Nitrogen-and phosphorus-containing lewis base catalyzed [4+2] and [3+2] annulation reactions of isatins with but-3-yn-2-one

Article abstract of DOI:10.1002/ejoc.201101338

Nitrogen- and phosphorus-containing Lewis base catalyzed [4+2] and [3+2] annulations of isatins with but-3-yn-2-one proceeded smoothly to give the corresponding spiro[indoline-3,2′-pyran]-2,4′(3′H)-diones and spiro[furan-2,3′-indoline]-2′,4(5H)-diones in

Full text of DOI:10.1002/ejoc.201101338

FULL PAPER
DOI: 10.1002/ejoc.201101338
Nitrogen- and Phosphorus-Containing Lewis Base Catalyzed [4+2] and [3+2]
Annulation Reactions of Isatins with But-3-yn-2-one
Zhong Lian[a] and Min Shi*[a]
Keywords: Nitrogen heterocycles / Spiro compounds / Reaction mechanisms / Lewis bases
Nitrogen- and phosphorus-containing Lewis base catalyzed
[4+2] and [3+2] annulations of isatins with but-3-yn-2-one
proceeded smoothly to give the corresponding spiro-
[indoline-3,2Ј-pyran]-2,4Ј(3ЈH)-diones and spiro[furan-2,3Ј-
indoline]-2Ј,4(5H)-diones in good-to-excellent yields under
mild conditions. The substrate scope has been carefully ex-
amined. Moreover, the additive effect of water has also been
investigated in detail along with plausible reaction mecha-
nisms based on previous literature and our own investi-
gations.
Oxindoles that incorporate a quaternary stereogenic cen-
ter at C-3 are attractive targets in organic synthesis because
of their significant biological activities as well as wide-rang-
Results and Discussion
The investigation started with the reaction of N-Bn-pro-
ing utility as intermediates in the synthesis of alkaloids, tected isatin 1a (1.0 equiv.) and but-3-yn-2-one (2;
drug candidates, and clinical pharmaceuticals.[1,2] Therefore 1.5 equiv.) in the presence of 1,4-diazabicyclo[2,2,2]octane
a number of useful synthetic methods have been developed (DABCO; 20 mol-%) in THF at room temperature (20 °C).
in pursuit of this interesting structural motif, including We found that the oxygen-containing six-membered cyclic
intermolecular alkylations,[3] palladium-catalyzed cou- product 1-benzylspiro[indoline-3,2Ј-pyran]-2,4Ј(3ЈH)-dione
plings,[4] cycloadditions,[5] sigmatropic rearrangements,[6] (3a) was obtained in 17% yield (Table 1, entry 1). The struc-
carbanion nucleophilic additions to ketones or ketimines of ture of product 3a was assigned on the basis of spectro-
isatin,[7] and annulations of allenoates.[8,9] Recently we re- scopic analyses and unambiguously confirmed by X-ray dif-
ported an efficient method for the construction of this im- fraction of single crystals of 3a. The ORTEP drawing of the
portant structural motif through the annulation of isatin- structure is shown in Figure 1.[12] Increasing the amount of
derived electron-deficient alkenes with allenoates[10] and is- DABCO employed to 1.0 equiv. (100 mol-%) afforded prod-
atylidene malononitriles with Morita–Baylis–Hillman uct 3a in 85% yield (Table 1, entry 2). However, further in-
(MBH) carbonates in the presence of phosphanes.[11] In- creasing the amount of DABCO employed to 1.2 or
spired by the results, we envisaged that by using but-3-yn- 1.5 equiv. did not improve the yield of product 3a (Table 1,
2-one as the reactant, novel spiro cycloadducts might be entries 3 and 4). When the reaction was carried out with 1/
formed in nitrogen- or phosphorus-containing Lewis base 2/DABCO = 1:1:1 or 1:2:1 in THF at room temperature, it
catalyzed annulation reactions. In this paper we disclose a was found that the corresponding annulation products 3a
novel nitrogen-containing Lewis base mediated [4+2] annu- were obtained in 73 and 85% yields, respectively (Table 1,
lation and an interesting phosphorus-containing Lewis base entries 5 and 6). The use of other nitrogen-containing Lewis
catalyzed [3+2] annulation of isatins with but-3-yn-2-one to bases such as 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU),
produce the corresponding spiro[indoline-3,2Ј-pyran]- triethylamine (TEA), 4-(dimethylamino)pyridine (DMAP),
2,4Ј(3ЈH)-diones and spiro[furan-2,3Ј-indoline]-2Ј,4(5H)-di- and diisopropylethylamine (DIPEA) did not lead to further
ones, respectively, in good yields under mild conditions improvements in the yield of 3a (Table 1, entries 7–10),
(Scheme 1).
which indicates that DABCO is the best promoter for this
reaction. An examination of solvent effects revealed that
THF is the solvent of choice for this novel annulation reac-
tion (Table 1, entries 11–14).
Having identified the optimal reaction conditions, we
next set out to examine the substrate scope of this [4+2]
annulation reaction catalyzed by DABCO by using various
isatin derivatives 1 with different substituents on the benz-
[a] State Key Laboratory of Organometallic Chemistry, Shanghai
Institute of Organic Chemistry, Chinese Academy of Sciences,
354 Fenglin Road, Shanghai 200032, China
Fax: +86-21-64166128
E-mail: mshi@mail.sioc.ac.cn
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201101338.
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Scheme 1. Nitrogen- and phosphorus-containing Lewis base catalyzed [4+2] and [3+2] annulations.
reactions of isatin derivatives 1l–1q bearing different nitro-
gen protecting groups also proceeded efficiently to produce
the corresponding spiro cycloadducts 3l–3q in moderate-to-
good yields (Table 2, entries 11–16). We also found that the
products 3a–3q are quite stable during their isolation by
silica gel column chromatography.
We found that another spiro cycloadduct, 1Ј-benzyl-5-
methylene-3H-spiro[furan-2,3Ј-indoline]-2Ј,4(5H)-dione (4a),
was formed from a [3+2] annulation in 74% yield by using
triphenylphosphane (20 mol-%) as the catalyst (Table 3, en-
try 1). Its structure was unambiguously determined by X-
ray analysis of the single crystal of its analogue 4j (see
Table 4, entry 9). Its structure is shown in Figure 2.[13] Ex-
amination of various phosphane catalysts for this reaction
Figure 1. ORTEP drawing of the crystal structure of 3a.
ene ring. The results are summarized in Table 2. The reac- indicated that PPh2Me is the best catalyst for this reaction
tions proceeded smoothly to give the corresponding prod- (Table 3, entries 2–4). However, reducing or increasing the
ucts 3b–3k in moderate-to-good yields irrespective of amount of but-3-yn-2-one (2) employed did not improve the
whether electron-withdrawing or -donating groups were in- yields of 4a in the presence of PPh2Me (20 mol%; Table 3,
troduced at the 4-, 5-, 6-, or 7-position of the benzene ring entries 5 and 6). The use of 10 mol-% PPh2Me as catalyst
of N-Bn-protected isatins 1, which suggests that the elec- produced 4a in 61% yield (Table 3, entry 7). Solvent screen-
tronic nature of the substituents does not have an impact ing indicated that THF is still the solvent of choice for this
on the reaction (Table 2, entries 1–10). Note also that the interesting [3+2] annulation reaction (Table 3, entries 8–11).
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Eur. J. Org. Chem. 2012, 581–586

Lewis Base Catalyzed Annulations of Isatins with Butynone
Table 1. Optimization of the conditions for the [4+2] annulation
reaction.[a]
Table 3. Optimization of the conditions of the [3+2] annulation re-
action.[a]
Entry 1a/2
Cat.
x [mol-%]
Solvent
Yield [%][b]
1
2
3
4
5
6
7
8
1:1.5
1:1.5
1:1.5
1:1.5
1:1
DABCO
DABCO
DABCO
DABCO
DABCO
DABCO
DMAP
DBU
20
THF
THF
THF
THF
THF
THF
THF
THF
THF
17
85
84
85
73
85
80
trace
73
56
62
75
73
82
Entry 1a/2
Cat.
x (mol-%)
Solvent
Yield [%][b]
100
120
150
100
100
100
100
100
100
100
100
100
100
1
2
3
4
1:1.5
1:1.5
1:1.5
1:1.5
1:1
PPh3
20
20
20
20
20
20
10
20
20
20
20
THF
THF
THF
THF
THF
THF
THF
toluene
DCM
CH3CN
Et2O
74
PPh2Me
PPhMe2
PBu3
PPh2Me
PPh2Me
PPh2Me
PPh2Me
PPh2Me
PPh2Me
PPh2Me
86 (97)[c]
60
44
66
1:2
5
1:1.5
1:1.5
1:1.5
1:1.5
1:1.5
1:1.5
1:1.5
1:1.5
6
7
8
9
10
11
1:2
85
1:1.5
1:1.5
1:1.5
1:1.5
1:1.5
61 (59)[d]
63
9
Et3N
10
11
12
13
14
DIPEA
DABCO
DABCO
DABCO
DABCO
THF
79
73
83
toluene
DCM
CH3CN
Et2O
[a] Compound 1a (0.2 mmol) and the catalyst were dissolved in
solvent (2.0 mL) and then compound 2 was added to the reaction
mixture. The reaction mixture was stirred for 1 h. [b] Isolated
yields. [c] The yield was determined by 1H NMR spectroscopic
analysis of the crude by using 1,3,5-trimethoxybenzene as internal
standard. [d] The reaction mixture was stirred for 5 h.
[a] Compound 1a (0.2 mmol) and the catalyst were dissolved in
solvent (2 mL) and then compound 2 was added to the reaction
solution. The resulting reaction mixture was stirred for 0.5 h. [b]
Isolated yields.
Table 2. Substrate scope of the [4+2] annulation reaction.[a]
Table 4. Substrate scope of the [3+2] annulation reaction.[a]
Entry
R1
R2
Yield [%][b]
1
2
3
4
5
6
7
8
5-F
Bn, 1b
Bn, 1c
Bn, 1d
Bn, 1e
Bn, 1f
3b, 84
3c, 82
3d, 70
3e, 76
3f, 80
3g, 65
3h, 73
3i, 70
3j, 68
3k, 67
3l, 66
3m, 68
3n, 87
3o, 86
3p, 64
Entry
R1
R2
Yield [%][b,c]
5-CH3
5-Cl
5-Br
6-Br
7-Br
5,7-(CH3)2
4-Cl
4-Br
5-CH3O
5-CH3
5-Br
H
1
2
3
4
5
6
7
8
5-F
Bn, 1b
Bn, 1c
Bn, 1d
Bn, 1e
Bn, 1f
Bn, 1g
4b, 87 (82)
4c, 98 (83)
4d, 78 (74)
4e, 88 (72)
4f, 95 (76)
4g, 65 (63)
4h, 92 (71)
4i, 98 (73)
4j, 89 (88)
4k, 82 (75)
4l, 64 (61)
4m, 83 (79)
4n, 90 (88)
4o, 83 (78)
5-CH3
5-Cl
5-Br
6-Br
7-Br
5,7-(CH3)2 Bn, 1h
5-CH3O
H
H
H
H
H
H
Bn, 1g
Bn, 1h
Bn, 1i
9
Bn, 1j
10
11
12
13
14
15
16
Bn, 1k
CPh3, 1l
CPh3, 1m
Me, 1n
allyl, 1o
CPh3, 1p
Bn, 1i
Me, 1j
allyl, 1k
CPh3, 1l
(anthracen-10-yl)methyl, 1m
Boc, 1n
mom, 1o
9
10
11
12
13
14
H
H
H
(anthracen-10-yl)methyl, 1q 3q, 65
[a] Compound 1 (0.2 mmol) and DABCO (0.2 mmol) were dis-
solved in THF (2 mL) and then compound 2 (0.3 mmol) was added
to the reaction mixture. The resulting reaction mixture was stirred
for 0.5 h. [b] Isolated yields.
[a] Compound 1 (0.2 mmol) and PPh2Me (0.04 mmol) were dis-
solved in THF (2.0 mL) and then compound 2 (0.3 mmol) was
added to the solution. The resulting reaction mixture was stirred
for 1 h. [b] Isolated yields. [c] The yields given in parentheses were
1
determined by H NMR analysis of the crudes by using 1,3,5-tri-
methoxybenzene as internal standard.
1
The yield determined by H NMR spectroscopic analysis
of the crude using 1,3,5-trimethoxybenzene as internal stan-
dard was 97% (Table 3, entry 2), which indicates that prod-
Next we examined the substrate scope of this reaction by
uct 4a partially decomposed during the isolation process by using a variety of isatin derivatives 1. The results of these
silica gel column chromatography.
experiments are summarized in Table 4. In general we iso-
Eur. J. Org. Chem. 2012, 581–586
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Z. Lian, M. Shi
FULL PAPER
are not very stable and that they decompose partially dur-
ing the purification process (Table 4, entries 1–14). Their
structures were determined by IR, NMR, and MS.
The mechanism for the formation of 3a shown in
Scheme 2 may be invoked to rationalize the reaction out-
comes. Initially, as Lewis base, DABCO deprotonates but-
3-yn-2-one (2) to generate an enolate intermediate.[14] Nu-
cleophilic addition of this species to the carbonyl group of
N-Bn-protected isatin 1a gives intermediate A. Intramolecu-
lar Michael addition of the O– anion to the alkynyl group
Figure 2. ORTEP drawing of the crystal structure of 4j.
lated the oxygen-containing heterocyclic compounds 4 in
moderate-to-good yields. All of the reactions proceeded
smoothly under the standard conditions. The yields of the
corresponding spiro five-membered heterocyclic products
4b–4i were not influenced significantly by the electronic na-
ture of the substituents on the benzene ring of 1 (Table 4,
entries 1–8). Changing the nitrogen protecting group to
methyl, allyl, CPh3, (anthracen-10-yl)methyl, Boc, or mom
(methoxymethyl) also afforded the corresponding products
4j–4o in moderate-to-good yields, which suggests a wide
substrate scope for this reaction (Table 4, entries 9–14). It
should be emphasized here that these spiro cycloadducts Scheme 2. A plausible mechanism for the formation of 3a.
Scheme 3. A plausible mechanism of the formation of 4a.
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Eur. J. Org. Chem. 2012, 581–586

Lewis Base Catalyzed Annulations of Isatins with Butynone
in intermediate A gives intermediate B, which subsequently cellent yields by N- and P-containing Lewis base mediated/
undergoes protonation to produce the corresponding prod- catalyzed annulation of N-protected isatins 1 with but-3-
uct 3a. Because DABCO serves as a Brønsted base in this yn-2-one under mild conditions. The annulation protocol is
reaction, a stoichiometric amount of DABCO is required.
suitable for a variety of N-protected isatin derivatives.
The mechanism for the formation of 4a is proposed in Moreover, two plausible mechanisms have been proposed
Scheme 3. First, the reaction of PPh2Me with but-3-yn-2- on the basis of previous literature reports. Efforts are un-
one (2) generates the zwitterion intermediate C,[15] which derway to elucidate the mechanistic details of these two an-
undergoes a 1,3-hydrogen shift to give enolate intermediate nulation reactions and to explore other annulation reac-
D.[16] Nucleophilic addition of enolate D to the carbonyl tions with N- and P-containing Lewis bases.
group of N-Bn-protected isatin 1a produces intermediate F.
Intramolecular addition of the O– anion to the alkenyl
group in intermediate F gives ylide-type intermediate G,
which subsequently undergoes a 1,2-hydrogen shift to af-
Experimental Section
General Procedure for the Formation of 3a: Under argon, N-pro-
ford intermediate H. The elimination of phosphane gives
the final product 4a.[17]
tected isatin 1a (0.2 mmol), but-3-yn-2-one (2; 0.3 mmol), DABCO
(0.2 mmol), and THF (2.0 mL) were added to a Schlenk tube. The
Furthermore, the additive effects of water in the above
mixture was stirred at room temperature for 0.5 h and the reaction
was monitored by TLC. Then the solvent was removed under re-
duced pressure and the residue was purified by flash column
chromatography (silica gel, PE/EtOAc, 2:1) to afford compound 3a
reactions were also examined under the standard conditions
and it was found that water can accelerate the phosphane-
catalyzed annulation reaction, as reported by other groups
(see the Supporting Information for details).[18] Note that
as a white solid in 85% yield.
the spiro cycloadducts are not very stable and they decom-
pose slightly in the presence of water.
General Procedure for the Formation of 4a: Under argon, N-pro-
tected isatin 1a (0.2 mmol), but-3-yn-2-one (2; 0.3 mmol), PPh2Me
To gain more mechanistic insights we performed an iso-
(0.04 mmol), and THF (2.0 mL) were added to a Schlenk tube. The
topic labeling experiment by adding 1.0 equiv. of D2O to
mixture was stirred at room temperature until the reaction was
the reaction system; the reaction was carried out under the
standard conditions (Scheme 4). It was found that the prod-
uct [D]4a was obtained in 83% yield with 50% D content
(see the Supporting Information for details). Control ex-
periments suggested that product 4a could not incorporate
deuterium under the standard reaction conditions in the
presence of D2O and thus the deuterium is incorporated
during the reaction, which supports a stepwise mechanism.
complete. Then the solvent was removed under reduced pressure
and the residue was purified by flash column chromatography (sil-
ica gel, PE/EtOAc, 5:1) to give compound 4a as a white solid in
86% yield.
Supporting Information (see footnote on the first page of this arti-
cle): 1H and 13C NMR spectra of the compounds shown in
Tables 1–4.
Acknowledgments
We thank the Shanghai Municipal Committee of Science and Tech-
nology (08dj1400100-2), the National Basic Research Program of
China (973)-2009CB825300, and the National Natural Science
Foundation of China (NSFC) for financial support (grant numbers
21072206, 20472096, 20872162, 20672127, 20821002, and
20732008). We also thank Mr. Jie Sun for performing X-ray diffrac-
tion analyses.
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21.2831(19), b = 9.6616(9), c = 15.0176(14) Å, α = 90, β = 90,
γ = 90°, V = 3088.1(5) Å3, Pna2(1)/c, Z = 4, Dcalcd. = 1.313 g/
cm3, F(000) = 1280, final R indices [IϾ2σ(I)]: R1 = 0.0529,
wR2 = 0.1278. CCDC-807844 contains 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.
[13] Crystal data for 4j: C13H11NO3, Mr = 229.23, colorless,
0.208ϫ0.165ϫ0.057 mm, orthorhombic, a = 19.993(3), b =
5.5764(9), c = 10.1469(17) Å, α = 90, β = 90, γ = 90°, V =
1131.3(3) Å3, Pca2(1), Z = 4, Dcalcd. = 1.346 g/cm3, F(000) =
480, final R indices [IϾ2σ(I)]: R1 = 0.0574, wR2 = 0.1283.
CCDC-823432 contains 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.
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Received: September 14, 2011
Published Online: November 30, 2011
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