Synthesis of a (β-acetamido-α-acetoxyethyl)boronic ester via azido boronic esters

(Azidomethyl)boronic esters of 1,2-dicyclohexyl-1,2-ethanediol (“DICHED”) and pinanediol have been prepared from the corresponding (bromomethyl)boronic esters. Conversion to (2-azido-1-chloro- or bromoethyl)boronic esters by reaction with a (dihalomethyl)lithium followed. Attempted displacement of halide from DICHED (2-azido-1-haloethyl)boronates with alkoxides failed. Reaction of either pinanediol or DICHED (2-azido-1-chloromethyl)boronate with sodium acetate in acetic acid yielded the 1-acetoxy derivative as a ∼1:1 mixture of diastereomers, indicating probable involvement of an α-boryl carbocation intermediate. Hydrogenation of the pinanediol azido boronic ester over platinum in a solution of hydrogen chloride in dioxane was accompanied by deacetylation to form the impure (2-amino-1-hydroxyethyl)boronic ester hydrochloride. Attempted purification of this material resulted in deboronation to ethanolamine. Acetylation yielded pinanediol (2-acetamido-1-acetoxyethyl)boronate.     

Organosilatrane building blocks

Phenylsilatrane analogues containing reactive amino, bromo, boronic ester, and alkynyl functional groups for coupling reactions have been prepared. Pinacol boronic ester and ethynyl analogues were synthesized from 4-bromophenylsilatrane by palladium catalyzed reactions. The silatrane functional group was shown to be stable during the palladium catalysis procedures and silica-gel purification, making the molecules amenable to further synthetic manipulation. The described phenylsilatranes are useful building blocks for forming more complex organosilatrane species.     

A new boronic-acid based strategy to synthesize 4(5)-(het)aryl-1H-imidazoles

This paper describes the synthesis of a new N-THP protected 5-(1H)-imidazolyl boronic acid pinacol ester and its use in Suzuki cross-coupling reactions with a wide range of (het)aryl halides to provide 4(5)-(het)aryl-1H-imidazoles.     

雪松二醇-(R)-1氯-1-苯基甲基硼酸酯(phCHClBO_2C_(15)H_(24))的不对称合成和晶体结构

利用雪松二醇苯基硼酸酯进行不对称合成反应，制得标题化合物并测定结构．其晶体属正交晶系，空间群为P212121。结晶学多数为：a=5．728（3），b=8.543（3），c=41．267（7）A，V=2019．7A3；Z=4，Dc=1．23g／cm3，μ（CuKa）=17.7cm－1，R=0．0072，Rw=20．0077．独立可观察反射点数（I＞3σ（I））为739个。由晶体结构图可看出，由于雪松二醇基团的空间住阻效应，反应产物有很高的非对称选择性。     

“Solid-Liquid” Vitrimers Based on Dynamic Boronic Ester Networks

The "solid-liquid" behavior of vitrimers have not been systematically investigated. Herein, a series of "solid-liquid" vitrimers bearing varying contents of dynamic boronic ester bonds were synthesized via thiol-ene click reactions. These vitrimers allow for flexibile modulation of their network structures and thus show a range of intriguing properties including high stretchability, flexible transition from elasticity to plasticity, strong strain rate dependence, and solid-liquid performance. The dynamic association rate of boronic ester bonds within these vitrimers could be apparently accelerated via increasing the content of boronic ester, which could be used to shape-program the flat vitrimer films into various complex 3 D structures just with external force. Materials with such versatile dynamic behavior may open up a range of new applications.     

Stability of boronic esters - Structural effects on the relative rates of transesterification of 2-(phenyl)-1,3,2-dioxaborolane

Relative rates of reaction of the achiral cyclic phenylboronic ester 2-(phenyl)-1,3,2-dioxaborolane with a wide variety of structurally modified diols, have been studied to understand the factors influencing the relative stabilities of boronic esters. It is found that the alkyl substituents on the α-carbons of diols slow down the transesterification, but produce thermodynamically more stable boronic ester. Six-membered boronic esters are thermodynamically more stable than their corresponding five-membered analogs. Amongst cyclic 1,2-diols, cis-1,2-cyclopentanediol displaces ethylene glycol instantaneously whereas trans-1,2-cyclopentanediol is totally unreactive, which suggests that the cis-stereochemistry of the 1,2-diol is a prerequisite for transesterification. Among the 1,5-diols, diethanolamine displaces ethylene glycol quite rapidly forming a more stable bicyclic chelate in which nitrogen is attached to boron by a coordinating bond (as evident by ¹¹B NMR spectroscopy). The oxygen atom of di(ethylene glycol) and the sulfur atom of 2,2′-thiodiethanol do not assist in displacing the ethylene glycol from their boronic esters.     

Homologation and alkylation of boronic esters and boranes by 1,2‐metallate rearrangement of boron ate complexes

Organoboranes and boronic esters readily undergo nucleophilic addition, and if the nucleophile also bears an α‐leaving group, 1,2‐metallate rearrangement of the ate complex results. Through such a process a carbon chain can be extended, usually with high stereocontrol and this is the focus of this review. A chiral boronic ester (substrate control) can be used for stereocontrolled homologations with (dichloromethyl)lithium in the presence of ZnCl₂. Subsequent alkylation by an organometallic reagent also occurs with high levels of stereocontrol. Chiral lithiated carbanions (reagent control) can also be used for the reaction sequence with achiral boronic esters and boranes. Aryl‐stabilized sulfur ylide derived chiral carbanions can be homologated with a range of boranes including vinyl boranes in good yield and high diastereo‐ and enantioselectivity. Lithiated alkyl chlorides react with boronic esters, again with high stereocontrol, but both sets of reactions are limited in scope. Chiral lithiated carbamates show the greatest substrate scope and react with both boronic esters and boranes with excellent enantioselectivity. Furthermore, iterative homologation with chiral lithiated carbamates allows carbon chains to be “grown” with control over relative and absolute stereochemistry. The factors responsible for stereocontrol are discussed. © 2009 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 9: 24–39; 2009: Published online in Wiley InterScience ( www.interscience.wiley.com ) DOI 10.1002/tcr.20168     

A Comparative Study of the Relative Stability of Representative Chiral and Achiral Boronic Esters Employing Transesterification

A comparative study of the transesterification of five representative chiral and achiral boronic esters with various structurally modified diols was undertaken to qualitatively understand the factors influencing the relative stability of these boronic esters. Several factors such as chelation, conformation, steric bulk of the substituents, size of the heterocycle, and entropy influence the relative rate of transesterification as well as the stability of the boronic esters. Amongst these boronic esters, pinanediol phenylboronic ester was found to be the most stable boronic ester whereas DIPT boronic ester appeared to be thermodynamically the least stable one. The transesterification with sterically hindered diols was observed to be relatively slow, but afforded thermodynamically more stable boronic esters. Boronic esters derived from cis-cyclopentanediols and the bicyclo[2.2.1]heptane-exo,exo-2,3-diols are relatively more stable. This study not only presents the qualitative picture of relative stability of various boronic esters, but also provides helpful hints regarding the possible recovery of chiral auxiliaries. Many C ₂-symmetric chiral auxiliaries, such as 2,3-butanediol, 2,4-pentanediol, DIPT, and cis-cyclohexane-1,2-diol, can be retrieved by simple transesterification of the corresponding boronic esters with commercial inexpensive diols, such as pinacol, 1,3-propanediol, and neopentyl glycol.     

Regio‐ and Stereoselective Homologation of 1,2‐Bis(Boronic Esters): Stereocontrolled Synthesis of 1,3‐Diols and Sch 725674

1,2‐Bis(boronic esters), derived from the enantioselective diboration of terminal alkenes, can be selectively homologated at the primary boronic ester by using enantioenriched primary/secondary lithiated carbamates or benzoates to give 1,3‐bis(boronic esters), which can be subsequently oxidized to the corresponding secondary‐secondary and secondary‐tertiary 1,3‐diols with full stereocontrol. The transformation was applied to a concise total synthesis of the 14‐membered macrolactone, Sch 725674. The nine‐step synthetic route also features a novel desymmetrizing enantioselective diboration of a divinyl carbinol derivative and high‐yielding late‐stage cross‐metathesis and Yamaguchi macrolactonization reactions.     

Enantioselective difunctionalization of alkenes by a palladium-catalyzed Heck/borylation sequence

A palladium catalyzed enantioselective Heck/borylation reaction of alkene-tethered aryl iodides was realized, delivering a variety of 2,3-dihydrobenzofuranyl boronic esters in high yield with excellent enantioselectivity. Asymmetric synthesis of chromane boronic ester, indane boronic ester and indoline boronic ester was also accomplished. The protocol offers an efficient access to the corresponding chiral benzocyclic boronic esters, which are notably important chemical motifs in synthetic transformations.

A palladium catalyzed enantioselective Heck/borylation reaction of alkene-tethered aryl iodides was realized, delivering a variety of 2,3-dihydrobenzofuranyl boronic esters in high yield with excellent enantioselectivity.     

A Comparative Study of the Relative Stability of Representative Chiral and Achiral Boronic Esters Employing Transesterification

Summary. A comparative study of the transesterification of five representative chiral and achiral boronic esters with various structurally modified diols was undertaken to qualitatively understand the factors influencing the relative stability of these boronic esters. Several factors such as chelation, conformation, steric bulk of the substituents, size of the heterocycle, and entropy influence the relative rate of transesterification as well as the stability of the boronic esters. Amongst these boronic esters, pinanediol phenylboronic ester was found to be the most stable boronic ester whereas DIPT boronic ester appeared to be thermodynamically the least stable one. The transesterification with sterically hindered diols was observed to be relatively slow, but afforded thermodynamically more stable boronic esters. Boronic esters derived from cis-cyclopentanediols and the bicyclo[2.2.1]heptane-exo,exo-2,3-diols are relatively more stable. This study not only presents the qualitative picture of relative stability of various boronic esters, but also provides helpful hints regarding the possible recovery of chiral auxiliaries. Many C ₂-symmetric chiral auxiliaries, such as 2,3-butanediol, 2,4-pentanediol, DIPT, and cis-cyclohexane-1,2-diol, can be retrieved by simple transesterification of the corresponding boronic esters with commercial inexpensive diols, such as pinacol, 1,3-propanediol, and neopentyl glycol. This paper is dedicated to the memory of my mentor, the late Professor Herbert C. Brown (1912–2004). Professor Herbert C. Brown deceased on December 19, 2004. The work described herein was carried out at Purdue University during my stay as a post-doctoral research associate     

Synthesis of (E)-prop-1-ene-1,3-diyldibenzene derivatives via direct decarboxylative coupling of α,β-unsaturated carboxylic acids with benzyl boronic acid pinacol ester

The first copper-catalyzed cross-coupling reaction between benzyl boronic acid pinacol ester and α,β-unsaturated carboxylic acids was described. The ready availability of the starting materials and excellent E selectivity make this protocol a safe and operationally convenient strategy for the efficient synthesis of (E)-prop-1-ene-1,3-diyldibenzene derivatives.     

折叠链聚酯脲的合成与表征及其自组装行为研究

利用四甲基胍促进二羧酸与二溴代化合物的高效酯化聚合反应,设计、合成了一种新型手风琴式折叠链结构的聚酯脲.具有特殊结构的单体分别是4,4′-二羧基二苯基脲和3,5-二(溴代烷氧基)-苯甲酸酯,因此得到的聚酯脲具有类似接枝共聚物的结构.通过核磁氢谱(~1H-NMR)和傅里叶红外光谱(FTIR)对聚酯脲的结构及分子量进行了表征,结果显示,得到了分子量接近2×10~4的聚酯脲.通过核磁跟踪研究聚合反应动力学,结果表明,聚合反应速度与二溴单体的烷基链长度有关,二溴单体的烷基链较长时,聚合速率较慢.热重分析(TGA)结果显示,这种聚酯脲具有良好的热稳定性;由示差扫描量热(DSC)测试结果获知聚酯脲的熔融温度为57°C,表明它具有结晶性.脲基之间的氢键作用和苯环产生的π-π相互作用驱动这种聚酯脲在溶液中进行自组装.通过透射电子显微镜(TEM)研究聚酯脲的自组装行为,结果表明,该聚酯脲在氯仿和甲醇的混合有机溶剂中,静置4 h后,组装成片层结构;继续静置到3天后,形成了稳定的囊泡结构的聚集体,囊泡壁厚度约7 nm,接近折叠链宽度的预测值;小角X射线(XRD)测试结果表明聚酯脲是有序结构,进一步证实了合成的聚酯脲具有折叠链构象.     

Synthesis and optical behaviour of monodispersed oligo(fluorenylidene)s

The synthesis of the first series of monodispersed oligo(fluorenylidene)s is reported. The synthetic sequence envisages as key steps the obtainment (a) of a bis-pinacolboronate fluorenylidene dimer by a Ni(cod)₂ promoted homocoupling of the suitable 7-bromo-fluorenylidene boronic ester and (b) of the bis-pinacolboronate fluorenylidene trimer and tetramer by a Ni(cod)₂ promoted coupling of a 7-bromo-fluorenylidene boronic ester with 0.5 equiv of the corresponding 2,7-dibromofluorenylidene derivative. The optical properties of the obtained oligomers were studied. In the case of OF3 the optical behaviour was compared to that of a suitably synthesized fluorenone-containing model compound.     

2-二氟甲氧(硫)基吡啶-5-硼酸频哪醇酯类化合物的合成

以吡啶类化合物作为起始原料,先经二氟甲基化反应在羟基或巯基上引入二氟甲基基团,再用铱催化剂活化吡啶环的C-H并直接引入硼酸频哪醇酯基团,得到目标化合物,其产物结构经¹H NMR、¹³C NMR、MS和元素分析确证。该方法具有合成路线较短、反应条件温和、原料廉价易得以及产率较高等优点。     

Switchable Surface Wettability by Using Boronic Ester Chemistry

Here, we report for the first time the use of a boronic ester as an efficient tool for reversible surface post‐functionalization. The boronic ester bond allows surfaces to be reversibly switched from hydrophilic to hydrophobic. Based on the well‐known boronic acid/glycol affinity, this strategy offers the opportunity to play with surface hydrophobic properties by adding various boronic acids onto substrates bearing glycol groups. The post‐functionalization can then be reversed to regenerate the starting glycol surface. This pathway allows for the preparation of various switchable surfaces for a large range of applications in biosensors, liquid transportation, and separation membranes.     

Crystallization-controlled dynamic self-assembly and an on/off switch for equilibration using boronic ester formation

Macrocyclic boronic esters of different sizes can be prepared selectively from the same starting diboronic acid and 1,2-diol by means of an interesting dynamic self-assembly phenomena. More specifically, two kinds of macrocyclic boronic esters could be formed diastereoselectively and nearly quantitatively under neutral conditions by the addition of an appropriate guest molecule that acts as a template. Although a mixture of tetrol 1 and di(boronic acid) 2 in methanol gave only insoluble polymeric boronic esters, a soluble macrocyclic boronic ester, homo-[2+2], was obtained selectively in the presence of toluene as a guest molecule. Furthermore, when benzene was employed as a guest molecule, the selective formation of another macrocyclic boronic ester, hetero-[3+3], occurred. Interestingly, each of these macrocycles could be converted into the other in the presence of methanol and the appropriate guest molecule; however, under aprotic conditions, guest molecules encaged by the macrocyclic boronic ester could be exchanged without affecting its structure. Thus the presence or absence of a protic solvent could be used as a regulator to switch on or off the dynamic equilibrium of the system. In addition, investigation of the effect of reaction time, direct observation of the reaction mixture by NMR spectroscopy, and carrying out the reaction using optically active tetrol suggested that precipitation plays an essentially important role in the selective formation of the macrocyclic boronic esters. Thus, although both of [2+2] and [3+3] were present as solutes in the reaction mixture, the type of added guest molecule induced the selective precipitation of only one form of macrocyclic boronic ester, hence displacing the equilibrium of the system.     

基于聚醚胺(PEA)动态交联网络的多重响应性表面褶皱图案

刺激响应性表面图案赋予了材料动态可调的表面性能,是智能材料领域研究的热点,然而如何通过简单有效的方法构建这类动态表面图案也是该领域的难点.本文将动态硼酸酯键和光可逆二聚基团引入到聚醚胺(PEA)交联网络中,通过双层褶皱体系构建一系列具有光和湿度刺激响应性表面褶皱图案.在365 nm紫外光照和加热的条件下,蒽基团(AN)的光二聚与硼酸键的形成使得上表层聚醚胺模量变大,产生微米级表面褶皱图案;在254 nm紫外光照射或水蒸气作用下,聚醚胺网络解交联,表面褶皱图案消失;利用光化学时空分辨的特性,通过光掩膜板光照还可以制备多层次动态表面褶皱图案.这种多重刺激响应性表面褶皱图案为构建智能聚合物表面提供了新思路,在传感和防伪等领域具有潜在的应用前景.     

NAD(P)H辅酶模型在Mg2+离子催化条件下还原N-芳基芴亚胺反应的研究

对Hantzsch酯在Mg²⁺存在和不存在的情况下还原N-芳基芴亚胺的反应进行了研究, 并与BNAH的类似还原做了系统的比较.研究结果表明:Mg²⁺在该还原反应中起亲电催化剂的作用;还原能力较BNAH弱的Hantzsch酯在反应中所呈现的强的反应性是由于其3, 5-位两个极性谈基氧通过静电作用降低过渡态的能量的缘故;本文反应届H-一步转移机理.     

脂肪酶催化一步酯化协同拆分合成S-萘普生淀粉酯前药

利用CRL脂肪酶选择性催化外消旋萘普生甲酯与玉米淀粉进行转酯化反应合成光学纯S-萘普生淀粉酯前药,同时达到拆分外消旋萘普生的目的。考察了有机溶剂、脂肪酶用量、底物浓度比、反应温度对酯化协同拆分反应的影响,结果表明在异辛烷中脂肪酶CRL可以催化S-萘普生甲酯与淀粉发生转酯化反应同时完成外消旋萘普生的拆分,并且在脂肪酶用量为10%、底物浓度比为1:3、异辛烷用量为15mL、反应温度为60℃的条件下反应6d,外消旋萘普生甲酯的转化率为27.2%,产物对应体过量值eep高达99.4%可以作为萘普生的前药进行应用。