芳烃与烷烃化合物参与的光化学与电化学硼化反应

有机硼化合物是重要的有机合成砌块,并被广泛应用于材料与医药领域.发展实用、简洁的硼化反应合成有机硼化合物一直是有机硼化学的核心课题之一.近年来,光化学和电化学硼化反应取得了快速发展,已成为合成有机硼化合物的重要方法.从能量来源及反应底物类型的角度出发,总结了芳烃与烷烃化合物参与的光化学、电化学和光电化学硼化反应的研究进展,同时也对今后光化学与电化学硼化反应的发展方向进行了展望.     

基于自由基机理的有机硼酯化反应

有机硼酸和硼酸酯化合物是以Suzuki-Miyaura偶联为代表的多种重要化学反应的底物.发展有机硼化合物的高效合成方法具有重要意义.近十年来,基于自由基机理的有机硼酯化反应得以发展,并迅速成为高效构建碳硼键的一类重要方法.自由基硼酯化反应的一般策略为:利用不同反应条件产生的碳自由基活泼中间体与联硼化合物反应,生成相应的有机硼酸或硼酸酯.本文根据反应产生的碳自由基种类的不同,将硼酯化反应分为基于芳基自由基和基于烷基自由基两大部分.各部分依据自由基前体种类的不同,又具体分为基于碳氮、碳氧、碳卤等化学键的硼酯化反应以及羧酸脱羧硼酯化反应.最后,我们进一步总结分析了未来自由基硼酯化反应的研究趋势.     

铜催化烯烃的不对称加成硼化反应研究进展

铜催化烯烃的不对称加成硼化是构建手性碳硼键的有效方法,成为近年来有机化学的研究热点之一.从烯烃底物类型及反应类型的角度出发,总结了铜催化的烯烃的不对称加成硼化反应的研究进展.介绍了硼氢化反应及其串联反应以及包含硼化的双官能团化反应,以及以上反应的机理及发展现状,并对今后铜催化烯烃的不对称加成硼化反应的发展方向进行了展望.     

共轭双烯硼化质子化反应的研究进展

共轭双烯的硼化质子化反应由于反应条件温和以及官能团兼容性广泛,目前已经成为合成烯丙基硼化物以及高烯丙基硼化物的重要方法之一.随着多个课题组在本领域取得重要进展,共轭双烯的硼化质子化反应已经实现高化学选择性、区域选择性以及对映选择性转化.此外一些基于硼化质子化的高效串联反应已被设计并实现,并且有的方法已经被证实可以用于生物活性分子的高效合成.近年来,无过渡金属催化的共轭烯烃硼化质子化反应也被实现.本综述将总结共轭双烯的硼化质子化反应的研究进展,介绍各个反应的底物范围,并讨论反应的机理过程.     

路易斯碱-硼自由基在硼化反应、自由基催化和还原反应中的应用

自由基反应具有高效迅捷、选择性优良及官能团容忍性好等优点,是构建有机化合物的有效策略和方式之一.路易斯碱-硼自由基具有独特的结构和反应性能,在有机合成中表现出了良好的应用潜力.总结了我们课题组在路易斯碱-硼自由基促进的有机分子转化方面取得的一些进展.研究成果主要包括以下三个方面:路易斯碱-硼自由基促进的硼化反应、路易斯碱-硼自由基催化反应,以及路易斯碱-硼自由基引发的还原反应.这些反应具有条件温和,官能团容忍性好,产率高,化学、区域选择性好等优点.     

碳硼烷硼顶点选择性亲核取代反应

碳硼烷是一类由两个碳氢及十个硼氢顶点组成的笼状分子,在医学、材料、配位化学和金属有机化学等领域都有重要的应用,因此发展高效、简便的方法高选择性获取碳硼烷官能化衍生物具有重要的理论和现实意义.近年来,通过亲电取代、过渡金属催化、亲核取代等策略,实现了碳硼烷硼–氢键高效、高选择性官能化.本文根据硼–氢键的不同反应位点,评述了利用亲核取代反应策略进行碳硼烷选择性官能团化的研究进展,详细讨论了反应底物普适性、选择性控制及反应机理,并对该领域后续研究所面临的挑战和发展前景进行了展望.     

铁催化酮羰基的硼化反应合成α-羟基硼酸酯

报道了一种铁催化烷基酮类化合物硼化合成三级α-羟基硼酸酯的反应,使用了可商业购买的FeBr₂作为催化剂,加入醇作为添加剂来加速反应的进行,同时避免副反应的发生.通过该方法合成了一系列三级α-羟基硼酸酯化合物,反应具有很好的底物兼容性以及官能团兼容性.该铁催化剂对于大位阻的酮类化合物的硼化反应,表现出优于铜催化的活性.同时该反应可应用于克级规模的制备,随后通过对三级α-羟基硼酸酯的C-O键进行官能化,将所得的三级α-羟基硼酸酯转化为三级烷基硼酸酯以及偕二硼、偕硅硼类化合物.     

铑催化的硼氢化反应:卤化物和分子筛对苯乙烯类反应的区域选择性的影响

苯乙烯类化合物用邻苯二酚硼烷(CB)进行的铑催化的硼氢化反应是按马氏规则进行,与经典的硼氢化反应完全相反.一些金属卤化物、Lewis acid和分子筛可以进一步强化上述的反转的区域选择性.     

苯甲酮不对称还原反应的理论研究

本文用AM1分子轨道方法研究了1,3,2-噁唑硼烷对苯甲酮的不对称催化还原.反应经历了噁唑硼烷-硼烷配合物的形成及其与苯甲酮的结合、氢转移及脱去噁唑硼烷形成手性产物二级醇-硼烷配合物四步过程.获得了各步的反应热、速度控制步骤的过渡态结构和位能曲线及其相应的反应活化能,计算发现反应机理中的第3步氢转移产物有四员环结构特征.     

气相色谱-质谱联用法对三乙基硼合成反应副产物的研究

利用气相色谱/质谱联用技术对三乙基硼合成反应的产物进行了定性研究.进样量为5 μL,以HP-5毛细管柱(30.0 m×250 μm, 0.25 μm)为气相色谱柱,在柱温90℃、气化室温度120℃、载气为氦气、流量为0.8 mL/min的条件下,三乙基硼合成产物得到了很好分离.通过对该反应产物进行人工质谱解析,并结合计算机谱库检索,鉴定出三乙基硼合成反应的5种副产物.其中二乙基环硼氧烷在其它文献中未见报道.通过对反应过程的研究,讨论了多种副产物产生的机理,佐证了副产物的结构,为三乙基硼及其类似物的研究奠定了基础.     

Synthetic, spectroscopic and structural studies of two novel phosphanyl(organyl)borane compounds

The titanium (II) complex, Cp₂Ti(HBcat)₂, catalyzes the hydroboration of diphenylvinylphosphine by catecholborane and pinacolborane to afford exclusive anti-Markovnikov phosphanyl(organyl)boranes cleanly, rapidly and in good yields. Spectroscopic and X-ray studies of the phosphanyl(organyl)borane products show no evidence of boron-phosphorus interaction, indicating that the compounds preclude formation of Lewis pairs.     

Substrate-controlled highly diastereoselective synthesis of primary and secondary diorganozinc reagents by hydroboration/boron-zinc exchange sequence

The scope of substrate-controlled diastereoselective hydroborations can be considerably enhanced by a boron-zinc exchange reaction, providing organozinc derivatives that react with a broad range of electrophiles. Even normally unreactive boronic esters, obtained by Rh-catalyzed hydroboration with catecholborane, react readily with iPr2Zn providing the corresponding zinc reagents in high diastereoselectivity.     

A radical procedure for the anti-Markovnikov hydroazidation of alkenes

A one-pot procedure for the efficient hydroazidation of alkenes involving hydroboration with catecholborane followed by reaction with benzenesulfonyl azide in the presence of a radical initiator is described. The regioselectivity is controlled by the hydroboration step and corresponds in most cases to an anti-Markovnikov regioselectivity. This procedure is applicable to a wide range of alkenes and gives excellent results with 1,2-disubstituted and trisubstituted alkenes.     

Mechanistic and synthetic aspects of hydroboration with a simple atropisomeric ligand prepared from 1-(1′-(isoquinolyl)-2-naphthol

A novel triarylphosphite ligand has been prepared directly from both enantiomers of BINOL and a single enantiomer of 1′-(isoquinolyl)-2-naphthol. In one of the two cases cationic Rh complex proved to be reasonably effective in the asymmetric hydroboration of electron-poor styrenes. It was possible to identify binuclear reactive intermediates when the hydroboration pre-catalyst was examined in the presence of catecholborane at low temperatures.     

Intramolecular Cyclopropanation of 1,4‐Dienes through Hydroboration–Homologation: Easy Access to Bicyclo[3.1.0]hexanes

An intramolecular cyclopropanation reaction involving B‐(1‐chloroalkyl)catecholborane intermediates generated from 1,4‐dienes through hydroboration with catecholborane and Matteson homologation was developed. This sequential procedure leading to bicyclo[3.1.0]hexanes involves the formation of three new sigma C?C bonds at the same carbon atom. A mechanistic study supports the involvement of carbocationic intermediates.     

Catalytic asymmetric hydroboration of heterofunctional allylic substrates: an efficient heterogenized version

The hydroboration of heterofunctional allylic systems with catecholborane (HBcat) using neutral and cationic rhodium complexes modified with P–P and P–N bidentate chiral ligands has been described in order to produce the secondary heteroorganoboronate ester as a major product with moderate enantioselectivity. The immobilization of cationic chiral rhodium complexes onto clays has beneficial effects on the recyclability and reuse of the catalytic system in particular for the hydroboration of allyl aryl sulfones.     

Rhodium-catalyzed asymmetric cyclization/hydroboration of 1,6-enynes

[reaction: see text] Reaction of enyne 1 with catecholborane catalyzed by a 1:1 mixture of [Rh(COD)(2)](+)SbF(6)(-) and (S)-BINAP (5 mol %) followed by Pd-catalyzed arylation with p-IC(6)H(4)CF(3) gave benzylidenecyclopentane 5 in 65% yield with 88% ee. Rhodium-catalyzed asymmetric cyclization/hydroboration followed either by Pd-catalyzed arylation or by oxidation was applied to the synthesis of a number of chiral, nonracemic carbocycles and heterocycles.     

In quest of factors that control the enantioselective catalytic Markovnikov hydroboration/oxidation of vinylarenes

This study attempts to rationalise the unpredictable performance of transition metal catalysed asymmetric hydroboration of vinylarenes on varying the precursor of the catalyst from cationic to neutral species, [M(cod)(L-L)]BF4, [M(mu-Cl)(cod)]2/(L-L), the metal (M=Rh and Ir), and the hydroborating reagent (catecholborane, pinacolborane). The approaches are based on the agreement between experimental data provided by (R)-Binap and (R)-Quinap modified catalytic systems and computational data evidenced by DFT calculations and QM/MM strategies. Unprecedentedly high enantiomeric excesses in the hydroboration/oxidation of vinylarenes with both electron-withdrawing substituents ((R)-(+)-1-p-F-phenylethanol, ee up to 92 %) and electron-releasing substituents ((R)-(+)-1-p-MeO-phenylethanol, ee up to 98 %), can be attributed to a rhodium halide key intermediate.     

Convenient method for the preparation of catecholborane and promotion of the formation of alkenyl catecholborane using BH3 complexes

Catecholborane is prepared in benzene by passing B₂H₆, generated from I₂/NaBH₄, through a suspension of catechol at 25°C. The reagent prepared in this way is used for hydroboration-oxidation of representative alkenes and alkynes at 80°C. Hydroboration of 1-alkynes followed by iodination with I₂/NaOH gives the corresponding trans-1-alkenyl iodides in 70–72% yield. The alkenyl catecholboranes can be prepared at 25°C by performing the reaction in the presence of 10 mole% of H₃B:N(C₂H₅)₂Ph or H₃B:THF. The reaction is believed to go through hydroboration of the alkynes by borane followed by exchange with catecholborane. Studies of the preparation of dialkylphenoxyboranes and alkenyldiphenoxyboranes through hydroboration of 1-decene and 1-decyne by use of H₃B:N(C₂H₅)₂Ph and phenol are also reported.     

An unprecedented recyclable catalyst system for asymmetric hydroboration

Immobilised preformed chiral homogeneous catalysts were subjected to catalytic hydroboration of styrene with catecholborane and the activity, regio- and enantioselectivity observed were similar to those found when the corresponding homogeneous catalyst was used, remaining constant for several consecutive runs.