Photoredox-Catalyzed Isomerization of Highly Substituted Allylic Alcohols by C?H Bond Activation

Article abstract of DOI:10.1002/anie.202000743

Photoredox-catalyzed isomerization of γ-carbonyl-substituted allylic alcohols to their corresponding carbonyl compounds was achieved for the first time by C?H bond activation. This catalytic redox-neutral process resulted in the synthesis of 1,4-dicarbonyl compounds. Notably, allylic alcohols bearing tetrasubstituted olefins can also be transformed into their corresponding carbonyl compounds. Density functional theory calculations show that the carbonyl group at the γ-position of allylic alcohols are beneficial to the formation of their corresponding allylic alcohol radicals with high vertical electron affinity, which contributes to the completion of the photoredox catalytic cycle.

Full text of DOI:10.1002/anie.202000743

A Journal of the Gesellschaft Deutscher Chemiker
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International Edition
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Accepted Article
Title: Photoredox-Catalyzed Isomerization of Highly-Substituted Allylic
Alcohols via C-H bond activation
Authors: Zhen Yang, Kai Guo, Zhongchao Zhang, Anding Li, Yuanhe
Li, and Jun Huang
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10.1002/anie.202000743
Angewandte Chemie International Edition
Photoredox-Catalyzed Isomerization of Highly-Substituted Allylic
Alcohols via C-H bond activation
Kai Guo,+ Zhongchao Zhang,+ Anding Li,+ Yuanhe Li, Jun Huang,* Zhen Yang,*
Dedicated to Professor Henry N. C. Wong on the occasion of his 70th birthday.
metal-catalyzed catalytic isomerization of allylic alcohols to
corresponding carbonyl compounds in one-pot redox-neutral
processes3-8 (Scheme 1, path C).9 However, the isomerization
becomes more difficult as the number of substituted groups
increases1b on the double bond especially for the secondary
allylic substituted alcohols. This trend is explained by the fact
that it is difficult for transition-metal complexes to bind and react
with heavily substituted olefins, and not surprisingly, a limited
number of methods6d,7d have been reported for the isomerization
of allylic alcohols with a tetrasubstituted double bond.
Abstract: Photoredox-catalyzed isomerization of γ-carbonyl-
substituted allylic alcohols to their corresponding carbonyl
compounds was achieved for the first time via C-H bond activation.
This catalytic redox-neutral process provided a way for the synthesis
of 1,4-dicarbonyl compounds. Notably, allylic alcohols bearing
tetrasubstituted olefins can also be transferred into their
corresponding carbonyl compounds. The density functional theory
calculations show that the carbonyl group at the γ-position of allylic
alcohols are beneficial to the formation of their corresponding allylic
alcohol radicals with high vertical electron affinity, which contributes
to the completion of the photoredox catalytic cycle.
a) Proposed protocol for the isomerization of allylic alcohols
R2
R2
Introduction
R1
R3
R1
R3
C-H bond cleavage
OH R4
allylic alcohol (
OH R4
The development of chemical reactions for isomerization of
allylic alcohols to corresponding carbonyl compounds is a fertile
field in organic synthesis.1 Conventional methods for this
transformation usually follow a two-step sequential process
(Scheme 1, path A or B), featuring an oxidation/reduction or
reduction/oxidation path, which is uneconomical in terms of both
atoms and steps.1,2
allylic alcohol radical (F)
HAT
A
PRC-
)
PRC-
Photoredox-catalyzed
hydrogen atom
transfer process
SET
H
SET
HAT
hv
PRC*
PRC
R2
PRC
HAT
R2
R1
R3
R1
R3
Regioselective protonation
& Tautomerization
OH R4
allylic alcohol anion (
O
R4
D
)
G
)
ketone (
b) Vertical electron affinities calculation
Species EAvert (kcal/mol)
OH
R3=OMe
31.5
37.8
47.2
53.2
60.5
64.9
OH
+ e-
R3=Me
Me
allylic alcohol
R3
Me
R3
R3=H
R3=CONHMe
R3=COOMe
R3=COMe
allylic alcohol
anion (G)
radical (F)
Scheme 1. Approaches to the isomerization of allylic alcohols.
c) This work: Photoredox-catalyzed isomerization
Considerable progress has been made in past decades in
blue LEDs
R2
b
R2
[*]
K. Guo, Z.-C. Zhang, A.-D. Li, Prof. Dr. J. Huang, Prof. Dr. Zhen
Yang
State Key Laboratory of Chemical Oncogenomics and Key
Laboratory of Chemical Genomics, Peking University Shenzhen
Graduate School, Shenzhen 518055 (China)
E-mail: junhuang@pku.edu.cn
R3
PRC HAT HBA
R1
H
g
R3
a
R1
H
Photoredox Isomerization
OH R4
O
R4
ketone (D)
R3
allylic alcohol (A)
= CO2R; COR or CONHR
Scheme 2. Photoredox-catalyzed isomerization of highly
substituted allylic alcohols
E-mail: zyang@pku.edu.cn
Y.-H. Li, Prof. Dr. Zhen Yang
Key Laboratory of Bioorganic Chemistry and Molecular
Engineering of Ministry of Education and Beijing National
Laboratory for Molecular Science (BNLMS), and Peking-Tsinghua
Center for Life Sciences, Peking University, Beijing 100871
(China)
Recently, photoredox-catalyzed bond activation as a redox-
neutral and atom- and step-economical strategy has come to the
forefront in organic synthesis.10 We became interested in light-
induced isomerization of highly substituted allylic alcohols to
their corresponding carbonyl compounds through a process of
C–H bond activation in the presence of hydrogen atom transfer
(HAT) catalysts.11
Prof. Dr. Zhen Yang
Shenzhen Bay laboratory, Shenzhen, 518055, China
[+]
These authors contributed equally to this work.
Supporting information for this article is given via a link at the end
of the document.
1
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10.1002/anie.202000743
Angewandte Chemie International Edition
We envisaged that the proposed isomerization could be
initiated by single-electron oxidation (oxidative SET process) of
a HAT catalyst in the presence of an excited photoredox catalyst
(PRC*). The resultant radical cation species (HAT•+) could
abstract the α-H from the corresponding allylic alcohol (A) to
afford an allylic alcohol radical species (F), which could then
undergo single-electron reduction (reductive SET process) to
furnish an allylic alcohol anion (G), followed by protonation and
tautomerization to give a ketone (D) (Scheme 2a).
However, in reality, the proposed reductive SET process of
the allylic alcohol radical (F) is difficult,10b which prevents the
formation of the allylic alcohol anion (G); as a result, the
proposed photoredox catalysis could not occur. To better
To explore the proposed chemistry, we selected allylic alcohol
1m as a test substrate to investigate its isomerization to
corresponding ketoester 2m. Initially we attempted the
isomerization reaction of 1m using cat-I (1 mol%) as a catalyst
in acetonitrile under irradiation with a blue LED lamp without
additives. However, product 2m was not observed after
irradiation for 24 h (Table 1, entry 1). We then carried out the
reaction in the presence of quinuclidine as the HAT catalyst11a-h
(10 mol%). Under the tested conditions, isomerized product 2m
was obtained in 24% yield on the basis of 28% substrate
conversion (entry 2). Next, we conducted the reaction in the
presence of tetrabutylammonium dihydrogen phosphate (TBAP)
as a hydrogen-bond acceptor (HBA)11a,18b,19 catalyst (25 mol%)
to activate the αC–H bond.11a Pleasingly, ketoester 2m was
obtained in 81% yield on the basis of 100% substrate conversion
(entry 3).
understand this issue, we conducted
a
computational
experiment.12 Our results indicated that the tendency for the
reduction of allylic alcohol radicals (F) will increase as the
vertical electron affinities13 (EAvert) of substituents at the γ-
substitution position of allylic alcohols are increased. That is,
allylic alcohols substituted with γ-carbonyl groups (–CONHMe, –
CO2Me, and –COMe) might have a stronger tendency to
participate in the reductive SET process than allylic alcohols
bearing γ-substituents such as –OMe, –Me, and –H groups
(Scheme 2b).
Table 1. Reaction Optimization.
entry
1
PRC
HAT
-
HBA
-
sol.
conv./yield (%)a
0/0
cat-I
CH3CN
2
3
cat-I
cat-I
cat-I
no cat
cat-I
cat-I
cat-I
cat-I
cat-I
cat-I
cat-I
cat-I
cat-I
cat-I
cat-II
cat-III
cat-IV
quinuclidine
quinuclidine
quinuclidine
quinuclidine
DABCO
-
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3OH
DCM
28 / 24
100 / 81
0/0c
TBAP
4
TBAP
5
TBAP
0/0
6
TBAP
60 /50
38 / 27
27 / 18
10 / 7
7
quinuclidine
quinuclidine
quinuclidine
quinuclidine
quinuclidine
quinuclidine
quinuclidine
quinuclidine
quinuclidine
quinuclidine
quinuclidine
quinuclidine
NaH2PO4
n-Bu4NPF6
Cs2CO3
TBAP
8
9
10
11
12
13
14
15
16
17
18
15 / 13 b
26 /23 b
56 / 50 b
96 / 80 b
<5 / <5 d
<5 / <5 e
38 / 25
8 / 0
TBAP
TBAP
toluene
DCE
TBAP
Scheme 3. Bioactive compounds containing 1,4-dicarbonyl.
TBAP
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
Herein, we report our recent effort to develop a strategy that
allows structurally diverse γ-carbonyl-substituted allylic alcohols
(A) to be converted into corresponding carbonyl compounds (D)
through deconjugative isomerization by combining photoredox
and HAT catalysts (Scheme 2c). The developed chemistry could
allow sterically hindered γ-carbonyl-substituted allylic alcohols to
be isomerized to their corresponding 1,4-dicarbonyl compounds,
which are the critical motifs in many biologically active
compounds (Scheme 3). 1,4-Dicarbonyl compounds are also
essential substrates to prepare cyclopentenones and
heterocycles,14,15 such as furans, pyrroles, and thiophenes,
which are important components in numerous biologically active
molecules,16 pharmaceuticals, insecticides, and perfumes.17
TBAP
TBAP
TBAP
TBAP
10 / 0
Reaction conditions: A 10-mL glass vial was charged with allylic alcohol (0.2
mmol), photoredox catalyst (1 mol%), HAT catalyst (10 mol%), HBA catalyst
(25 mol%) in an appropriate solvent (1 mL). Irradiated by two blue LEDs (18 W
each) at ambient temperature (40 °C). [a] Yield was determined by isolated
product and conversion was determined on the basis of the isolated recover
starting material. [b] The yield and conversion were measured by GC with
1,3,5-trimethoxybenzene as the internal standard. [c] Without LED irradiation.
[d] Charged with O2 balloon. [e] additive: 3.0 eq. TEMPO. cat-I
{Ir[dF(CF3)ppy]2(dtbbpy)}PF6; cat-II [Ir(ppy)2(dtbbpy)]PF6; cat-III
[Ru(bpy)3]Cl2·6H2O, and cat-IV = Mes-Acr+ClO4.
=
=
=
Results and Discussion
To demonstrate the unique roles of the LED and cat-I in the
observed isomerization reaction, we carried out the same
2
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10.1002/anie.202000743
Angewandte Chemie International Edition
reaction without light irradiation or cat-I. As expected, no product
2m was observed (entry 4 and 5), indicating that both light
irradiation and the photoredox catalyst were essential elements
for the observed isomerization. To investigate the effect of the
HAT and HBA catalyst on the outcome of the isomerization
reaction, we replaced quinuclidine with DABCO,11,18b,19 which
resulted in the low yield (entry 6). When the reaction was carried
out in the presence of NaH2PO4 as HBA, an improved result was
observed (entry 7). On the other hand, the reaction became
worse when n-Bu4NPF6 was used as HBA (entry 8). In addition,
both the conversion and yield of the reaction were reduced
under basic condition (Cs2CO3, entry 9).
We then evaluated the effects of solvent and additives on the
reactions. When dichloroethane was used as the solvent, 2m
was obtained in 80% yield on the basis of 96% substrate
conversion (entry 10). When the reactions were conducted in the
presence of oxygen or TEMPO, the yield of 2m was decreased
(entries 14 and 15), indicating that oxygen or TEMPO might
quench the radical formed during isomerization. We eventually
evaluated other catalysts (cat-II, cat-III, and cat-IV), none of
which gave better results (entries 16–18).
allylic alcohol hydrogen-bonded complex (A-h) to afford allylic
alcohol
radical
hydrogen-bonded
complex
F-h
and
quinuclidinium cation M (BDE of H–N+ in quinuclidinium cation M
= 100 kcal/mol).18b The release of H2PO4 can afford allylic
-
alcohol radical species F to complete HBA catalytic cycle.
Single-electron reduction (reductive SET) of electron-deficient
red
radical F by IrII[dF(CF3)ppy]2(dtbbpy) (J) (E1/2 = –1.37 V vs
SCE in CH3CN)20 then gives allylic alcohol anion G, and
regenerate photoredox catalyst {IrIII[dF(CF3)ppy]2(dtbbpy)}+ (H),
which completes the photoredox catalytic cycle. Therefore, the
regioselective protonation of allylic alcohol anion
G can
simultaneously regenerate the HAT catalyst and afford enol E,
while tautomerization of enol E can afford desired ketone D.
With the optimized conditions in hand, we then evaluated the
effect of olefin substituents on the outcome of isomerization.
Accordingly, a collection of primary and secondary allylic
alcohols with a representative set of olefin substitution patterns
and functional groups were synthesized and subjected to the
reaction under the optimized conditions. As shown in Table 2,
the primary allylic alcohol 1a furnished corresponding aldehyde
2a. Then, the isomerization of a series secondary allylic alcohols
was carried out to explore the effect of substituents on the
isomerization reaction. Secondary allylic alcohols with an alkyl
group at the α position were tested first. As the steric hindrance
of substituted groups increased, the reactivity of the
isomerization reaction decreased (2b–2e). The isomerization of
The proposed catalytic cycle for the visible-light-driven redox
isomerization of allylic alcohol is shown in figure 1. The
irradiation of {IrIII[dF(CF3)ppy]2(dtbbpy)}+ (H) by visible light
produces excited-state species, *{IrIII[dF(CF3)ppy]2(dtbbpy)}+ (I),
ox
which can function as an oxidant (E1/2 = +1.21V vs SCE in
CH3CN)20 and be quenched by the HAT catalyst, quinuclidine (K) secondary allylic alcohols with an aryl group at the α position
ox
(E1/2
=
+1.1V vs SCE in CH3CN)21, to produce
provided excellent yields (2f–2l). This isomerization strategy
IrII[dF(CF3)ppy]2(dtbbpy) (J) and quinuclidinium radical cation (L). showed good tolerance to both electron-rich and electron-
Quinuclidinium radical cation (L) can then abstract a hydrogen
deficient substituents at the α position when ortho-, meta-, and
para-substituted aromatic groups were tested. Most reactions
atom (BDE of αC–H in allylic alcohol < 90 kcal/mol)18a from an
Figure 1. Proposed catalytic cycle (R3 = COOR; COR or CONHR).
3
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10.1002/anie.202000743
Angewandte Chemie International Edition
afforded the desired products in moderate to excellent yields,
indicating that this method is quite general for preparing
structurally diverse ketoesters. The low yields of product 2a
were attributed to their volatile properties. In addition, we
examined the scope of the isomerization reaction using C=C
trisubstituted secondary allylic alcohols as substrates (Table 2).
As expected, not only γ-CO2R-substituted allylic alcohols (2m–
2o) but also γ-COR-substituted allylic alcohols (2p–2r) were
converted to the corresponding products.
tetrasubstituted primary allylic alcohol (1aa) provided the
corresponding aldehyde. Additionally, α-aromatic-substituted
secondary allylic alcohols (2ab–2ad) performed better in the
isomerization reaction than α-alkyl-substituted secondary allylic
alcohols (2ae–2ag). The low yields of products 2ae–2ag were
caused by the slow conversion of the starting materials to their
corresponding products, presumably because the less
accessibility of quinuclidinium-based radical cation to the olefins.
In all cases, unreacted starting material accounted for the
missing yield. These results were encouraging because better
yields can be expected when the reaction time is extended. In
addition, ketones, esters, and amides were applicable as
activating groups at the γ-position of allylic alcohols. It is notable
that this photo-redox-HAT isomerization method can well
tolerate with aryl chloride, aryl bromide, ketone, etc. which are
usually sensitive functional groups in transition-metal catalyzed
reactions. Substrates with more highly substituted double bonds
were less reactive than those with less substituents. This trend
was attributed to the more substituted olefins being difficult for
the quinuclidinium-based radical cation (L in Figure 1) to access.
Unsurprisingly, the isomerization of allylic alcohols with a
tetrasubstituted double bond was more difficult and required a
longer reaction time than was the case for allylic alcohols with
fewer substituents on the double bond. As a result, their
corresponding yields were also relatively low. Because the
isomerization was a radical-based reaction, it was relatively
sensitive to the steric effect of the substrate. Substrates bearing
tetrasubstituted olefins afforded a pair of diastereoisomers with
the trans isomer as the major product. The relative
stereochemistry of product 2y was determined by X-ray
crystallography. Since transition-metal-catalysed isomerisations
of allylic alcohols with tetra-substituted olefins are rare,22
therefore, our developed photoredox-catalysed isomerization
strategy might become a useful method to isomerize allylic
alcohols with tetra-substituted double bonds to the
corresponding carbonyl compounds in an atom-, step-, and
redox-economical fashion.
Table 2. Scope of C=C Di- and Trisubstituted Allylic Alcohols.
To gain insight into the reaction mechanism, an isotopic
labeling experiment was conducted using deuterated 1f-d1. The
isomerization of 1f-d1 was conducted under the optimized
conditions (Scheme 4a). Deuterium atoms were found in both β-
C (9% D) and γ-C (26% D) by 1H NMR spectroscopic analysis of
the isolated product (2f-d1), which was different from the ideal
result (50% D in γ-C). This difference was attributed to
deuterium–proton exchange between the labeled quinuclidinium
−
cation intermediate and other proton source (such as H2PO4 ),
To extend the application scope, the isomerization of C=C
tetrasubstituted secondary allylic alcohols with different carbon
skeletons was established. As shown in Table 3, the
isomerization of derivatives of cyclopent-2-en-1-ol, cyclohex-2-
en-1-ol, and cyclohept-2-en-1-ol provided the corresponding
ketones in good yield (2s–2u). The high dr values of 2w–2z
were attributed to the reversibility of enol–keto tautomerization of
the corresponding ketones, which could produce the
thermodynamically stable products. Importantly, a γ-CONHR-
substituted allylic alcohol (1z) also provided the desired product
(2z) using this photoredox strategy. The scope of γ-COR-
substituted allylic alcohols in the isomerization reaction was
defined using derivatives of cyclopent-1-en-1-ylmethanol and
cyclohex-1-en-1-ylmethanol (Table 3). The isomerization of
indicating that protonation of the allylic alcohol anion
intermediate was an intermolecular process rather than an
intramolecular concerted process. Besides, the α-aryl ketones 2f
was subjected to the optimized conditions the presence of D2O
to investigate the subsequent tautomerization. As shown in
scheme 4b, the deuterium atoms were not found in γ-C (100%
H). Combining the result of the isomerization of 1f-d1 in scheme
3a, these results support that the deuterium atoms in γ-C (26%
D) of 2f-d1 was introduced via the proposed protonation process
of allylic alcohol anion species (G in scheme 2a). Furthermore,
the deuterium atoms were found in β-C (82.5% D), implicating
that the α-aryl ketones (2w-2aa) show high dr presumably due to
a subsequent epimerization.
4
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10.1002/anie.202000743
Angewandte Chemie International Edition
Table 3. Scope of Tetrasubstituted Allylic Alcohols.
*The reaction was carried out in 1.0 mmol scale.
5
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10.1002/anie.202000743
Angewandte Chemie International Edition
radical species IN3-A. In contrast, the HAT process (Figure 3)
gives allylic alcohol radical IN3-B via transition state TS1-B from
IN2-B26 (Figure 3) with an energy barrier of 13.9 kcal/mol, which
is 2.3 kcal/mol higher than that via TS1-A.27 The calculation
results implied that the HAT process in both paths A and B
(Figures 2 and 3) was irreversible. Upon formation of the allylic
alcohol radical, electron transfer occurred between the electron-
deficient allylic alcohol radical (serving as an oxidant) and [IrII]
(serving as a reductant), affording the allylic alcohol anion
species (IN4-A in path A and IN4-B in path B) and completing
the photoredox catalytic cycle by releasing ground-state [IrIII]+. In
path A, IN4-A can give enol complex IN5-A via transition state
TS2-A with a relatively low energy barrier of 0.6 kcal/mol. In
addition, C1 protonation of IN4-A via TS2-A-C1, which can
afford substrate IN1, was selected to investigate the observed
regioselective protonation process. As shown by the dashed line
in path A, the C1 protonation of IN4-A via TS2-A-C1 requires an
energy barrier of 13.2 kcal/mol, which is 12.6 kcal/mol higher
than that of C3 protonation process. In path B, IN4-B can
provide the enol complex IN5-B via TS2-B with a relatively low
energy barrier of 1.2 kcal/mol. The energy barrier of C1
protonation via TS2-B-C1 is 11.8 kcal/mol, which is 10.6
kcal/mol higher than that of the C3 protonation process via TS2-
B.28 In addition, the orbital composition analysis29 shows that
composition of C3 in the HOMO of allylic alcohol anions (IN4-A
and IN4-B) is higher than that of C1, therefore, the atomic orbital
2p of C3 is easier to rehybridize than that of C1, indicating that
C3 is more reactive than C1 to be protonated.
Scheme 4. Isotopic labeling experiment.
To acquire
a better understanding of this isomerization
reaction, a series of density functional theory (DFT) calculations
were conducted (see Supporting Information for details). As
shown in Figures 2 and 3, two different pathways (path A: with
−
−
H2PO4 ; path B: without H2PO4 ) were calculated to understand
the reaction mechanism.23 Irradiation of [IrIII]+ produced excited
triplet species *[IrIII]+ (geometry after relaxation) with a triplet
energy (ET) of 60.0 kcal/mol.24 This triplet species can undergo a
reduction quenching process with quinuclidine species to afford
[IrII] and quinuclidinium radical cation species. In the presence of
the quinuclidinium radical cation–dihydrogen phosphate complex
−
(H2PO4 ·C7H13+), IN1 can produce hydrogen-bonded complex
IN2-A (Figure 2). The HAT process25 then occurs via transition
state TS1-A with an energy barrier of 11.6 kcal/mol, providing
These results showed that HBA had little effect on the C3
Figure 2. Energy profiles from IN1 to enol species IN7-A (path A). Path A (blue line) is the reaction mechanism involving phosphate.
C, H, O, N, and P atoms are shown in gray, white, red, blue, and orange, respectively. Solvated Gibbs free energies (in MeCN) are
given in kcal/mol. Bond lengths are given in angstroms (Å).
6
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10.1002/anie.202000743
Angewandte Chemie International Edition
Figure 3. Energy profiles from IN1 to enol species IN7-B (path B). Path B (purple line) is the reaction mechanism without phosphate.
C, H, O, N, and P atoms are shown in gray, white, red, blue, and orange, respectively. Solvated Gibbs free energies (in MeCN) are
given in kcal/mol. Bond lengths are given in angstroms (Å).
protonation processes. In both path A and B, the C3 protonation
processes were more energetically favorable than C1
protonation processes. After protonation, the quinuclidine was
released from the complexes of IN5-A or IN5-B followed by the
enol tautomerization to complete the catalytic cycle.
Laboratory for Marine Science and Technology (Grant Nos.
2015ASKJ02, and LMDBKF201802)
Conflict of interest
Conclusion
The authors declare no conflict of interest.
A photoredox-catalyzed isomerization of highly substituted
allylic alcohols bearing electron-withdrawing groups to their
corresponding carbonyl compounds under mild conditions was
developed for the first time. Our experimental and theoretical
studies indicated that the allylic alcohol isomerization was a
stepwise process, and highlighted the beneficial role of the
electron-deficient γ-carbonyl substituents for the formation of the
allylic alcohol radical species and the process of the single-
electron reduction.
Keywords: highly substituted • allylic alcohols • isomerization •
photoredox • C-H bond activation
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D. R. C. Van, E. Bouwman, E. Drent, J. Organomet. Chem.
2002, 650, 1; b) R. Uma, C. Crévisy, R. Grée, Chem. Rev.
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2011, 40, 341; e) N. Ahlsten, A. Bartoszewicz, B. Martín-
Matute, Dalton Trans. 2012, 41, 1660; f) P. LorenzoLuis, A.
Romerosa, M. Serrano-Ruiz, ACS Catal. 2012, 2, 1079; g) D.
Cahard, S. Gaillard, J. L. Renaud, Tetrahedron Lett. 2015,
56, 6159; h) H. Li, C. Mazet, Acc. Chem. Res. 2016, 49,
1232.
[2] For discussions on green chemistry, see: a) B. M. Trost,
Science 1991, 254, 1471; b) B. M. Trost, Angew. Chem. Int.
Ed.. 1995, 34, 259; Angew. Chem. 1995, 107, 285; c) R. A.
Sheldon, I. Arends, U. Hanefeld, Green Chemistry and
Catalysis; Wiley-VCH: Weinheim, Germany, 1997; d) P. T.
Anastas, J. C. Warner, Green Chemistry: Theory and
Acknowledgements
This work was financially supported by the National Key
Research and Development Program of China (Grant No.
2018YFC0310905), National Science Foundation of China
(Grant Nos. 21632002, 21702011, 21871012), Shenzhen Basic
Research Program (Grant Nos. JCYJ20180302150314340 and
JCYJ20170818090044432),
and
the
Scientific
and
Technological Innovation Project supported by Qingdao National
7
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9
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10.1002/anie.202000743
Angewandte Chemie International Edition
Kai Guo,+ Zhongchao Zhang,+ Anding Li,+
Yuanhe Li, Jun Huang,* Zhen Yang,*
Photoredox-Catalyzed Isomerization of Tetrasubstituted
Allylic Alcohols via C-H bond activation
Photoredox-catalyzed isomerization of highly-substituted
allylic alcohols to corresponding carbonyl compounds was
achieved for the first time via C-H bond activation. The DFT
calculations show that the carbonyl group at the γ-position of
allylic alcohols contributes to the completion of the
photoredox catalytic cycle.
10
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