 2 5 2 5 6 6 98% 2 5 2 5 6 6 白 100 egioselectivity( 区域选择性 ) rtho- or Para- ( 邻 - 或对 -) 8
2 2 Endo product ( 内型 ) Exo product ( 外型 ) 生成内型反应速度快, 但外型更稳定 Alkynes Nomenclature Summary eactions (acidity-formation of metal acetylides, reduction-lindlar Pd ^ Na/N, hydroboration, electrophilic addition with ^ 2 ^ 2, oxidation with ^ KMn 4 )--- mechanism Preparation (dehydrohalogenation of dihalides, alkylation of metal acetylides)--- mechanism onjugated dienes 1,2- and 1,4-additions---mechanism Thermodynamic versus kinetic control Diels-Alder reaction---mechanism 9