- Addition compounds of alkali-metal hydrides. 23. Preparation of potassium triisopropoxyborohydride in improved purity
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Commercial potassium triisopropoxyborohydride, K(i-PrO)3BH, or the usual material prepared at 25 °C from potassium hydride and triisopropoxyborane in tetrahydrofuran contains a significant impurity, detectable in the 11B NMR spectrum. This impurity, probably potassium tetraisopropoxyborohydride, significantly decreases the yield when the reagent is used to hydride thexylmonoalkylchloroboranes, ThxBR1Cl, for the synthesis of mixed thexyldialkylboranes. This impurity can be removed by refluxing a THF solution of the impure potassium triisopropoxyborohydride over potassium hydride. Alternatively, the reaction of triisopropoxyborane with excess KH in refluxing THF gives a product essentially free of the impurity. Storage of the solution KIPBH over a small excess of potassium hydride (～10%) maintains the product essentially free of the impurity. Use of this material permits the preparation of essentially quantitative yields of the desired mixed thexyldialkylboranes, ThxBR1R2, via the hydridation of the intermediate ThxBR1Cl in the presence of a second olefin.
- Brown, Herbert C.,Nazer, Behrooz,Sikorski, James A.
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- Base-Catalyzed Aryl-B(OH)2 Protodeboronation Revisited: From Concerted Proton Transfer to Liberation of a Transient Aryl Anion
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Pioneering studies by Kuivila, published more than 50 years ago, suggested ipso protonation of the boronate as the mechanism for base-catalyzed protodeboronation of arylboronic acids. However, the study was limited to UV spectrophotometric analysis under acidic conditions, and the aqueous association constants (Ka) were estimated. By means of NMR, stopped-flow IR, and quenched-flow techniques, the kinetics of base-catalyzed protodeboronation of 30 different arylboronic acids has now been determined at pH > 13 in aqueous dioxane at 70 °C. Included in the study are all 20 isomers of C6HnF(5-n)B(OH)2 with half-lives spanning 9 orders of magnitude: a and Sδ values, kinetic isotope effects (2H, 10B, 13C), linear free-energy relationships, and density functional theory calculations, we have identified a mechanistic regime involving unimolecular heterolysis of the boronate competing with concerted ipso protonation/C-B cleavage. The relative Lewis acidities of arylboronic acids do not correlate with their protodeboronation rates, especially when ortho substituents are present. Notably, 3,5-dinitrophenylboronic acid is orders of magnitude more stable than tetra-and pentafluorophenylboronic acids but has a similar pKa.
- Cox, Paul A.,Reid, Marc,Leach, Andrew G.,Campbell, Andrew D.,King, Edward J.,Lloyd-Jones, Guy C.
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supporting information
p. 13156 - 13165
(2017/09/26)
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- Synthesis of 3-(5-methylthiophen-2-yl)coumarins and their photochromic dihetarylethene derivatives
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Novel unsymmetrical di(thienyl)maleic acid anhydride, including coumarin moiety, has been designed and synthesized. Its photochromism study and fatigue resistance estimation are reported. Microwave-assisted procedure has been successfully used for synthesis of 3-(5-methylthiophen-2-yl)coumarins.
- Bochkov, Andrei Y.,Krayushkin, Mikhail M.,Yarovenko, Vladimir N.,Barachevsky, Valery A.,Beletskaya, Irina P.,Traven, Valery F.
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p. 891 - 898
(2013/08/23)
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- A new method for the chemoselective reduction of aldehydes and ketones using boron tri-isopropoxide, B(OiPr)3: Comparison with boron tri-ethoxide, B(OEt)3
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A chemoselective Meerwein-Ponndorf-Verley reduction process of various aliphatic and allylic α,β-unsaturated aldehydes and ketones is described. This chemoselective reduction is catalysed by boron triisopropoxide B(Oi Pr)3. Kinetics of reduction of aldehydes and ketones to corresponding alcohols were also examined and rate constant of each carbonyl compounds were measured. Rate constant and reduction yield of each carbonyl compounds in the presence of B(Oi Pr)3 were compared with those in the presence of B(OEt)3. The alcohols that are the reduction product were analysed by GC-MS. The rate constants and alcohol yields were found to be higher with B(OEt)3 than with B(Oi Pr) 3. The mechanism proposed involves a six-membered transition state in which both the alcohol and the carbonyl are coordinated to the same boron centre of a boron alkoxide catalyst. Indian Academy of Sciences.
- Uysal, Burcu,Oksal, Birsen S.
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body text
p. 681 - 685
(2012/06/18)
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- In vitro antibacterial and antifungal activities of some sulfur-nitrogen-oxygen and oxygen-nitrogen-oxygen donor bifunctional tridentate schiff bases and their boron(III) complexes
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Antimicrobial properties of sulfur, nitrogen, and oxygen bonded organoboron (III) complexes with biologically potent ligands viz., 2-hydroxy-N-phenyl benzamide hydrazine carboxamide(HO∩N∩OH), 2-hydroxy-N-phenyl benzamide hydrazine carbothioamide (HO∩N∩∩SH), and 2-hydroxy-N-phenyl benzamide hydrazine carbodithioic acid (HO∩N∩SH), have been studied. The unimolar and bimolar reactions of triisopropoxy borane with dibasic tridentate ligands resulted in the formation of colored solids, which have been characterized by elemental analysis, molecular weight determinations, and conductance measurements. The UV, IR, and NMR (1H, 13C, and 11B) spectral studies indicate a tetra-coordinated geometry for the resulting complexes. The ligands and their complexes have been screened for their fungicidal and bactericidal activities, and the results indicate that they exhibit significant antimicrobial properties. Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.
- Yadav, Sunita,Swami, Monika,Singh
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experimental part
p. 394 - 401
(2010/07/03)
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- Effect of the secondary reduction on the enantioselectivity and function of additives in the chiral oxazaborolidine-catalyzed asymmetric borane reduction of ketones
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The secondary reduction in the direct and oxazaborolidine-catalyzed asymmetric borane reduction of ketones was investigated by the use of GC/MS tracing titration and control experiments. The results indicate that the secondary reduction affects the enantioselectivity only in noncoordinated solvents at low temperature and not under the usual catalytic reduction conditions because the intermediate alkoxyborane is unstable and quickly converts to borane and dialkoxyborane. The function of an alcohol additive in the asymmetric borane reduction of ketones is to consume excess borane in the reduction system thus inhibiting noncatalytic reduction, which leads to increased enantioselectivity in the catalytic reduction.
- Liu, Han,Du, Da-Ming,Xu, Jiaxi
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p. 1067 - 1074
(2007/10/03)
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- Application of Mechanochemical Catalysis to the Synthesis of Boric Acid Esters
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The syntheses of triisopropyl borate and other boric acid esters under conditions of mechanochemical activation (MCA) with the use of zeolite catalysts were presented. The proposed method showed short synthesis times, low energy consumption, higher yields of target products, and the absence of byproducts. The mechanism of the catalytic esterification of boric acid under conditions of MCA was described. The conversion was no > 30%. The introduction of zeolites into the reaction zone increased the degree of conversion because of water removal from the reaction medium. Lower conversions of 2-butanol were related to its high viscosity, as a result of which the intensity of MCA was considerably decreased.
- Molchanov,Goidin,Golovin,Zolotovskaya,Bogdanov,Volodin
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p. 536 - 541
(2008/10/08)
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- Practical and efficient procedure for the in situ preparation of B-alkoxyoxazaborolidines. Enantioselective reduction of prochiral ketones
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A new method for the in situ elaboration of B-alkoxyoxazaborolidines is presented. Their use in the enantioselective reduction of prochiral aromatic ketones provides excellent chemical and optical yields of chiral alcohols.
- Ponzo, Viviana L.,Kaufman, Teodoro S.
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p. 495 - 496
(2007/10/03)
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- Convergent synthesis of alpha -aryl- beta -ketonitriles
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The present invention relates to processes for the production of alpha -aryl- beta -ketonitriles, which serve as synthetic intermediates in the preparation of a series of biologically important molecules such as corticotropin releasing factor (CRF) receptor antagonists.
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- Beitraege zur Chemie des bors, 226: Funktionalisierung von Alkinylboranen-Umsetzung mit Nucleophilen
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The synthesis of alkynylboranes RR'B-CC-R" 1-3 and their reactions with various nucleophiles are described (R, R' = Me2N, Cl, alkyl; R" = Me, Ph).Although these compounds can be looked upon as inorganic Michael systems, nucleophiles such as alcohols, amines, amides and various carbon nucleophiles attack exclusively at the boron atom (analogous to a 1,2- attack).Thus, a nonvenient means of functionalization of alkynylboranes at the boron atom with preservation of the B-CC moiety is described, and alkynylboranes with R,R' = Me2N, N(H)iPr, pyr, OiPr, Me, Mes, CC-SiMe3 were obtained in good yield and characterized by spectroscopic methods.The pathway for the reaction of (Me2N)2B-CC-Ph with carbon nucleophiles to tris(alkyl)boranes has been elucidated.The implications both for the electronic properties and the chemical reactivity of alkynylboranes are discussed.Keywords: Alkynylboranes, Nucleophilic attack, Organoboron compounds, Inorganic Michael systems; Boron; Alkyne
- Feulner, Herta,Metzler, Nils,Noeth, Heinrich
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- Organoboranes. 56. Systematic study of the reactions of 1-alkenylboronic esters with representative organolithium and grignard reagents to provide an efficient, selective synthesis of organyl-1-alkenylborinic esters
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A selective reaction of the ate complexes formed with 1-alkenylboronic esters and organolithium or Grignard reagents, by treatment with either Br?nsted or Lewis acids at -78 °C to give the corresponding organylalkenylborinic esters, is explored in this study. This systematic, detailed study reveals that the nature of the alkoxy group on boron, the nature and the amount of the alkyllithium or Grignard reagent used, the solvent, the reaction temperature, and the nature and amount of the acid used all play significant roles in influencing both the yield and the selectivity achieved for the formation of the desired organylalkenylborinates. Optimized procedures for the syntheses of representative organylalkenylborinic esters in high yield are summarized.
- Brown, Herbert C.,Vasumathi, Nagarajan,Joshi, Navalkishore N.
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p. 1058 - 1067
(2008/10/08)
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- Ready Preparation of Trialkoxyboranes and Dialkoxyboranes by LiBEt3H-Promoted Reaction of BH3 in Tetrahydrofuran with Alcohols
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A catalytic amount of LiBEt3H (1percent) promoted markedly the reactions of BH3 in tetrahydrofuran (THF) with stoichiometric amounts of alcohols (1:2 and 1:3) to provide corresponding trialkoxyboranes and dialkoxyboranes quantitatively under mild reaction conditions.
- Masuda, Yuzuru,Nunokawa, Yutaka,Hoshi, Masayuki,Arase, Akira
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p. 349 - 352
(2007/10/02)
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- Synthesis and characterization of boron complexes of nitrogen, oxygen and sulphur donor ligands
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The 1:1 and 1:2 molar reactions of triisopropoxyborane with ONO and ONS donors, semicarbazones and thiosemicarbazones of 2-hydroxy-2-phenylacetophenone and 3-hydroxy-2-butanone, lead to the formation of (PriO)B(ON O), (ON OH)B(ON O), (Pr1O)B(ON S) and (ON SH)B(ON S) types of complexes.These have been characterized by elemental analysis, conductivity measurements and molecular weight determinations.Electronic, IR, 1H NMR, 13C NMR and 11B NMR spectral studies have been used to deduce the structures of the resulting boron complexes.
- Singh, V. P.,Singh, R. V.,Tandon, J. P.
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p. 564 - 568
(2007/10/02)
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- Diastereo- and Enantioselective Aldehyde Addition Reactions of 2-Allyl-1,3,2-dioxaborolane-4,5-dicarboxylic Esters, a Useful Class of Tartrate Ester Modified Allylboronates
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The preparation and aldehyde addition reactions of the title compounds (1a-c) are described.These tartrate ester based reagents are the most highly enetioselective group of allylboronate esters reported to date.Reagent 1b prepared from diisopropyl tartrate reacts with achiral aldehydes to give homoallylic alcohols in good yield and high enantioselectivity (71-87percent ee).Interestingly, the greatest selectivity is obtained with α-branched aldehydes such as pivaldehyde (82percent ee) and cyclohexanecarboxaldehyde (87percent ee).These reagents also exhibit useful levels of matched and mismatched diastereoselection in reactions with chiral aldehydes.For example, the reaction of glyceraldehyde acetonide (4) and 1b is selective either for erythro alcohol 6 (96:4) or the threo diastereomer 7 (92:8) depending on the chirality of 1b and the reaction solvent.The asymmetric induction in these reactions appears to originate from a novel stereoelectronic effect involving n/n repulsive interactions between the aldehydic oxygen atom and an ester carbonyl in the disfavored transition state B.
- Roush, William R.,Walts, Alan E.,Hoong, Lee K.
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p. 8186 - 8190
(2007/10/02)
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- Addition compounds of alkali-metal hydrides. 24. A general method for preparation of potassium trialkoxyborohydrides. A new class of reducing agents
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The generality of the synthesis of potassium triisopropoxyborohydride, stabilized toward disproportionation by storing over excess potassium hydride, was examined with seven additional organoborates of varying steric requirements. The reaction of trimethoxy- and triethoxyborane with potassium hydride proceeded readily at room temperature, but the products could not be stabilized by the presence of excess potassium hydride. Triphenoxyborane reacted readily, even at -10°C, and stabilization was achieved. Tri-sec-butoxy- and tricyclopentoxyborane required refluxing in THF for 12-24 h, and the products were stabilized over potassium hydride. Finally, the reactions of tris(2-methylcyclohexoxy)- and tri-tert-butoxyborane were even slower, requiring a number of days for completion. Both products were stabilized toward disproportionation over potassium hydride. Indeed, potassium tri-tert-butoxyborohydride was quite stable toward disproportionation without excess potassium hydride. The stereoselectivities of these reagents in the reduction of representative cyclic ketones were examined. The stereoselectivities varied in an erratic manner with the steric requirements of the alkoxy group and did not approach the stereoselectivities previously achieved with lithium tri-sec-butylborohydride and lithium trisiamylborohydride.
- Brown, Herbert C.,Cha, Jin Soon,Nazer, Behrooz
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p. 2929 - 2931
(2008/10/08)
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- Borimide und Borylnitrene beim Zerfall von Diaminoazidoboranen
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Gas phase thermolysis of azidoboranes (R2N)2BN3 (1a, b) at 450-485 deg C gives the products 2a (by retro ene-reaction) and 4b (by intramolecular 1,2-alkylohydrogenation), respectively, both from boron imides R2N-B=N-NR2 (9a, b) as intermediates; furthermore, 3a is isolated from the thermolysis of 1a via a borylnitrene (R2N)2B-N by intramolecular 1,1-alkylohydrogenation.The photolysis of 1a, b generates the borylnitrenes 10a, b as intermediates, which are stabilized by an intermolecular reaction to 7a and 8b, respectively; the nitrene 10a can by trapped by ethyloboration with BEt3.
- Pieper, Werner,Schmitz, Dieter,Paetzold, Peter
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p. 3801 - 3812
(2007/10/02)
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- ORGANOBORANES. XXV. HYDRIDATION OF DIALKYLHALOBORANES. NEW PRACTICAL SYNTHESES OF DIALKYLBORANES UNDER MILD CONDITIONS
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Practical methods for the synthesis of dialkylboranes (R2BH) via the hydridation of dialkylhaloboranes (R2BX) have been developed.Convenient methods available for the preparation of R2BX via the hydroboration of alkenes with monohaloborane complexes (H2BX*SMe2) make this approach valuable for the preparation of various dialkylboranes, R2BH, many of which are not available by direct hydroboration of alkenes with borane itself.The suitability of various hydriding agents, such as borane derivatives, complex metal hydrides, and alkoxy metal hydrides, for the hydridationof R2BX was examined, utilizing B-halo-9-borabicyclononane as a representative dialkylhaloborane.In this case, the unusual stability of the resulting dialkylborane, 9-BBN, permits direct estimation of the reaction products by 11B NMR spectroscopy.The generality of the procedure has been demonstrated.
- Brown, Herbert C.,Kulkarni, Surendra U.
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p. 299 - 308
(2007/10/02)
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- A new route to boron nitride
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A new synthesis is described for preparation of boron nitride from the reaction of an alkyl polyborate-ammonia complex (RO)3B25O36·(NH3)8 with ammonia in the temperature range of 400-800°. The ammonia complex is obtained via a novel disproportionation of a trialkoxyboroxine to the corresponding trialkoxyborane and the ammonia complex. Boron nitride obtained under these conditions possesses a turbostratic structure.
- Economy,Anderson
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p. 989 - 992
(2007/10/05)
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