- Electrophilic Fluorination of Alkenes via Bora-Wagner–Meerwein Rearrangement. Access to β-Difluoroalkyl Boronates
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The electrophilic fluorination of geminal alkyl substituted vinyl-Bmida derivatives proceeds via bora-Wagner–Meerwein rearrangement. According to DFT modelling studies this rearrangement occurs with a low activation barrier via a bora-cyclopropane shaped TS. The Bmida group has a larger migration aptitude than the alkyl moiety in the Wagner–Meerwein rearrangement of the presented electrophilic fluorination reactions.
- Biosca, Maria,Himo, Fahmi,Szabó, Kálmán J.,Wang, Qiang
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supporting information
p. 26327 - 26331
(2021/11/16)
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- Copper-Catalyzed Double C(sp3)-Si Coupling of Geminal Dibromides: Ionic-to-Radical Switch in the Reaction Mechanism
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A method for converting geminal dibromides into 1,1-disilylated alkanes is reported. The reaction is promoted by a copper(I) catalyst generated in situ from CuBr·SMe2 as a precatalyst and 4,4′-di-tert-butyl-2,2′-bipyridine (dtbpy) as a ligand. A Si-B reagent is used as the silicon pronucleophile. It is shown that the two C(sp3)-Si bond-forming events differ in mechanism, with the first being ionic and the second being radical.
- Hazrati, Hamideh,Oestreich, Martin
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supporting information
p. 5367 - 5369
(2018/09/13)
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- Synthesis of vinyl boronates from aldehydes by a practical boron-Wittig reaction
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A highly stereoselective boron-Wittig reaction between stable and readily accessible 1,1-bis(pinacolboronates) and aldehydes furnishes a variety of synthetically useful di- and trisubstituted vinyl boronate esters.
- Coombs, John R.,Zhang, Liang,Morken, James P.
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supporting information
p. 1708 - 1711
(2015/04/14)
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- Conversion of Aldehydes into 1,1-Dibromoalkanes
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Aliphatic and aromatic aldehydes have been converted into 1,1-dibromoalkyl derivatives using a 1:1 mixture of triphenyl phosphite and bromine as reagent.
- Hoffmann, R. W.,Bovicelli, P.
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p. 657 - 659
(2007/10/02)
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- Photochemistry of Alkyl Halides. 9. Geminal Dihalides
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The photobehavior of the geminal dihalides (diiodomethyl)cyclohexane (7), (bromoiodomethyl)cyclohexane (11), (dibromomethyl)cyclohexane (17), (diiodomethyl)cyclopentane (22), 3,3-dimethyl(diiodomethyl)cyclobutane (27), and 8,8-diiodo-2,6-dimethyl-2-octene (31) has been studied and compared with that previously observed for diiodomethane.In all solvents the corresponding vinyl halides (iodomethylene)cyclohexane (13), (bromomethylene)cyclohexane (21), (iodomethylene)cyclopentane (23), 3,3-dimethyl(iodomethylene)cyclobutane (28), or cis- and trans-3,7-dimethyl-1-iodo-1,6-octadiene (33) were obtained, which are thought to arise from α-halo cationic intermediate formed via initial light-induced homolytic cleavage of the carbon-iodine bond followed by electron transfer within the resulting caged radical pair, as shown in Schemes II and III.In the case of diiodide 31 competing intramolecular trapping of the α-iodo cation afforded in addition the cyclized isopulegyl iodide (34).In polar solvents the vinyl iodides were accompanied by the nonhalogenated products methylenecyclohexane (15), 1-methylcyclopentene (25), cyclohexene (26), 4,4-dimethylcyclopentene (29), and cis- and trans-carane (35), which are thought also to arise from the α-halo cationic intermediate. 1.1-Diiodo-2,2-dimethylpropane (1b) afforded 2-methyl-2-butene (6b).Except for carane (35) from diiodide 31 there was no detectable formation of cyclopropanes.In methanol the nucleophilic substitution products (dimethoxymethyl)cyclohexane (14), (dimethoxymethyl)cyclopentane (24), and 1,1-dimethoxy-2,2-dimethylpropane (30) were obtained.It is concluded that geminal dihalides undergo predominant, if not exclusive, photoreaction via initial clea vage of a single carbon-halogen bond in analogy with monohalides and that carbene intermediates are not formed.A similiar conclusion has been reached previously for diiodomethane in the photocyclopropanation of alkenes.
- Kropp, Paul J.,Pienta, Norbert J.
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p. 2084 - 2090
(2007/10/02)
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