Rh(III)-Catalyzed Cascade Reactions of Sulfoxonium Ylides with α-Diazocarbonyl Compounds: An Access to Highly Functionalized Naphthalenones

Article abstract of DOI:10.1021/acs.orglett.9b00340

An unprecedented cascade reaction of benzoyl sulfoxonium ylides with α-diazocarbonyl compounds leading to the formation of highly functionalized naphthalenones containing a β-ketosulfoxonium ylide moiety is presented. Promisingly, the naphthalenone derivative thus obtained was found to be a versatile intermediate toward diversely functionalized naphthalene derivatives including substituted 1-naphthol, 2-hydroxynaphthalen-1(2H)-one, naphthalen-1,2-dione, and 2-(methylsulfinyl)naphthalen-1-ol.

Full text of DOI:10.1021/acs.orglett.9b00340

Letter
pubs.acs.org/OrgLett
Cite This: Org. Lett. XXXX, XXX, XXX−XXX
Rh(III)-Catalyzed Cascade Reactions of Sulfoxonium Ylides with
α‑Diazocarbonyl Compounds: An Access to Highly Functionalized
Naphthalenones
Xi Chen, Muhua Wang, Xinying Zhang,* and Xuesen Fan*
Henan Key Laboratory of Organic Functional Molecules and Drug Innovation, Key Laboratory of Green Chemical Media and
Reactions, Ministry of Education, Collaborative Innovation Center of Henan Province for Green Manufacturing of Fine Chemicals,
School of Chemistry and Chemical Engineering, Henan Normal University, Xinxiang, Henan 453007, China
S
* Supporting Information
ABSTRACT: An unprecedented cascade reaction of benzoyl
sulfoxonium ylides with α-diazocarbonyl compounds leading to
the formation of highly functionalized naphthalenones contain-
ing a β-ketosulfoxonium ylide moiety is presented. Promisingly,
the naphthalenone derivative thus obtained was found to be a
versatile intermediate toward diversely functionalized naph-
thalene derivatives including substituted 1-naphthol, 2-hydrox-
ynaphthalen-1(2H)-one, naphthalen-1,2-dione, and 2-
(methylsulfinyl)naphthalen-1-ol.
Scheme 1. Diverse Transformations of Benzoyl Sulfoxonium
Ylide
unctionalized naphthalene derivatives such as naphthale-
nones are prevalent in natural products, optical/electronic
F
materials, and pharmaceuticals.1,2 Due to their importance,
several synthetic protocols for the preparation of naphthalenone
derivatives have been developed.3 While these literature
methods are generally efficient and reliable, new methods
starting from easily accessible substrates and accomplished
through short and simple synthetic procedures with improved
atom-economy are still highly desirable.
As reliable synthetic intermediates, sulfonium/sulfoxonium
ylides have been routinely used in various transformations due
to their easy accessibility, moisture/air-stability, and diverse
reactivity.4−6 Meanwhile, directing group-assisted functionaliza-
tion of inert C−H bonds represents one of the hottest topics in
6
Rh(III) catalyst. From this study, we serendipitously found
novel access toward highly functionalized naphthalenones
containing a β-ketosulfoxonium ylide moiety (Scheme 1, (3)).
Our study was initiated by treating benzoyl sulfoxonium ylide
1a with α-diazocarbonyl compound 2a in the presence of
[RhCp*Cl2]2 and AgSbF6 in DCE. From this reaction, 3a was
obtained along with its acylmethylation derivative 4a in yields of
17% and 23%, respectively (Table 1, entry 1). It is worthwhile to
be noted herein that the unexpected formation of 3a and 4a is
mechanistically interesting in that it reveals a different reaction
pattern compared with either that of benzoyl sulfoxonium ylides
with simple diazo compounds (Scheme 1, (2)) or that of
benzoyl sulfoxonium ylides with alkynes (Scheme 1, (1)). In
addition, this reaction is also synthetically fascinating as it
discloses a novel approach toward unique naphthalenone
derivatives bearing a β-ketosulfoxonium ylide unit. A literature
̈
synthetic chemistry in past decades. In this aspect, Aιssa and Li
have independently disclosed Rh(III)-catalyzed C(sp2)−H
acylmethylation of arenes by using β-ketosulfoxonium ylides
as stable and safe carbene surrogates.7 Later, Li and others
applied this strategy into the preparation of various carbocycles
and heterocycles through initial alkylation with sulfoxonium
ylides followed by an intramolecular condensation.8 Further-
more, Li et al. disclosed a Rh(III)-catalyzed C(sp2)−H
functionalization on the phenyl ring of benzoyl sulfoxonium
ylides with alkynes to afford naphthols (Scheme 1, (1)).9 More
recently, Maulide et al. reported a Ru(II)-catalyzed cross-
olefination of sulfoxonium ylides with diazo compounds through
exquisitely exploiting the intrinsic difference in the reactivity of
diazo compounds and sulfoxonium ylides as carbene precursors
and nucleophiles (Scheme 1, (2)).10 Inspired by these elegant
pioneering studies and as a continuation of our own interest in
the chemistry of sulfoxonium ylides11 and diazo compounds,12
we have explored the reaction of benzoyl sulfoxonium ylides
with α-diazocarbonyl compounds under the catalysis of a
Received: January 28, 2019
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.9b00340
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
a
temperature on this reaction was also explored (entries 15−18).
As a result, the optimum temperature for the formation of 4a was
determined as 80 °C, while that for 3a was found to be 100 °C. It
was also observed that in the absence of AgSbF6, the formation
of either 3a or 4a was not observed (entries 19−20). Finally,
with toluene or TFE as the reaction medium, [RhCp*-
(MeCN)3](SbF6)2, [RhCp*(OAc)2]2, [Ir(cod)Cl2]2, or [Ru-
(cymene)2Cl2]2 was tried as possible catalyst to replace
[RhCp*Cl2]2. However, they were found to be less efficient
than [RhCp*Cl2]2 (see SI for the details).
With the establishment of the optimum reaction conditions,
the substrate scope for the synthesis of 3 was studied. First, the
suitability of diversely substituted benzoyl sulfoxonium ylides 1
was investigated by using 2a as a model substrate. The results
listed in Scheme 2 showed that 1 bearing either a methyl or
methoxy unit on the para-position of the phenyl ring took part in
this reaction smoothly to afford 3b and 3c. In addition, 1 bearing
either an electron-donating group (EDG) such as methyl or
methoxy or an electron-withdrawing group (EWG) such as
Table 1. Optimization for the Formation of 3a or 4a
b
yield (%)
ratio of 1a/
T
(°C)
entry
2a
catalyst
solvent
3a 4a
1
2
3
4
5
6
7
8
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
[RhCp*Cl2]2
[RhCp*Cl2]2
[RhCp*Cl2]2
[RhCp*Cl2]2
[RhCp*Cl2]2
[RhCp*Cl2]2
[RhCp*Cl2]2
[RhCp*Cl2]2
[RhCp*Cl2]2
[RhCp*Cl2]2
[RhCp*Cl2]2
[RhCp*Cl2]2
[RhCp*Cl2]2
[RhCp*Cl2]2
[RhCp*Cl2]2
[RhCp*Cl2]2
[RhCp*Cl2]2
[RhCp*Cl2]2
[RhCp*Cl2]2
[RhCp*Cl2]2
DCE
dioxane
THF
CH3CN
TFE
HFIP
toluene
PhCl
toluene
toluene
toluene
TFE
TFE
TFE
80
80
80
80
80
80
80
80
80
80
80
80
80
80
100
60
100
120
80
100
17
15
11
15
43
42
trace
trace
trace
trace
trace
45
46
41
trace
trace
51
23
8
14
10
trace
trace
29
28
48
58
50
trace
trace
trace
53
9
1:2
10
11
12
13
14
15
16
17
18
1:2.2
1:2.5
1.2:1
1.5:1
2.0:1
1:2.2
1:2.2
1.2:1
1.2:1
1:2.2
1.2:1
a b
,
Scheme 2. Substrate Scope for the Synthesis of 3
toluene
toluene
TFE
TFE
TFE
43
trace
trace
ND
ND
50
ND
ND
c
19
20
c
TFE
a
Conditions: 1a (0.5 mmol for entries 1−11, 15−16, 19), 2a (0.5
mmol for entries 12−14, 17−18, 20), catalyst (0.02 mmol, 4 mol %),
b
AgSbF6 (0.08 mmol, 16 mol %), solvent (3 mL), N2, 24 h. Isolated
c
yield. In the absence of AgSbF6.
search revealed that, while bis-substituted sulfoxonium ylides are
important synthetic intermediates with unique reactivity and
applications, reliable methods for their preparation have only
been sporadically reported,13 and some of these known methods
usually suffer from drawbacks such as tedious synthetic steps,
limited substrate scope, and expensive reagents. Very recently,
Burtoloso et al. disclosed an elegant preparation of acylic α-aryl
β-ketosulfoxonium ylides via the reactions of β-ketosulfoxonium
ylides with the in situ generated aryne intermediates.14
However, to the best of our knowledge, the synthesis of α-
cycloalkenyl β-ketosulfoxonium ylides has not been previously
reported.
To develop this novel reaction into a reliable and practical
approach toward bis-substituted β-ketosulfoxonium ylides,
several parameters possibly affecting this reaction were screened.
First, different solvents were tried. It was thus found that using
dioxane, THF, or CH3CN as the reaction medium could not
improve the efficiency or selectivity compared with that using
DCE (entries 2−4 vs 1). In further screening, we were pleased to
find that the reaction run in TFE (2,2,2-trifluoroethanol) or
HFIP (hexafluoroisopropanol) could selectively give 3a as the
predominant product in substantially improved yields (entries 5
and 6). However, when the reaction was run in toluene or PhCl,
4a could be formed as a major product (entries 7 and 8). Next,
by using TFE or toluene as the optimum solvent, the effect of
different molar ratio of 1a:2a on the efficiency for the formation
of 3a or 4a was explored (entries 9−14). It was thus found that
the best ratio for the formation of 4a is 1:2.2 (entry 10), while
that for the formation of 3a is 1.2:1 (entry 12). Next, the effect of
a
Conditions: 1 (0.6 mmol), 2 (0.5 mmol), [RhCp*Cl2]2 (0.02 mmol,
4 mol %), AgSbF6 (0.08 mmol, 16% mmol), TFE (3 mL), 100 °C, N2,
b
24 h. Isolated yield.
B
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Organic Letters
Letter
a b
,
chloro or bromo on the meta-position of the phenyl ring are also
suitable substrates for this reaction to give 3d−3g. Notably, the
reactions of substrates bearing a meta-chloro or bromo unit gave
a mixture of two regioisomers (3e and 3e′, 3f and 3f′).
Promisingly, when 1 with an ortho-methyl, -chloro, or -bromo
substituted phenyl unit were treated with 2a, the corresponding
reactions proceeded equally well to give 3h−3j without showing
obvious steric effect. Second, by using 1a as a model substrate,
the generality of different α-diazocarbonyl compounds 2 for this
reaction was studied. It was observed that 2-diazo-3-oxo-3-
phenylpropanoates bearing various functional groups including
methyl, methoxy, chloro, bromo, or trifluoromethyl on the
phenyl ring took part in this reaction efficiently to give 3k−3q.
Meanwhile, it was noted that the electronic nature of the phenyl
moiety rendered a slight effect on this reaction in that substrates
bearing EDGs on the phenyl ring generally gave higher yields
than those bearing EWGs (3l vs 3m). When alkyl substituted α-
diazocarbonyl compounds were used, the reactions proceeded
successfully to give 3r and 3s. Just like ethyl 2-diazo-3-oxo-3-
phenylpropanoate, the reactions of methyl 2-diazo-3-oxo-3-
phenylpropanoate and tert-butyl 2-diazo-3-oxobutanoate with
1a proceeded well to give 3t and 3u. We were delighted to find
that 3-diazopentane-2,4-dione could also serve as the α-
diazocarbonyl substrate to react with 1a to give 3v in 55%
yield. Finally, benzoyl sulfoxonium ylides with strong EWGs (F
and CF3) attached on the para-position of the phenyl ring were
also tried. From the corresponding reactions, 3w and 3x were
obtained. Meanwhile, it should be noted that the structure of 3b
was unambiguously confirmed by its X-ray single crystal
diffraction analysis.
Scheme 3. Substrate Scope for the Synthesis of 4
After establishing a novel synthesis of 3, we continued our
study by exploring the substrate scope for the synthesis of 4, the
acylmethylation derivative of 3. For this purpose, a series of
benzoyl sulfoxonium ylides 1 were allowed to react with
different α-diazocarbonyl compounds 2 such as ethyl/methyl 2-
diazo-3-oxo-3-phenylpropanoates bearing a diversely substi-
tuted phenyl unit, or ethyl 2-diazo-3-(furan-2-yl)-3-oxopropa-
noate, respectively. From these reactions, the corresponding
products 4a−4t were obtained in yields ranging from 45% to
75%, thus resulting in a reliable and general synthetic protocol
toward the structurally more complex naphthalenones contain-
ing a β-ketosulfoxonium ylide unit (Scheme 3). Notably, the
structure of 4h was confirmed by its NMR data and X-ray single
crystal diffraction analysis.
a
Conditions: 1 (0.5 mmol), 2 (1.1 mmol), [RhCp*Cl2]2 (0.02 mmol,
4 mol %), AgSbF6 (0.08 mmol, 16 mol %), toluene (3 mL), 80 °C,
b
N2, 24 h. Isolated yield.
Scheme 4. Formation of 5 from an Alkyl Substituted α-
Diazocarbonyl Substrate
Scheme 5. Reaction of 1a with Terminal α-Diazoester and
Ketone
Interestingly, when tert-butyl 2-diazo-3-oxobutanoate was
used as the diazo substrate to react with 1a, the corresponding
reaction afforded a benzo[de]chromene derivative 5, most likely
with 4u as an intermediate (Scheme 4).
As a further exploration of the scope, simple terminal diazo
ester and ketone were allowed to react with 1a. It turned out that
the reaction of 1a with ethyl 2-diazoacetate in TFE or toluene
gave unidentifiable mixtures (Scheme 5, (1)). Meanwhile, the
reaction of 1a with 2-diazo-1-phenylethan-1-one in TFE or
toluene afforded 1-phenyl-2-(2,2,2-trifluoroethoxy)ethan-1-one
(A) or 1,4-diphenylbut-2-ene-1,4-dione (B) (Scheme 5, (2)).
To get some insight into the reaction mechanism accounting
for the formation of 3a, the following experiments were
conducted. First, 1a was treated with CD3OD in the presence
of [RhCp*Cl2]2 and AgSbF6 in TFE at 100 °C for 30 min, from
which deuterium incorporations at the ortho-position of the
phenyl ring (6%) and the α-position of the carbonyl unit (27%)
were observed (Scheme 6). These results indicate that the C−H
bond cleavage process should be reversible.
Scheme 6. Reversibility of C−H Bond Cleavage
Second, a competitive reaction between 1a with 2a and 1a-d5
with 2a was carried out. From this reaction, an intermolecular
kinetic isotopic effect value (KH/KD) of 3.5 was determined
(Scheme 7). This result shows that the cleavage of the ortho-C−
C
DOI: 10.1021/acs.orglett.9b00340
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Organic Letters
Letter
H bond might be involved in the rate-limiting step of this
cascade process.
Scheme 10. Gram-scale Synthesis of 3a
Scheme 11. Synthetic Applications of 3a
Scheme 7. Intermolecular Kinetic Isotope Effect Study
Based on the above-described mechanistic studies and related
reports,9,12 a plausible mechanism accounting for the formation
of 3a from the reaction of 1a with 2a is proposed in Scheme 8.
Scheme 8. Proposed Mechanism for the Formation of 3a
important 4-hydroxy-2-phenyl-1-naphthoate (6), 3-hydroxy-4-
oxo-2-phenyl-3,4-dihydronaphthalene-1-carboxylate (7), 4-hy-
droxy-3-(methylsulfinyl)-2-phenyl-1-naphthoate (8),15 and 3,4-
dioxo-2-phenyl-3,4-dihydronaphthalene-1-carboxylate (9)16
were obtained in moderate to excellent yields.
In conclusion, we have developed a general, efficient, and
sustainable synthesis of novel naphthalenone derivatives
containing a β-ketosulfoxonium ylide moiety through direct
C−H functionalization and subsequent annulations of benzoyl
sulfoxonium ylides with α-diazocarbonyl compounds. To our
knowledge, this is the first example in which α-cycloalkenyl β-
ketosulfoxonium ylides are prepared. Moreover, the synthetic
significance of the novel naphthalenone derivative thus obtained
was showcased by its easy transformations into a series of
synthetically and biologically interesting naphthalene deriva-
tives. With notable features such as easily accessible substrates,
convenient synthetic procedure, and good atom economy, the
chemical transformations described in this Letter are expected to
find broad applications in related areas.
Initially, coordination of the carbonyl oxygen of 1a with Rh(III)
and subsequent cyclometalation through C−H bond cleavage
gives rise to a five-membered rhodacycle I. I then reacts with 2a
to afford a rhodium-carbene species II through releasing N2.
Next, migratory insertion of carbene into the Rh−C bond
affords a six-membered rhodacycle intermediate III. Proto-
nolysis of III leads to the formation of intermediate IV and
regenerates the Rh(III) catalyst. In the final stage of this cascade
reaction, IV undergoes an intramolecular nucleophilic addition
to form V, from which 3a is formed through β-elimination.
As for the plausible mechanism accounting for the formation
of 4a, it should first involve the formation of 3a from the cascade
reaction of 1a with 2a as described in Scheme 8. Then, a Rh(III)-
catalyzed acylmethylation of 3a with 2a under the assistance of
the naphthalenone carbonyl unit takes place to afford 4a. This
proposal is confirmed by the following control experiment that
treatment of 3a with 2a under standard reaction conditions
could afford 4a in a yield of 83% (Scheme 9).
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.orglett.9b00340.
Copies of 1H and 13C NMR spectra of all products and the
X-ray crystal structures and data of 3b, 4h, and 8 (PDF)
Accession Codes
CCDC 1887533, 1887549, and 1887578 contain the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge via www.ccdc.cam.ac.uk/data_request/
cif, or by emailing data_request@ccdc.cam.ac.uk, or by
contacting The Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
Scheme 9. Formation of 4a from the Reaction of 3a with 2a
AUTHOR INFORMATION
Corresponding Authors
■
To see whether this newly developed synthesis of
naphthalenone derivatives bearing a β-ketosulfoxonium ylide
unit is suitable for larger scale application, the preparation of 3a
was carried out in 5 mmol scale. Under these circumstances, 3a
was obtained in a yield of 42% (Scheme 10).
To showcase the synthetic potential of the naphthalenones
bearing a β-ketosulfoxonium ylide unit obtained above, several
structural elaborations of 3a were carried out (Scheme 11).
From these transformations, the synthetically and biologically
*E-mail: xuesen.fan@htu.cn.
*E-mail: xinyingzhang@htu.cn.
ORCID
Xinying Zhang: 0000-0002-3416-4623
Xuesen Fan: 0000-0002-2040-6919
Notes
The authors declare no competing financial interest.
D
DOI: 10.1021/acs.orglett.9b00340
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
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ACKNOWLEDGMENTS
■
We are grateful to the National Natural Science Foundation of
China (NSFC) (21572047), Plan for Scientific Innovation
Talents of Henan Province (184200510012), and 111 Project
(D17007) for financial support.
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DOI: 10.1021/acs.orglett.9b00340
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