Triphenylphosphine-Catalyzed Alkylative Iododecarboxylation with Lithium Iodide under Visible Light

Article abstract of DOI:10.1021/acs.orglett.0c03173

Under irradiation of 456 nm blue light-emitting diodes, PPh3 catalyzes the iododecarboxylation of aliphatic carboxylic acid derived N-(acyloxy)phthalimide with lithium iodide as an iodine source. The reaction delivers primary, secondary, and bridgehead te

Full text of DOI:10.1021/acs.orglett.0c03173

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Letter
Triphenylphosphine-Catalyzed Alkylative Iododecarboxylation with
Lithium Iodide under Visible Light
Ming-Chen Fu, Jia-Xin Wang, and Rui Shang*
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ABSTRACT: Under irradiation of 456 nm blue light-emitting
diodes, PPh3 catalyzes the iododecarboxylation of aliphatic
carboxylic acid derived N-(acyloxy)phthalimide with lithium iodide
as an iodine source. The reaction delivers primary, secondary, and
bridgehead tertiary alkyl iodides in acetone solvent, and the alkyl
iodide products were easily used to generate C−N, C−O, C−F,
and C−S bonds to allow various decarboxylative transformations without using transition-metal or organic-dye-based photocatalysts.
ecarboxylative transformations1 that convert a carbox-
ylate group into a functionality that is a versatile handle
providing an expedient method for alkylative iododecarbox-
ylation.16 The principle of radical generation is based on the
photoactivation of an electron donor−acceptor (EDA)
encounter complex in an organic solvent cage to generate
free-radical ions after diffusion (Figure 1B).17 Solvation and
noncovalent interactions between substrates play crucial roles
in determining the productive photoactivation and subsequent
diffusion process.18 This principle of photoactivation can be
utilized to design a catalytic cycle for bond formation with a
catalyst that facilitates electron transfer from a donor moiety to
an acceptor moiety and to suppress undesired back electron
transfer to induce further fragmentation of radical ion species19
(Figure 1B). As depicted in Figure 1C, an iodide salt, PPh3,
and an RAE transiently assemble to form a chromophore that
absorbs up to blue visible light in the UV−vis spectrum (see
Supporting Information for details). The EDA encounter
complex can be a transiently assembled species in a solvent
cage that is held through weak, noncovalent interactions,20,21
and hence is not isolable. Photoactivation of the EDA
encounter complex results in an electron transfer process
that forms an [I-PPh3]• radical and a phthalimide radical
anion, which triggers subsequent decarboxylation to deliver an
alkyl radical. It is worth mentioning that, although similar UV−
vis absorption spectra were observed in the absence of PPh3
(see Supporting Information for more details), the presence of
PPh3 is crucial to suppress back electron transfer from the
phthalimide radical anion to •I, by forming thermodynamically
stable [I-PPh3]•, and to prevent formation of I2, which was
found to be detrimental.16 The alkyl radical reacts with [I-
D
for various further transformations, such as the recent
development of alkylative decarboxylative borylation,2,3 are of
great significance in organic synthesis. Alternatively, a low-cost
alkylative iododecarboxylation reaction has similarly high
merits for use with aliphatic carboxylic acids in organic
synthesis. The importance of decarboxylative halogenation of
aliphatic carboxylates in organic synthesis is reflected in several
named reactions, such as the Hunsdiecker reaction,4 the Kochi
reaction,5 and Barton halogenative decarboxylation6 (Figure
1A). Decarboxylative halogenation generates organohalides,
which are among the most versatile building blocks in modern
organic synthesis.7 Alkyl iodide represents the most reactive
electrophile among the various alkyl halides; thus, efficient
iododecarboxylation offers a platform for a variety of
decarboxylative transformations.8 Iododecarboxylation of
aromatic carboxylic acids and their derivatives has been
extensively reported.9 Notably, a recent report by Larrosa et
al.10 delineated an efficient transition-metal-free iododecarbox-
ylation of arene carboxylic acid using molecular iodine.
Reported examples of iododecarboxylation of aliphatic
carboxylic acid derivatives include halogenative decarboxyla-
tion of Barton esters with iodoform,11 oxidative methods using
PhI(OAc)2/I2 or N-iodoamides under light,12 decarboxylation
of bridgehead carboxylic acid with t-BuOCl and HgI2,13 and a
recent photoredox method using iridium photoredox catalyst
and N-iodosuccinimide.14 The propensity of iodine cations to
undergo electrophilic substitution with arenes presents another
challenge in chemoselective iododecarboxylation for complex
molecules containing electron-rich arene moieties.15 A method
using an alkali iodide salt under mild redox neutral conditions
would thus be useful for transformation of complex substrates,
but has not been developed.
Received: September 21, 2020
We posited that photoactivation of transiently assembled
chromophores composed of a redox-active ester (RAE), an
iodide salt, and a triarylphosphine for alkyl radical generation,
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© XXXX American Chemical Society
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Figure 1. Iododecarboxylation using PPh3 and MI. (A) traditional
decarboxylative halogenation reactions. (B) Concept of photo-
activation of encounter electron-donor−acceptor complex in solvent
cage for radical generation and a way to design photocatalysis. D =
electron donor substrate, A = electron acceptor substrate, CT =
charge transfer, ET = electron transfer. (C) Working hypothesis of
triphenyl phosphine catalyzed decarboxylative iodination.
Figure 2. Key reaction-controlling parameters of decarboxylative
iodination. The yield was determined by H NMR using diphenyl-
1
methane as internal standard. NHPI, N-hydroxyphthalimide
PPh3]• to produce alkyl iodides and regenerate PPh3; hence,
the reaction is catalytic in PPh3. The simplicity and low cost of
this protocol, taken together with the high electrophilicity of
alkyl iodides under either SN2 or metal-catalyzed conditions,
provide an expedient pathway for a variety of decarboxylative
transformations.
subsequent radical decarboxylation. Following our previous
assumption,16 a cation−π interaction is critical to associate the
LiI/RAEs chromophore with PPh3, which is essential to
suppress undesired back electron transfer in the excitation
state. As the strength of the cation−π interaction is largely
predicted by electrostatics, large alkali cations (K, Rb, Cs) have
relatively weaker cation−π interaction compared to small
cations of higher charge density. Solvation heavily affects the
reaction outcome by influencing formation of a transiently
assembled EDA encounter complex18 and iodine abstraction of
generated radical (second row of Figure 2). Amide solvents
such as DMF and DMA primarily resulted in the formation of
decarboxylative HAT products. Acetonitrile (MeCN), ethyl
acetate (EtOAc), dichloromethane (DCM), and trifluoroto-
luene (PhCF3) were all unsuitable solvents. Tetrahydrofuran
(THF) was a suitable solvent, whereas the use of dioxane as
solvent gave no product. A mixed THF/acetone solvent system
appeared to be optimal. The remarkable and subtle solvent
effect was also demonstrated by testing ketone derivatives as
solvent. Acetone is an optimal solvent, and using butan-2-one
gave a reduced yield. In sharp contrast, the use of nonan-5-one
or 3-methylbutan-2-one as the solvent resulted in no
decarboxylative transformation.
The optimized reaction conditions are shown at the top of
Figure 2. In a transparent Schlenk tube, a mixture of RAE (1)
(0.2 mmol), lithium iodide (0.3 mmol), and a catalytic amount
of PPh3 (10 mol %) in degassed acetone solvent (0.1 M) was
irradiated under blue LEDs at room temperature for 24 h. The
desired iodination product 2 was obtained in 91% yield, and
only a trace amount of decarboxylative hydrogen atom transfer
1
(HAT) byproduct 3 was detected by H NMR analysis. LiI
was observed to be not fully soluble under the optimal
conditions. Key controlling parameters are shown in Figure 2.
The results of testing various alkali iodides, shown in the first
row of Figure 2, showed that as the cation radius of the alkali
metal increases (from Li to Cs), the yield of 2 gradually
decreases. Reduction byproduct 3 through the HAT process
from solvent was detected in significant amounts when RbI or
CsI was used. The conversion of 1 dramatically decreased
when CaI2 was used, resulting in a low yield (46%) of 2. The
use of either ZnI2 or n-Bu4NI as the iodine source was entirely
ineffective. These results revealed a significant cation effect and
suggest that the cations affect assembly of the chromophore in
a solvent cage, and hence affect the rate of electron transfer and
Examination of a series of phosphines with different sterics
and electronic natures (third row in Figure 2; see the
B
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Supporting Information for more details) showed that the
simplest PPh3 appeared to be the best. Addition of 10 mol %
OPPh3 to the reaction mixture had no effect on the
outcome, whereas the addition of 20 mol % I2 entirely killed
the reaction. The reaction was not sensitive to the catalytic
amount (20 mol %) of water, but addition of 20 mol % of
NHPI was detrimental. Irradiation with blue LED was
essential. The application of green light of 520 nm was totally
ineffective, whereas light of wavelengths 467, 440, 427, or 390
nm was comparably effective, a phenomenon that correlates
with the UV−vis absorption spectrum (fourth row of Figure
2). Besides light and PPh3, the concentration is also crucial. A
concentration of 0.1 M in acetone was optimal. Further
concentrated solution (0.25 M) resulted in poor solubility of
substrates and low yield. Dilution was unfavorable for
chromophore assembly and significantly reduced the reaction
efficiency. Tetrachloro-N-hydroxyphthalimide-derived RAE
gave a slightly lower yield compared with N-hydroxy-
phthalimide, whereas other activation groups, such as 3-
hydroxy-1,2,3-benzotriazin-4(3H)-one, 1-hydroxybenzo-
triazole, and N-hydroxysuccinimide were ineffective. N-
Hydroxyphthalimide ester of arene carboxylic acid was not
reactive under the optimal conditions. The quantum yield of
this reaction was measured to be 0.69 (see the Supporting
Information for details), which is consistent with a closed
redox cycle involving a radical quenching step (Figure 1C).
The scope of the reaction is summarized in Figure 3. A
broad range of alkyl carboxylates with various functionalities
was readily converted into the corresponding primary,
secondary, and bridgehead tertiary alkyl iodides. Functional
groups such as ether (4, 14), imide (5), aryl bromide (6), aryl
aldehyde (7), aryl pinacol boronate (8), alkene (9), ester (10,
26, 27), amide (15, 16), trifluoromethyl (12), aryl chloride
(13), aryl iodide (20), ketone (24), and hydroxy (25) were
compatible. Iodination of the electron-rich arene moiety (4, 6,
10) was not observed. N-Protected piperidine iodides, such as
N-tert-butoxycarbonyl (16), benzyloxycarbonyl (17, 19), and
benzoyl (18, 20), were obtained in good yields. Both cyclic
and acyclic secondary carboxylic acid derived RAEs reacted
well (14−22). For the reaction leading to 21, the byproduct of
intramolecular radical cyclization on the ortho-C−H of phenyl
was detected. Heteroarene moieties, such as thiophene (11)
and furan (15), were tolerated without undergoing electro-
philic C−H iodination. RAEs derived from bridgehead
carboxylic acids gave bridgehead tertiary iodides in good to
excellent yields (23−27). Decarboxylative iodination at the
benzylic position did not proceed probably due to the stability
of the benzylic radical. Katritzky salt derived from cyclohexyl
amine failed to react under the optimal conditions for RAEs.
The mild redox-neutral conditions of the protocol
encouraged us to test synthetic modifications of a series of
RAEs derived from natural products and pharmaceuticals. As
shown in Figure 4, RAEs derived from linoleic acid (28), oleic
acid (29), erucic acid (30), and undecenoic acid (31)
smoothly underwent decarboxylative iodination with the
stereochemical integrity of the alkene moieties remaining
intact. RAEs derived from medicinal compounds and complex
natural products, such as pregabalin (32, 33), mycophenolic
acid (34), gabapentin (35, 36), dehydrocholic acid (37),
chloroambucil (38), baclofen (39), estrone (40), and
lithocolic acid (41), also reacted smoothly to deliver the
corresponding iodides. The relatively low yield of chloroam-
bucil (38) could be partially explained by a competitive
Figure 3. Scope for iododecarboxylation of aliphatic RAEs. Reaction
conditions: redox-active esters (1.0 equiv, 0.2 mmol), LiI (1.5 equiv,
0.3 mmol), PPh3 (10 mol %), acetone (2 mL), blue LEDs (456 nm),
rt, 24 h. Isolated yield. aMixed solvent of THF (1 mL) and acetone (1
mL) was used. bThe yield was determined by 1H NMR using
diphenylmethane as internal standard.
Finkelstein reaction. It is worth noting that the unprotected
phenolic hydroxyl in mycophenolic acid (34) is compatible.
For estrone analogue 40, the electron-rich phenyl ring, which is
susceptible to electrophilic halogenation, remained unaffected.
The alkyl iodides derived from these natural products and
pharmaceuticals are suitable for introduction into bioactive
structure motifs to construct complex molecules or for further
diversification.
The reaction did not work well for obtaining ordinary
tertiary iodide, probably because of the low bond-dissociation
energy of the tertiary alkyl−I bond and its tendency to
generate a tertiary carbon cation.22 Testing RAE derived from
gemfibrozil resulted in the formation of a mixture of alkene
regioisomers (eq 1) with no product of iododecarboxylation
detected.
Iododecarboxylation of 4-alkylcyclohexane-1-carboxylate
showed little diastereoselectivity (eq 2). RAEs possessing 4-
C
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Scheme 1. Radical Cyclization Experiments
Figure 4. Iododecarboxylation of natural products and pharmaceut-
icals. Reaction conditions: redox-active esters (1.0 equiv, 0.2 mmol),
LiI (1.5 equiv, 0.3 mmol), PPh3 (10 mol %), acetone (2 mL), blue
Figure 5. Decarboxylative elimination.
a
LEDs (456 nm), rt, 24 h. Yields of isolated products. Mixed solvent
b
of THF (1 mL) and acetone (1 mL) was used. PPh3 (20 mol %).
Facile access to alkenes expands the synthetic utility of this
low-cost and mild protocol.
The products of iododecarboxylation can be further used to
construct C−O, C−N, C−F, and C−SCN bonds (see
Supporting Information p S32 for more details), allowing
their subsequent use without requiring the expensive
catalysts.25−27 Subsequent formation of C−N and C−SCN
bonds can also be achieved in one pot in good yields without
isolation of alkyl iodides (see Supporting Information p S35).
The procedures thus provide alternative methods for
decarboxylative oxygenation, amination, fluorination, and
thiocyanation, underlining its wide applicability to various
synthetic tasks.
In summary, a PPh3-catalyzed iododecarboxylation protocol
for use with aliphatic carboxylates and lithium iodide under
irradiation with blue light has been developed.28 The reaction
uses lithium iodide as the iodine source, proceeds under mild,
redox-neutral conditions, and hence is suitable for modification
of complex natural products and pharmaceuticals. The
activation principle of this protocol is based on the
photoactivation of an EDA encounter complex in a solvent
cage, and a catalyst for this process facilitates electron transfer
and suppresses back electron transfer. The protocol has the
advantages of low cost and simplicity and allows versatile
follow-up transformations to be applied, thereby expanding the
use of aliphatic carboxylic acids in organic synthesis.
methyl and 4-tert-butyl as substituents produced iodination
products of similar yields with similar trans-/cis- ratios,
revealing that iodine abstraction of alkyl radical from [I-
PPh3]• is less sensitive to steric effect. Radical cyclization
experiments proved that the reactions proceed through a
process involving free alkyl radicals (Scheme 1). Reactions
using 1.5 equiv of LiCl or LiBr in the presence of 10 mol % of
LiI did not produce any decarboxylative chlorination or
bromination product (eq 3), suggesting that a carbon cation is
not oxidatively generated with [I-PPh3]•.
Simply treating the obtained cyclic secondary alkyl iodides
with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) at 60 °C in
one pot generated the alkene products in high yields (Figure 5,
49−53). Decarboxylative elimination of these carboxylic acid
was recently reported using either photoredox/transition-metal
synergistic catalysis23 or palladium catalysis under light.24
ASSOCIATED CONTENT
* Supporting Information
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The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.orglett.0c03173.
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(6) (a) Barton, D. H. R.; Crich, D.; Motherwell, W. B. New and
improved methods for the radical decarboxylation of acids. J. Chem.
Soc., Chem. Commun. 1983, 939−941. (b) Barton, D. H. R.; Crich, D.;
Motherwell, W. B. A practical alternative to the Hunsdiecker reaction.
Tetrahedron Lett. 1983, 24, 4979−4982.
Experimental procedures, reaction parameters, mecha-
nistic investigation, characterization data, and NMR
spectra (PDF)
(7) (a) Cristol, S. J.; Firth, W. C., Jr. Communications. A convenient
synthesis of alkyl halides from carboxylic acids. J. Org. Chem. 1961, 26,
280−281. (b) Wang, Z.; Zhu, L.; Yin, F.; Su, Z.; Li, Z.; Li, C. Silver−
catalyzed decarboxylative chlorination of aliphatic carboxylic acids. J.
Am. Chem. Soc. 2012, 134, 4258−4263. (c) Yin, F.; Wang, Z.; Li, Z.;
Li, C. Silver−catalyzed decarboxylative fluorination of aliphatic
carboxylic acids in aqueous solution. J. Am. Chem. Soc. 2012, 134,
10401−10404.
(8) (a) Johnson, R. G.; Ingham, R. K. The degradation of carboxylic
acid salts by means of halogen-the Hunsdiecker reaction. Chem. Rev.
1956, 56, 219−269. (b) Kaiho, T. Iodine chemistry and applications;
Wiley-VCH: Weinheim, 2015).
(9) (a) Barton, D. H. R.; Lacher, B.; Zard, S. Z. The invention of
radical reactions: Part XVI. Radical decarboxylative bromination and
iodination of aromatic acids. Tetrahedron 1987, 43, 4321−4328.
(b) Cornella, J.; Rosillo-Lopez, M.; Larrosa, I. A novel mode of
reactivity for Gold(I): The decarboxylative activation of (hetero)-
aromatic carboxylic acids. Adv. Synth. Catal. 2011, 353, 1359−1366.
(c) Patra, T.; Mukherjee, S.; Ma, J.; Strieth-Kalthoff, F.; Glorius, F.
Visible-light-photosensitized aryl and alkyl decarboxylative function-
alization reactions. Angew. Chem., Int. Ed. 2019, 58, 10514−10520.
(10) Perry, G. J. P.; Quibell, J. M.; Panigrahi, A.; Larrosa, I.
Transition-metal-free decarboxylative iodination: New routes for
decarboxylative oxidative cross-couplings. J. Am. Chem. Soc. 2017,
139, 11527−11536.
AUTHOR INFORMATION
■
Corresponding Author
Rui Shang − Department of Chemistry, University of Science and
Technology of China, Hefei 230026, China; Department of
Chemistry, School of Science, The University of Tokyo, Tokyo
113-0033, Japan; orcid.org/0000-0002-2513-2064;
Email: rui@chem.s.u-tokyo.ac.jp
Authors
Ming-Chen Fu − Department of Chemistry, University of Science
and Technology of China, Hefei 230026, China
Jia-Xin Wang − Department of Chemistry, University of Science
and Technology of China, Hefei 230026, China
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.orglett.0c03173
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the National Natural Science
Foundation of China (GG2065010002), KY (2060000119),
Natural Science Foundation of Anhui (2008085MB40), and
the USTC Research Funds of the Double First-Class Initia-tive
(YD2060002003).
(11) Barton, D. H. R.; Crich, D.; Motherwell, W. B. The invention of
new radical chain reactions. Part VIII. Radical chemistry of
thiohydroxamic esters; A new method for the generation of carbon
radicals from carboxylic acids. Tetrahedron 1985, 41, 3901−3924.
(12) (a) Concepcion, J. I.; Francisco, C. G.; Freire, R.; Hernandez,
R.; Salazar, J. A.; Suarez, E. Iodosobenzene diacetate, an efficient
reagent for the oxidative decarboxylation of carboxylic acids. J. Org.
Chem. 1986, 51, 402−404. (b) Kulbitski, K.; Nisnevich, G.;
Gandelman, M. Metal-Free Efficient, General and Facile Iododecar-
boxylation Method with Biodegradable Co-Products. Adv. Synth.
Catal. 2011, 353, 1438−1442.
REFERENCES
■
(1) (a) Qin, T.; Cornella, J.; Li, C.; Malins, L. R.; Edwards, J. T.;
Kawamura, S.; Maxwell, B. D.; Eastgate, M. D.; Baran, P. S. A general
alkyl−alkyl cross−coupling enabled by redox−active esters and
alkylzinc reagents. Science 2016, 352, 801−805. (b) Liang, Y.;
Zhang, X.; MacMillan, D. W. C. Decarboxylative sp3 C−N coupling
via dual copper and photoredox catalysis. Nature 2018, 559, 83−88.
(c) Edwards, J. T.; Merchant, R. R.; McClymont, K. S.; Knouse, K.
W.; Qin, T.; Malins, L. R.; Vokits, B.; Shaw, S. A.; Bao, D.−H.; Wei,
F.−L.; Zhou, T.; Eastgate, M. D.; Baran, P. S. Decarboxylative
alkenylation. Nature 2017, 545, 213−218. (d) Zhang, X.; Smith, R.
T.; Le, C.; McCarver, S. J.; Shireman, B. T.; Carruthers, N. I.;
MacMillan, D. W. C. Copper−mediated synthesis of drug−like
bicyclopentanes. Nature 2020, 580, 220−226.
(13) Abeywickrema, R. S.; Della, E. W. Decarboxylative iodination;
A convenient synthesis of bridgehead iodides. J. Org. Chem. 1980, 45,
4226−4229.
́
́
(14) Candish, L.; Standley, E. A.; Gomez-Suarez, A.; Mukherjee, S.;
Glorius, F. Catalytic access to alkyl bromides, chlorides and iodides
via visible light-promoted decarboxylative halogenation. Chem. - Eur. J.
2016, 22, 9971−9974.
(15) Narobe, R.; Dusel, S. J. S.; Iskra, J.; Konig, B. Photocatalytic
̈
̈
oxidative iodination of electron-rich arenes. Adv. Synth. Catal. 2019,
361, 3998−4004.
(16) (a) Fu, M.-C.; Shang, R.; Zhao, B.; Wang, B.; Fu, Y.
Photocatalytic decarboxylative alkylations mediated by triphenylphos-
phine and sodium iodide. Science 2019, 363, 1429−1434. (b) Wang,
Y.-T.; Fu, M.-C.; Shang, R.; Fu, Y. Photocatalytic decarboxylative
alkenylation of α-amino and α-hydroxy acid-derived redox active
esters by NaI/PPh3 catalysis. Chem. Commun. 2020, 56, 2495−2498.
(17) (a) Lima, C. G. S.; Lima, T. de M.; Duarte, M.; Jurberg, I. D.;
(2) Fawcett, A.; Pradeilles, J.; Wang, Y.; Mutsuga, T.; Myers, E. L.;
Aggarwal, V. K. Photoinduced decarboxylative borylation of
carboxylic acids. Science 2017, 357, 283−286.
(3) (a) Li, C.; Wang, J.; Barton, L. M.; Yu, S.; Tian, M.; Peters, D. S.;
Kumar, M.; Yu, A. W.; Johnson, K. A.; Chatterjee, A. K.; Yan, M.;
Baran, P. S. Decarboxylative borylation. Science 2017, 356,
No. eaam7355. (b) Wang, J.; Shang, M.; Lundberg, H.; Feu, K. S.;
Hecker, S. J.; Qin, T.; Blackmond, D. G.; Baran, P. S. Cu−Catalyzed
Decarboxylative Borylation. ACS Catal. 2018, 8, 9537−9542.
Paixao, M. W. Organic synthesis enabled by light-irradiation of EDA
̃
̈
complexes: Theoretical background and synthetic applications. ACS
Catal. 2016, 6, 1389−1407. (b) Bosque, I.; Bach, T. 3-
Acetoxyquinuclidine as catalyst in Electron Donor−Acceptor
complex-mediated reactions triggered by visible light. ACS Catal.
2019, 9, 9103−9109.
(4) (a) Hunsdiecker, H.; Hunsdiecker, C. Uber den abbau der salze
̈
aliphatischer sauren durch brom. Ber. Dtsch. Chem. Ges. B 1942, 75,
291−297. (b) Trost, B. M.; Fleming, I. The Hunsdiecker and Related
Reactions in Comprehensive Organic Synthesis, Vol. 7; Pergamon Press:
Oxford, 1991; p 717.
́
̌
(18) (a) Kysel, O.; Juhasz, G.; Mach, P.; Kosík, G. Theoretical study
of solvent effect on π-EDA complexation II. Complex between TCNE
and two benzene molecules. Chem. Pap. 2007, 61, 66−72.
(b) Litwinienko, G.; Beckwith, A. L. J.; Ingold, K. U. The frequently
overlooked importance of solvent in free radical syntheses. Chem. Soc.
(5) (a) Kochi, J. K. A new method for halodecarboxylation of acids
using Lead(IV) acetate. J. Am. Chem. Soc. 1965, 87, 2500−2502.
(b) Kochi, J. K. Formation of Alkyl Halides from Acids by
Decarboxylation with Lead(IV) Acetate and Halide Salts. J. Org.
Chem. 1965, 30, 3265−3271.
E
https://dx.doi.org/10.1021/acs.orglett.0c03173
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
pubs.acs.org/OrgLett
Letter
Rev. 2011, 40, 2157−2163. (c) Weaver, M. J.; McManis, G. E., III.
Dynamical solvent effects on electron-transfer processes: Recent
progress and perspectives. Acc. Chem. Res. 1990, 23, 294−300. (d) Li,
X.; Ogihara, T.; Abe, M.; Nakamura, Y.; Yamago, S. The effect of
viscosity on the diffusion and termination reaction of organic radical
pairs. Chem. - Eur. J. 2019, 25, 9846−9850.
(19) (a) Kavarnos, G. J.; Turro, N. J. Photosensitization by
reversible electron transfer: Theories, experimental evidence, and
examples. Chem. Rev. 1986, 86, 401−449. (b) McClain, E. J.; Monos,
T. M.; Mori, M.; Beatty, J. W.; Stephenson, C. R. J. Design and
Implementation of a Catalytic Electron Donor−Acceptor Complex
Platform for Radical Trifluoromethylation and Alkylation. ACS Catal.
2020, 10, 12636−12641.
(20) (a) Kochi, J. K. Electron transfer and charge transfer: Twin
themes in unifying the mechanisms of organic and organometallic
reactions. Angew. Chem., Int. Ed. Engl. 1988, 27, 1227−1266.
(b) Fukin, G. K.; Lindeman, S. V.; Kochi, J. K. Molecular structures
of cation···π(arene) interactions for alkali metals with π- and σ-
modalities. J. Am. Chem. Soc. 2002, 124, 8329−8336. (c) Rosokha, S.
V.; Kochi, J. K. Fresh look at electron-transfer mechanisms via the
donor/acceptor bindings in the critical encounter complex. Acc. Chem.
Res. 2008, 41, 641−653.
(21) Crisenza, G. E. M.; Mazzarella, D.; Melchiorre, P. Synthetic
methods driven by the photoactivity of Electron Donor−Acceptor
complexes. J. Am. Chem. Soc. 2020, 142, 5461−5476.
(22) Blanksby, S. J.; Ellison, G. B. Bond dissociation energies of
organic molecules. Acc. Chem. Res. 2003, 36, 255−263.
(23) (a) Sun, X.; Chen, J.; Ritter, T. Catalytic dehydrogenative
decarboxyolefination of carboxylic acids. Nat. Chem. 2018, 10, 1229−
1233. (b) Tlahuext-Aca, A.; Candish, L.; Garza-Sanchez, R. A.;
Glorius, F. Decarboxylative olefination of activated aliphatic acids
enabled by dual organophotoredox/copper catalysis. ACS Catal. 2018,
8, 1715−1719. (c) Nguyen, V. T.; Nguyen, V. D.; Haug, G. C.; Dang,
H. T.; Jin, S.; Li, Z.; Flores-Hansen, C.; Benavides, B. S.; Arman, H.
D.; Larionov, O. V. Alkene synthesis by photocatalytic chemo-
enzymatically compatible dehydrodecarboxylation of carboxylic acids
and biomass. ACS Catal. 2019, 9, 9485−9498.
(24) Cheng, W.-M.; Shang, R.; Fu, Y. Irradiation-induced palladium-
catalyzed decarboxylative desaturation enabled by a dual ligand
system. Nat. Commun. 2018, 9, 5215.
(25) (a) Mao, R.; Balon, J.; Hu, X. Decarboxylative C(sp3)-O cross-
coupling. Angew. Chem., Int. Ed. 2018, 57, 13624−13628. (b) Mao,
R.; Frey, A.; Balon, J.; Hu, X. Decarboxylative sp3 C−N coupling via
dual copper and photoredox catalysis. Nat. Catal. 2018, 1, 120−126.
(26) Liang, Y.; Zhang, X.; MacMillan, D. W. C. Decarboxylative sp3
C−N coupling via dual copper and photoredox catalysis. Nature 2018,
559, 83−88.
(27) Webb, E. W.; Park, J. B.; Cole, E. L.; Donnelly, D. J.; Bonacorsi,
S. J.; Ewing, W. R.; Doyle, A. G. Nucleophilic (radio)fluorination of
redox-active esters via radical-polar crossover enabled by photoredox
catalysis. J. Am. Chem. Soc. 2020, 142, 9493−9500.
(28) This manuscript was previously submitted to ResearchSquare
as a preprint, see: Fu, M.-C.; Wang, J.-X.; Shang, R. ResearchSquare
2020, DOI: 10.21203/rs.3.rs-51576/v1.
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