Efficient synthesis of aryl hydroxylactams by reducing imides with activated zinc dust

Article abstract of DOI:10.1080/00397910500383485

A series of aryl hydroxylactams (2a, 2b, 2d-2g, 2i-2k, 2m, and 2n) was synthesized by partially reducing aryl cyclic imides in moderate to excellent yields with activated zinc dust alone in acetic acid. This method was regiospecific and can be employed as an alternative for reported methods to partially reduce aryl cyclic imides. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397910500383485

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Efficient Synthesis of Aryl Hydroxylactams by
Reducing Imides With Activated Zinc Dust
Xiu‐hua Yuan a , Min‐jie Zhang a , Chuan‐qing Kang a , Hai‐quan Guo a ,
Xue‐peng Qiu a & Lian‐xun Gao a
a State Key Laboratory of Polymer Physics and Chemistry , Changchun
Institute of Applied Chemistry, Graduate School of Chinese Academy
of Sciences , Changchun, China Phone: 086‐0431‐5262203 Fax:
086‐0431‐5262203
Published online: 19 Aug 2006.
To cite this article: Xiu‐hua Yuan , Min‐jie Zhang , Chuan‐qing Kang , Hai‐quan Guo , Xue‐peng Qiu & Lian‐xun
Gao (2006) Efficient Synthesis of Aryl Hydroxylactams by Reducing Imides With Activated Zinc Dust, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry, 36:4,
435-444, DOI: 10.1080/00397910500383485
To link to this article: http://dx.doi.org/10.1080/00397910500383485
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Synthetic Communicationsw, 36: 435–444, 2006
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910500383485
Efficient Synthesis of Aryl Hydroxylactams
by Reducing Imides With Activated
Zinc Dust
Xiu-hua Yuan, Min-jie Zhang, Chuan-qing Kang,
Hai-quan Guo, Xue-peng Qiu, and Lian-xun Gao
State Key Laboratory of Polymer Physics and Chemistry,
Changchun Institute of Applied Chemistry, Graduate School
of Chinese Academy of Sciences, Changchun, China
Abstract: A series of aryl hydroxylactams (2a, 2b, 2d–2g, 2i–2k, 2m, and 2n) was
synthesized by partially reducing aryl cyclic imides in moderate to excellent yields
with activated zinc dust alone in acetic acid. This method was regiospecific and can
be employed as an alternative for reported methods to partially reduce aryl cyclic
imides.
Keywords: Hydroxylactams, regiospecific, synthesis, zinc dust
INTRODUCTION
As important structural segments in sedatives, hypnotics, and muscle
relaxants such as zopiclone,[1] pazinaclone,[2] desmethylzopiclone,[3] and
pagoclone,[4] hydroxylactams have attracted much attention from chemists.
Hydroxylactams were also used as key precursors[5] for the synthesis of
lactams. Several approaches have been developed to obtain hydroxylactams,
in which reduction of cyclic imides to hydroxylactams was a very
Received in Japan June 27, 2005
Address correspondence to Lian-xun Gao, State Key Laboratory of Polymer
Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese
Academy of Sciences, Graduate School of Chinese Academy of Sciences,
Changchun 130022, China. Tel.: 086-0431-5262203; Fax: 086-0431-5685653;
E-mail: lxgao@ciac.jl.cn
435

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X. Yuan et al.
practical pathway. Many reagents, such as NaBH4,[6] LiAlH4,[7] iBu2AlH,[8]
formates,[9] oxalates,[10] Al(Hg),[11] Zn(Hg),[12] and Zn(TiCl4),[13] have
been used to realize this kind of transformation.
Recently, we dedicated ourselves to the synthesis of 2-(2,6-dioxopiperi-
din-3-yl) phthalimidine (EM-12), an important thalidomide (1a)
analogue.[14] When we tried to reflux thalidomide and 5 equivalents of
activated Zn dust in acetic acid according to the literature,[15] not EM-12
but hydroxylactam 2a was afforded almost quantitatively. Hydroxylactam
2b was also afforded when this method was applied to another thalidomide
analogue 2-(2,5-dioxopyrrolidin-3-yl)-1H-isoindole-1,3(2H)-dione (1b).
Interestingly, two carbonyl groups of glutarimide moiety in 1a and those of
succinimide moiety in 1b were intact during the reductions. As for as we
know, if NaBH4,[6b] LiAlH4,[7b] or Bu2AlH[8b] were used, one carbonyl
i
group of glutarimide moiety in 1a and one of succinimide moiety in 1b
would be reduced to hydroxyl groups at the same time. We describe herein
an efficient synthesis of a series of hydroxylactoms by partially reducing
aryl cyclic imides with activated zinc dust alone in acetic acid. This method
can be employed as an alternative to reported methods to reduce aryl cyclic
imides partially.
Fifteen other different aryl cyclic imides 1c–1q were selected as
candidates to evaluated the reduction (Scheme 1). The results were
summarized in Table 1. No hydroxylactams were afforded in the reductions
of imides 1h, 1l, and 1o (Table 1, entries 8, 12, 15). This might be caused
by the formation of complexes[16] of Zn2þ and the reactants or the products.
But when the volume of N-substituting groups was large enough (Table 1,
entries 1, 2, 7, 9–11, 13, 14) and or intramolecular hydrogen bonds, which
could prevent the formation of complexes, could be formed in the products
with aromatic nitrogen (Table 1, entries 6, 7, 11, 14), hydroxylactams (2a,
2b, 2f, 2g, 2i–2k, 2m, and 2n) were formed almost quantitatively even
though the reaction was handled at relatively high temperature (908C)
with prolonged reaction time. It was found that lactams were formed
when the N-substituting groups were methyl and i-propyl at this reaction
temperature, but the side reaction could be inhibited at a lower temperature
(608C). For the reduction of phthalimide (1c), no hydroxylactam was
separated because the products were too complex even though the
Scheme 1. Synthesis of aryl hydroxylactams with activated zinc dust.

Synthesis of Aryl Hydroxylactams
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X. Yuan et al.

Synthesis of Aryl Hydroxylactams
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X. Yuan et al.
Figure 1. The structure of 2m and 2n.
reaction was handled at 608C. For the reductions of 2-(4-chloro-phenyl)-
isoindole-1,3-dione (1m) (Table 1, entry 13) and 6-(2,6-dioxopiperidin-
3-yl)-5H-pyrrolo-[3,4-b]pyridine-5,7(6H)-dione (1n) (Table 1, entry 14), it
was possible to form two hydroxylactams respectively with different
carbonyl groups being reduced. But only the carbonyl group ortho to the
chloro atom in the phthalimide moiety in 1m and that ortho to
the aromatic nitrogen in 1n were afforded respectively (Figure 1). The
structure of the hydroxylactam 2m was identified through a combination of
one- and two-dimensional COSY (correlated spectroscopy), HMQC (hetero-
nuclear multiple-quantum coherence), HMBC (heteronuclear multiple-bond
correlation), and NMR spectroscopy. As for the reduction of 1n, if the
reduced carbonyl group were the meso carbonyl group to the aromatic
nitrogen, complexes should be formed such as 1h, 1l, and 1o and no
product would be afforded. This indicated that the reduction was
regiospecific.
The carbon atom connected to the newly formed hydroxyl group was a
chiral center, so all the products were the mixtures of two groups of
epimers for imides 1a, 1b, and 1n (Table 1, entries 1, 2, 14) with one chiral
1
center before being reduced. This was indicated in the H NMR spectrum
of 2a, 2b, and 2n (Figure 2).
However, no products were afforded when this method was applied to
reduce N-benzylglutarimide (1p) or N-phenylsuccinimide (1q). This
indicated that this method could only be applied to reduce those imides
derived from aromatic dicarboxylic acids.
In summary, eleven aryl hydroxylactams (2a, 2b, 2d–2g, 2i–2k, 2m,
and 2n) were synthesized by reducing aryl cyclic imides with 5 equivalents
of activatived Zn dust in acetic acid. This method was especially suitable for
those aryl cyclic imides with a large volume of N-substituting groups
(Table 1, entries 1, 2, 7, 9–11, 13, 14) and/or where intramolecular
hydrogen bonds could be formed in the products (Table 1, entries 6, 7, 11,
14). Moreover, the reaction was regiospecific (Table 1, entries 13, 14) and
the imide moieties that were not connected directly with the aromatic ring
were kept intact (Table 1, entries 1, 2, 14). This method can be employed
as an alternative for reported methods to reduce partially N-substituted
aryl cyclic imides.

Synthesis of Aryl Hydroxylactams
441
Figure 2. 1H NMR of 2a, 2b, and 2n.
EXPERIMENTAL
General Procedures
All chemicals were purchased from commercial suppliers and used without
further purification. NMR spectra were recorded on Bruker-AV 400- and
300-MHz spectrometers. The 1H and 13C chemical shifts were obtained
with DMSO-d6 or acetone-d6 as solvents and TMS as internal standard.
ESI-MS measurements were measured with a LCQ instrument. Melting
points were measured with a hot-stage microscope XT-4. Elemental
analyses were carried out with a GmbH VarioEL V2.8 instrument.
The imide 1a was synthesized by melting (170–1758C) the mixture of
phthalic anhydride and L-glutamine in vacuum,[17] mp: 272–2748C (lit.[18]
274–2768C). The imide 1b was prepared as in the literature,[19] mp 211–2128C
(lit.[19] 213–2158C). The imides 1d–1j and 1m were prepared by refluxing
corresponding anhydrides and amines in acetic acid. 1d: mp 134–1358C (lit.[20]
133–1348C); 1e: mp 86–878C (lit.[21] 85–868C); 1f: mp 231–2348C (lit.[22]
2328C); 1g: mp 160–1618C (lit.[23] 162–1648C); 1h: mp 175–1768C, 1H NMR
(400 MHz, dmso-d6): d 8.67 (s, 1H, pyrazine), 8.78 (s, 2H, pyrazine), 8.05–8.03
(m, 2H, Ar), 7.98–7.96 (m, 2H, Ar); 1i: mp 205–2068C (lit.[24] 206–2078C);
1j: mp 192–1948C (lit.[25] 1948C); 1m: mp 227–2288C (lit.[26] 227–2298C).
1k and 1l were prepared using Stuk’s[5] method, 1k: mp .3008C
(lit.[5] . 3008C), 1H NMR (300 MHz, dmso-d6): d 12.35 (s, 1H, HO),

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X. Yuan et al.
8.36–8.33 (d, 1H, J ¼ 8.1 Hz, Ar), 8.05–7.95 (m, 5H, Ar), 7.42–7.39 (d, 1H,
J ¼ 8.1 Hz, Ar), 6.67–6.64 (d, 1H, J ¼ 8.1 Hz, Ar); 1l: mp 265–2678C (lit.[5]
2688C).
1n and 1o were synthesized in two steps similar to the synthesis of
N-(3,4,5-trimethoxyphenyl)-pyrazine-2,3-dicarboxy imide.[27] 1n: mp 256–
2588C (dec.) (lit.[28] 258–2598C); 1o: mp 287–2898C (lit.[29] 298–3008C),
1H NMR (300 MHz, dmso-d6): d 9.11 (s, 2H, pyrazine), 7.68–7.66 (d, 2H,
J ¼ 6.9 Hz, Ar), 7.52–7.50 (d, 2H, J ¼ 6.9 Hz, Ar).
1p and 1q were synthesized using Reddy’s method.[30] 1p: colorless oil,
1H NMR (300 MHz, dmso-d6): d 7.43–720 (m, 5H, Ar), 4.97 (s, 2H, CH2–
Ar), 2.68 (t, J ¼ 6.5 Hz, 4H, CH2CO), 1.94–1.92 (m, 2H, CH2); 1q: mp
154–1568C (lit.[30] 156–1578C). All products were purified by column
chromatography on silica gel (230–400 mesh).
Typical Procedure: Synthesis of 2-(4-Chlorophenyl)-3-
hydroxyisoindolin-1-one (2j)
1j(1.0g, 3.9 mmol)and60mlofacetic acidsuccessivelywereaddedtoa100-ml,
one-necked flask. The mixture was stirred and heated at 608C. After 10min,
1.28g (19.5 mmol) of Zn dust activated with 1N HCl for 3–5 min were added
to the mixture in one portion. The resulting mixture was stirred until the
starting material was consumed as evidenced by TLC, which generally
required 20min. The hot solution was filtered to remove the solid. The filtrate
was condensed and purified by silica-gel column chromatography (petroleum/
ethyl acetate 5/2 as eluent) to give 2i (0.91 g, yield: 92%). Mp 198–2008C
(lit.[31] 199–2018C). 1H NMR (300MHz, dmso-d6): d 7.85–7.83 (d, 2H,
J ¼ 6.9 Hz, Ar), 7.82–7.62 (m, 4H, Ar), 7.52–7.50 (d, 2H, J ¼ 6.9 Hz, Ar),
6.93–6.89 (d, 1H, J ¼ 9.9 Hz, OH), 6.57–6.53 (d, 1H, J ¼ 10.2Hz, H–C–Ar).
3-Hydroxy-2-methylisoindolin-1-one (2d). Mp 129–1308C (lit.[32] 130–
1318C), 1H NMR (400 MHz, dmso-d6): d 7.69–7.50 (m, 4H, Ar), 6.58–6.55
(d, 1H, J ¼ 8.8 Hz, OH), 5.73–5.71 (d, 1H, J ¼ 8.8 Hz, H–C–Ar), 2.95
(s, 3H, CH3).
3-Hydroxy-2-isopropylisoindolin-1-one (2e). Mp 97–988C, 1H NMR
(300 MHz, acetone-d6): d 7.65–7.51 (m, 4H, Ar), 6.03–5.99 (d, 1H,
J ¼ 10.5 Hz, OH), 5.31–5.24 (m, 1H, H–C–Ar), 4.37–4.26 (m, 1H, CH),
1.47–1.45 (d, 3H, J ¼ 6.9 Hz, CH3), 1.42–1.40 (d, 3H, J ¼ 6.9 Hz, CH3).
13C NMR (300 MHz, acetone-d6): d 166.46, 145.52, 132.91, 131.98, 129.50,
123.55, 122.62, 81.38, 43.95, 21.65, 19.85. Anal. calcd. for (C11H13NO2,
%): C, 69.09; H, 6.85; N, 7.32. Found: C, 69.03; H, 6.89; N, 7.25.
3-Hydroxy-2-pyridin-2-ylisoindolin-1-one (2f). Mp 144–1468C (lit.[33]
1458C) 1H NMR (300 MHz, dmso-d6): d 8.50–8.48 (m, 1H, pyridine),
8.21–8.19 (d, 1H, J ¼ 8.8 Hz, pyridine), 7.91–7.62 (m, 5H, pyridine and
Ar), 7.22–7.17 (m, 1H, pyridine), 6.91–6.89 (d, 1H, J ¼ 7.6 Hz, OH),
6.82–6.80 (d, 1H, J ¼ 7.6 Hz, H-C-Ar).

Synthesis of Aryl Hydroxylactams
443
2-(5-Bromopyridin-2-yl)-3-hydroxyisoindolin-1-one (2g). Mp 198–
1
1998C (lit.[34] 1988C), H NMR (300 MHz, dmso-d6): d 8.61–8.60 (d, 1H,
J ¼ 2.4 Hz, Ar), 8.23–8.16 (m, 2H, Ar), 7.83–7.63 (m, 4H, Ar), 6.93–6.84
(m, 2H, OH, CH-Ar).
2-(2,6-Dimethylphenyl)-3-hydroxyisoindolin-1-one (2i). Mp 218–2208C,
1H NMR (300MHz, dmso-d6): d 7.78–7.62 (m, 4H, Ar), 7.23–7.17 (m, 3H,
Ar), 6.92 (s, 1H, OH), 6.12 (s, H-C-Ar), 2.21 (s, 3H, CH3), 2.09 (s, 3H, CH3).
13C NMR (300MHz, dmso-d6): d 166.40, 146.08, 139.59, 137.19, 135.30,
133.23, 131.90, 130.42, 128.98, 128.89, 128.82, 124.80, 123.67, 83.61, 19.33,
18.57. Anal. calcd. for (C16H15NO2, %): C, 75.87; H, 5.97; N, 5.53. Found: C,
75.78; H, 5.85; N, 5.46.
3-Hydroxy-2-(7-hydroxy-1,8-naphthyridin-2-yl)isoindolin-1-one (2k).
Mp . 3008C, 1H NMR (300 MHz, dmso-d6): d 11.78 (s, 1H, HO–Ar),
8.17–7.66 (m, 7H, Ar), 6.83–6.49 (m, 3H, OH, Ar, H–C–Ar). 13C NMR
was not available because its poor solubility in all solvents. ESI-MS m/z
292.3 (MH-). Anal. calcd. for (C16H11N3O3, %): C, 65.50; H, 3.78; N,
14.33. Found: C, 65.39; H, 3.85; N, 14.22.
7-Chloro-2-(4-chlorophenyl)-3-hydroxyisoindolin-1-one (2m). Mp 207–
1
2088C, H NMR (400 MHz, dmso-d6): d 7.84–7.82 (d, 2H, J ¼ 8.8 Hz, Ar),
7.77–7.75 (m, 4H, Ar), 7.66–7.62 (m, 1H, Ar), 7.53–7.51 (d, 2H,
J ¼ 8.8 Hz, Ar), 7.02–7.00 (d, 1H, J ¼ 10.4 Hz, OH), 6.63–6.6 (d, 1H,
J ¼ 10.4 Hz, H–C–Ar). 13C NMR (400 MHz, dmso-d6): d 164.25, 140.71,
135.97, 133.57, 133.25, 131.76, 129.27, 128.89, 128.61, 123.58, 121.84,
81.29. Anal. calcd. for (C14H9Cl2NO2, %): C, 57.17; H, 3.08; Cl, 24.11; N,
4.76. Found: C, 57.19; H, 3.00; Cl, 24.20; N, 4.59.
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