Silver triflate-catalyzed or electrophile-mediated tandem reaction of n'-(2-alkynylbenzylidene)hydrazides with dimethyl acetylenedicarboxylate

Article abstract of DOI:10.1002/adsc.200900131

Different outcomes were generated under different conditions for the tandem reactions of N'-(2-alkynylbenzylidene)hydrazides with dimethyl acetylenedicarboxylate (DMAD) catalyzed by silver triflate or in the presence of electrophiles. The unexpected isoqu

Full text of DOI:10.1002/adsc.200900131

FULL PAPERS
DOI: 10.1002/adsc.200900131
Silver Triflate-Catalyzed or Electrophile-Mediated Tandem
Reaction of N’-(2-Alkynylbenzylidene)hydrazides with Dimethyl
Acetylenedicarboxylate
Zhiyuan Chen,a Qiuping Ding,a Xingxin Yu,a and Jie Wua,b,*
a
Department of Chemistry, Fudan University, 220 Handan Road, Shanghai 200433, Peopleꢀs Republic of China
Fax : (+86)-216-510-2412; e-mail: jie_wu@fudan.edu.cn
State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of
b
Sciences, 354 Fenglin Road, Shanghai 200032, Peopleꢀs Repubic of China
Received: February 25, 2009; Revised: May 5, 2009; Published online: June 23, 2009
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/adsc.200900131.
Abstract: Different outcomes were generated under triflate or in the presence of bromine, while the
different conditions for the tandem reactions of N’- fused 1,2-dihydroisoquinolines were afforded when
(2-alkynylbenzylidene)hydrazides with dimethyl ace- iodine was employed in the above tandem reactions.
tylenedicarboxylate (DMAD) catalyzed by silver tri-
flate or in the presence of electrophiles. The unex- Keywords: N’-(2-alkynylbenzylidene)hydrazides; di-
pected isoquinoline-based azomethine ylides were methyl acetylenedicarboxylate; electrophiles; silver
obtained when the reaction was catalyzed by silver triflate; tandem reactions
Introduction
philes. Interestingly, different outcomes were generat-
ed under the different conditions mentioned above.
Tandem carbon-carbon bond formations are powerful The unexpected isoquinoline-based azomethine ylides
methods for the synthesis of structurally complex were obtained when the reaction was catalyzed by
molecules from relatively simple starting materials in silver triflate or run in the presence of bromine, while
a convergent way.[1,2] In particular, the development the fused 1,2-dihydroisoquinolines were afforded
of tandem reactions for the efficient construction of when iodine was employed in the tandem reactions.
small molecules is an important goal in combinatorial
chemistry from the viewpoints of operational simplici-
ty and assembly efficiency. Recently, we have devel- Results and Discussion
oped efficient methods for the construction of 1,2-di-
hydroisoquinolines via tandem reactions starting from The starting materials N’-(2-alkynylbenzylidene)hy-
2-alkynylbenzaldehydes.[3] Following
a
biological drazides were easily accessible via condensation of 2-
screening it was shown that this kind of compound alkynylbenzaldehydes with hydrazine. The reaction
was active as a PTP1B (protein tyrosine phosphatase) was initially studied with N’-(2-alkynylbenzylidene)-
inhibitor (IC50: 4.6 mM). With the expectation to find hydrazide 1a and dimethyl acetylenedicarboxylate
more active hits as well as part of a continuing effort (DMAD), which were selected as suitable substrates
in our laboratory for the expeditious synthesis of bio- for reaction development (Scheme 1). We conceived
logically relevant heterocyclic compounds, we started that in the presence of a suitable Lewis acid catalyst,
to investigate the possibility to develop novel meth- N’-(2-alkynylbenzylidene)hydrazide 1a would be con-
ods to build up new 1,2-dihydroisoquinoline-based verted to the intermediate 2a. Subsequently, a further
structures. Herein, we disclose our recent efforts for dipolar cycloaddition reaction might occur in the
the generation of fused 1,2-dihydroisoquinolines and presence of dipolarophiles (such as dimethyl acety-
related N-heterocycles via tandem cyclization-[3+2]
cycloaddition of N’-(2-alkynylbenzylidene)hydrazide
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
with dimethyl acetylenedicarboxylate (DMAD) cata- ty of this proposed route, we started to investigate the
lyzed by silver triflate or in the presence of electro- possibility for the one-pot tandem electrophilic cycli-
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Scheme 1. One-pot tandem reaction of N’-(2-alkynylbenzylidene)hydrazide 1a with dimethyl acetylenedicarboxylate
(DMAD).
zation-[3+2] cycloaddition of N’-(2-alkynylbenzyl- version of compound 3a to 4a. The rearrangement in-
À
idene)hydrazide with dimethyl acetylenedicarboxylate volves homolysis of the N N bond in compound 3a
(DMAD).
and subsequent cyclization to afford the aziridine in-
As described above, in the presence of a Lewis termediate. Thermal ring-opening of aziridine could
acid, N’-(2-alkynylbenzylidene)hydrazide 1a could be give the unexpected ylide 4a.[5,6] Under these standard
transformed to the intermediate 2a via electrophilic conditions, other Lewis acids were re-examined for
cyclization. At the outset, various Lewis acids were the reaction of N’-(2-alkynylbenzylidene)hydrazide 1a
screened and silver triflate (10 mol%) was demon- with dimethyl acetylenedicarboxylate. Only a small
strated as the best choice when this reaction was per- amount of isoquinolinium-2-yl
ACHTUNGTRENNUNG
formed at 708C in dichloroethane (Scheme 1). The re- with recovery of the starting material when ironACHTUNGTRENNUNG
action went to completion and an almost quantitative chloride was employed as a catalyst. A 50% yield of
yield of product 2a was generated. Other metal cata- product 4a was obtained when palladium chloride was
lysts employed displayed lower yields. For example, used as a replacement. GoldACTHNUTRGNEU(GN III) chloride as catalyst
an 82% yield of product 2a was isolated when copper was found to be effective as well for this transforma-
triflate was utilized in the reaction. The starting mate- tion (61% yield), while an inferior result (35% yield)
rial N’-(2-alkynylbenzylidene)hydrazide 1a could not was observed when copper triflate was utilized in the
be consumed even after 24 h at 708C when the reac- reaction.
tion was catalyzed by iron
G
G
With this promising result in hands and having de-
triflate. In the silver triflate-catalyzed reaction of N’- fined an efficient catalytic system [silver triflate
(2-alkynylbenzylidene)hydrazide 1a, dimethyl acety- (10 mol%), dichloroethane, sodium acetate, molecular
ACHTUNGTRENNUNGlenedicarboxylate (DMAD) was added subsequently. sieves], the scope of tandem cyclization-[3+2] cyclo-
To our delight, the formation of a product was ob- addition-rearrangement one-pot reactions of N’-(2-al-
served although only 15% yield was isolated. Further kynylbenzylidene)hydrazide 1 with dimethyl acety-
screening revealed that the yield could be increased
ACHTUNGTRENlNGNU enedicarboxylate was next explored and the results
to 35% when the one-pot reaction was performed at are summarized in Table 1. For most cases, N’-(2-alky-
room temperature. Addition of other Lewis acids as nylbenzylidene)hydrazide 1 reacted with dimethyl
co-catalysts could not improve the result. We finally acetylenedicarboxylate catalyzed by silver triflate
realized that in the presence of molecular sieves and leading to the corresponding products 4 in good to ex-
sodium acetate, the isolated yield of the product cellent yields. For instance, reaction of he fluoro-sub-
could be increased to 70% (Scheme 1). Solvent stituted N’-(2-alkynylbenzylidene)hydrazide 1b with
screening demonstrated that dichloroethane (DCE) dimethyl acetylenedicarboxylate gave rise to the de-
was the best choice in the reaction. However, struc- sired product 4b in 80% yield (Table 1, entry 2). An
tural identification revealed that the product generat- inferior yield was displayed when the substrate 1c
ed was compound 4a, instead of the desired fused di- with an electron-donating group attached on the aro-
hydroisoquinoline 3a. We also observed a similar matic ring of N’-(2-alkynylbenzylidene)hydrazide was
transformation for the reaction of 2-alkynylbenzald- employed in the reaction (45% yield, Table 1,
ACHTUNGTRENNUNG
oxime, dimethyl acetylenedicarboxylate, and bro- entry 3). When R2 was replaced by the 4-methoxy-
mine.[5] In the reaction process, an aziridine is gener- phenyl group, reactions also proceeded well to furnish
ally assumed to be involved in the rearrangement of the corresponding products in good yields (Table 1,
4-isoxazoline.[6] Based on these results, we reasoned entries 4 and 5). Similar results were observed when
that a similar approach could be assumed for the con-
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Table 1. Silver triflate-catalyzed tandem reactions of N’-(2-alkynylbenzylidene)hydrazides 1 with dimethyl acetylenedicarbox-
ylate.
Entry
1
Substrate 1
Product 4
Yield [%][a]
70
1a
4a
2
3
4
1b
1c
1d
4b
4c
4d
80
45
70
5
6
7
8
1e
1f
1g
1h
4e
4f
4g
4h
83
51
81
65
9
1i
4i
68
[a]
Isolated yield based on N’-(2-alkynylbenzylidene)hydrazide 1. PMP: p-methoxyphenyl.
the tosyl group attached on the nitrogen was changed of bromine, iodine, or iodine monochloride was dis-
to a phenylsulfonyl group (Table 1, entries 6–9).
closed recently.[9] We found that the reactions of N’-
Meanwhile, we also tested the tandem reactions via (2-alkynylbenzylidene)hydrazide 1 with dimethyl ace-
an eletrophile-mediated cyclization. The electrophilic tylenedicarboxylate (DMAD) in the presence of bro-
cyclization of heteroatomic nucleophiles with tethered mine also gave rise to the expected bromo-containing
alkynes has been well-known for preparing many het- products 5, although the yields were lower
erocyclic ring systems.[7–9] Usually, iodine and bromine (Scheme 2). For example, when N’-(2-alkynylbenzyl-
were used in the reactions since the resulting iodo- or idene)hydrazide 1d was employed as the substrate in
bromo-containing products could be easily transferred the reaction of dimethyl acetylenedicarboxylate with
to more complex products by palladium-catalyzed bromine, a 41% yield of compound 5a was isolated. A
cross-coupling reactions. The electrophilic cyclization similar yield (45%) of product 5b was observed when
of N’-(2-alkynylbenzylidene)hydrazide in the presence substrate 1e was utilized in this tandem reaction. We
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Scheme 2. One-pot tandem reactions of N’-(2-alkynylbenzylidene)hydrazides 1, dimethyl acetylenedicarboxylate, and bro-
mine.
on the triple bond in the N’-(2-alkynylbenzylidene)hy-
drazide 1 was replaced by other groups (such as 4-me-
thoxyphenyl, butyl, cyclopropyl groups), the reactions
also proceeded smoothly to furnish the desired prod-
ucts in good yields (Table 2, entries 3–5).
The possible mechanism was also proposed
(Scheme 3). As described previously, electrophilic
cyclization of N’-(2-alkynylbenzylidene)hydrazide 1
with iodine would afford the corresponding isoquino-
linium-2-ylamide 7.[9] This compound subsequently
underwent [3+2] cycloaddition in the presence of di-
methyl acetylenedicarboxylate (DMAD) leading to
the intermediate 8. Finally, the aromatization oc-
curred to generate the unexpected product 6.
As mentioned above, the iodo-containing products
6 could be easily elaborated via palladium-catalyzed
cross-coupling reactions. Thus, the palladium-cata-
lyzed reaction of the fused 1,2-dihydroisoquinoline 6c
Figure 1. X-ray ORTEP illustration of compound 5c.
with phenylboronic acid in DMF-H2O at room tem-
also tried the reaction of N’-(2-alkynylbenzylidene)- perature occurred to afford the corresponding prod-
hydrazide 1j with an n-butyl group attached on the uct 6f in 86% yield. Compound 6d reacted with 4-me-
triple bond, and the corresponding product 5c was thoxyphenylacetylene, giving rise to the desired cou-
generated in 17% yield. The structure of compound pling product 6g in 81% yield (Scheme 4).
5c was verified by X-ray diffraction analysis
(Figure 1).
Surprisingly, a different outcome was generated Conclusions
when iodine was utilized as a replacement for bro-
mine. Compared with the results obtained in the pres- In conclusion, we have described an efficient tandem
ence of bromine in the reactions, the sulfonyl group cyclization-[3+2] cycloaddition reaction of N’-(2-al-
was released during the reaction process. In these kynylbenzylidene)hydrazides with dimethyl acetylene-
iodine-involved reactions, the yields of the corre- dicarboxylate catalyzed by silver triflate or run in the
sponding products were dramatically improved presence of electrophiles. Different outcomes were
(Table 2). For instance, N’-(2-alkynylbenzylidene)hy- generated under the different conditions. The halide-
drazide 1a reacted with dimethyl acetylenedicarboxy- containing products could be further elaborated by
late and iodine in the presence of sodium acetate palladium-catalyzed cross-coupling reactions to intro-
leading to the desired product 6a in 91% yield duce more diversity, which generated the highly func-
(Table 2, entry 1). A similar result was obtained when tionalized fused 1,2-dihydroisoquinolines. Small li-
the fluoro-containing substrate 1b was used in the re- brary construction as well as biological screening of
action (90% yield, Table 2, entry 2). The structure of these small molecules is ongoing, and the results will
compound 6b was also verified by X-ray diffraction be reported in due course.
analysis (Figure 2). When the phenyl group attached
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Table 2. One-pot tandem reactions of N’-(2-alkynylbenzylidene)hydrazides 1, dimethyl acetylenedicarboxylate, and iodine.
Entry
1
Substrate 1
Product 6
Yield [%][a]
1a
6a
91
2
3
4
1b
1d
1j
6b
6c
6d
6e
90
76
93
63
5
1k
[a]
Isolated yield based on N’-(2-alkynylbenzylidene)hydrazides 1. PMP: p-methoxyphenyl.
Experimental Section
General Procedure for Silver Triflate-Catalyzed
Tandem Reaction of N’-(2-Alkynylbenzylidene)-
hydrazide 1 with Dimethyl Acetylenedicarboxylate
A
mixture of N’-(2-alkynylbenzylidene)hydrazide
1
(0.40 mmol, 1.0 equiv.) and silver triflate (10 mol%) in anhy-
drous dichloroethane (4.0 mL) was stirred at 708C for 3 h.
Then the mixture was cooled to 08C in an ice-water bath,
4 ꢂ MS (100 mg) and sodium acetate (0.48 mmol, 1.2 equiv.)
were added. Subsequently, a solution of dimethyl acetylene-
dicarboxylate (0.80 mmol, 2.0 equiv.) in dichloroethane
(2.0 mL) was added dropwise and the mixture was slowly
warmed to room temperature. After completion of the reac-
tion as indicated by TLC, the reaction mixture was filtered
and the solvent of the filtrate was removed on a rotary
evaporator, followed by purification on silica gel which pro-
vided the corresponding product 4.
Figure 2. X-ray ORTEP illustration of the fused 1,2-dihy-
droisoquinoline 6b.
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Scheme 3. Possible mechanism for one-pot tandem reactions of N’-(2-alkynylbenzylidene)hydrazides 1, dimethyl acetylenedi-
carboxylate, and iodine.
Scheme 4. Synthesis of highly functionalized fused 1,2-dihydroisoquinolines via palladium-catalyzed cross-coupling reactions.
Data of a selected example: Compound 4a; yield: 70%;
1H NMR (400 MHz, CDCl3): d=2.40 (s, 3H), 3.37 (s, 3H),
3.90 (s, 3H), 7.20 (d, J=7.8 Hz, 2H), 7.24–7.36 (m, 4H),
7.38–7.46 (m, 1H), 7.73 (d, J=7.3 Hz, 2H), 7.87–7.89 (m,
1H), 8.02–8.12 (m, 4H), 9.09 (s, 1H); 13C NMR (100 MHz,
CDCl3): d=21.4, 52.7, 53.4, 126.2, 126.5, 127.0, 127.1, 128.2,
128.8, 129.9, 130.4, 130.5, 131.9, 137.1, 138.6, 141.2, 141.5,
149.7, 154.6, 162.6, 166.3; HR-MS: m/z=517.1440, calcd. for
C28H24N2O6S [M+H]+: 517.1433.
ration of the solvent followed by purification on silica gel
provided the corresponding product 5.
Data of a selected example: Compound 5a; yield: 41%;
1H NMR (400 MHz, CDCl3): d=2.42 (s, 3H), 3.47 (s, 3H),
3.83 (s, 3H), 3.87 (s, 3H), 6.40–6.70 (br, 1H), 6.90 (d, J=
6.4 Hz, 1H), 7.14–7.26 (m, 4H), 7.74 (d, J=7.8 Hz, 2H),
7.95–7.98 (m, 1H), 8.10–8.25 (m, 2H), 8.45 (d, J=8.3 Hz,
1H), 9.13 (s, 1H); 13C NMR (100 MHz, CDCl3): d=21.4,
51.2, 52.7, 55.2, 113.5, 113.6, 124.1, 124.9, 126.6, 126.7, 127.1,
127.9, 128.9, 130.2, 130.4, 130.8, 131.0, 138.3, 138.4, 141.2,
149.4, 153.9, 161.1, 166.1; HR-MS: m/z=625.0672, calcd. for
C29H25BrN2O7S [M+H]+: 625.0644.
General Procedure for Tandem Reaction of N’-(2-
Alkynylbenzylidene)hydrazides 1, DMAD, and
Bromine
General Procedure for the Tandem Reaction of N’-
(2-Alkynylbenzylidene)hydrazides 1, DMAD, and
Iodine
Bromine (0.48 mmol, 1.2 equiv.) in 2.0 mL of dichlorome-
thane was added dropwise to a mixture of the N’-(2-alkynyl-
benzylidene)hydrazide 1 (0.40 mmol, 1.0 equiv.), and sodium
acetate (0.48 mmol, 1.2 equiv.) in dichloromethane (4.0 mL)
at 08C. Subsequently, a solution of dimethyl acetylenedicar-
boxylate (DMAD) (0.8 mmol, 2.0 equiv.) in dichlorome-
thane (2.0 mL) was added, and the mixture was slowly
warmed to room temperature. After completion of the reac-
tion as indicated by TLC, the reaction mixture was diluted
with dichloromethane (10 mL), washed with saturated aque-
ous Na2S2O3 (20 mL), dried over anhydrous Na2SO4. Evapo-
Iodine (0.48 mmol, 1.2 equiv.) in 1.0 mL of dichloromethane
was added dropwise to a mixture of N’-(2-alkynylbenzyli-
AHCTUNGTREGdNNNU ene)hydrazide 1 (0.40 mmol, 1.0 equiv.), and sodium ace-
tate (0.48 mmol, 1.2 equiv.) in dichloromethane (4.0 mL) at
08C. Subsequently, a solution of dimethyl acetylenedicar-
boxylate (DMAD) (0.80 mmol, 2.0 equiv.) in dichlorome-
thane (2.0 mL) was added and the mixture was slowly
warmed to room temperature. After completion of the reac-
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Zhiyuan Chen et al.
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tion as indicated by TLC, the reaction mixture was diluted
with dichloromethane (10 mL), washed with saturated aque-
ous Na2S2O3 (20 mL), dried over anhydrous Na2SO4. Evapo-
ration of the solvent followed by purification on silica gel
provided the corresponding product 6.
Data of selected example: Compound 6a; yield: 91%;
1H NMR (400 MHz, CDCl3): d=3.88 (s, 3H), 4.01 (s, 3H),
7.42–7.44 (m, 2H), 7.54–7.60 (m, 3H), 7.67–7.75 (m, 2H),
8.25 (d, J=7.8 Hz, 1H), 8.87 (d, J=8.3 Hz, 1H); 13C NMR
(100 MHz, CDCl3): d=52.6, 52.7, 92.0, 108.1, 123.0, 125.6,
128.7, 129.1, 129.7, 130.2, 130.6, 131.2, 133.5, 137.0, 137.6,
141.0, 144.9, 162.9, 164.8. HR-MS: m/z=487.0147, calcd. for
C21H15IN2O4 [M+H]+: 487.0155. (For details, please see
Supporting Information).
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CCDC 713190 (5c) and CCDC 713191 (6b) contain the
supplementary crystallographic data for this paper. These
data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif.
Supporting Information
1
Experimental procedures, characterization data, and H and
13C NMR spectra of all new compounds are available as
Suppoprting Iformation.
Acknowledgements
Financial support from National Natural Science Foundation
of China (20772018), Shanghai Pujiang Program, and Pro-
gram for New Century Excellent Talents in University
(NCET-07-0208) is gratefully acknowledged.
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