doi: 10.1021/acs.chemrev.0c00813.
Epub 2020 Nov 17.
Decarboxylative Halogenation of Organic Compounds
Affiliations
- PMID: 33200917
- PMCID: PMC7884003
- DOI: 10.1021/acs.chemrev.0c00813
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Decarboxylative Halogenation of Organic Compounds
Chem Rev.
.
Abstract
Decarboxylative halogenation, or halodecarboxylation, represents one of the fundamental key methods for the synthesis of ubiquitous organic halides. The method is based on conversion of carboxylic acids to the corresponding organic halides via selective cleavage of a carbon-carbon bond between the skeleton of the molecule and the carboxylic group and the liberation of carbon dioxide. In this review, we discuss and analyze major approaches for the conversion of alkanoic, alkenoic, acetylenic, and (hetero)aromatic acids to the corresponding alkyl, alkenyl, alkynyl, and (hetero)aryl halides. These methods include the preparation of families of valuable organic iodides, bromides, chlorides, and fluorides. The historic and modern methods for halodecarboxylation reactions are broadly discussed, including analysis of their advantages and drawbacks. We critically address the features, reaction selectivity, substrate scopes, and limitations of the approaches. In the available cases, mechanistic details of the reactions are presented, and the generality and uniqueness of the different mechanistic pathways are highlighted. The challenges, opportunities, and future directions in the field of decarboxylative halogenation are provided.
Conflict of interest statement
The authors declare no competing financial interest.
Figures
Cl2 instead of Br2. I2 instead
of Br2.
Asterisk indicates a bromine
introduced via electrophilic bromination.
Reaction performed in nitrobenzene
at 180 °C; hv–reaction was irradiated
with light.
3–6 equiv of acetic acid
were added; GC yields based on amounts of Pb(OAc)4.
Grob
modification, DMF/AcOH
5:1 as a solvent. Barton
modification. Acetate protecting
group was partially removed. THF as a solvent. Pyridine
as a solvent.
Conditions: Pb(OAc)4, LiCl, benzene, reflux. Pb(OAc)4, NCS, DMF/AcOH
5:1, 40 °C. Pb(OAc)4, I2,
benzene, reflux. in the
presence of 3 mol % AIBN, CCL4 as solvent. Br2 instead of I2.
Reaction performed in a benzene–sulpholane
mixture at 55–80 °C. Isolated yields. Yields based on the evolved CO2 are
given in parentheses.,−
One
equiv of LiCl instead of
I2, benzene as solvent. Five equiv of PhI(OAc)2 and LiCl instead of
I2, benzene as solvent.
Reaction with PhI(OAc)2 and LiX in HFIP. Reaction
with PhI(OAc)2 and Br2 in dibromomethane; asterisk
indicates an iodine introduced via electrophilic iodination.
Precursors to Barton-type esters and their analogues.
Irradiation with a 400 W high-pressure
mercury lamp with a Pyrex filter.
Reaction performed in EtOAc:CCl4 1:1. “X”
source: ICH2Cl, BrCCl3, or CCl4.
No DABCO added. No water
added. Irradiation with
a 100 W high-pressure mercury
lamp (Pyrex filter); 1–3 equiv of DABCO.
The product was isolated as
a mixture of alkenes.
Asterisks indicate the reaction
performed with 391 as a catalyst instead of DABCO and
−20 °C – 0 °C instead of room temperature.
Asterisks indicate a halogen
introduced via electrophilic halogenation.
Asterisks indicate a halogen
introduced via electrophilic halogenation.
Asterisks indicate a halogen
introduced via electrophilic halogenation
Asterisks indicate
the position
of an electrophilic halogenation in the main side product. Isolated
yields. NMR yields are given in square brackets.
Asterisks indicate the position
of an electrophilic halogenation in the main side product; isolated
yields.
Asterisks indicates
the position
of an electrophilic halogenation in the side product. Isolated yields.
NMR yields are given in square brackets.
Asterisks indicate
the position
of an electrophilic halogenation in the side product. Figures in brackets
indicate monobromide:dibromide ratios.
Yields of diiodides are given
in brackets. Asterisks indicate an iodine atom introduced via electrophilic
iodination.
Asterisks indicate the position
of an electrophilic halogenation in the main side product.
Reaction in the presence of
10 mol % Pd(OAc)2. A yield of the diiodinated product is given in parentheses. Asterisks
indicates the position of an additional electrophilic iodination.
Figures in parentheses are yields
for CuI, CuI–Pd(OAc)2 or for CuI–CuX systems.
Figures in parentheses indicate
the amount of dibromide.
Yield for PyHBr3 instead
of Br2.
Starting acid E/Z = 87:13.
At −40 °C. E:Z = 1:1. E:Z = 89:11. Startingacid E:Z = 87:13.
Yields of the reaction in CH3CN/H2O (97:3) under 260 W MW irradiation.
E/Z ratio.
In toluene at 65
°C. Starting acid E/Z = 3:97. E/Z-ratio.
E/Z-ratio. Isolated yields
for the E-isomer.
E/Z ratio.
Benzoic acid as the starting
material
RCY – radiochemical
yield.
Reaction with Selectfluor and
NaOH in CH3CN.
Reaction carried in a water–acetone
mixture as a solvent.
[18F]Selectfluor
bis(triflate) was used. RCY – radiochemical yield.
Reaction with AgOTf,
Selectfluor
and CF3COOH.
Ratio of diastereomers is given
in parentheses.
1Ag/TiO2 –
mechanically mixed Ag2O and TiO2 containing
1 wt % of Ag; TON – turnover number.
3,3,3-Triphenylpropionic acid
as the starting material. AgF·HF used instead of AgF and KF.
RCC – radiochemical
conversion.
TEBAB – triethylbenzylammonium
bromide.
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