Categories: C-Br Bond Formation >
Synthesis of benzyl bromides
Recent Literature
In a continuous-flow protocol for the bromination of benzylic compounds with
only a small excess of N-bromosuccinimide, the radical reactions were
activated with a readily available household compact fluorescent lamp (CFL)
using a simple flow reactor design based on transparent fluorinated ethylene
polymer tubing. All of the reactions were carried out using acetonitrile as the
solvent, thus avoiding hazardous chlorinated solvents such as CCl4.
D. Cantillo, O. de Frutos, J. A. Rincon, C. Mateos, C. O. Kappe, J. Org. Chem., 2014,
79, 223-229.
Substoichiometric amounts of thiourea additives mediate the halogenation of
alcohols under mild conditions. In the the absence of thiourea, oxidation of the
alcohol is observed, whereas the substrate can be recovered when excess thiourea is
used. Both bromination and chlorination were highly efficient for primary,
secondary, tertiary, and benzyl alcohols and tolerate a broad range of
functional groups.
A. R. Mohite, R. S. Phatake, P. Dubey, M. Agbaria, A. I. Shames, N. G.
Lemcoff, O. Reany, J. Org. Chem., 2020, 85,
12901-12911.
Silicaphosphine (Silphos), [P(Cl)3−n(SiO2)n] is a new
heterogeneous reagent that converts alcohols and thiols to their corresponding
bromides and iodides in the presence of molecular halogen in refluxing CH3CN
in high to quantitative yields. Separation of the Silphos oxide byproduct can be
achieved by a simple filtration.
N. Iranpoor, H. Firouzabadi, A. Jamalian, F. Kazemi, Tetrahedron, 2005,
61, 5699-5704.
An efficient conversion of alcohols and β-amino alcohols to the corresponding
chlorides can be carried out at room temperature in methylene
chloride, using 2,4,6-trichloro[1,3,5]triazine and N,N-dimethyl formamide.
Addition of NaBr allows the synthesis of bromides. Optically active carbinols
react under inversion.
L. de Luca, G. Giacomelli, A. Porcheddu, Org. Lett., 2002,
4, 553-555.
The combination of Ph3P and easily available 1,2-dihaloethanes (XCH2CH2X; X =
Cl, Br, or I), was very effective for a mild deoxygenative halogenation of
alcohols and aldehydes. The use of (EtO)3P instead of Ph3P
enables a convenient purification process, as the byproduct (EtO)3P═O
could be removed by aqueous washing. A dehydroxy-fluorination proceeds well in
the presence of ICH2CH2I and CsF as fluoride source in DMF.
J. Chen, J.-H. Lin, J.-C. Xiao, Org. Lett.,
2018, 20, 3061-3064.
Under very mild oxidative conditions, 1,4-dihydropyridines (DHPs), derived
from aldehydes, generate C(sp3)-radicals that couple with halogen
radicals, which are generated from inexpensive halogen sources (NaBr, NaI, or
HCl), to yield alkyl halides. The reaction tolerates a broad range of functional
groups and achieves excellent site selectivity.
S. Liang, T. Kumon, R. A. Angnes, M. Sanchez, B. Xu, G. B. Hammond,
Org. Lett., 2019, 21, 3848-3854.
Silver-Catalyzed Decarboxylative Bromination of Aliphatic Carboxylic Acids
X. Tan, T. Song, Z. Wang, H. Chen, L. Cui, C. Li, Org. Lett.,
2017, 19, 1634-1637.
Aryl aldehydes couple readily with allylmetals to afford haloallylated products
in the presence of boron trihalides. The reactions tolerate a variety of
functional groups. Simple aqueous workup of haloallylation reactions, followed
by treatment with 1,8-diazabicyclo[5.4.0]undec-7-ene, provides a straightforward
route to synthetically useful (E)-1,3-dienes.
M. P. Quinn, M.-L. Yao, G. W. Kabalka, Synthesis, 2011,
3815-3820.
