Direct synthesis of sulfonated dihydroisoquinolinones from: N -allylbenzamide and arylsulfinic acids via TBHP-promoted cascade radical addition and cyclization

Article abstract of DOI:10.1039/c6cc04983d

A novel synthesis of sulfonated dihydroisoquinolinones via cascade radical addition and cyclization was developed in the presence of tert-butyl hydroperoxide (TBHP). The reactions generated the desired sulfonated dihydroisoquinolinones in good yields from readily available arylsulfinic acids and N-allylbenzamides under metal-free conditions.

Full text of DOI:10.1039/c6cc04983d

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DOI: 10.1039/C6CC04983D
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COMMUNICATION
Direct synthesis of sulfonated dihydroisoquinolinones from N-
allylbenzamide and arylsulfinic acids via TBHP-promoted
cascade radical addition and cyclization
Received 00th January 2016
Accepted 00th January 2016
Dong Xia,a Yang Li,a Tao Miao,*a Pinhua Li,a Lei Wang*a,b
DOI: 10.1039/x0xx00000x
www.rsc.org/
A novel synthesis of sulfonated dihydroisoquinolinones via
cascade radical addition and cyclization was developed in
presence of tert-butyl hydroperoxide (TBHP). The reactions
generated the desired sulfonated dihydroisoquinolinones in
good yields from readily available arylsulfinic acids and
allylbenzamides under metal-free conditions.
N-
Dihydroisoquinolone derivatives, as one of the important class
heterocycles have been widely found in complex natural
products and drug molecules, which display diverse biological
properties such as anti-tumor, anti-inflammatory, anti-allergic
and estrogenic behaviour.1 Due to their fascinating biological
and
pharmacological
activities,
the
synthesis
of
dihydroisoquinolone derivatives have received much attention.
Traditional synthetic approach to dihydroisoquinolone is based
on the condensation of homophthalic anhydride with imines in
the presence of acid or base catalyst or under thermal
conditions.2 Recently, transition metal catalyzed constructions
of dihydroisoquinolone frameworks have been demonstrated to
be the powerful and efficient routes.3 Especially, Guimond,3a
Glorius,3b Daugulis,3c Wang,3d and others3e-g have elegantly
developed the synthesis of dihydroisoquinolones via Rh-, Ru-,
Co- or Re-catalyzed oxidative annulations of benzamides and
alkenes on the basis of CH activation and functionlization
strategy (Scheme 1a). Furthermore, the reactions of N-
allylbenzamides could provide promising access to substituted
dihydroisoquinolones through a free radical process.4 For
example, Han and Pan reported a facile DTBP-promoted
radical cyclization of N-allylbenzamide with alcohols for
synthesis of 4-hydroxyalkyl-substituted 3,4-dihydroisoquinolin-
1(2H)-one (Scheme 1b).4a Meanwhile, The sulfone is a key
organic structural motif in a variety of biologically active
Scheme 1. Synthetic strategies for dihydroisoquinolones.
compounds, pharmaceuticals and synthetic intermediates, especially
for aryl alkyl sulfones (Figure 1).5 For example, I can be used as
antiproliferative activity against cancer cell,5b and II is an important
intermediate for synthesis of isoquinoline-derived target molecules.5c
In addition, the sulfonyl group is a strong electron-withdrawing
group, and can facilitate the deprotonation of a neighboring carbon
atom to generate α-carbanion with a base, the corresponding
carbanion can be used for various transformations.6 So, development
of new and efficient methodologies for the incorporation of a
sulfonyl group into dihydroisoquinolinones from simple, readily
available starting materials remains highly desirable in organic
chemistry.
a Department of Chemistry, Huaibei Normal University, Huaibei, Anhui 235000, P
R China; E-mail: leiwang@chnu.edu.cn; taomiaochem@163.com
Tel.: +86-561-380-2069; fax: +86-561-309-0518.
Figure 1. Selected examples of important aryl alkyl sulfones.
b State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic
Chemistry, Chinese Academy of Sciences, Shanghai 200032, P R China
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See DOI:
10.1039/x0xx00000x
Arylsulfinic acids (salts) are relatively stable and versatile
intermediates in organic synthesis.7 In the past decades,
considerable efforts have been devoted to the synthesis of
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organic sulfones using arylsulfinic acids (salts) as sulfonylation using TBHP as an oxidant under metal-free condition, which
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reagents. As a result, remarkable achievements in cross- undergoes smoothly through a sequencDeOrIa: 1d0i.c1a0l39a/Cdd6CitCio0n49a8n3Dd
coupling of aromatic sulfinic acids (salts) with arylhalides, intramolecular cyclization to sulfonated dihydroisoquinolones
arylborons and allylic amines have been accomplished by using in high atom-economy and excellent functional group tolerance
Pd, Cu and Fe catalysts, and arylsulfinic salts as the precursor (Scheme 1).
of sulfonyl anion reacted with metal catalysts to form a key
In our initial study, N-allyl-N-methyloxybenzamide (1a) and
sulfonyl-metal intermediates.8 However, the use of transition p-tolylsulfinic acid (2a) were chosen as the model substrates to
metals limits their applicability. Most recently, addition of optimize the reaction conditions with different solvent and
sulfonyl radical to carbon-carbon multiple bonds provided an oxidant. When CH3CN was used as a solvent with TBHP as an
important alternative for the synthesis of functionalized oxidant, the model reaction of 1a with 2a generated the
sulfones under metal-free conditions.9 For example, Lei and co- corresponding sulfonated dihydroisoquinolinone 3a in 45%
workers described oxysulfonylation of alkenes or alkynes yield (Table 1, entry 1). However, other solvents including
employing arylsulfinic acids as the sulfonyl radical precursor DMSO (dimethyl sulphoxide), 1,4-dioxane, DMF (N,N-
using molecular oxygen as oxidant.9a,b Subsequently, our group dimethylformamide), THF (tetrahydrofuran), methanol, toluene,
developed visible-light photocatalytic difunctionalization of DCE (1,2-dichloroethane) and H2O were inferior and afforded
arylacrylamides and arylpropiolates with arylsulfinic acids to desired 3a in 1042% yields (Table 1, entries 29). Much to our
offer sulfone-containing oxindoles and coumarins through a pleasure, 74% yield of 3a was achieved when a mixed solvent of
tandem CS/CC bond formation.9e,f With our continuing acetonitrile and H2O in 1:1 (V/V) was used as reaction medium
interest in application of arylsulfinic acids as sulfonylation
agents, herein, we wish to disclose a novel and efficient
arylsulfonylation of N-allylbenzamides with arylsulfinic acids
Table 1. Optimization of the reaction conditions.a
Entry
Oxidant
TBHP
TBHP
TBHP
Solvent
CH3CN
DMSO
DMF
Yield (%) b
1
2
3
45
22
31
4
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
DCP
1,4-dioxane
THF
27
21
10
15
28
42
74
61
51
40
28
27
36
38
34
50 c
52 d
5
6
CH3OH
7
toluene
8
DCE
9
H2O
10
11
12
13
14
15
16
17
18
19
20
H2O/CH3CN (1:1)
H2O/CH3CN (1:1)
H2O/CH3CN (1:1)
H2O/CH3CN (1:1)
H2O/CH3CN (1:1)
H2O/CH3CN (1:1)
H2O/CH3CN (1:1)
H2O/CH3CN (1:1)
H2O/CH3CN (1:1)
H2O/CH3CN (1:1)
H2O/CH3CN (1:1)
TBPB
DTBP
CHP
H2O2
O2
K2S2O8
Na2S2O8
TBHP
TBHP
a
Reaction conditions: 1a (0.25 mmol), 2a (0.75 mmol), oxidant (3.0
equiv), solvent (3.0 mL), at 120 oC for 24 h. TBHP = tert-butyl
hydroperoxide (70% solution in water); DCP = dicumyl peroxide; TBPB
= tert-butyl peroxybenzoate; DTBP = di-tert-butyl peroxide; CHP =
Scheme 2. Reaction of 1a with arylsulfinic acids [Reaction conditions: 1a
(0.25 mmol), 2 (0.75 mmol), TBHP (3.0 equiv), CH3CN/H2O (1:1, 3.0 mL),
120 oC, 24 h; isolated yield of the product based on 1a.]
b
cumene hydroperoxide; H2O2 (30% aqueous solution). Isolated yield
based on 1a. c TBHP (2.0 equiv) was used, d 2a (2.0 equiv) was used.
2 | Chem. Commun., 2016, 00, 1-4
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(Table 1, entry 10). Next, the effect of the oxidant on the model useful structural motif in biologically active molecules,10
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DOI: 10.1039/C6CC04983D
reaction was examined. When DCP (dicumyl peroxide) was instead with 1a to generate the corresponding product 3h in 64% yield. In
of TBHP, the model reaction generated the desired product 3a in the case of disubstituted arylsulfinic acids, the reaction underwent
61% yield (Table 1, entry 11). Other organic oxidants, such as smoothly, affording products 3n and 3o in moderate yields.
TBPB, DTBP, CHP, H2O2, K2S2O8, Na2S2O8 and O2 led to 3a in Furthermore, more bulky 1,1'-biphenyl- and 2-naphthyl-sulfinic
2751% yields (Table 1, entries 12−18). Reducing amount of acids could participate in the reaction well, furnishing the
TBHP or 2a from 3.0 equiv to 2.0 equiv, the model reaction dihydroisoquinolinones 3p and 3q in accepted yields. It should be
produced 3a in 50% and 52% yields, respectively (Table 1, entries noted that aliphatic sulfinic acid such as n-butylsulfinic acid could
19 and 20).
also be used in the reaction to provide the desired product 3r in 47%
With the optimized conditions in hand, we explored the synthetic yield.
viability of the reactions using N-allyl-N-methyloxybenzamide (1a)
After studying the scope of arylsulfinic acids, we turned our
with a variety of arylsulfinic acids, and the results are summarized in attention toward N-allylbenzamide derivatives. As shown in Scheme
Scheme 2. In general, a number of arylsulfinic acids containing both 3, N-allylbenzamides have a broad scope and high compatibility with
electron-donating and electron-withdrawing groups on the aromatic functional groups, such as methyl, tert-butyl, phenyl, trifluoromethyl
rings underwent the radical addition and cyclization to provide the and halogen groups, and gave the corresponding products (3s3ak)
corresponding arylsulfonylation products (3a–3q) in 50−76% yields. in moderate to good yields. It is important to note that this domino
In particular, the sterically-hindered substituted arylsulfinic acid, reaction is compatible with I, Br and Cl at para-position of the
such as ortho-fluoro- and ortho-methoxybenzenesulfinic acids were aromatic rings, which can undergo the further transformation for the
suitable substrates in the transformation, leading to the desired synthesis of more complex molecules. Meanwhile, substrate 1 with
products 3l and 3m in 51% and 50% yield, respectively. Notably, 3,5-dimethyl groups on phenyl ring could undergo the tandem
arylsulfinic acid bearing a trifluoromethyl (CF3) group, which is a
reaction to afford the 3ag and 3ah in good yields. To investigate the
regioselectivity of this cyclization, the reaction of 1 with meta-
substituted group was conducted. As expected, meta-substituted
substrate 1 gave a mixture of two regioselective products 3ai and
3ai' in a ratio of 1:1.3 with total 60% yield. An obviously
regioselectivity was obtained when 3,4-dichloro substituted 1 reacted
with 2a, providing 3aj as sole product in 52% yield. The structure of
3aj was further confirmed by single-crystal X-ray diffraction
analysis (Supporting Information for detail). Furthermore, N-ethyl
protected N-allylbenzamide was also examined, providing product
3ak in 45% yield. However, the reaction of N-phenyl and N-H,N-
allylbenzamides failed to react with p-tolylsulfinic acid (2a) under
the standard reaction conditions (3al, 3am). Finally, substrate with
substituted double bond N-β-methyl-allyl-N-methyloxybenzamide
was found to be suitable for this protocol, and reacted with p-
tolylsulfinic acid (2a) to generate target product 3an in 71%.
For understanding the mechanism of tandem reaction, the well
known radical-trapping reagents, such as TEMPO (2,2,6,6-
tetramethylpiperidine-N-oxyl) and BHT (2,6-di-tert-butyl-4-methyl-
phenol) was added in 2.0 equiv to the model reaction respectively,
Scheme 3. Reaction of 1 with arylsulfinic acids [Reaction conditions: 1 (0.25
mmol), 2 (0.75 mmol), TBHP (3.0 equiv), CH3CN/H2O (1:1, 3.0 mL), 120
oC, 24 h; isolated yield based on 1.]
Scheme 4. Possible mechanism.
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4
DrO a1s0h.i 3d9/SC.6MCCa04u9b8a3D,
transformation involved a radical process. Based on our observations
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