A new β-keto amide synthesis

Article abstract of DOI:10.1055/s-2002-34845

In a modification of the Wierenga-Skulnick β-ketoester synthesis, the dianions of malonic acid mono-amides were condensed with acid chlorides. Acidic workup led to decarboxylation and isolation of the corresponding β-keto amides in good-to-excellent yield

Full text of DOI:10.1055/s-2002-34845

PAPER
2191
A New -Keto Amide Synthesis
A
N
ew -KetoAm
a
ide Synthes
n
is ping Chen,a Scott McN. Sieburth*b
a
Department of Chemistry, State University of New York at Stony Brook, Stony Brook NY 11794-3400 USA
b
Department of Chemistry, Temple University, 1901 N. 13th St., Philadelphia, PA 19010 USA
Fax +1(215)2041532; E-mail: sieburth@astro.temple.edu
Received 14 June 2002; revised 22 July 2002
dianion of a malonate mono-ester 2a (Scheme 1), this re-
action has not been adapted to the preparation of keto
amides 3b.24 As part of an ongoing study,25 we have ex-
plored this chemistry using 2b,2c and found it to be a use-
Abstract: In a modification of the Wierenga Skulnick -ketoester
synthesis, the dianions of malonic acid mono-amides were con-
densed with acid chlorides. Acidic workup led to decarboxylation
and isolation of the corresponding -keto amides in good-to-excel-
lent yields. A similar procedure with cyanoacetic acid gave -keto ful adaptation for both -keto amides 3b, -keto nitriles
nitriles.
3c. We now report examples of each below.
Key words: amides, carboxylic acids, condensation, ketones, ni-
triles
O
O
H+
Li
EWG
EWG
+
R
Cl
R
– CO2
LiO
O
1
2
3 a EWG = CO2R'
The development of synthetic methods for preparing -
keto amides has been pursued for at least a century,1 and
seemingly every possible bond disconnection has been
explored. Some methods are limited to a specific structur-
al type, such as the use of ketene dimers2 and , -dichlor-
oenones.3 The apparently straightforward addition of
amines to -keto acids4 is limited due to the instability of
keto-acid intermediates.5 Direct aminolysis of -keto
esters6 can be compromised by the competing formation
of vinylogous urethanes (enamines of the ketones). Nev-
ertheless, catalysis of this reaction by DMAP,7 transition
metals,8 and enzymes9 have been reported. Moreover,
aminolysis of -keto thioesters is an efficient protocol.10
Cross-Claisen condensation-like reaction of esters with
amide enolate mono- and di-anions has proven to be use-
b
c
= CONR'2
= CN
Scheme 1 Condensation/decarboxylation to give -ketoesters and
its adaptation to -ketoamides and nitriles.
Preparation of 5 is a typical example. Treatment of the
malonic acid-amide 4 with two equivalents of n-butyllith-
ium was followed by addition of butyryl chloride. Aque-
ous acid workup led to isolation of -keto amide 5 in good
yield. A similar result using phenyl acetyl chloride, pro-
vided 6. Use of dimethylamide 726 gave the keto amide 8
in a reduced yield. Weinreb amides27 10–12 could also be
prepared using amide-acid 9. The use of a secondary
amide-containing substrate led to a poor yield of keto
amide products and therefore only tertiary amides were
pursued.
The preparation of -keto nitriles28 was also examined,
using the dilithium dianion of commercially available cy-
anoacetic acid (13), a transformation reported by Kirsten
and Schrader.29 This reagent coupled well with acid chlor-
ides, giving the corresponding -keto-nitriles in high
yield.30,31
12
ful.11 Isocyanates can be condensed with ketones and
with enamines.13 Conversely, 1,1-diaminoethylenes cou-
ple with acid chlorides to produce -ketoamides.14
Among the most general approaches for -keto amide
synthesis are the ones that use Meldrum’s acid and related
dioxolanones. Meldrum’s acid can be condensed with an
acid chloride and then subjected to aminolysis.5,15 Dioxol-
anones can also be treated directly with an amine to give
-keto amides.16 Alternatively, heating a dioxolanone in
the presence of an amine leads to trapping of an interme-
diate acyl ketene.17 Acyl ketene generation by Wolff rear-
rangement and in situ amine trapping has also been
reported.18 Additional general methods include isoxazoli-
um salt fragmentation,19 the coupling of aldehydes and -
diazoamides,20 and joining dithianes with bromoaceta-
mides.21
In all cases, the yields reported in Table 1 are for pure,
chromatographically isolated products. In several cases
the products were found to be a mixture of keto and enol
tautomers,32 more so in the ketoamides than with the ke-
tonitriles.
Acid-amide reagent 4 was prepared by aminolysis of Mel-
drum’s acid with N-trimethysilylpiperidine, following the
method of Rigo,33 whereas 7 and 9 were prepared follow-
ing the method described by Gellman.26
Despite extensive use of Wierenga and Skulnick’s
modification22 of the Ireland Marshall method23 for the
synthesis of -keto-esters 3a, from acid chloride 1 and the
This procedure allows for a simple, efficient and general
approach to tertiary -keto amides in yields higher than
many of the earlier transformations.
Synthesis 2002, No. 15, Print: 29 10 2002.
Art Id.1437-210X,E;2002,0,15,2191,2194,ftx,en;M02502SS.pdf.
© Georg Thieme Verlag Stuttgart · New York
ISSN 0039-7881

2192
Y. Chen, S. McN. Sieburth
PAPER
2300, Brucker AC-250 or AC-400 spectrometers. IR spectra were
recorded on a Mattson Galaxy Series 3000 spectrometer FTIR.
Mass spectral data were obtained from the Mass Spectrometer Fa-
cility of the University of California at Riverside and the Mass
Spectrometer Facility of Drexel University. Melting points were
measured using a Thomas Hoover capillary melting point apparatus
and are uncorrected.
Table 1 Acid to Ketone Transformations
O
O
i. 2 n-BuLi
EWG
EWG
HO
O
R
ii.
R
Cl
iii. HCl
3-Oxo-3-(1-pyrrolidinyl)propanoic Acid (4)
Starting Material
Product, Yield
To a soln of Meldrum’s acid (1.44 g, 10 mmoL) in CH2Cl2 (15 mL)
was added 1-(trimethylsilyl)-pyrrolidine (1.43 g, 10 mmoL) and the
resulting soln was stirred for 2 h. MeOH (0.8 mL) was added and
after 10 min the mixture was concentrated. Purification by flash
chromatography (EtOAc–hexanes, 1:1 followed by MeOH–
CH2Cl2, 7:93 ) gave 4 as a colorless solid (1.07 g, 68%).
O
O
O
O
HO
N
N
74%
4
5
O
O
O
Mp 102–104 °C.
IR (KBr): 2980, 2947, 2887, 1774, 1739, 1608, 1452, 1375 cm–1.
1H NMR (CDCl3): = 3.51–3.55 (m, 2 H), 3.42–3.46 (m, 2 H), 3.32
(s, 2 H), 1.99–2.06 (m, 2 H), 1.89–1.94 (m, 2 H).
13C NMR (CDCl3): = 168.6, 168.1, 47.1, 46.8, 36.4, 26.1, 24.6.
Ph
Ph
N
N
72%
6
8
O
O
O
O
O
HO
HO
N
N
56%
MS (CI+): m/z (%) = 158 (12) [M + H], 114 (38), 57 (100).
7
9
HRMS: m/z calcd for C7H11NO3 [M + H], 158.0817; found,
158.0816.
O
O
O
O
N
71%
3-Oxo-3-(methoxy(methyl)amino)propanoic Acid (9)
To an ice bath cooled soln of NaOH (3.2 g, 80 mmol) in H2O (10
mL) was added N,O-dimethylhydroxyamine hydrochloride (7.80 g,
80 mmoL) and Meldrum’s acid (2.88 g, 20 mmoL). The resulting
soln was stirred at r.t. for 70 h. After cooling the soln to 0 °C, concd
HCl (4.8 mL) was added. The aq phase was extracted with CHCl3
(5 15 mL). The combined organics were dried over MgSO4 and
concentrated. Purification by flash chromatography (EtOAc–hex-
anes, 1:4 followed by MeOH–CH2Cl2, 4:96) gave 9 as a colorless
oil (2.21 g).
10
O
O
Ph
O
N
57%
11
O
O
O
N
73%
12
IR (Neat): 3500–2500, 1734, 1626 cm–1.
1H NMR (CDCl3): = 3.74 (s, 3 H), 3.56 (s, 2 H), 3.25 (s, 3 H).
13C NMR (CDCl3): = 170.3, 168.9, 61.9, 37.8, 32.5.
O
O
N
N
HO
92%
13
14
MS (CI+): m/z (%) = 148 (66) [M + H], 130 (100), 104 (14), 88.0
(6), 61 (21).
O
N
Ph
77%
HRMS: m/z calcd for C7H12NO3, 148.0610; found, 148.0611.
15
-Keto Amide Synthesis; Typical Procedure
O
To a –78 °C soln of the acid (2 mmol) and 2-2 -bipyridyl (ca. 1 mg)
in THF (12 mL) was added BuLi (a 2.0 M soln in hexanes) until a
pink color persisted, indicating that a slight excess was present. The
temperature was allowed to rise to –10 °C, additional BuLi was
added as needed to maintain the pink color (for a total of ca. 2 mL),
and then the soln was cooled to –78 °C. The acid chloride (1 mmol)
was added and then stirred for 0.5 h. The soln was poured into a sep-
aratory funnel containing Et2O (30 mL) and 1 N HCl (10 mL). The
organic phase was washed with sat. NaHCO3 (2 15 mL) and dried
over MgSO4. Concentration followed by purification using flash
chromatography.
N
91%
16
O
N
O
55%
17
N-(3-Oxohexanoyl)pyrrolidine (5)
A colorless oil and a mixture of tautomers.
All reactions were carried out under nitrogen. THF, Et2O, CH2Cl2
and DMF were dried with a Grubbs-style36 Solvent Purification
System (Lab Contour, Irvine, CA). All other reagents or solvents
were used as acquired. Analytical thin layer chromatography was
performed on Analtech GHLF silica gel plates using UV light, io-
dine and phosphomolybdic acid for visualization. Flash column
chromatography was performed using silica gel 60 (230–400 mesh).
1H NMR and 13C NMR spectra were recorded on a Varian Gemini
Rf 0.17 (EtOAc–hexanes, 1:1).
IR (Neat): 2962, 2876, 1718, 1639, 1593, 1481, 1438, 1369 cm–1.
1H NMR (CDCl3): = 14.6 (s, 0.25 H), 4.92 (s, 0.25 H), 3.35–3.45
(m, 5.5 H), 2.52 (t, 1.5 H, J = 7.0 Hz), 2.10 (t, 0.5 H, J = 7.0 Hz),
1.77–1.92 (m, 4 H), 1.51–1.59 (m, 2 H), 0.85–0.91 (m, 3 H).
Synthesis 2002, No. 15, 2191–2194 ISSN 0039-7881 © Thieme Stuttgart · New York

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A New -Keto Amide Synthesis
2193
13C NMR (CDCl3): = 205.1, 177.8, 170.8, 165.6, 88.6, 50.9, 50.6,
50.4, 47.6, 46.5, 46.3, 45.4, 38.0, 26.4, 26.2, 24.8, 20.2, 17.3, 14.0,
13.9.
13C NMR (CDCl3): = 203.3, 177.0, 171.4, 166.2, 137.6, 134.8,
130.8, 130.3, 129.9, 129.6, 128.4, 127.9, 90.4, 51.1, 50.6, 50.3,
48.2, 47.3, 47.0, 46.2, 43.2, 27.1, 26.9, 25.6.
MS (CI+): m/z (%) = 184 (100) [M + H], 98 (7), 70 (6).
MS (FAB+): m/z (%) = 254 (100) [M + Na], 232 (25) [M + H], 176
(28).
HRMS: m/z calcd for C10H18NO2, 184.1338; found, 184.1337.
HRMS: m/z calcd for C12H16NO3, 232.1338; found, 232.1336.
N-(4-Phenyl-3-oxobutanoyl)pyrrolidine (6)
A colorless oil and a mixture of tautomers.
N-Methoxyl-N-methyl 4-methyl-3-oxopentanamide (12)
A colorless oil and a mixture of tautomers.
Rf 0.15 (EtOAc–hexanes, 1:1).
Rf 0.30 (EtOAc–hexanes, 1:1).
IR (Neat): 2972, 2937, 1718, 1664, 1629, 1465, 1383 cm–1.
IR (Neat): 3062, 3029, 2972, 2939, 1723, 1660, 1495, 1454, 1423,
1384, 1182 cm–1.
1H NMR (CDCl3): = 13.8 (s, 0.17 H), 5.38 (s, 0.17 H), 3.62–3.68
(2 s, 4.7 H), 3.18–3.20 (2 s, 3 H), 2.70–2.73 (m, 0.83 H), 2.37–2.45
(m, 0.17 H), 1.12–1.15 (m, 6 H).
13C NMR (CDCl3): = 207.8, 183.8, 173.4, 168.8, 84.0, 61.6, 46.1,
41.4, 34.7, 32.4, 20.2, 18.3.
1H NMR (CDCl3): = 7.14–7.28 (m, 5 H), 13.7 (s, 0.17 H), 5.31 (s,
0.17 H), 3.74 (s, 1.5 H), 3.56 (s, 0.58 H), 3.50 (s, 1.5 H), 3.44 (s,
2.44 H), 3.10 (s, 2.75 H).
13C NMR (CDCl3): = 201.8, 177.1, 172.7, 168.4, 136.6, 133.9,
130.0, 129.6, 129.2, 128.9, 127.7, 127.3, 87.6, 61.7, 61.6, 50.5,
47.2, 42.5, 32.4, 32.2.
MS (CI+): m/z (%) = 174 (100) [M + H], 113 (29), 62 (46), 57 (25).
HRMS: m/z calcd for C8H16No3, 174.1130; found, 174.1128.
MS (CI+): m/z (%) = 222 (100) [M + H], 161 (13), 91 (8), 62 (25).
HRMS: m/z calcd for C14H18NO2, 222.1130; found, 222.1129.
3-Oxo-hexanenitrile (14)34
A colorless oil.
N,N-Dimethyl 4-phenyl-3-oxobutanamide (8)
Rf 0.19 (EtOAc–hexanes, 1:4).
A colorless oil and a mixture of tautomers.
IR (Neat): 2967, 2939, 2879, 2259, 1729, 1463, 1381, 1318 cm–1.
Rf 0.25 (EtOAc–hexanes, 1:1).
1H NMR (CDCl3): = 3.26 (s, 2 H), 2.34 (t, 2 H, J = 7.2 Hz), 1.40
(m, 2 H), 0.70 (t, 2 H, J = 7.2 Hz).
13C NMR (CDCl3): = 198.1, 114.4, 44.4, 32.4, 17.2, 13.8.
MS (CI+): m/z (%) = 112 (67) [M + H], 71 (100), 57 (75).
HRMS: m/z calcd for C6H10NO, 112.0762; found, 112.0766.
IR (Neat): 3061, 3029, 2932, 1721, 1641, 1496, 1399, 1367 cm–1.
1H NMR (CDCl3): = 14.8 (s, 0.3 H), 7.14–7.27 (m, 5 H), 5.00 (s,
0.3 H), 3.77 (s, 1.4 H), 3.44 (s, 1.3 H), 3.42 (s, 0.6 H), 2.90 (s, 0.9
H), 2.88 (s, 0.9 H), 2.84 (s, 2.1 H), 2.76 (s, 2.1 H).
13C NMR (CDCl3): = 202.5, 176.7, 172.4, 167.1, 136.8, 134.0,
130.0, 129.6, 129.1, 129.0, 128.9, 127.6, 87.6, 50.3, 48.6, 48.3,
42.6, 41.4, 38.2, 36.0.
3-Oxo-4-phenyl-butyronitrile (15)30
A colorless oil.
MS (CI+): m/z (%) = 206 (100) [M + H], 114 (11), 72 (9).
HRMS: m/z calcd for C12H16NO2, 206.1181; found, 206.1172.
Rf 0.30 (EtOAc–hexanes, 1:3).
IR (Neat): 3064, 3031, 2948, 2914, 2259, 1731, 1497, 1455, 1343,
1316 cm–1.
1H NMR (CDCl3): = 7.35–7.42 (m, 3 H), 7.23–7.25 (m, 2 H), 3.87
(s, 2 H), 3.52 (s, 2 H).
N-Methoxy-N-methyl 3-oxohexanamide (10)
A colorless oil and a mixture of tautomers.
Rf 0.35 (EtOAc–hexanes, 1:1).
13C NMR (CDCl3): = 196.0, 132.4, 129.6, 129.1, 127.7, 114.3,
49.5, 31.7.
IR (Neat): 2955, 2938, 2876, 1720, 1663, 1635, 1463, 1421, 1381,
1189 cm–1.
1H NMR (CDCl3): = 13.8 (s, 0.15 H), 5.36 (s, 0.15 H), 3.64–3.66
(2 s, 2 H), 3.53 (s, 1.6 H), 3.16–3.18 (2 s, 2 H), 2.48 (t, 1.7 H, J = 7.2
Hz), 2.15 (t, 0.3 H, J = 7.6 Hz), 1.55–1.62 (m, 2 H), 0.87–0.94 (m,
3 H).
MS (CI+): m/z (%) = 160 (100) [M + H], 119 (49), 91 (68),70 (8),57
(14).
HRMS: m/z calcd for C10H10NO, 160.0762; found, 160.0763.
4-Methyl-3-oxo-pentanenitrile (16)34,35
A colorless oil.
13C NMR (CDCl3): = 201.8, 176.6, 170.6, 166.2, 84.1, 59.3, 45.8,
42.9, 35.6, 30.0, 29.7, 17.8, 14.9, 11.6.
Rf 0.18 (EtOAc–hexanes, 1:4).
MS (CI+): m/z (%) = 174 (100) [M + H], 113 (26), 71 (12), 62 (51),
IR (Neat): 2976, 2938, 2880, 2262, 1725, 1467, 1387, 1305 cm–1.
57 (34).
1H NMR (CDCl3): = 3.42 (s, 2 H), 2.58–2.65 (m, 1 H), 1.00 (d, 6
HRMS: m/z calcd for C8H16NO3, 174.1130; found, 174.1127.
H, J = 4.4 Hz).
N-Methoxyl-N-methyl-4-phenyl-3-oxobutanamide (11)
13C NMR (CDCl3): = 201.9, 114.5, 40.9, 30.6, 18.2.
MS (CI+): m/z (%) = 112 (51) [M + H], 71 (100), 57 (42).
HRMS: m/z calcd for C6H10NO, 112.0762; found, 112.0763.
A colorless oil.
Rf 0.31 (EtOAc–hexanes, 1:1).
IR (Neat): 3061, 3030, 2972, 2876, 1718, 1637, 1489, 1454,
1371cm–1.
1H NMR (CDCl3): = 14.7 (s, 0.32 H), 7.14–7.25 (m, 5 H), 4.85 (s,
0.32 H), 3.79 (s, 1.4 H), 3.33–3.40 (m, 3.8 H), 3.21 (t, 0.6 H, J = 6.8
Hz), 3.13 (t, 1.4 H, J = 6.8 Hz), 1.69–1.82 (m, 4 H).
4-(3-Methyl-2-furanyl)-3-oxo-butyronitrile (17)
A colorless oil.
Rf 0.51 (EtOAc–hexanes, 1:1).
IR (Neat): 2950, 2925, 2268, 1736, 1540, 1395, 1317, 1058 cm–1.
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Y. Chen, S. McN. Sieburth
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1H NMR (CDCl3): = 7.25 (d, 1 H, J = 1.6 Hz), 6.18 (d, 1 H, J = 1.6
Hz), 3.71 (s, 2 H), 3.42 (s, 2 H), 1.93 (s, 3 H).
13C NMR (CDCl3): = 194.0, 142.5, 141.7, 119.1, 113.8, 40.4, 31.5,
10.2.
(17) (a) Sato, M.; Ogasawara, H.; Komatsu, S.; Kato, T. Chem.
Pharm. Bull. 1984, 32, 3848. (b) Clemens, R. J.; Hyatt, J. A.
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1988, 720.
MS (CI+): m/z (%) = 164 (100) [M + H], 95 (35), 57 (17).
HRMS: m/z calcd for C9H10NO2, 164.0712; found, 164.0712.
(19) DeShong, P.; Cipollina, J. A.; Lowmaster, N. K. J. Org.
Chem. 1988, 53, 1356.
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Acknowledgement
This work was supported, in part, by the National Institutes of He-
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Synthesis 2002, No. 15, 2191–2194 ISSN 0039-7881 © Thieme Stuttgart · New York