Diisobutylaluminum Hydride Research Articles

Synthesis of Dihydrobenzosiloles and Silacyclopentanes by Double Hydroalumination of Terminal Alkynes

AbstractWe have developed an efficient method for the synthesis of 2,3-dihydro-1H-1-benzosiloles in 19% to 90% isolated yield from 1-hydrosilyl-2-ethynylbenzenes by using two equivalents of diisobutylaluminum hydride. The reaction mechanism involves regioselective double hydroalumination of the alkyne moiety followed by cyclization to a 2-alanyldihydrobenzosilole. A silacyclopentane (silolane) was also synthesized in 97% isolated yield from the corresponding 4-silylbut-1-yne under the same reaction conditions. Although the substrate-scope study was conducted on a 0.5-mmol scale, a gram-scale reaction of (2-ethynylphenyl)(diphenyl)silane under the optimized reaction conditions successfully afforded the desired product in 94% isolated yield without loss of reactivity.

Solution Structure and Dynamics of Hf-Al and Hf-Zn Heterobimetallic Adducts Mimicking Relevant Intermediates in Chain Transfer Reactions.

Cationic cyclometalated hafnocenes [CpPrCpCH2CH2CH2Hf][B(C6F5)4] (4Pr) and [CpiBuCpCH2CH(Me)CH2Hf][B(C6F5)4] (4aiBu and 4biBu) were synthesized from the corresponding [(CpPr)2HfMe][B(C6F5)4] (1Pr) and [(CpiBu)2HfMe][B(C6F5)4] (1iBu) complexes via C-H activation. 4aiBu, 4biBu, and 4Pr, mimicking a propagating M-polymeryl species (M = transition metal) with or without a β-methyl branch on the metalated chains, serve to investigate whether and how the nature of the last inserted olefin molecules changes the structure, stability, and reactivity of the corresponding heterobimetallic complexes, formed in the presence of aluminum- or zinc-alkyl chain transfer agents (CTAs), which are considered relevant intermediates in coordinative chain transfer polymerization (CCTP) and chain shuttling polymerization (CSP) technologies. NMR and DFT data indicate no major structural difference between the resulting heterobridged complexes, all characterized by the presence of multiple α-agostic interactions. On the contrary, thermodynamic and kinetic investigations, concerning the reversible formation and breaking of heterobimetallic adducts, demonstrate that isomer 4aiBu, in which the β-Me is oriented away from the reactive coordination site on Hf, but not 4biBu, having the β-Me pointing in the opposite direction, is capable of reacting with CTAs. Quantification of kinetic rate constants highlights that the formation process is rate limiting and that the nature of the last inserted α-olefin unit modulates transalkylation kinetics. The reaction of 4aiBu, 4biBu, and 4Pr with diisobutylaluminum hydride (DiBAlH) allows the interception and characterization of new heterobinuclear and heterotrinuclear species, featuring both hydride and alkyl bridging moieties, which represent structural models of elusive intermediates in CCTP and CSP processes, capturing the instant when an alkyl chain has just transferred from a transition metal to a main group metal, while the two metals remain engaged in a single heterobimetallic intermediate.

Access to α-all-carbon quaternary amides through the hydroamidation of allenes using DIBAL-H and isocyanates

A regio- and stereoselective hydroamidation of allenes using diisobutylaluminum hydride and isocyanates is described, resulting in the formation of α-quaternary amides.

Synthesis of α‐Quaternary Carboxylic Acids through Cu‐Catalyzed Hydrocarboxylation of Allenes with Diisobutylaluminum Hydride and Carbon Dioxide

AbstractA regioselective method for synthesizing β,γ‐unsaturated α‐quaternary carboxylic acids through the copper‐catalyzed hydrocarboxylation of allenes with CO2 is described. Allenes undergo hydroalumination with diisobutylaluminum hydride, followed by carboxylation of the resulting allylaluminum intermediate. The presence of an N‐heterocyclic carbene ligand is essential for enhancing the reactivity of the reaction. The good functional group compatibility of the reaction allows the synthesis of a wide range of functionalized α‐quaternary carboxylic acids with high regio‐ and stereoselectivities for synthetic and medicinal applications.

P- and N-type InAs nanocrystals with innately controlled semiconductor polarity.

InAs semiconductor nanocrystals (NCs) exhibit intriguing electrical/optoelectronic properties suitable for next-generation electronic devices. Although there is a need for both n- and p-type semiconductors in such devices, InAs NCs typically exhibit only n-type characteristics. Here, we report InAs NCs with controlled semiconductor polarity. Both p- and n-type InAs NCs can be achieved from the same indium chloride and aminoarsine precursors but by using two different reducing agents, diethylzinc for p-type and diisobutylaluminum hydride for n-type NCs, respectively. This is the first instance of semiconductor polarity control achieved at the synthesis level for InAs NCs and the entire semiconductor nanocrystal systems. Comparable field-effective mobilities for holes (3.3 × 10-3 cm2/V·s) and electrons (3.9 × 10-3 cm2/V·s) are achieved from the respective NC films. The mobility values allow the successful fabrication of complementary logic circuits, including NOT, NOR, and NAND comprising photopatterned p- and n-channels based on InAs NCs.

Harnessing the Peterson Reaction for the Stereospecific Synthesis of Z-Vinyl Ethers.

Vinyl ethers are valuable synthetic intermediates which are also found as natural products, including aflatoxins, rifamycins and plasmalogens. The latter are ubiquitous phospholipids in human cells and contain a vinyl ether moiety with specifically Z configuration. Although numerous methods are available for synthesis of vinyl ethers, there is a lack of methods for obtaining Z isomers of molecules of the type RCH=CHOR' that are applicable to plasmalogens. A variant of the Peterson reaction is described that generates such molecules with very high stereoselectivity (Z/E ratio: 99 : 1). (R,R)/(S,S)-1-alkoxy-2-hydroxyalkylsilanes were synthesized from 1-trimethylsilylalkynes by a sequence of reduction with di-isobutylaluminium hydride to a (Z)-1-trimethylsilylalkene, epoxidation of the alkene to a 2-trimethylsilyl-3-substituted epoxide and regioselective, boron-trifluoride catalyzed ring-opening of the epoxide by reaction with an alcohol. Conversion of the (R,R)/(S,S)-1-alkoxy-2-hydroxyalkylsilanes to vinyl ethers (RCH=CHOR') was achieved under basic conditions as in a standard Peterson reaction. However, near exclusive formation of a Z vinyl ether was only achieved when the reaction was performed using potassium hydride in the non-polar solvent α,α,α-trifluorotoluene, more polar solvents giving increasing amounts of the E isomer. The sequence described embraces a variety of substituents and precursors, proceeds in overall high yield and is readily scalable.

Conversions of seven-membered terpene lactones towards low-molecular bioregulators

The review describes the low-temperature reduction of (-)-mentholactone with diisobutylaluminum hydride in methylene chloride studied by the authors. It was found that, depending on the reaction conditions, it proceeds with the formation of three products: 7 S -isopropyl-4 R -methyloxepan-2 S -ol [(-)-mentholactol], 8-hydroxy-2,6 R -dimethyloctan-3-one or 2 S -isobutoxy-7 S -isopropyl-4 R -methyloxepane, for each of which the probable routes are given and the conditions for selective formation are selected. A new reaction in the chemistry of organoaluminum compounds has been discovered - the formation of isobutyl acetals of 2-oxepanols during low-temperature (-70°C) reduction of 7-membered lactones with two-fold or more molar amounts of diisobutylaluminum hydride in methylene chloride. On the basis of (-)-mentholactol, its aluminate, and 8-hydroxy-2,6R-dimethyloctan-3-one, a number of low molecular weight bioregulators, including optically active pheromones of insect pests in agriculture and forestry, have been synthesized.

Pilot-Scale Synthesis and Purification of α-Asaronol for Antiepileptic Drug Development

A simple and efficient pilot-scale process was developed for the synthesis and purification of α-asaronol ((E)-3′-hydroxyasarone). 4.29 kg of α-asaronol 4 (purity 99.92%) was produced in one batch, starting with 2,4,5-trimethoxybenzaldehyde 1 and ethyl hydrogen malonate 2 as raw materials to form intermediate ethyl (E)-3-(2,4,5-trimethoxyphenyl)acrylate 3 (yield 93.3%) by the Knoevenagel condensation reaction, which was then reduced by diisobutylaluminum hydride to produce α-asaronol 4 with a yield of 89.2%. Liquid chromatography-mass spectrometry (LC-MS) and nuclear magnetic resonance (NMR) spectroscopy analysis revealed four major impurities in the synthesis process, namely, (2,4,5-trimethoxyphenyl)methanol, 3-(2,4,5-trimethoxyphenyl)propan-1-ol, 5,5′-((1E,1′E)-oxybis(prop-1-ene-3,1-diyl)) bis(1,2,4-trimethoxybenzene), and diethyl 2-(2,4,5-trimethoxybenzyl)malonate. By adapting a commonly used recrystallization process through optimization, a large-scale purification method was developed for the purification of α-asaronol, achieving a purity of 99.92% by recrystallization. The pilot study lays the groundwork for the large-scale, high-yield, and high-purity preparation of the candidate drug.

Diisobutylaluminium hydride mediated efficient synthesis of Morita–Baylis–Hilman adducts through α‐functionalization of alkyl propiolates

AbstractGenerally, oxindole derivatives are biologically important molecules and valuable building blocks in organic synthesis. Herein, we report a diisobutylaluminium hydride mediated efficient one‐pot synthesis of oxindole derivatives using N‐substituted isatins with methyl or ethyl propiolates at lower temperature (−78°C) through Morita‐Baylis‐Hillman (MBH) reaction. Within a short reaction time, a wide range of N‐alkyl or N‐aryl 3‐hydroxy oxindole derivatives (MBH adducts) were easily accessed in excellent yields under mild reaction conditions.

A study of the DIBAL-promoted selective debenzylation of α-cyclodextrin protected with two different benzyl groups.

An α-cyclodextrin protected with 2,4-dichlorobenzyl groups on the primary alcohols and ordinary benzyl groups on the secondary alcohols was prepared and subjected to DIBAL (diisobutylaluminum hydride)-promoted selective debenzylation. Debenzylation proceeded by first removing two dichlorobenzyl groups from the 6A,D positions and then removing one or two benzyl groups from the 3A,D positions.

β‐Myrcene Coordination Polymerization: Experimental and Kinetic Modeling Study

AbstractThe present work presents phenomenological models to describe the coordination polymerization of β‐myrcene using the Ziegler–Natta catalyst system composed by neodymium versatate (NdV3), diisobutylaluminum hydride (DIBAH), and dimethyldichlorosilane. The kinetic parameters required to simulate the reactions are estimated, and the amount of DIBAH used as a chain transfer agent (CTA) is obtained by a data reconciliation strategy since it can participate in side reactions. Several experiments are performed at different conditions to evaluate the impact of key operation variables on the control of monomer conversion and average molar masses. It is shown that the initial NdV3, β‐myrcene, and DIBAH concentrations exert strong influences on the course of the polymerization. The kinetic mechanism of Coordinative Chain Transfer Polymerization (CCTP) fits well with the data of final average molar masses and monomer conversion, while the dynamic trajectories of these variables are fitted better by kinetic mechanisms of more conventional coordination polymerizations, considering site deactivation and termination by chain transfer. In all cases, the proposed models are able to predict the experimental data well after successful parameter estimation and reconciliation of CTA concentrations, indicating that the kinetic mechanism can be characterized by different kinetic regimes.

Analysis of the Mechanism of Polybutadiene Synthesis in the Presence of the Neodymium Versatate + Diisobutylaluminum Hydride + Ethylaluminum Sesquichloride Catalytic System within the Solution of the Inverse Kinetic Problem

Analysis of the Mechanism of Polybutadiene Synthesis in the Presence of the Neodymium Versatate + Diisobutylaluminum Hydride + Ethylaluminum Sesquichloride Catalytic System within the Solution of the Inverse Kinetic Problem

Synthesis of β,γ‐unsaturated ketones with quaternary centers through regioselective hydroacylation of allenes with acyl chlorides

AbstractThe one‐pot synthesis of β,γ‐unsaturated ketones bearing all‐carbon quaternary centers at the α‐position via a highly regioselective hydroacylation of allenes using acyl chlorides and aluminum hydride is reported. The Cu‐catalyzed hydroalumination of 1,1‐disubstituted and 1,1,3‐trisubstituted allenes with diisobutylaluminum hydride resulted in allylaluminum reagents that underwent regioselective acylation in the presence of acid chlorides. Various derivatives of allenes and acyl chlorides were compatible with this process, and α‐quaternary ketones were obtained in high yields with excellent regioselectivity.

Catalytic [2+2+2] Tandem Cyclization with Alkyl Substituted Methylene Malonate Enabling Concise Total Synthesis of Four Malagasy Alkaloids

Catalytic [2+2+2] Tandem Cyclization with Alkyl Substituted Methylene Malonate Enabling Concise Total Synthesis of Four Malagasy Alkaloids

Controlled reduction of activated primary and secondary amides into aldehydes with diisobutylaluminum hydride.

A practical method is disclosed for the reduction of activated primary and secondary amides into aldehydes using diisobutylaluminum hydride (DIBAL-H) in toluene. A wide range of aryl and alkyl N-Boc, N,N-diBoc and N-tosyl amides were converted into the corresponding aldehydes in good to excellent yields. Reduction susceptible functional groups such as nitro, cyano, alkene and alkyne groups were found to be stable. Broad substrate scope, functional group compatibility and quick conversions are the salient features of this methodology.

Acceleration of Sm(III) → Sm(II) reduction under the combined action of the chemical reductant diisobutylaluminum hydride and UV irradiation

It was found a significant acceleration of the reduction of Sm(III) during the joint action of the chemical reductant iBu2AlH (Bu = C4H9) and UV irradiation on the SmCl3·(THF)x–iBu2AlH complex. This complex is formed in interaction of iBu2AlH with the SmCl3·6H2O suspension in THF. The reduction process of Sm(III) is effectively controlled due to change in time of the photoluminescence and absorption spectra of the reaction solution. The complexometric method and elemental analyzes, as well as the UV–visible and IR spectroscopy were used for identification of the chemical composition of the SmCl2·(THF)2 complex, which was isolated from the reaction solution of a more bulky complex SmCl2·(THF)x–iBu2AlH. This bulky complex, like other known lanthanide Ziegler-Natta catalysts, is perspective as a catalyst for a number of organic reactions. Besides, it is advanced as a very efficient enhancer of chemiluminescent redox reactions of organoaluminum compounds. The mechanism of the Sm(III) ion reduction is proposed, which includes photolysis of the Al–H bond in the iBu2AlH hydride with the formation of atomic hydrogen (H). The latter, attacking complex SmCl3·(THF)x–iBu2AlH, reduces of Sm(III) to Sm(II).

Mathematical modeling and multiobjective optimization complex catalyst hydroalumination reaction of olefins with diisobutylaluminium hydride

A mathematical model for the catalyst hydroalumination reaction of olefins with diisobutylaluminium hydride has been developed. In solving the direct kinetic problem applies multi-step method Gere variable order. When solving systems of ordinary differential equations in chemical kinetics, it is necessary to fulfill the balance relations at each sampling point. That ensures the fulfillment of the law of conservation of matter and the convergence of the numerical method. For the catalytic reaction of hydroalumination olefins in the presence of the organoaluminum compound diisobutylaluminum hydride, the problem of multicriteria optimization reaction conditions was solved based on a detailed kinetic model. The solutions found make it possible to optimally select the reaction conditions to achieve the maximum yield of target products, which can be based on the subsequent introduction of the laboratory reaction into production.

A novel gas assay for ultra-small amounts of molecular oxygen based on the chemiluminescence of divalent europium

We have developed a novel assay O2-gas that allows selective determination of ultra-small amounts of molecular oxygen in gases, up to 0.18 ppm, which is one of the most sensitive assay reported so far. The assay operates with the registration of very bright chemiluminescence (CL) arising at the oxidation of diisobutylaluminum hydride iBu2AlH with oxygen in the presence of europium(II,III) compounds in the [Eu2+/3+-iBu2AlH-THF-O2] systems, where Eu2+/3+ = EuCl3·6H2O, Eu(fod)3, and EuBr2; Bu = C4H9. These systems showed the optimal spectral-brightness characteristics of CL for oxygen analysis, that have been established as a result of testing the effect of the nature of the ligand at the europium cation, organoaluminum compound, solvent, temperature, and other factors. The three systems have been successfully tested in the verification measurements of the oxygen concentration in artificial standard oxygen-argon mixtures. The CL response time to the introduction of O2 does not exceed 6 sec. The dependence of CL on oxygen concentration remains linear in the range from 44.68 to 0.18 ppm.

Synthesis of Polysubstituted Germoles and Benzogermoles Using a Substoichiometric Amount of Diisobutylaluminum Hydride.

We developed a synthetic route to unsymmetrically polysubstituted germoles bearing different substituents from 1-hydrogermyl-4-silyl-1,3-enynes. The reaction proceeded with 0.5 equiv of diisobutylaluminum hydride. Various 2-silylgermoles including benzogermoles were obtained in good to excellent yields. 2-Germylbenzogermoles could be also successfully synthesized from 1-hydrogermyl-4-germyl-1,3-enynes under the same reaction conditions.

A novel case of atom-efficient C-C bond formation of small molecules catalyzed by the facile organoaluminum compound

The environmentally friendly and inexpensive organoaluminum compound, diisobutylaluminum hydride (HAliBu2), acts as an efficient pre-catalyst for C-C bond formation by the addition of terminal alkynes to carbodiimides, which is a rare sample that the group 13 complexes to be used for catalyzing such reactions. Preliminary mechanistic studies revealed that the reaction is mainly carried out by initial hydroalumination of carbodiimide and followed by protonolysis with acetylene. A carbodiimide molecule was inserted into the Al-C bond of the generated alkynyl aluminum compound. The final product was obtained by the second protonolysis with acetylene.