2534-77-2Relevant academic research and scientific papers
Aqueous Microdroplets Capture Elusive Carbocations
Kumar, Anubhav,Mondal, Supratim,Banerjee, Shibdas
supporting information, p. 2459 - 2463 (2021/02/16)
Carbocations are short-lived reactive intermediates in many organic and biological reactions that are difficult to observe. This field sprung to life with the discovery by Olah that a superacidic solution allowed the successful capture and nuclear magnetic resonance characterization of transient carbocations. We report here that water microdroplets can directly capture the fleeting carbocation from a reaction aliquot followed by its desorption to the gas phase for mass spectrometric detection. This was accomplished by employing desorption electrospray ionization mass spectrometry to detect a variety of short-lived carbocations (average lifetime ranges from nanoseconds to picoseconds) obtained from different reactions (e.g., elimination, substitution, and oxidation). Solvent-dependent studies revealed that aqueous microdroplets outperform organic microdroplets in the capture of carbocations. We provide a mechanistic insight demonstrating the survival of the reactive carbocation in a positively charged aqueous microdroplet and its subsequent ejection to the gas phase for mass spectrometric analysis.
Decarboxylative Bromination of Sterically Hindered Carboxylic Acids with Hypervalent Iodine(III) Reagents
Kanazawa, Junichiro,Koyamada, Kenta,Miyamoto, Kazunori,Uchiyama, Masanobu,Watanabe, Ayumi
supporting information, p. 1328 - 1334 (2020/08/14)
Sterically hindered three-dimensional (3D) alkyl halides are promising precursors for various reactions; however, they are difficult to synthesize via conventional reactions. We present an efficient and practical method for decarboxylative bromination of sterically hindered 3D aliphatic carboxylic acids using commercially available (diacetoxyiodo)benzene and potassium bromide, one of the most stable and cheapest bromine sources in nature. The present method features a metal-free/Br2-free system, mild reaction conditions, one-pot operation under air at room temperature, wide functional group compatibility, and gram-scale synthetic capability. This highly efficient reaction cleanly converts a broad range of carboxylic acids, the most inexpensive and readily available sources of highly strained/naturally occurring/drug-related scaffolds, into the corresponding alkyl bromides in good to high yields.
Hydroalumination of alkenes by the LiAlH4*3AlBr3 system
Gorobets, E. V.,Shitikova, O. V.,Lomakina, S. I.,Tolstikov, G. A.,Kuchin, A. V.
, p. 1573 - 1578 (2007/10/02)
The hydroalumination of a series of alkenes and some fused aromatic hydrocarbons by the LiAlH4*3AlBr3 system in low-polar solvents was studied.Alkenes with mono-, di-, tri-, and tetraalkyl substituted, mono- and diaryl substituted double bonds and anthracene react at room temperature to give the corresponding dibromoaluminoalkanes in high yields.Benzylidenefluorene, tetraphenylethylene, naphthalene, and phenanthrene do not undergo hydroalumination under these conditions.Camphene, bicyclooct-2-ene, and norbornene afford the corresponding organoaluminum compounds with high stereoselectivity.Oxidation and halo- and acyldemetallation of the resulting alkyl- and arylalanes were carried out.
The halogenolysis of organoboranes
Morrill,Lu,Brister,O'Shaughnessy,Belfield
, p. 973 - 976 (2007/10/02)
Transmercuration of tri-exo-2-norbornylborane followed by chlorinolysis of the resultant organoborane is a low yield (≤5%) method of producing exo-2-norbornyl chloride. The primary source of this low yield is the inefficient transmercuration of the sterically restricted organoborane. Yields of alkyl halide are substantially higher (up to 63%) when the organoborane undergoes direct chlorinolysis promoted by boron trichloride. Even higher yields (approaching 80%) are obtained when brominolysis of the organoborane is carried out. Controls suggest that at least part of the reason for the higher yield with bromine is due to the greater stability of the product under the reaction conditions. Despite the general retention aspects (exo-borane gives largely exo-halide) of these halogenolyses, deuterium labeling studies show that these reactions are accompanied by substantial Wagner-Meerwein rearrangement, very possibly due to boron trihalide induced rearrangement of the norbornyl halide product.
Photochemistry of alkyl halides. 12. Bromides vs Iodides
Kopp, Paul J.,Adkins, Rick L.
, p. 2709 - 2717 (2007/10/02)
Conditions have been developed for optimizing ionic photobehavior material balances from alkyl bromides. Hydroxide ion as an efficient for the byproduct HBr while giving minimal competing photoreduction via electron transfer to the alkyl bomide. The photobehavior of bromides 1, 11, 25, and 40 has examined and with that of the corresponding iodides 2, 12, 26, 41 under conditions. In each case, the bromide higher yields of products derived from out of cage radical intermidiates than the corresponding iodide. However, with the 2-norbornyl bromides 11 and iodides 12 showed that, of products not formed from the out of cage 2-norbornyl radical 13, the bromides 11 gave a higher percentage of products from the ionic intermediates 15 and 16 than did the iodides. Thus, electron transfer within the radical pair 14 is apparently more rapid for bromides than iodides, as expected on the of the relative electronegativities of bromine iodine. It is that the substantially higher yields of out of radical products from alkyl bromides may be due in to formation of the radical pair with greater excess energy, which results in more rapid escape from the cage. The epimeric 2-norbornyl bromides 11x and 11n underwent no detectable interconversion and afforded somewhat different product ratios. The more hindered epimer 11n underwent conversion to products at a slower than 11x. By contrast, 12x and 12n underwent substantial interconversion via out of transfer of an iodine atom from iodide 12 to radical 13. Epimerization was significantly attenuated in the more viscous solvent tert-butyl alcohol.
Base-Promoted 1,2-Eliminations from endo-2-Bicycloheptyl Halides and Arenesulfonates
Bartsch, Richard A.,Lee, Jong Gun
, p. 5247 - 5252 (2007/10/02)
Base-solvent systems that provide clean bimolecular 1,2-elimination from endo-2-bicycloheptyl halides and arenesulfonates by suppressing competitive solvolysis and nortricyclene-forming 1,3-elimination are developed.The stereochemistries of elimination from exo-3-deuterio-endo-2-bromobicycloheptane (10) and exo-3-deuterio-endo-2-bicycloheptyl 2,4,6-triisopropylbenzenesulfonate (11) are assessed using these base-solvent systems.The competitive syn-endo and anti-exo-H elimination modes are found to be strongly influenced by base association.However, for dissociated alkoxide bases, the elimination stereochemistry is unaffected by changes in leaving group from halide to arenesulfonate, in base strength, and in base size.
DESIGN AND REACTIVITY OF ORGANIC FUNCTIONAL GROUPS - 2-PYRIDYLSULFONATES AS NUCLEOFUGAL ESTERS: REMARKABLY MILD TRANSFORMATIONS INTO HALIDES AND OLEFINS
Hanessian, Stephen,Kagotani, Masahiro,Komaglou, Kossi
, p. 1115 - 1120 (2007/10/02)
The novel 2-pyridylsulfonate esters are excellent leaving groups for the preparation of bromides and olefins under very mild reaction conditions.Displacements occur with inversion of configuration.
Catalytic Bromide and Iodide Exchange of Alkyl Chlorides with HBr and HI
Yoon, K. B.,Kochi, J. K.
, p. 3028 - 3036 (2007/10/02)
The need to develop efficient methods for the conversion of the generally cheaper, readily available alkyl chlorides to the more reactive, synthetically useful alkyl bromides and iodides is addressed by the use of gaseous HBr and HI in the presence of a ferric halide catalyst.The simple catalytic procedure is especially applicable to secondary and tertiary alkyl chlorides as well as vicinal dichlorides at ambient temperatures in aprotic solvents such as dichloromethane and carbon tetrachloride.The unique role of the FeBr3 catalyst to effect a reversible exchange of bromide via carbenium intermediates is discussed.
ORGANOBORANES FOR SYNTHESIS. 10. THE BASE-INDUCED REACTION OF BROMINE WITH ORGANOBORNES. A CONVENIENT PROCEDURE FOR THE CONVERSION OF ALKENES INTO ALKYL BROMIDES VIA HYDROBORATION
Brown, Herbert C.,Lane, Clinton F.
, p. 2763 - 2772 (2007/10/02)
The reaction of trialkylboranes with bromine is greatly accelerated by base.Bromination in the presence of sodium hydroxide provides alkyl bromide along with a large amount of the corresponding alcohol.The use of sodium methoxide as a base eliminates this undesirable side reaction and provides an improved yield of alkyl bromide.Consequently, hydroboration, followed by bromination in the presence of sodium methoxide, provides a convenient new procedure for the conversion of alkenes into alkyl bromides.The organoboranes, obtained via hydroboration of terminal alkenes, react with the utilization of all three alkyl groups attached to boron, providing nearly quantitative yields of alkyl bromides. This procedure also accommodates common organic functional groups, as demonstrated by the preparation of methyl 11-bromoundecanoate and 11-bromoundecyl acetate from the corresponding functionally substituted alkenes.Under these conditions, secondary and bulky primary alkyl groups react more sluggishly.However, a procedure involving simultaneous addition of bromine and methanolic sodium methoxide provides improved results for such derivatives.Surprisingly, the base-induced bromination of tri-exo-nobornylborane results in an inversion of configuration at the reaction center to give predominantly endo-2-bromonorbornane.A mechanism is proposed to account for this remarkable inversion.
Efficient Conversion of Alkyl Chlorides into Bromides
Yoon, K. B.,Kochi, J. K.
, p. 1013 - 1014 (2007/10/02)
The convenient and selective catalytic conversion of secondary and tertiary alkyl chlorides into bromides with hydrogen bromide in the presence of small amounts of anhydrous iron(III) bromide is described.
