Substitution of acyl for acetyl with N-acylbenzotriazoles catalyzed by samarium triiodide

Article abstract of DOI:10.1080/00397910701263684

Catalyzed by samarium triiodide (SmI3), substitution of acyl with N-acylbenzotriazoles for acetyl in acetoacetic esters and acetylacetone proceeds smoothly under neutral conditions in open air, affording the corresponding β-keto esters and β-diketones in good yields. Copyright Taylor & Francis Group, LLC.

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Substitution of Acyl for Acetyl with
N‐Acylbenzotriazoles Catalyzed by Samarium
Triiodide
Xuefei Zou a , Xiaofei Jia b , Xiaoxia Wang a & Guanqun Xie a
a Zhejiang Key Laboratory for Reactive Chemistry on Solid Surfaces , College
of Chemistry and Life Sciences, Zhejiang Normal University , Jinhua, China
b Chemistry Department , College of Science, Tianjin University , Tianjin,
China
Published online: 22 May 2007.
To cite this article: Xuefei Zou , Xiaofei Jia , Xiaoxia Wang & Guanqun Xie (2007) Substitution of Acyl
for Acetyl with N‐Acylbenzotriazoles Catalyzed by Samarium Triiodide, Synthetic Communications: An
International Journal for Rapid Communication of Synthetic Organic Chemistry, 37:10, 1617-1625, DOI:
10.1080/00397910701263684
To link to this article: http://dx.doi.org/10.1080/00397910701263684
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Synthetic Communicationsw, 37: 1617–1625, 2007
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910701263684
Substitution of Acyl for Acetyl with
N-Acylbenzotriazoles Catalyzed by
Samarium Triiodide
Xuefei Zou
Zhejiang Key Laboratory for Reactive Chemistry on Solid Surfaces,
College of Chemistry and Life Sciences, Zhejiang Normal University,
Jinhua, China
Xiaofei Jia
Chemistry Department, College of Science, Tianjin University, Tianjin,
China
Xiaoxia Wang and Guanqun Xie
Zhejiang Key Laboratory for Reactive Chemistry on Solid Surfaces,
College of Chemistry and Life Sciences, Zhejiang Normal University,
Jinhua, China
Abstract: Catalyzed by samarium triiodide (SmI3), substitution of acyl with N-acyl-
benzotriazoles for acetyl in acetoacetic esters and acetylacetone proceeds smoothly
under neutral conditions in open air, affording the corresponding b-keto esters and
b-diketones in good yields.
Keywords: N-acylbenzotriazoles, b-diketones, b-ketoesters, SmI3
b-Keto esters and b-diketones are very important intermediates in organic
synthesis, and their new reactions and applications continue to be an area of
interest.[1]
Received in Japan August 10, 2006
Address correspondence to Xiaoxia Wang, Zhejiang Key Laboratory for Reactive
Chemistry and Life Sciences, Zhejiang Normal University, Jinhua 321 004, China.
E-mail: wangxiaoxia@zjnu.cn
1617

1618
X. Zou et al.
Among numerous methods developed for the syntheses of b-keto esters
and b-diketones,[2,3] acyl exchange of the acetyl in acetoacetic ester or acet-
ylacetone with acyl halides in the presence of either a base[4a–d] or a metal
salt[4e–g] remains one frequently employed method. Despite being practical
in many cases, acyl halides as highly active acylating agents can favor
O-acylation of the enol form of ethyl acetoacetate or acetylacetone instead
of C-acylation.[5] Moreover, acylation with acyl chlorides generally suffers
from sensitivity to moisture and difficulty in handling.
Alternatively, esters,[6a] nitriles,[6b] and anhydrides[6c] may serve as less
active acylating agents, but usually harsh conditions and tedious procedures
are required. Very recently, it was reported N-acylbenzotriazoles were able
to undergo C-acylation of ethyl acetoacetate and acetonyl acetone with the
acetyl being cleaved spontaneously. The reaction offered a novel method
for the preparation of b-keto esters and b-diketones[7] in that N-acylbenzotria-
zoles—a kind of mild and stable crystalline acylating agents[8]—were intro-
duced. Nevertheless, the method is subject to certain disadvantages such as
using strong alkaline (NaH) conditions and requiring inert atmospheric protec-
tion. Herein we report that under neutral conditions and in open air, the sub-
stitution of acyl for acetyl with N-acylbenzotriazoles can be realized with
SmI3 as a catalyst to afford the expected b-keto esters and b-diketones with
good efficiency (Scheme 1 and Table 1).
The appropriate amount of SmI3 was found to be 20 mol% of the
substrate. THF other than CH3CN[4e] was chosen as the solvent, which was
based on the fact that N-acylbenzotriazoles, unlike acyl chlorides, would
not induce the ring opening of THF in the presence of SmI3. Finally, the
acyl exchange was carried out in refluxing THF with 0.2 equiv. of SmI3.
As shown in Table 1, this method is especially efficient for the synthesis
of b-aroyl substituted acetoacetic esters (Table 1, entries 1–7, 10). The sub-
stitution of aroyl for acetyl (naphthoyl is an exception, Table 1, entry 11)
could proceed to a complete stage within 2 h, which is in contrast to the
recently reported acyl exchange reaction where 14[7] or more than 30[4g]
h
were required. The acyl substitution with aliphatic N-acylbenzotriazoles
proceeded smoothly under the same conditions, though relatively low
Scheme 1.

Table 1. SmI3-catalyzed substitution of acyl for acetyl with N-acylbenzotriazoles
Entry
1
R
Substrates 2
Products 3
Time (h)
1.5
Yields (%)a
75
2
3
4
5
6
7
1.5
1.5
1
73
76
80
82
87
78
1
1
2
8
9
20
20
70
72
(continued)

Table 1. Continued
Entry
10
R
Substrates 2
Products 3
Time (h)
1
Yields (%)a
80
11
20
70
12
13
20
10
71
78
14
15
16
12
10
20
70
82
No reaction
17
18
16
16
No reaction
No reaction
aYields of pure isolated products.

Substitution of Acyl for Acetyl with N-Acylbenzotriazoles
1621
reactivity was observed. Time as long as 20 h was taken for the reaction to
1
afford comparable yields (Table 1, entries 8, 9, 12). H NMR spectra show
that the b-keto esters 3a–3l exist in CDCl3 solution with their keto forms
predominant.
The analogous substitution for acetyl in acetylacetone with N-acylbenzo-
triazoles also proved successful with 10 h or longer reaction time required
(Table 1, entries 13–15). Unlike b-keto esters, the enol forms of b-diketone
4a–4c predominate in the CDCl3 solution.
Further investigation was carried out with an attempt to find wider appli-
cation of the reaction, with discouraging results. For example, unsaturated
N-acylbenzotriazole 11 was used with the intention to prepare compound 5a
(Table 1, entry 16). The reaction did not occur at all, indicating the remarkable
influence of the C55C bond existing therein. The reaction between N-acylben-
zotriazole 1b and dibenzoyl methane was also examined to elucidate the possi-
bility of substitution of one aroyl for the other. However, no reaction occurred
even after 16 h (Table 1, entry 17). The acylation of other active methylene
compounds such as malonitrile with N-acylbenzotriazole under the SmI3-
catalyzed conditions failed too (Table 1, entry 18).
In conclusion, the scope and limitation of the acyl substitution with
N-acylbenzotriazoles catalyzed by SmI3 were explored. Substitutions of
acyl for acetyl in ethyl acetoacetate, methyl acetoacetate, and acetylacetone
with N-acylbenzotriazoles were found to proceed smoothly under neutral con-
ditions without the necessity of inert gas protection. The operational simplicity
and good efficiency makes the reaction practical for the preparation of b-keto
esters and b-diketones.
EXPERIMENTAL
Tetrahydrofuran was distilled from sodium benzophenone immediately prior
1
to use. Melting points are uncorrected. H NMR (400-MHz) spectra were
recorded on a Bruker AV400 NMR instrument as CDCl3 solutions using
TMS as internal standard. Chemical shifts (d) are reported in parts per
million (ppm), and coupling constants (J ) are given in Hertz. IR spectra
were recorded in film or using KBr disks with a Nexus 670 FTIR spectrometer.
General Procedure for the Preparation of b-Ketoesters
Anhydrous THF (10 mL) and I2 (0.076 g, 0.3 mmol) were added to samarium
powder (0.03 g, 0.2 mmol) in a flask. The mixture was stirred at room temp-
erature for 1 h. To the SmI3–THF suspension thus prepared, acetoacetic ester
(1 mmol) and N-acylbenzotriazole (1 mmol) were added. The reaction
mixture was refluxed until the disappearance of N-acylbenzotriazole (the
time taken is indicated in Table 1). Then the reaction was quenched with

1622
X. Zou et al.
dilute hydrochloric acid (0.1 mol/L, 3 mL) and extracted with diethyl ether
(3 Â 30 mL). The combined extracts were washed with saturated solution of
Na2S2O3 and brine and were dried over anhydrous Na2SO4. Removal of the
solvent under reduced pressure afforded the crude product, which was
purified by preparative thin-layer chromatography (TLC) on silica gel
(eluent: ethyl acetate/cyclohexane 1:6) to give b-ketoesters 3.
Data
Compound 3a: oil.[7] nmax(film)/cm21: 3063, 2983, 2938, 1740, 1687, 1624.
1
Keto tautomer: H NMR (CDCl3) 7.95–7.92 (m, 2H), 7.48–7.40 (m, 3H),
4.23 (q, J ¼ 8.0 Hz, 2H), 3.99 (s, 2H), 1.25 (t, J ¼ 8.0 Hz, 3H).
Compound 3b: oil.[7] nmax(film)/cm21: 2956, 2854, 1742, 1683, 1624. Keto
1
tautomer: H NMR (CDCl3) 7.85 (d, J ¼ 7.8 Hz, 2H), 7.28 (d, J ¼ 7.8 Hz,
2H), 4.21 (q, J ¼ 7.1 Hz, 2H), 3.97 (s, 2H), 2.42 (s, 3H), 1.26
(t, J ¼ 7.1 Hz, 3H).
Compound 3c: oil.[4g] nmax(film)/cm21: 2983, 2938, 2842, 1739, 1678. Keto
1
tautomer: H NMR (CDCl3) 7.92 (d, J ¼ 6.8 Hz, 2H), 6.94 (d, J ¼ 6.8 Hz,
2H), 4.20 (q, J ¼ 8.0 Hz, 2H), 3.95 (s, 2H), 3.85 (s, 3H), 1.26
(t, J ¼ 8.0 Hz, 3H).
Compound 3d: oil.[7]
n
max(film)/cm21: 2928, 2851, 1746, 1691. Keto
1
tautomer: H NMR (CDCl3) 7.89 (d, J ¼ 8.7 Hz, 2H), 7.45 (d, J ¼ 8.7 Hz,
2H), 4.22 (q, J ¼ 8.0 Hz, 2H), 3.98 (s, 2H), 1.25 (t, J ¼ 8.0 Hz, 3H).
Compound 3e: oil.[4g] nmax(film)/cm21: 3091, 3062, 2920, 2851, 1744, 1687.
Keto tautomer: 1H NMR (CDCl3): 7.82 (d, J ¼ 8.4 Hz, 2H), 7.65
(d, J ¼ 8.4 Hz, 2H), 4.22 (q, J ¼ 8.0 Hz, 2H), 3.98 (2H, s), 1.25
(t, J ¼ 8.0 Hz, 3H).
Compound 3f: yellow plates, mp 71–738C (lit.[9] 738C). nmax(KBr)/cm21
:
3114, 3083, 2994, 2909, 1735, 1643, 1619. Keto tautomer: 1H NMR
(CDCl3) 8.34 (m, 2H), 8.28 (m, 2H), 4.23 (q, J ¼ 8.0 Hz, 2H), 4.04 (s, 2H),
1.26 (t, J ¼ 8.0 Hz, 3H).
Compound 3g: oil.[7]
n
max(film)/cm21: 3137, 2923, 1740, 1677. Keto
1
tautomer: H NMR (CDCl3): 7.63 (d, J ¼ 1.6 Hz, 1H), 7.28–7.29 (1H, m),
6.57–6.59 (1H, m), 4.21 (2H, q, J ¼ 7.2 Hz), 3.86 (2H, s), 1.26 (3H, t,
J ¼ 7.2 Hz).
Compound 3h: oil.[9] nmax(film)/cm21: 2965, 2938, 2877, 1742, 1717, 1647,
1624. Keto tautomer: 1H NMR (CDCl3) 4.19 (q, J ¼ 8.0 Hz, 2H), 3.44 (s, 2H),

Substitution of Acyl for Acetyl with N-Acylbenzotriazoles
1623
2.53 (t, J ¼ 8.0 Hz, 2H), 1.65 (m, 2H), 1.28 (t, J ¼ 8.0 Hz, 3H), 0.92,
(t, J ¼ 8.0 Hz, 3H).
Compound 3i: oil.[10a]
n
max(film)/cm21: 2927, 2856, 1743, 1716, 1650,
1624. Keto tautomer: 1H NMR (CDCl3) 4.19 (q, J ¼ 8.0 Hz, 2H), 3.44
(s, 2H), 2.54, (t, J ¼ 8.0 Hz, 2H), 1.59, (m. 2H), 1.28 (m, 15H), 0.88 (m, 3H).
Compound 3j: yellow plates, mp 105–1068C (lit.[10b] 104–1058C).
n
max(KBr)/cm21 3111, 3054, 2963, 2916, 2851, 1746, 1662, 1631. Keto
1
tautomer: H NMR (CDCl3) 8.33 (m, 2H), 8.27 (m, 2H), 4.07 (s, 2H), 3.80
(s, 3H).
Compound 3k: white solid, mp 60–628C (lit.[10c] 60–618C). nmax(KBr)/
1
cm21: 2963, 2870, 1756, 1685. Keto tautomer: H NMR (CDCl3) 8.35–
7.22 (m, 7H), 4.15 (s, 2H), 3.80 (s, 3H).
Compound 3l: oil.[1a] nmax(film)/cm21: 2930, 2832, 1755, 1716, 1654, 1623.
1
Keto tautomer: H NMR (CDCl3) 3.73 (s, 3H), 3.46 (s, 2H), 2.54 (t, 2H,
J ¼ 7.2 Hz), 1.58–1.61 (m, 2H), 1.27–1.31 (m, 6H), 0.88 (t, 3H, J ¼ 7.0 Hz).
Compound 4a: solid, mp 50–528C (lit.[7] 52–538C). nmax(KBr)/cm21: 3447,
2924, 2848, 1721, 1605. Enol tautomer: H NMR (CDCl3) 16.17 (br s, 1H),
1
7.88 (m, 2H), 7.45–7.53 (m, 3H), 6.19 (s, 1H), 2.21 (s, 3H).
Compound 4b: oil.[11] nmax(film)/cm21: 3427, 2923, 2858, 1716, 1612. Enol
tautomer: 1H NMR (CDCl3) 16.26 (br s, 1H), 7.77 (d, J ¼ 8.0 Hz, 2H), 7.23
(d, J ¼ 8.0 Hz, 2H), 6.14 (s, 1H), 2.39 (s, 3H), 2.17 (s, 3H).
Compound 4c: yellow plates, mp 108–1108C (lit.[6c] 1118C). nmax(KBr)/
1
cm21: 3423, 3110, 3073, 1627. Enol tautomer: H NMR (CDCl3) 15.90 (br
s, 1H), 8.29 (m, 2H), 8.02 (m, 1H), 6.24 (s, 1H), 2.26 (s, 3H).
ACKNOWLEDGMENTS
We are grateful to the Natural Science Foundation of Zhejiang Province
(Project No. Y405035) and Zhejiang Analysis and Testing Fund (Project
No. KYZ04Y04076) for financial support.
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