RhIII-Catalyzed C-H Allylation of Amides and Domino Cycling Synthesis of 3,4-Dihydroisoquinolin-1(2H)-ones with N-Bromosuccinimide

Article abstract of DOI:10.1002/ejoc.201501551

A Rh^III-catalyzed C-H allylation of electron-deficient arenes, heteroarenes, and alkenes at room temperature was developed with allyl bromide. The reaction was carried out in diethyl ether without dehydration, and C-H activation was assisted by the directing anionic nitrogen of the aniline-derived amide. Following the allylation, a domino cycling synthesis of 3,4-dihydroisoquinolin-1(2H)-ones with N-bromosuccinimide (NBS) through intramolecular aminobromination of the introduced double bond was achieved. A C-H allylation of amides with allyl halides at room temperature and a tandem synthesis of 3,4-dihydroisoquinolin-1(2H)-ones with N-bromosuccinimide (NBS) are reported.

Full text of DOI:10.1002/ejoc.201501551

DOI: 10.1002/ejoc.201501551
Communication
Organic Methodology
RhIII-Catalyzed C–H Allylation of Amides and Domino Cycling
Synthesis of 3,4-Dihydroisoquinolin-1(2H)-ones with
N-Bromosuccinimide
Huimin Dai,[a] Chao Yu,[a] Changsheng Lu,[a] and Hong Yan*[a]
Abstract: A RhIII-catalyzed C–H allylation of electron-deficient amide. Following the allylation, a domino cycling synthesis of
arenes, heteroarenes, and alkenes at room temperature was de-
veloped with allyl bromide. The reaction was carried out in di-
ethyl ether without dehydration, and C–H activation was as-
sisted by the directing anionic nitrogen of the aniline-derived
3,4-dihydroisoquinolin-1(2H)-ones with N-bromosuccinimide
(NBS) through intramolecular aminobromination of the intro-
duced double bond was achieved.
Introduction
allyl halides are no longer the appropriate allyl electrophiles
because of either low activity[7b,7c,13a,14] or severe α-olefination
isomerization.[18,19]
We have developed a new allylation. It can be conducted at
room temperature with commercial solvents and is also applica-
ble to both aroyl- and acrylamide substrates. Moreover, the allyl
sources are not restricted to carbonates, esters, or alcohols, but
allyl halides can also be used.
Aminohalogenation of olefins is one of the most fundamen-
tal and useful reactions in organic chemistry,[20] which can pro-
duce versatile building blocks for chemical synthesis, in particu-
lar in the preparation of drugs,[21] and the domino cycling syn-
thesis of 3,4-dihydroisoquinolin-1(2H)-ones through intra-
molecular aminobromination of the corresponding allyl prod-
ucts was achieved without extra catalyst.
The allyl group is one of the prominent structural motifs in
many bioactive natural products,[1] and allylic intermediates
can be conveniently transformed to other functionalized
products.[2] Therefore, allylation of organic compounds has at-
tracted much attention. For instance, the classic Claisen re-
arrangement of allyl, aroyl, or acrylate esters[3] and Friedel–
Crafts allylation of electron-rich arenes[4] are useful in rapidly
accessing a variety of allylarenes. However, poor regio- and
stereoselectivity, low yield, harsh conditions, and narrow sub-
strate scope have limited the application of these reactions. In
order to avoid these deficiencies, transition-metal-catalyzed
allylation has been developed, including decarboxylative allyl-
ation,[5] preactivated C–C cross coupling,[6] and, the most at-
tractive, direct C–H allylation. In the cases of electron-deficient
arenes such as polyfluoroarenes, allylation can be performed by
Pd or Cu catalysis with the assistance of a base,[7] otherwise,
Results and Discussion
directing groups have to be used. The directing-group-assisted We started by examining the reaction between N-(3,4,5-tri-
C–H allylation can expand to a wider range of arenes as well as methoxyphenyl)benzamide (1a) and allyl bromide (2a). C–H ac-
olefins. The reaction consists of three basic protocols: (1) allene tivation selectively occurred at the ortho position of the aroyl
insertion into the C–M bond;[8] (2) C–C coupling with α or γ ring, and allylation product 3a was isolated. No byproducts de-
selectivity;[9–11] (3) ꢀ-LG (LG: leaving group) elimination follow- rived from ꢀ-H elimination or α-olefination isomerization of 3a
ing olefin insertion[12] with γ-selectivity.[13–17] However, these were detected. The influence of different catalysts was evalu-
protocols have several drawbacks. For instance, all the reported ated, and [Cp*RhCl2]2 showed the best activity with a yield of
reactions have been performed in anhydrous solvents, and very 45 % when AgOAc in acetonitrile was added (Table 1, entries
few can be conducted at room temperature. Furthermore, only 1–4). Next, a range of solvents were screened: diethyl ether was
three examples are applicable to both arenes and ole- the best with a yield of 73 % for 3a (Table 1, entry 9). Silver
fins.[8a,9,13d] In the case of the third protocol mentioned above, salts (Table 1, entries 9–13) were also examined, and those with
non-coordinating anions showed no activity, which indicates
the importance of the coordination effect of the anion. To our
[a] State Key Laboratory of Coordination Chemistry,
surprise, raising the temperature to 40 °C led to a lower yield
of 3a (50 %) (Table 1, entry 14), and using an anhydrous solvent
did not improve the yield (Table 1, entry 15). Moreover, oxygen
did not retard the reaction (Table 1, entry 16). We tested both
the steric and electronic effects of anilines (Table 1, entry 17–
20), and 1a seemed to produce the best yield.
School of Chemistry and Chemical Engineering,
Nanjing University,
Nanjing, Jiangsu 210093, China
E-mail: hyan1965@nju.edu.cn
http://chem.nju.edu.cn
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/ejoc.201501551.
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Table 1. Optimization of the reaction conditions.[a,b]
the reaction can tolerate different substituents on the starting
benzamides such as methoxy, halogen, cyano, and nitro. And
these groups could be subjected to further chemical transfor-
mations. However, electron-withdrawing groups seemed to re-
tard the reaction, especially the nitro group (34 %). In addition,
the lower yield (38 %) of 3n indicated the effect of steric hin-
drance. For substrate 1l containing an electron-withdrawing
group at the 3-position, the allylation preferred the 6-position
relative to the 2-position. But for 1m, the substitution was only
observed at the 6-position because of the stronger electron-
withdrawing ability of the nitro group. However, the allylation
of 1k showed no regioselectivity. This indicates the role of the
electronic effect. It is noteworthy that moderate yields were
obtained for heterocycles such as furan and thiophene. More-
over, this reaction is also suitable for acrylamides that lead to
the corresponding 1,4-diene skeletons in high yields. No by-
products, such as conjugated alkene moieties, were isolated.
Entry Catalyst
Additive
Solvent
Yield (%)
R = Ar1 = 3,4,5-trimethoxyphenyl, 1a
3
3′
1
2
3
4
5
6
7
8
[Cp*RhCl2]2
[Cp*IrCl2]2
[(p-cymene)RuCl2]2
PdCl2
AgOAc
AgOAc
AgOAc
AgOAc
AgOAc
AgOAc
AgOAc
AgOAc
AgOAc
AgOBz
AgOTf
AgBF4
MeCN
MeCN
MeCN
MeCN
MeOH
THF
45
<10
–
6
–
–
–
–
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
14
56
15
12
73
51
43
<10
–
7
8
–
–
14
13
–
–
–
PhMe
DCE
9
Ether
Ether
Ether
Ether
Ether
Ether
Ether
Ether
10
11
12
13
14[c]
15[d]
16[e]
AgSbF6
AgOAc
AgOAc
AgOAc
50
66
69
10
13
14
R
17[f]
18[f]
19[f]
20[f]
Phenyl, 1b
59
–
61
53
13
–
10
11
2,4,6-trimethylphenyl, 1c
4-methylphenyl, 1d
4-fluorophenyl, 1e
[a] Unless otherwise noted, the reactions were carried out at room tempera-
ture with 1a–e (0.2 mmol, 1 equiv.), 2a (42 μL, 2.5 equiv.), additive (2.1 equiv.),
and catalyst (4 mol-%) in solvent (5 mL) for 12 h. [b] Isolated yield. [c] 40 °C.
[d] Anhydrous solvent. [e] No O2. [f] The same conditions as those for entry
9.
Furthermore, we explored the influence of various allyl sour-
ces (allyl halides 2a–c, esters 2d–h, and carbonate 2i; see
Table S1). The tested allyl electrophiles were all active, and allyl
iodide 2b gave the best result with a yield of 77 %. Noticeably,
allyl halides are not suitable for the previously published metal-
catalyzed C–H allylation, except for some Csp2–Csp3 coupled ex-
amples[11] and organometallic reagents,[22] as they suffer from
either low activity[7b,7c,13a,14] or severe α-olefination isomeriza-
tion.[18,19] The yield of our reaction was affected by both the
coordinating and the leaving abilities of the functional groups
in the allyl electrophiles. Since 2a can lead to a higher yield
than that achieved with allyl acetate (2d), it most likely per-
forms allylation directly, rather than forming an allyl ester inter-
mediate. In view of both the availability and price of allyl hal-
ides, 2a was chosen as the allyl electrophile, despite the higher
yield with 2b. Thus, the following optimized conditions were
chosen: diethyl ether as solvent, room temperature, 4 mol-%
[Cp*RhCl2]2 as catalyst, and 2.1 equiv. AgOAc as additive.
With the optimized reaction conditions in hand, the scope
and limitations of the reaction with respect to amides were
investigated (Scheme 1). Gratifyingly, this reaction enabled the
selective ortho-allylation of various benzamides to generate the
corresponding products in yields from 34 % to 93 %. Notably,
Scheme 1. Reaction scope of amides. General conditions: The reactions were
carried out at room temperature using 1a and 1f–t (0.4 mmol), 2a (84 μL,
2.5 equiv.), AgOAc (140.2 mg, 2.1 equiv.), and [Cp*RhCl2]2 (9.9 mg, 4 mol-%)
in Et2O (10 mL) for 12 h. Isolated yield. “3a, 73 % (di, 14 %)” means the
isolated yield of the monoallylated product 3a is 73 % and the 1H NMR spec-
troscopic yield of diallylated product is 14 %. The diallylated products of 1l–
n and 1o were not observed. The ratio of 3I2 to 3I6 was determined by 1H
NMR spectroscopy.
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A possible mechanism for the allylation of aroyl- and acryl-
amides by allyl bromide is proposed in Scheme 2 on the basis
of control experiments and the detected intermediates. The cat-
alytic cycle is initiated by amide-directed ortho-C–H activation
to form intermediate I, which carries a five-membered metallic
ring. The directing group is most likely an anionic nitrogen, as
Me-1a showed no activity under the same conditions
[Scheme 3(a)]. Furthermore, the formation of I is irreversible,
since no deuterated 1j was isolated when D2O was added
[Scheme 3(b)]. The structure of I is supported by its ESI-HRMS
1
data (with molecular peak at [M – H]–, m/z = 582.1342) and H
NMR spectroscopic data (showing the loss of the NH hydrogen
and only four hydrogen atoms on the aroyl ring; see Figure S1
in the Supporting Information). Additionally, C–H activation
might be the rate-determining step of the reaction, as the inter-
molecular deuterium isotopic effect was observed to be 1.5
[Scheme 3(c)] and the intramolecular isotopic effect was 2.6
[Scheme 3(d)]. Then the double bond of allyl bromide might be
inserted into the C–Rh bond in I,[23] followed by ꢀ-Br elimina-
tion to afford the desired product, 3a. The ꢀ-Br elimination
should be facilitated by the existence of AgOAc[24] (Path a,
Scheme 2); however, oxidative addition of the C–Br bond to Rh
is also a possible pathway for the reaction (Path b, Scheme 2).
Scheme 3. Mechanistic investigation.
Scheme 2. Proposed mechanism.
Considering the useful aminohalogenation and versatile
transformations of allylic intermediates,[25,26] we tried using N-
bromosuccinimide (NBS) for the domino synthesis of hetero-
cycles. The conditions were optimized as shown in Table S2. To
our delight, we were able to prepare 3,4-dihydroisoquinolin-
1(2H)-ones from the corresponding amides in a one-pot reac-
tion. These compounds belong to one of the most important
families of heterocycles and frequently appear as the core
framework in bioactive compounds.[27,28] Since the C–F cou-
pling constants provide more information on the structure, the
structure of compound 4g was confirmed by 2DNMR spectro-
scopy (COSY, HSQC & HMBC, Figures S5–S7). However, bromina-
Scheme 4. Reaction scope of 3,4-dihydroisoquinolin-1(2H)-one. The details of
the reaction are in the Supporting Information (Part VII).
Bicyclic compound 5u has been demonstrated to be useful
tion took place at the original aniline ring as well, which might for inhibiting phosphatidyl inositol-3 kinase (P13 kinase). The
be ascribed to the presence of electron-donating groups. The activity of P13 kinase is associated with lots of diseases, includ-
domino synthesis was proved to be applicable to both aroyl- ing but not limited to cancer and inflammatory disease.[29]
and acrylamides (Scheme 4). However, it is not suitable for sub- Compound 4u, previously prepared from the expensive starting
strates 1b, 1d, and 1e, unless anhydrous solvent is used for the material 6-methylanthranilic acid in seven steps,[29] is the key
cyclization.
intermediate for the synthesis of 5u. Now, by means of the
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Communication
Supporting Information (see footnote on the first page of this
article): Experimental details, characterization data, and copies of
the 1H NMR and 13C NMR spectra for all key intermediates and final
products.
allylation and NBS cyclization strategy, we are able to prepare
4u in 21 % isolated yield from cheap 2-methyl-benzoic acid in
four steps. In this reaction, only 1.1 equiv. NBS was added to
avoid bromination of the aniline ring (Scheme 5).
Acknowledgments
We gratefully acknowledge the National Basic Research Pro-
gram of China (2013CB922101), the National Natural Science
Foundation of China (21271102, 21472086, and 21531004), and
the Natural Science Foundation of Jiangsu Province
(BK20130054).
Keywords: Allylation · C–H activation · Heterocycles ·
Synthetic methods
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Typical Procedure for Allylation of Amides: A 25 mL flask was
charged with substrate 1a–t (0.40 mmol, 1.0 equiv.), [Cp*RhCl2]2
(9.9 mg, 0.016 mmol, 4 mol-%), AgOAc (140.2 mg, 0.84 mmol,
2.1 equiv.), diethyl ether (10 mL), and 2a (84 μL, 1 mmol, 2.5 equiv.)
in air. The flask was capped, and the reaction mixture was stirred
for 12 h at room temperature. Then CH2Cl2 (2 mL) was added into
the flask to dissolve potential organic precipitates. The mixture was
filtered, and the precipitate was washed with CH2Cl2 (2 mL × 3).
The filtrate was then concentrated in a rotary evaporator under
reduced pressure, and the resulting residue was purified by silica
gel column chromatography, using EtOAc/hexane as the eluent.
Typical Procedure for Preparing Heterocycles 4a, 4g, 4h–l, 4o,
4p, 4r, 4t Based on the Allylation: After the general procedure for
allylation (0.4 mmol), CH2Cl2 (2 mL) was added into the flask to
dissolve potential organic precipitates. The mixture was filtered, and
the precipitate was washed with CH2Cl2 (2 mL × 3). The filtrate was
concentrated in a rotary evaporator under reduced pressure, and
NBS (249.2 mg, 1.4 mmol, 3.5 equiv.) and solvent (5 mL) were added
to the flask. After that, the flask was capped and submerged into a
preheated 40 °C oil bath for 1 h. After cooling to room temperature,
the solvent was removed under reduced pressure. The resulting
residue was purified by silica gel column chromatography using
EtOAc/hexane (1:30) as the eluent.
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Published Online: February 22, 2016
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1259
© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim