烯烃锆氢化反应的研究

本文报道几种烯烃锆氢化-氧化反应。锆氢化试剂(η~5-C_5H_5)2_Zr(CI)H(1)与苯乙烯(2),对-甲基苯乙烯(3),α-甲基苯乙烯(4)以及2,4,4-三甲基戊烯-1(5)反应,生成的烷基锆络合物经叔丁基过氧化氢处理得到醇。从5仅得到2,4,4-三甲基戊醇-1,而从(?)(R,R=＇H或CH_3)除主要得到S-醇外,还得到一定量的α-醇。这是在烯烃的锆氢化反应中未曾发现过的。对芳香族烯烃锆氢化反应的非区域专一性,从空间效应和电子效应两方面作了定性的解释。     

锆氢化反应研究I.酯类及双官能团化合物的锆氢化反应

本工作以一氯一氢二茂锆为还原试剂,对苯甲酸乙酯和苯甲酸甲酯进行还原,对还原的条件及水解产物的分离鉴定进行了研究。并对同时含酯基与其它官能团的几种化合物进行了选择性还原,列出了官能团还原先后的顺序,对结果进行了讨论。     

锆氢化反应研究 Ⅰ.酯类及双官能团化合物的锆氢化反应

本工作以一氯一氢二茂锆为还原试剂,对苯甲酸苯乙酯和苯甲酸甲酯进行还原,对还原的条件及水解产物的分离鉴定进行了研究。并对同时含酯基与其它官能团的几种化合物进行了选择性还原,列出了官能团还原先后的顺序,对结果进行了讨论。     

锆氢化反应热力学函数的计算

用B3LYP/SDD密度泛函方法计算了ZrH的微观性质,气态ZrH(D,T)的能量(E),熵(S)以及 Zr与氢同位素气体反应的热力学函数.在ZrH(s)、ZrD(s)和ZrT(s)的E和S的计算中,近似以分 子总能量中的振动能Ev代替固态能量,以电子和振动熵SEv代替固态熵.在这种近似下,计算了 不同温度下Zr与H2、D2、T2反应的ΔH、ΔG、ΔS及氢化反应平衡压力,导出了与温度 的依赖关系.计算结果表明,ZrH(s)的生成热为161.34 kJ穖ol-1,与实验值(173.5 kJ穖ol -1)接近,表明这种近似处理方法是合理的,可以用于研究贮氢材料氢化反应的热力学.     

芳硒基乙炔的锆氢化反应

芳硒基乙炔与Cp~2Zr(H)Cl可顺利进行锆氢化反应,继而质子解生成芳硒基乙烯,若经卤化则生成E型α-卤代芳硒基乙烯。     

锆氢化反应的研究——Ⅱ.锆氢化试剂高立体选择性还原炔醇

本文报道了炔醇的锆氢化反应。炔醇和两分子锆氢化试剂在室温反应可使还原产物高选择性地停留于烯醇,所得顺式烯醇的立体选择性高达100％。直链脂族a-炔醇锆氢化产物的产率为79～88％。当炔醇的羟基远离炔键时,由于减少了空间位阻使锆氢化产物的产率有所提高;在炔醇的a碳上有甲基取代基时,由于增加了空间障碍而使顺式烯醇产率下降。此外,后者在强酸介质中,部分异构化为反式烯醇及少量烯丙基型重排产物。本法是从炔醇合成顺式烯醇的一种新方法,它的主要特点是反应条件温和,立体选择性好以及产率较高。     

锆氢化反应——有机合成的新方法

主族元素的氢化物过去进行过大量的研究。如硼、铝、锡等元素的氢化物都有大量的报导,而过渡元素的氢化物是近年来才发展起来的。其中锆的氢化络合物是1970年以后才出现的一类新的过渡金属络合物,稀土元素的氢化络合物也有报导。过渡元素的氢化络合     

锆氢化反应研究（Ⅳ）：—芳腈的锆氢化反应及其在合成中的应用

芳腈在温和条件下进行锆氢化反应,所得产物经水解得到芳醛;若经酰基化则得到N-酰基不饱和胺。后者不稳定,在室温下与甲醇发生加成反应得N-(α-甲氧基苄基)苯甲酰胺。过量的锆氢化试剂与芳腈反应,继之进行酰基化,得到二元酰基化产物,两个酰基分别加到腈基的碳与氮原子上。     

锆钴合金氢化反应热力学函数的计算

在有效原子实势近似下,采用Gaussian 98计算程序及B3LYP/SDD密度泛函方法计算得到了ZrCo和ZrCoH分子的结构、力常数、离解能,能量(E)、熵(S)以及ZrCo与氢同位素气体反应的热力学函数.在固态ZrCo、ZrCoH(D、T)的E和S的计算中,近似以气态分子总能量中的振动能EV代替该分子处于固态时的振动能量,以电子运动和振动运动熵SEv代替分子处于固态的熵,在这种近似下,计算了不同温度下ZrCo与H2、D2、T2反应的ΔH、ΔG、ΔS及氢化反应平衡压力,导出了氢化反应温度与平衡压力的依赖关系.计算得出：ZrCoH、ZrCoD、ZrCoT的生成焓(398～598 K）分别为82.81、81.54和80.49 kJ•mol－1,与实验结果有很好的一致性,表明这种近似处理方法是合理的,可以用于一些未知氢化物的热力学函数的近似计算.     

二茂基氯氢化锆在有机合成中的研究进展

综述了二茂基氯氢化锆在最近十年的反应进展,包括与各类不饱和碳键、成环及开环反应,并对其发展的新方向进行了展望.     

Directed hydrozirconation of homopropargylic alcohols

Homopropargylic alcohols undergo directed hydrozirconation with Schwartz reagent (Cp₂ZrHCl) to generate vinyl-metal species in which the metal fragment is proximal to the alkoxide. Electrophilic trapping yields tri-substituted olefins in good yields with good control of regio- and stereochemistry. Experiments with a homopropargylic ether confirmed the role of the hydroxyl group in the directed hydrometalation.     

A case for asymmetric hydrozirconation

Hydrozirconation of cis-2-butene with Cp*ZrHCl[N(t-Bu)C(Me)N(Et)], generated in situ through hydrogenolysis of Cp*ZrCl(SiMe2Ph)[N(t-Bu)C(Me)N(Et)] (5), proceeds in high yield to produce a 1:2 mixture of the kinetically stable, diastereomeric sec-butyl complexes, 3a and 3b. Hydrozirconation of trans-2-butene under identical conditions provides a 2:1 mixture of 3a and 3b. Isolation of diastereomerically pure 3a was achieved through reaction of Cp*ZrCl2[N(t-Bu)C(Me)N(Et)] (4) with sec-butyllithium to provide a 2:1 ratio of 3a and 3b, followed by fractional crystallization. Crystallographic analysis of 3a establishes the relative configuration of the sec-butyl group with respect to the chiral zirconium center, thereby permitting construction of diastereomeric transition states that explain the origin of high face selectivity in the hydrozirconation of cis-2-butene. Finally, both iodinative zirconium-carbon bond cleavage and insertion of tert-butyl isocyanide into the zirconium-carbon bond of the sec-butyl group of 3a were found to proceed in high yield and with retention of the secondary alkyl structure. Together, these results provide a critical platform upon which efforts directed toward the asymmetric hydrozirconation of alkenes can be based.     

Stereoselective synthesis of spirooxindole amides through nitrile hydrozirconation

Spirooxindole amides can be prepared by the intramolecular addition of functionalized indoles into acylimines that are accessed from nitriles by hydrozirconation and acylation. The stereochemical outcome at the quaternary center was controlled by the steric bulk of the substituent at the 2-position of the indole unit. The products are well-suited for diversification to prepare libraries.     

Multicomponent approach to the synthesis of oxidized amides through nitrile hydrozirconation

"Oxidized" amides, as represented by acyl aminals and acyl hemiaminals, are integral subunits of several natural products that exhibit useful biological activity. In this paper a multicomponent approach to these groups from acylimine intermediates is demonstrated. The acylimines are accessed through a sequence of nitrile hydrozirconation and acylation, making this highly versatile amide synthesis useful for a range of applications in target- and diversity-oriented synthesis.     

Access to enantiomerically enriched cis-2,3-disubstituted azetidines via diastereoselective hydrozirconation

An asymmetric variant of the hydrozirconation reaction has been established starting from Boc-protected chiral allylic amines. The resulting diastereoselectively formed N-functionalized organozirconiums can be considered as promising chirons. In this case, they have been transformed into enantiomerically enriched cis-2,3-disubstituted azetidines through a iodination/cyclization sequence.     

The first example of hydrozirconation of alkynes in room temperature ionic liquids

Hydrozirconation of terminal alkynes in 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF₆]) at 30 °C gave highly regio- and stereoselectively (E)-vinylzirconium complexes, which underwent a cross-coupling reaction with aryl halides in the presence of Pd(PPh₃)₄ to afford (E)-1,2-disubstituted ethenes in good to high yields. Our system not only avoids the use of easily volatile THF or CH₂Cl₂ as solvent but also solves the basic problem of palladium catalyst reuse.     

Olefin isomerisation versus hydrozirconation: a case of a stable beta-hydrogen-containing Zr-alkyl derivative

Details of the olefin isomerisation mechanism followed by monohydride constrained-geometry zirconium complexes have been clarified using the allyldimethylsilylcyclopentadienyl zirconium hydride model compound. DFT calculations on the model systems agree with the experimental results.     

Synthesis of C-methyldesoxy sugars: Desoxygenation of tertiary alcohol xanthogenates and hydrozirconation of exomethylene derivatives of carbohydrates

Conclusions Two methods for the synthesis of C-methyldesoxy-sugars were proposed by desoxygenation of tertiary alcohol xanthogenates and hydrozirconation of exomethylene derivatives of carbohydrates.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No, 2, pp. 441–445, February, 1986.     

Transformation of 1,5- and 1,6-dienes to carbocycles by hydrozirconation and oxidation with cerium(IV) compounds

Cyclopentane and cyclohexane derivatives are prepared from 1,5- and 1,6-dienes in a one pot procedure by hydrozirconation, then oxidation of the generated 5- and 6-alkenylzirconocene chlorides with ammonium hexanitratocerate.