- Stepwise mechanism for the bromination of arenes by a hypervalent iodine reagent
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A mild, metal-free bromination method of arenes has been developed using the combination of bis(trifluoroacetoxy)iodobencene and trimethylsilyl bromide. In situ-formed dibromo(phenyl)-λ3-iodane (PhIBr2) is proposed as the reactive intermediate. This methodology using PIFA/TMSBr has been applied with success to a great number of substrates (25 examples). The treatment of mono-substituted activated arenes led to para-brominated products (2u-z) in excellent 83-96% yields. Density functional theory calculations indicate a stepwise mechanism involving a double bromine addition followed by a type II dyotropic reaction with concomitant re-aromatization of the six-membered ring.
- Arrieta, Ana,Cossío, Fernando P.,Granados, Albert,Shafir, Alexandr,Vallribera, Adelina
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p. 2142 - 2150
(2020/03/11)
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- Enantioselective organocatalytic fluorination-induced Wagner-Meerwein rearrangement
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Cracked under strain: Strained allylic cyclobutanols and cyclopropanols readily undergo a ring expansion described by the title rearrangement. This reaction is promoted by catalytic amounts of 1 and displays high tolerance with respect to the substrate scope. The corresponding β-fluoro spiroketone products are isolated in high yields and with excellent stereoselectivities. EDG=electron-donating group, EWG=electron-withdrawing group. Copyright
- Romanov-Michailidis, Fedor,Guénée, Laure,Alexakis, Alexandre
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p. 9266 - 9270
(2013/09/12)
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- Reactivity and synthetic utility of 1-(arenesulfonyloxy) benziodoxolones
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The reactivity and synthetic use of 1-(arenesulfonyloxy)benziodoxolones were studied. In the presence of iodine, 1-(arenesulfonyloxy)benziodoxolones iodinated various aromatics to give iodoarenes in moderate to good yields. In particular, 1-(p-chlorobenzenesulfonyloxy)benziodoxolone showed the best reactivity. Using a halide salt such as lithium bromide or lithium chloride instead of iodine, the corresponding aryl bromides and chlorides were also obtained in good yields. In the absence of aromatics, 1- (arenesulfonyloxy)benziodoxolones gave rise to desulfonyloxyiodination reactions to give the corresponding aryl iodides via electrophilic ipso substitution on the aromatic rings. Furthermore, the l-(p- toluenesulfonyloxy)benziodoxolone/iodine system iodotosyloxylated alkynes in good yields. These reactions proceeded via the formation of arenesulfonyl hypoiodites.
- Muraki, Takahito,Togo, Hideo,Yokoyama, Masataka
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p. 2883 - 2889
(2007/10/03)
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- Synthetic use of 1-(p-toluenesulfonyloxy)-1,2-benziodoxol-3(1H)-one: Iodination of aromatic rings
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Treatment of various aromatic compounds with 1-(p-toluenesulfonyloxy)-1,2-benziodoxol-3(1H)-one 1A and iodine gave the corresponding iodinated compounds in good yields. Similarly, chlorination and bromination proceeded effectively. As compared with other trivalent iodine compounds, the iodinane 1A showed the best reactivity as a halogenation reagent.
- Muraki, Takahito,Togo, Hideo,Yokoyama, Masataka
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p. 286 - 288
(2007/10/03)
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- Phospholes with reduced pyramidal character from steric crowding III NMR and X-ray diffraction studies on 1-( 2,4,6-tri-isopropylphenyl)-3-methylphosphole
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The 2,4,6-tri-isopropylphenyl substituent was placed on the phosphorus of a phosphole to reduce the pyramidal character. That this was accomplished was revealed by single crystal X-ray diffraction analysis; with respect to the plane of C2-P-C5 in the phosphole ring, the ipso carbon of the benzene ring was deflected by only 58.0°, whereas the deflection is 66.9° in the uncrowded 1-benzylphosphole. This proves that the concept of reducing the pyramidal character (with the goal of increasing the electron delocalization) through steric crowding can be realized. In the crystal the two rings are in orthogonal planes, but this relation is not retained in solution; NMR studies show that the two edges of the benzene ring, as well as the 2,6-isopropyl groups, are identical.
- Keglevich, Gyoergy,Quin, Louis D.,Boecskei, Zsolt,Keserue, Gyoergy M.,Kalgutkar, Rajdeep,Lahti, Paul M.
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p. 109 - 116
(2007/10/03)
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- Hindered Organoboron Groups in Organic Chemistry. Part 22. Some Interesting Properties of 2,4,6-Triisopropylphenylborane (Tripylborane, TripBH2, A New Useful Monoarylborane
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2,4,6-Triisopropylphenylborane (tripylborane, TripBH2) is a solid, stable, hydroborating agent that hydroborates monosubstituted alkenes to give either TripBHR1 or TripBR12.TripBHR1 can be converted into mixed boranes TripBR1R2 (R1,R2 = primary alkyl, Rp) and TripBRpRs and TripBRs2 are also readily available.Oxidation of these products gives the corresponding alcohols in excellent yields, with a high selectivity for alkan-1-ols in the cases of groups derived from alk-1-enes.Cyanidation of TripBR2 proceeds to give ketones without migration of the aryl group.This establishes the low migratory aptitude of the aryl group and also that no scrambling of alkyl groups occurs.The tripyl group of TripBRp2 can be selectively removed.
- Smith, Keith,Pelter, Andrew,Jin, Zhao
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p. 395 - 396
(2007/10/02)
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- The First Reversible Thermal Dissociation of Distannanes, R3Sn-SnR3, Giving Stannyl Radicals, R3Sn.
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Thermal and reversible dissociation of organic distannanes, R3Sn-SnR3 (1) * 2 R3Sn. (2), have been found for the first time when a sufficient strain in 1 was generated by bulky substituents.For this, the residues R = phenyl, cyclohexyl, 1-adamantyl are not sufficient up to 230 deg C, but with R = 2,4,6-trialkylphenyl the dissociation temperature (ESR) is lowered to 20 deg C in the series alkyl = Me, Et, iPr.The ESR spectra of stannyl radicals 2 as well as $vSn-Sn(sym.) , δHDiss., and EA values for 1 are reported.New distannanes 1 and corresponding compounds R3SnBr and R3SnH are described.
- Buschhaus, Hans-Ulrich,Neumann, Wilhelm P.,Apoussidis, Theodoros
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p. 1190 - 1197
(2007/10/02)
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