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1.
Marilyn M. Olmstead James C. Fettinger Soya Gamsey Jacob W. Clary Bakthan Singaram 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(6):o333-o335
The structures of three chiral vinyldioxazaborocanes are reported, namely (2E)‐ and (2Z)‐6‐benzyl‐2‐buten‐2‐yl‐1,3,6,2‐dioxazaborocane, C27H30BNO2, (II) and (III), respectively, and (2Z)‐2‐buten‐2‐yl‐6‐isobutyl‐1,3,6,2‐dioxazaborocane, C24H32BNO2, (IV). These compounds may be useful in asymmetric reactions. In the structures reported here, the N—B donor–acceptor bond is longer than in any previously reported analogous compounds. 相似文献
2.
Organoboranes, readily available via the hydroboration of unsaturated organic compounds, exhibit a remarkable versatility
in their reactions. The boron atom in these organoboranes can be readily converted into a wide variety of organic groups under
very mild conditions, providing simple versatile syntheses of organic compounds. Exploration of these substitution reactions
reveal that, with rare exceptions, the organoboranes transfer the alkyl group to other elements of synthetic interest with
complete retention of stereochemistry. Recently we have discovered a method of synthesizing essentially optically pure organoborane
intermediates. These optically active alkyl groups attached to boron can also be transferred with complete retention of optical
activity. Consequently, it is now possible to achieve by a rational synthesis the preparation of almost any optically active
compound with a chiral center, either R- or S-, in essentially 100% enantiomeric excess. 相似文献
3.
Facile and convenient synthesis of B-amino-9-borabicyclo[3.3.1]nonanes. Aminoboration of lsocyanates
Bakthan Singaram 《Heteroatom Chemistry》1992,3(3):245-249
The reaction of 9-borabicyclo[3.3.1]nonane (9-BBN) with aliphatic and aromatic primary and secondary amines in tetrahydrofuran (THF) at 65°C proceeds rapidly and quantitatively with evolution of hydrogen and the formation of the corresponding B-amino-9-borabicyclo[3.3.1] nonane (B-amino-9-BBN). Simple evaporation of THF from the reaction mixture gives the B-amino-9-BBN derivatives in high yield and purity. These B-amino-9-BBN derivatives are reactive towards alkyl and aryl isocyanates. Consequently, the aminoboration of various isocyanates has been studied using B-phenylamino-9-BBN. Thus, two equivalents of isocyanates react with one equivalent of B-phenylamino-9-BBN to afford, following the hydrolysis of the intermediate with ethanolamine, N, N'-disubstituted-N -(phenylamido)-ureas in excellent yields. A plausible mechanism for this aminoboration reaction of isocyanates is also presented. 相似文献
4.
Clary JW Rettenmaier TJ Snelling R Bryks W Banwell J Wipke WT Singaram B 《The Journal of organic chemistry》2011,76(23):9602-9610
Grignard reagents (aliphatic, aromatic, heteroaromatic, vinyl, or allylic) react with 1 equiv of 4,4,5,5-tetramethyl-1,3,2-dioxaborolane (pinacolborane, PinBH) at ambient temperature in tetrahydrofuran (THF) to afford the corresponding pinacolboronates. The initially formed dialkoxy alkylborohydride intermediate quickly eliminates hydridomagnesium bromide (HMgBr) and affords the product boronic ester in very good yield. Hydridomagnesium bromide (HMgBr) in turn disproportionates to a 1:1 mixture of magnesium hydride (MgH(2)) and magnesium bromide (MgBr(2)) on addition of pentane to the reaction mixture. DFT calculations (Gaussian09) at the B3LYP/6-31G(d) level of theory show that disproportionation of HMgBr to MgH(2) and MgBr(2) is viable in the coordinating ethereal solvents. This reaction also can be carried out under Barbier conditions, where the neat PinBH is added to the flask prior to the in situ formation of Grignard reagent from the corresponding organic halide and magnesium metal. Pinacolboronic ester synthesis under Barbier conditions does not give Wurtz coupling side products from reactive halides, such as benzylic and allylic halides. The reaction between PinBH and various Grignard reagents is an efficient, mild, and general method for the synthesis of pinacolboronates. 相似文献
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6.
Trialkylboranes react rapidly with lithium alumimum hydride (LAH) in diethyl ether in the presence of triethylenediamine (TED) at 0° to form the corresponding lithium triakylborohydrides and aluminum hydride. The aluminum hydride precipitates out of solution as its triethylenediamine adduct. The reaction is applied to a wide variety of triakylboranes. Consequently, the present reaction provides a general, convenient synthesis of lithium trialkylborohydrides including those with exceptionally large steric requirements. 相似文献
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8.
Gamsey S Miller A Olmstead MM Beavers CM Hirayama LC Pradhan S Wessling RA Singaram B 《Journal of the American Chemical Society》2007,129(5):1278-1286
Several novel diboronic acid-substituted bipyridinium salts were prepared and, using a fluorescent reporter dye, were tested for their ability to selectively bind various monosaccharides and alpha-hydroxycarboxylates in an aqueous medium. The fluorescence sensing mechanism relies on the formation of a ground-state charge-transfer complex between the dye and bipyridinium. An X-ray crystal structure of this complex is described herein. Glucose selectivity over fructose and galactose was achieved by designing the bipyridinium-based receptors to be capable of attaining a 1:1 receptor/substrate stoichiometry via cooperative diboronic acid binding. 相似文献
9.
Gamsey S Suri JT Wessling RA Singaram B 《Langmuir : the ACS journal of surfaces and colloids》2006,22(21):9067-9074
A fluorescent anionic dye and a viologen appended with boronic acids, which serve as glucose receptors, have been synthesized and immobilized into a poly(2-hydroxyethyl methacrylate) hydrogel for use as a continuous glucose monitor. The fluorescence of the dye is modulated by the quenching efficiency of the viologen-based receptor, which in turn is dependent on the glucose concentration. Two monomeric versions of the quencher/receptor unit were prepared and their performance within the hydrogel evaluated. By tethering the quencher/receptor to the hydrogel matrix using a single-point attachment, slightly improved glucose sensing was observed. The hydrogels were tested for their ability to continuously and reversibly detect glucose over the course of several hours. The tests were carried out using a cuvette-based system, as well as a fiber-optic-based configuration. Under physiological conditions (0.1 M phosphate buffer, pH 7.4, 37 degrees C), the fluorescent hydrogels display an excellent dynamic response to glucose concentrations within the biologically significant range (2.5-20 mM). 相似文献
10.
[reaction: see text] Lithium aminoborohydride (LAB) reagents promote the amination of 2-fluoropyridine under mild reaction conditions, providing 2-(dialkylamino)pyridines in excellent yield and purity. Treatment of 2-fluoropyridine with 1.1 equiv of lithium aminoborohydride at room temperature affords complete conversion after 1 h. This is the first general way by which 2-(dialkylamino)pyridines may be directly obtained from fluoropyridines under ambient reaction conditions. 2-Chloropyridine can also be converted to 2-(dialkylamino)pyridine by simply increasing the number of LAB equivalents and the reaction temperature. 相似文献