Synthesis of ω-Oxo Amino Acids and trans-5-Substituted Proline Derivatives Using Cross-Metathesis of Unsaturated Amino Acids

Article abstract of DOI:10.1021/acs.joc.6b01571

A range of 7-oxo, 8-oxo, and 9-oxo amino acids, analogues of 8-oxo-2-aminodecanoic acid, one of the key components of the cyclic tetrapeptide apicidin, have been prepared by a three-step process involving copper-catalyzed allylation of serine-, aspartic acid-, and glutamic acid-derived organozinc reagents, followed by cross-metathesis of the resulting terminal alkenes with unsaturated ketones and hydrogenation. The intermediate 7-oxo-5-enones underwent a highly diastereoselective (dr ≥96:4) acid-catalyzed aza-Michael reaction to give trans-2,5-disubstituted pyrrolidines, 5-substituted proline derivatives. The aza-Michael reaction was first observed when the starting enones were allowed to stand in solution in deuterochloroform but can be efficiently promoted by catalytic amounts of dry HCl.

Full text of DOI:10.1021/acs.joc.6b01571

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Article
Synthesis of omega-Oxo Amino Acids and trans-5-Disubstituted Proline
Derivatives using Cross-methathesis of Unsaturated Amino Acids
Nabaz Salih, Harry Adams, and Richard Francis William Jackson
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.6b01571 • Publication Date (Web): 16 Aug 2016
Downloaded from http://pubs.acs.org on August 18, 2016
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Synthesis of ω-Oxo Amino Acids and trans-5-Disubstituted Proline Derivatives using Cross-
methathesis of Unsaturated Amino Acids
a
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Nabaz Salih, Harry Adams and Richard F. W. Jackson*
Department of Chemistry, The University of Sheffield, Dainton Building, Sheffield, S3 7HF,
UK;
e-mail: r.f.w.jackson@sheffield.ac.uk
a
Current address: Department of Chemistry, Faculty of Science, Soran University, Soran,
Erbil, Kurdistan Region, Iraq.
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A range of 7-oxo, 8-oxo and 9-oxo amino acids, analogues of 8-oxo-2-aminodecanoic acid,
one of the key components of the cyclic tetrapeptide apicidin, has been prepared by a
three-step process involving copper-catalysed allylation of serine-, aspartic acid- and
glutamic acid-derived organozinc reagents, followed by cross-metathesis of the resulting
terminal alkenes with unsaturated ketones, and hydrogenation. The intermediate 7-oxo-5-
enones underwent a highly diastereoselective (dr ≥96:4) acid-catalyzed aza-Michael reaction
to give trans-2,5-disubstituted pyrrolidines, 5-substituted proline derivatives. The aza-
Michael reaction was first observed when the starting enones were allowed to stand in
solution in deuterochloroform, but can be efficiently promoted by catalytic amounts of dry
HCl.
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Introduction
The synthesis of 8-oxo-2-aminodecanoic acid (Aoda) 1, one of the key components of the
1
-3
cyclic tetrapeptide apicidin 2, has attracted considerable attention, as a result of the
4
,5
6-10
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biological activity of apicidin, and closely related analogues.
A number of approaches
to the synthesis of Aoda 1 have been adopted, including the use of chiral pool starting
9
,11-14
15-18
materials,
and the use of chiral auxiliary groups.
Of most direct relevance to the
topic of this paper is the report on the use of radical addition of chiral non-racemic amino
1
2
acid fragments to enones. However, there is as yet no general approach to a range of
simple analogues of 8-oxo-2-aminodecanoic acid in which the position of the ketone and the
length of the side-chain can be straightforwardly varied.
We have developed a direct approach to the synthesis of enantiomerically pure α-amino
acids using a family of organozinc reagents 6-8, each prepared from the corresponding alkyl
19
iodide 3-5. Zinc reagents 6-8 can undergo Negishi cross-coupling with a variety of coupling
1
9
partners. Copper-promoted reaction of zinc reagent 6 with a range of electrophiles,
2
0
including allylic halides, is possible. Specifically copper-catalyzed reaction of zinc reagent 3
21
with allyl chloride gave protected butenylglycine 9, and the protected pentenylglycine 10
2
2
has also been prepared by related chemistry. We considered that extension of this
allylation reaction to the zinc reagent 8 should allow access to the homologous alkene 11.
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CO Me
CO Bn
CO Me
2
2
2
X
X
BocHN
BocHN
4 X = I
X
BocHN
3
6
X = I
X = ZnI
5 X = I
8 X = ZnI
7 X = ZnI
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CO Me
CO Bn
CO Me
2
2
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BocHN
BocHN
BocHN
9
10
11
There is significant literature precedent that amino acids incorporating a terminal alkene in
23,24
25,26
the sidechain can undergo cross-metathesis reaction
with simple alkenes
including
2
7,28
with electron-deficient alkenes.
A recent paper describes application of this approach to
2
9
cyclic tetrapetide derivatives. It therefore appeared entirely reasonable that the terminal
alkenes 9-11 might undergo cross-metathesis with simple enones. Subsequent
hydrogenation would be expected to give the desired analogues of 8-oxo-2-aminodecanoic
acid, in a straightforward and flexible manner.
Results and Discussion
Synthesis of the iodide 3 was carried out according to our previously reported methods
30
from appropriately protected derivatives of serine. Iodides 4 and 5 were prepared from
3
1
protected aspartic and glutamic acids by reduction via the mixed anhydride, an
32
improvement on the method using N-hydroxysuccinimide activation, followed by standard
conversion of the primary alcohol to the iodide (Scheme 1).
Scheme 1
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Conversion of the iodide 3 into the corresponding zinc reagent 6 using iodine to activate the
zinc metal prior to insertion, and copper catalysed allylation using allyl chloride, gave the
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1
expected product 9 in slightly higher yield (75%) than our previously reported method.
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Others have successfully prepared 9 using this general approach. Conversion of each of
the two iodides 4 and 5 into the corresponding zinc reagents using ultrasonication, followed
by allylation using allyl chloride in the presence of CuBr.DMS (0.1 eq.), gave the
corresponding allylated products in yields of 10 (64%) and 11 (38%), respectively (Scheme
2
). While the yield of 10 is comparable to that obtained for 9, the yield of 11 was
disappointing. In the latter case, the mass balance was the protonated zinc reagent 12, and
attempts to improve this yield, including omitting the use of sonication, were not successful.
Scheme 2
nd
Cross-metathesis reactions of each of the terminal alkenes 9-11 using the Grubbs 2
generation catalyst with a range of unsaturated ketones gave excellent yields of the
expected products 13-15 (Scheme 3, Table 1).
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Scheme 3. Cross-metathesis of terminal alkenes
R2
O
Grubbs 2nd generation
catalyst 5 mol%,
R2
n
n
0
1
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O
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R O C
NHBoc
R O C
NHBoc
2
o
2
CH Cl , 40 C, 7 h
2
2
1
9
1
, R = Me, n = 1
13a-c, n = 1
14a-c, n = 2
15a-c, n = 3
1
0, R = Bn, n =2
1
11, R = Me, n = 3
Table 1. Cross-metathesis of terminal alkenes
1
2
Substrate
n
1
1
1
2
R
R
Enone equiv.
Product
13a
Yield %
91
9
9
9
Me
Me
Me
Bn
CH
3
3.0
3.0
2.5
3.0
C
2
3
H
5
13b
92
C
H
7
13c
90
1
0
CH
3
14a
89
10
2
2
Bn
Bn
C2H5
5.0
2.5
14b
14c
90
86
1
1
0
1
3 7
C H
3
3
3
Me
Me
Me
CH
3
2.5
2.5
2.5
15a
15b
15c
82
82
91
11
C
2
3
H
5
7
1
1
C
H
Homodimers of 9-11 were detected in all the crude reaction mixtures by MS analysis. This
observation was not unexpected, since terminal alkenes are known to undergo rapid
3
4,35
homodimerization under similar conditions.
When the alkene 10 was subjected to
nd
Grubbs 2 generation catalyst in the absence of enone, the homodimer 16 was isolated in
excellent yield (98%). Subjection of 16 to the standard cross-metathesis conditions with 1-
hexen-3-one gave the expected product 14c (41%), together with recovered homodimer 16
(59%) (Scheme 4). Since the homodimer was not completely consumed under the reaction
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conditions used for the initial cross-metathesis, we can conclude that it is probably not an
intermediate in that process even though it is a substrate for the cross-metathesis reaction.
Scheme 4
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Hydrogenation of each of the enones 13-15 was carried out under standard conditions,
leading to the desired protected amino acids 17-19 (Scheme 5, Table 2). In the case of the
three benzyl esters 14a-c, the final isolated product was the corresponding free carboxylic
acid 18a-c, in principle ready for incorporation into a peptide.
Scheme 5
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Table 2. Hydrogenation of cross-metathesis products
1
2
1
Substrate
3a
13b
3c
n
1
1
1
2
R
R
Product
17a
R
Yield %
94
1
Me
Me
Me
Bn
CH
3
Me
Me
Me
H
0
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C
2
3
H
5
17b
99
1
C
H
7
17c
98
1
4a
4b
CH
3
18a
90
1
2
2
3
3
3
Bn
Bn
C
2
3
H
5
7
18b
18c
19a
19b
19c
H
89
98
94
99
99
1
4c
C
H
H
15a
15b
Me
Me
Me
CH
3
Me
Me
Me
C2H5
1
5c
3 7
C H
These results demonstrate that it is possible to prepare a range of simple analogues of 8-
oxo-2-aminodecanoic acid in which the position of the ketone and the length of the side-
chain can be straightforwardly varied, simply by choice of starting amino acid (serine,
aspartic acid or glutamic acid), and enone.
During the process of characterization of the enones 13a-c, and in particular upon allowing a
solution of each of these enones to stand in CDCl , they were each converted in high yield
3
into the corresponding pyrrolidines 20-22, in an intramolecular aza-Michael reaction. Use of
3 3
purified CDCl , in which any HCl present in the CDCl was removed by passage through UG1
alumina, prevented the aza-Michael reaction from occurring, allowing characterization of
the enones 13a-c. In separate experiments, each of the enones 13a-c was separately
2 2
treated with catalytic amounts of dry HCl in CH Cl which resulted in efficient cyclization to
give the same pyrrolidines 20-22 already observed (Scheme 6, Table 3). This established
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that the aza-Michael reaction was acid catalysed, something that has been observed
36-38
previously.
What was striking about each of the three pyrrolidines 20-22 resulting from
acid-catalyzed cyclization is that they appeared to be formed with very high
diastereoselectivity, with dr values ranging from 96:4 to 98:2 (determined by GC analysis,
and also corroborated by NMR in the case of 20a/20b). X-ray diffraction analysis of the
major product obtained by cyclisation of 13b provided a definitive answer, showing that the
major isomer was of trans-configuration 21b. In order to exclude the possibility that we had
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1
inadvertently selected a crystal of the minor isomer, the H NMR of the specific crystal used
for X-ray analysis was recorded. Although the concentration of the NMR sample was low,
1
the spectrum matched closely that of the bulk material. The H NMR spectra of the
products formed from acid catalysed cyclisation of 13a and 13c were essentially identical to
1
the H NMR spectrum of 21b (apart from the signals due to the different side-chains) which
confirms that the products therefore have structures 20b and 22b, respectively.
Scheme 6
Table 3. Acid-Catalyzed Cyclization of Amino Enones 13
Substrate
R
Product
20a/b
Conversion
Complete
Complete
*d.r. (cis : trans)
a,b
1
3a
3b
CH
3
0.04 : 0.96
b
1
C
2
H
5
21a/b
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b
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C
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H
7
22a/b
96 (4% SM)
0.02 : 0.98
a
1
b
Ratio determined by H NMR; ratio determined with GC.
Boc deprotection of each of the compounds 20b, 21b, 22b using trifluoroacetic acid
Scheme 7) gave the corresponding trifluoroacetate salts 23, 24, and 25 in essentially
0
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(
quantitative yield. Each of the trifluoroacetate salts 23, 24, and 25 was determined to be of
trans configuration by X-ray diffraction. Since the structure of 21b had already been
established as the trans-pyrrolidine, this demonstrated that the deprotection reaction had
proceeded without influencing the stereochemistry (for example by promoting a reversible
aza-Michael process), which means that the assignments already made by comparison of
1
the H NMR spectra of 20b and 22b with 21b are confirmed.
Scheme 7
A similar process has been reported previously, in which the cross-metathesis of Z-protected
unsaturated amines with enones in the presence of a Lewis acid (BF
3 2
.Et O) leads to 2,5-
disubstituted pyrrolidines with moderate levels of stereoselectivity (in the range 2:1 to 6:1
3
9
in favor of the trans-isomer). Strong acid catalysis (TfOH) has also been used to promote
the cyclization of a related Cbz-protected amino enone, again with a moderate levels of
3
8
stereoselectivity (39:61 in favor of the trans-isomer).
The high levels of
diastereoselectivity in the formation of trans-2,5-disubstituted pyrrolidines that we have
observed were therefore not expected on the basis of this literature precedent. The two
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principal differences between our substrates and those previously reported are the nature
of the nitrogen protecting group, and the presence of a carbomethoxy group. In addition,
the choice of acid catalyst may be important. Further studies on the influence of these
features appear to be warranted.
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Experimental Section
HRMS measuments were carried out using Electrospray ionisation, with a TOF mass
analyzer. IR spectra were recorded as thin films. Compound 3 was prepared by the
30
literature method. The preparation of compound 4 was carried out by the literature
3
1
method, but on a substantially larger scale than that reported. In our hands, 4 was
isolated as a yellow crystalline solid (mp 55-56 °C), as we had previously reported (mp 54-55
32
31
31,32
°
C), rather than as an oil. All other data for 4 matched that reported.
Compound 5
4
0
(
the methyl ester) was prepared by the general method reported for the synthesis of the
3
1
corresponding benzyl ester. GC analysis of compounds 20 – 22 was carried out using a
Phenomenex ZB-5 column (0.25 mm i.d. × 30 m., film thickness =250 µm.), oven
o
o
temperature = 145 C isothermal; carrier gas: H
2
at 1.4 mL/min.; injection: 250 C/split =
o
3
4.7:1; detection: FID at 300 C.
General Procedure A: Allylation reactions
A two-necked round bottomed flask was charged with a magnetic stirrer bar was fitted with
a rubber septum and three-way tap. The flask was flame-dried under vacuum and backfilled
with nitrogen three times. Zinc dust (see each procedure for amount) was added, flame-
dried and again evacuated and backfilled with nitrogen three times, with continuous
stirring. The flask was allowed to cool, dry DMF (1 mL/1 mmol of alkyl iodide) was added via
syringe, and the heterogeneous mixture stirred vigorously. Iodine (see each procedure for
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4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
amount) was added by rapid removal and replacement of the three-way tap under a stream
of nitrogen. The mixture was stirred for 1-2 minutes, until the solution was colorless. The
alkyl iodide (1.0 mmol) was added by rapid removal and replacement of the three-way tap
under a stream of nitrogen (in the case of compound 5, the alkyl iodide was dissolved in
DMF and added by syringe). The mixture was stirred and an exotherm was observed stirring
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
o
continued for a further 50 minutes at r.t. or 35-40 minutes at 35 C with sonication; these
details are specified with each example. The solid zinc dust was then allowed to settle,
giving a clear supernatant. During the activation period, a separate two-necked round
bottomed flask fitted with a magnetic stirrer bar, rubber septum and three-way tap was
flame-dried under vacuum and backfilled with nitrogen three times. The flask was allowed
to cool, CuBr.DMS (0.1 eq. relative to alkyl iodide) was added and gently heated then
evacuated and backfilled with nitrogen until the CuBr.DMS changed appearance from a
grey-brown to light green powder. The flask was allowed to cool, before adding dry DMF
(
0.6 mL/1 mmol of alkyl iodide) and allyl chloride (see each procedure for amount) dropwise
via syringe. The mixture was stirred at room temperature for about 5 minutes, at which
point the supernatant from the solution containing the organozinc reagent was added
dropwise via syringe, and the reaction mixture was stirred at room temperature for 3 h. The
crude reaction mixture was directly applied to SiO
EtOAc in petroleum ether.
2
column, using a gradient of 20-30%
Methyl (2S)-2-([(tert-butoxy)carbonyl]amino)hex-5-enoate (9)
General procedure A using zinc dust (1.95 g, 30 mmol, 2.5 eq.), iodine (0.6 g, 2.4 mmol, 0.2
eq.), 3 (3.94 g, 12 mmol, 1 eq.), CuBr.DMS (0.246 g, 1.2 mmol, 0.1 eq.), and allyl chloride
(
1.36 mL, 16.8 mmol, 1.4 eq.) gave methyl (2S)-2-([(tert-butoxy)carbonyl]amino)hex-5-
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8
9
D
enoate 9 (2.2 g, 9 mmol, 75 %) as a colorless oil. Zinc insertion took 50 minutes at r.t. [α] -
33
1
7.0 (c 1.0, MeOH), lit. : [α]
D
f
-20.7 ( c 0.97, MeOH); R = 0.57 (20% EtOAc in petroleum
1
ether); H NMR (400 MHz, CDCl
3
) δ ppm: 5.80 (1 H, ddt, J = 16.9, 10.3 and 6.6 Hz), 4.98-5.08
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(
3 H, m), 4.28-4.37 (1 H, m), 3.74 (3 H, s), 2.06-2.17 (2 H, m), 1.85-1.96 (1 H, m), 1.65-1.77 (1
13
3
H, m), 1.44 (9 H, s); C NMR (100 MHz, CDCl ) δ ppm: 173.3, 155.3, 136.9, 115.7, 79.8, 52.9,
-1
52.3, 31.9, 29.5, 28.3; IR (cm ), 3370, 1742, 1712, 1516, 1451, 1365, 1254, 1168; m/z (ES+)
+
found MH : 244.1549, C H NO requires 244.1549.
1
2
22
4
22
Benzyl (2S)-2-([(tert-butoxy)carbonyl]amino)hept-6-enoate (10)
General procedure A using zinc dust (1.17 g, 18 mmol, 3 eq.), iodine (0.335 g, 1.32 mmol,
0.22 eq.), 4 (2.5 g, 6 mmol, 1 eq.), CuBr.DMS (0.123 g, 0.6 mmol, 0.1 eq.), and allyl chloride
o
(
0.7 mL, 8.4 mmol, 1.4 eq.). Zinc insertion took 35 minutes with sonication at 35 C.
Purification by column chromatography (20% EtOAc in petroleum ether) followed by
preparative HPLC (XBridge Prep OBD C18 5µm 19 mm id x 250 mm, using 30:70
-1
water/acetonitrile, at a flow rate of 17 mL.min and UV detection at 210 nm) gave benzyl
(
2S)-2-([(tert-butoxy)carbonyl]amino)hept-6-enoate 10 (1.28 g, 3.8 mmol, 64% ) as a
2
2
colorless oil (t
R
= 8-10 min). [α]
D
-4.0 (c 1, CHCl
3
)
lit. : [α]
D 2 2 f
-5.5 ( c 1.4, CH Cl ), R = 0.5 (20%
1
EtOAc in petroleum ether). H NMR (400 MHz, CDCl
3
) δ ppm: 7.31-7.40 (5 H, m), 5.72 (1 H,
ddt, J = 16.9, 10.3 and 6.7 Hz), 5.22 (1 H, d, J = 12.4 Hz), 5.13 (1 H, d, J = 12.4 Hz), 5.05 (1 H,
d, J = 8.3 Hz), 5.02-4.92 (2 H, m), 4.30-4.39 (1 H, m), 1.96-2.12 (2 H, m), 1.75-1.88 (1 H, m),
13
1
3
.58-1.69 (1 H, m), 1.31-1.52 (11 H, m). C NMR (100 MHz, CDCl ) δ ppm: 172.7, 155.4,
-1
137.9, 135.5, 128.6, 128.4, 128.2, 115.1, 79.8, 66.9, 53.4, 33.1, 32.1, 28.3, 24.4; IR (cm ),
+
3
368, 1745, 1712, 1634, 1501, 1366, 1253, 1165, 1001, 912; m/z (ES+) found MH : 334.2028,
C
19 4
H28NO requires 334.2018.
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2
2
2
2
2
2
3
3
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5
5
5
5
5
5
5
6
4
1
Methyl (2S)-2-([(tert-butoxy)carbonyl]amino)oct-7-enoate (11)
General procedure A using zinc dust (487.5 mg, 7.5 mmol, 2.5 eq.), iodine (152.3 mg, 0.6
mmol, 0.2 eq.), 5 (1.10 g, 3 mmol, 1 eq.), CuBr.DMS (61.5 mg, 0.3 mmol, 0.1 eq.), and allyl
chloride (320 µl, 3.9 mmol, 1.3 eq.) gave methyl (2S)-2-([(tert-butoxy)carbonyl]amino)oct-7-
enoate 11 (311 mg, 1.15 mmol, 38%) as a colorless oil. Zinc insertion took 40 minutes with
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
o
1
sonication at 35 C. [α]
D f
-17.6 (c 1.25, MeOH); R = 0.52 (20% EtOAc in petroleum ether); H
NMR (400 MHz, CDCl ) δ ppm: 5.77 (1 H, ddt, J = 16.9, 10.1 and 6.8 Hz), 4.9-5.05 (3 H, m),
3
4
1
1
.25-4.33 (1 H, m), 3.73 (3 H, s), 1.99-2.1 (2 H, m), 1.69-1.86 (1 H, m), 1.53-1.68 (1 H, m),
1
3
3
.24-1.51 (4 H, m), 1.44 (9 H, s); C NMR (100 MHz, CDCl ) δ ppm: 173.4, 155.3, 138.5,
-1
14.6, 79.8, 53.3, 52.2, 33.4, 32.6, 28.4, 28.3, 24.6; IR (cm ), 3370, 1745, 1720, 1509, 1168;
+
m/z (ES+) found MH : 272.1850, C14
H
26NO
4
requires 272.1862.
General procedure B: Cross metathesis of unsaturated amino acids
A two-necked round bottomed flask with a magnetic stirrer bar was fitted with a condenser
equipped with a three-way tap on top and rubber septum. The flask was flame-dried under
vacuum and backfilled with nitrogen three times. The flask was allowed to cool, before the
unsaturated amino acid 9-11 and enone in dry degassed CH
2
Cl
2
(2 mL) were added via
Cl (1 mL)
nd
syringe. Grubbs 2 generation catalyst (5 mol% relative to substrate) in dry CH
2
2
was added by syringe, and the reaction mixture was heated at reflux for 7 h, allowed to cool
to room temperature and concentrated. The residue was purified by column
chromatography using a gradient of 15-35% EtOAc in petroleum ether.
Methyl (2S,5E)-2-([(tert-butoxy)carbonyl]amino)-7-oxooct-5-enoate (13a)
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8
9
General procedure B using 9 (97 mg, 0.4 mmol, 1 eq.), 3-buten-2-one (100 µl, 1.2 mmol, 3
nd
2 2
eq.) and Grubbs 2 generation catalyst (16 mg, 0.02 mmol, 5 mol%) in CH Cl (3 mL) gave
methyl (2S, 5E)-2-([(tert-butoxy)carbonyl]amino)-7-oxooct-5-enoate 13a (104 mg, 0.36
1
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
mmol, 91%) as an oil. [α] +40.0 (c 0.4, CHCl ); R = 0.13 (20% EtOAc in petroleum ether); H
D
3
f
NMR (400 MHz, CDCl
3
) δ ppm: 6.77 (1 H, dt, J = 16.0 and 6.7 Hz), 6.09 (1 H, br.d, J = 16.0 Hz),
5.08 (1 H, d, J = 8.1 Hz), 4.30-4.42 (1H, m), 3.76 (3 H, s), 2.19–2.39 (2 H, m), 2.25 (3 H, s),
1
3
1
1
.92-2.11 (1 H, m), 1.74-1.86 (1 H, m), 1.45 (9 H, s); C NMR (100 MHz, CDCl ) δ ppm: 198.3,
3
-1
72.7, 155.3, 146.1, 131.9, 80.1, 52.8, 52.4, 31.3, 28.3, 28.2, 26.9; IR (cm ), 3359, 1749,
+
1715, 1673, 1518, 1450, 1371, 1253, 1166; m/z (ES+) found MH : 286.1648, C14
H24NO
5
requires 286.1654.
Methyl (2S, 5E)-2-([(tert-butoxy)carbonyl]amino)-7-oxonon-5-enoate (13b)
General procedure B using 9 (97 mg, 0.4 mmol, 1 eq.), 1-penten-3-one (120 µl, 1.2 mmol, 3
nd
2 2
eq.) and Grubbs 2 generation catalyst (16 mg, 0.02 mmol, 5 mol%) in CH Cl (3 mL) gave
methyl (2S, 5E)-2-([(tert-butoxy)carbonyl]amino)-7-oxonon-5-enoate 13b (110 mg, 0.37
1
mmol, 92%) as an oil. [α]
NMR (400 MHz, CDCl
.13 (1 H, d, J = 7.6 Hz), 4.25-4.36 (1 H, m), 3.72 (3 H, s), 2.53 (2 H, q, J = 7.3 Hz), 2.17–2.35 (2
D
+36.4 (c 0.55, CHCl
3
); R
f
= 0.17 (20% EtOAc in petroleum ether); H
3
) δ ppm: 6.76 (1 H, dt, J = 15.8 and 6.8 Hz), 6.09 (1 H, d, J = 15.8 Hz),
5
1
3
H, m), 1.88-2.06 (1 H, m), 1.71-1.82 (1 H, m), 1.41 (9 H, s), 1.06 (3 H, t, J = 7.3 Hz); C NMR
(
100 MHz, CDCl ) δ ppm: 200.7, 172.8, 155.3, 144.6, 130.7, 80.0, 52.9, 52.4, 33.4, 31.3, 28.3,
3
-1
+
2
8.2, 8.0; IR (cm ), 3346, 1747, 1708, 1669, 1512, 1448, 1363, 1167; m/z (ES+) found MH :
300.1800, C H NO requires 300.1811.
1
5
26
5
Methyl (2S,5E)-2-([(tert-butoxy)carbonyl]amino)-7-oxodec-5-enoate (13c)
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8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
General procedure B using 9 (97 mg, 0.4 mmol, 1 eq.), 1-hexen-3-one (117 µl, 1 mmol, 2.5
nd
2 2
eq.) and Grubbs 2 generation catalyst (16 mg, 0.02 mmol, 5 mmol%) in CH Cl (3 mL) gave
methyl (2S,5E)-2-([(tert-butoxy)carbonyl]amino)-7-oxodec-5-enoate 13c (113 mg, 0.36
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
mmol, 90%) as an oil. [α] +30.7 (c 0.88, CHCl ); R = 0.17 (20% EtOAc in petroleum ether);
D
3
f
1
3
H NMR (400 MHz, CDCl ) δ ppm: 6.78 (1 H, dt, J = 15.8 and 6.8 Hz), 6.11 (1 H, d, J = 15.8 Hz),
5.08 (1 H, d, J =7.6 Hz), 4.27-4.39 (1 H, m), 3.75 (3 H, s), 2.5 (2 H, t, J = 7.3 Hz), 2.19–2.37 (2
H, m), 1.91-2.08 (1 H, m), 1.69-1.85 (1 H, m), 1.63 (2 H, sext., J = 7.4 Hz), 1.44 (9 H, s), 0.93 (3
1
3
3
H, t, J = 7.5 Hz); C NMR (100 MHz, CDCl ) δ ppm: 200.4, 172.8, 155.3, 144.7, 130.9, 80.1,
-1
52.9, 52.4, 42.2, 31.3, 28.3, 28.2, 17.6, 13.8; IR (cm ), 3359, 1750, 1714, 1675, 1521, 1448,
+
1
366, 1249, 1167; m/z (ES+) found MH : 314.1972, C H NO requires 314.1967.
1
6
28
5
Benzyl (2S,6E)-2-([(tert-butoxy)carbonyl]amino)-8-oxonon-6-enoate (14a)
General procedure B using 10 (133.4 mg, 0.4 mmol, 1 eq.), 3-buten-2-one (100 µl, 1.2 mmol,
nd
3
eq.) and Grubbs 2 generation catalyst (16 mg, 0.02 mmol, 5 mol%) in CH Cl (3 mL) gave
2 2
benzyl (2S,6E)-2-([(tert-butoxy)carbonyl]amino)-8-oxonon-6-enoate 14a (134 mg, 0.36
mmol, 89%) as an oil. [α]
D
-22.0 (c 0.91, MeOH); R
) δ ppm: 7.32-7.42 (5 H, m), 6.70 (1 H, dt, J = 16.0 and 6.9 Hz), 6.04
1 H, d, J = 16.0 Hz), 5.22 (1 H, d, J = 12.2 Hz), 5.14 (1 H, d, J = 12.2, Hz), 5.05 (1 H, d, J = 8.1
f
= 0.32 (30% EtOAc in petroleum ether);
1
H NMR (400 MHz, CDCl
3
(
Hz), 4.33-4.41 (1 H, m), 2.13-2.31 (5 H, m), 1.77-1.91 (1 H, m), 1.59-1.72 (1 H, m), 1.37-1.57
13
(
3
2 H, m), 1.44 (9 H, s); C NMR (100 MHz, CDCl ) δ ppm: 198.5, 172.5, 155.4, 147.1, 135.3,
-1
1
31.6, 128.6, 128.5, 128.3, 79.9, 67.1, 53.2, 32.3, 31.7, 28.3, 26.9, 23.7; IR (cm ), 3342,
+
1715, 1694, 1673, 1625, 1499, 1364, 1250, 1157; m/z (ES+) found MH : 376.2109, C H NO
5
2
1
30
requires 376.2124.
Benzyl (2S,6E)-2-([(tert-butoxy)carbonyl]amino)-8-oxodec-6-enoate (14b)
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8
9
General procedure B using 10 (134 mg, 0.4 mmol, 1 eq.), 1-penten-3-one (200 µl, 2 mmol, 5
nd
2 2
eq.) and Grubbs 2 generation catalyst (16 mg, 0.02 mmol, 5 mol%) in CH Cl (3 mL) gave
benzyl (2S,6E)-2-([(tert-butoxy)carbonyl]amino)-8-oxodec-6-enoate 14b (141 mg, 0.36
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
mmol, 90%) as an oil. [α] -19.5 (c 0.77, MeOH); R = 0.18 in ( 15% EtOAc in petroleum
D
f
1
ether); H NMR (400 MHz, CDCl
3
) δ ppm: 7.30-7.39 (5 H, m), 6.72 (1 H, dt, J = 16.0 and 6.8
Hz), 6.05 (1 H, br.d, J = 16.0 Hz), 5.21 (1 H, d, J = 12.2 Hz), 5.13 (1 H, d, J = 12.2 Hz), 5.08 (1 H,
d, J = 8.3 Hz), 4.30-4.40 (1 H, m), 2.52 (2 H, q, J = 7.3 Hz), 2.11-2.27 (2 H, m), 1.77-1.89 (1 H,
1
3
m), 1.58-1.71 (1 H, m), 1.36-1.56 (11 H, m), 1.10 (3 H, t, J = 7.3 Hz); C NMR (100 MHz,
CDCl
3
) δ ppm: 200.8, 172.4, 155.4, 145.6, 135.3, 130.4, 128.6, 128.4, 128.3, 79.8, 67.1, 53.2,
-1
3
3.3, 32.2, 31.7, 28.3, 23.7, 8.1; IR (cm ), 3362, 1741, 1696, 1673, 1629, 1499, 1248, 1159;
+
m/z (ES+) found MH : 390.2283, C22
H
32NO
5
requires 390.2280.
Benzyl (2S,6E)-2-([(tert-butoxy)carbonyl]amino)-8-oxoundec-6-enoate (14c)
General procedure B using 10 (133.4 mg, 0.4 mmol, 1 eq.), 1-hexen-3-one (117 µl, 1 mmol,
nd
2
2 2
.5 eq.) and Grubbs 2 generation catalyst (16 mg, 0.02 mmol, 5 mol%) in CH Cl gave
benzyl (2S,6E)-2-([(tert-butoxy)carbonyl]amino)-8-oxoundec-6-enoate 14c (140 mg, 0.35
1
mmol, 86%) as an oil. [α]
NMR (400 MHz, CDCl
D
-30.0 (c 0.1, MeOH); R
f
= 0.22 (15% EtOAc in petroleum ether); H
3
) δ ppm: 7.33-7.41 (5 H, m), 6.73 (1 H, dt, J = 16.0 and 6.8 Hz), 6.06 (1
H, br.d, J = 16.0), 5.22 (1 H, d, J = 12.2 Hz), 5.14 (1 H, d, J = 12.2 Hz), 5.04 (1 H, br.d, J = 8.3
Hz), 4.32-4.42 (1 H, m,), 2.48 (2 H, t, J = 7.3 Hz), 2.13-2.27 (2 H, m), 1.78-1.91 (1 H, m), 1.57-
13
1
3
.71 (3 H, m), 1.37-1.56 (11 H, m), 0.93 (3 H, t, J = 7.5 Hz); C NMR (100 MHz, CDCl ) δ ppm:
200.6, 172.5, 155.5, 145.7, 135.3, 130.7, 128.6, 128.5, 128.3, 80.2, 67.1, 53.2, 42.1, 32.3,
-
1
3
1
1.7, 28.3, 23.7, 17.6, 13.8; IR (cm ), 3357, 1747, 1712, 1675, 1629, 1499, 1457, 1365, 1256,
+
162; m/z (ES+) found MH : 404.2426, C23
H
5
34NO requires 404.2437.
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Methyl (2S,7E)-2-([(tert-butoxy)carbonyl]amino)-9-oxodec-7-enoate (15a)
General procedure B using 11 (108.5 mg, 0.4 mmol, 1 eq.), 3-buten-2-one (85 µl, 1 mmol,
nd
2
2 2
.5 eq.) and Grubbs 2 generation catalyst (16 mg, 0.02 mmol, 5 mol%) in CH Cl (3 mL)
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
gave methyl (2S,7E)-2-([(tert-butoxy)carbonyl]amino)-9-oxodec-7-enoate 15a (103 mg, 0.33
1
mmol, 82%) as an oil. [α]
NMR (400 MHz, CDCl
D
+20.0 (c 0.95, CHCl
3
); R
f
= 0.25 (30% EtOAc in petroleum ether); H
3
) δ ppm: 6.76 (1 H, dt, J = 16.0 and 6.9 Hz), 6.05 (1 H, d, J = 16.0 Hz),
5.04 (1H, br.d, J = 8.1 Hz), 4.24-4.34 (1 H, m), 3.73 (3 H, s), 2.17-2.26 (2 H, m), 2.23 (3 H, s),
13
1
.75-1.87 (1 H, m), 1.56-1.68 (1 H, m), 1.29-1.55 (4 H, m), 1.43 (9 H, s); C NMR (100 MHz,
3
CDCl ) δ ppm: 198.6, 173.2, 155.3, 147.7, 131.5, 79.9, 53.2, 52.3, 32.5, 32.1, 28.3, 27.6, 26.9,
-
1
+
2
3
4.8; IR (cm ), 3356, 1749, 1717, 1674, 1523, 1441, 1369, 1258, 1164; m/z (ES+) found MH :
14.1956, C16 requires 314.1967.
H
28NO
5
Methyl (2S, 7E)-2-([(tert-butoxy)carbonyl]amino)-9-oxoundec-7-enoate (15b)
General procedure B using 11 (108.5 mg, 0.4 mmol, 1 eq.), 1-penten-3-one (100 µl, 1 mmol,
nd
2
2 2
.5 eq.) and Grubbs 2 generation catalyst (16 mg, 0.02 mmol, 5 mol %) in CH Cl (3 mL)
gave methyl (2S,7E)-2-([(tert-butoxy)carbonyl]amino)-9-oxoundec-7-enoate 15b (108 mg,
0.33 mmol, 82%) as an oil. [α]
D
3 f
+23.7 (c 0.93, CHCl ); R = 0.22 (20% EtOAc in petroleum
1
ether); H NMR (500 MHz, CDCl
3
) δ ppm: 6.79 (1 H, dt, J = 16.0 and 6.9 Hz), 6.08 (1 H, br.d, J
=
16.0 Hz), 5.02 (1 H, br.d, J = 7.5 Hz), 4.25-4.34 (1 H, m), 3.74 (3 H, s), 2.55 (2 H, q, J = 7.3
Hz), 2.21 (2 H, dq, J = 1.3 and 7.2 Hz), 1.73-1.87 (1 H, m), 1.58-1.68 (1 H, m), 1.28-1.55 (4 H,
13
3
m), 1.44 (9 H, s), 1.09 (3 H, t, J =7.3 Hz); C NMR (125 MHz, CDCl ) δ ppm: 201.0, 173.2,
-1
155.3, 146.2, 130.2, 79.9, 53.2, 52.2, 33.2, 32.5, 32.1, 28.3, 27.6, 24.8, 8.1; IR (cm ), 3357,
+
1
746, 1715, 1634, 1674, 1514, 1460, 1167; m/z (ES+) found MH : 328.2111, C17
H
30NO
5
requires 328.2124.
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9
Methyl (2S,7E)-2-([(tert-butoxy)carbonyl]amino)-9-oxododec-7-enoate (15c)
General procedure B using 11 (108.5 mg, 0.4 mmol, 1 eq.), 1-hexen-3-one (117 µl, 1 mmol,
nd
2
2 2
.5 eq.) and Grubbs 2 generation catalyst (16 mg, 0.02 mmol, 5 mol%) in CH Cl (3 mL)
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
gave methyl (2S,7E)-2-([(tert-butoxy)carbonyl]amino)-9-oxododec-7-enoate 15c (125.4 mg,
0
.37 mmol, 91%) as an oil. [α]
D
3 f
+13.2 (c 0.38, CHCl ); R = 0.29 (20% EtOAc in petroleum
1
ether); H NMR (400 MHz, CDCl
3
) δ ppm: 6.77 (1 H, dt, J = 16.0 and 6.9 Hz), 6.07 (1 H, br.d, J
=
16.0 Hz), 5.04 (1 H, br. d, J = 8.3 Hz), 4.24-4.32 (1 H, m), 3.72 (3 H, s), 2.49 (2 H, t, J = 7.3
Hz), 2.19 (2 H, dq, J = 7.2 and 1.3 Hz), 1.74-1.85 (1 H, m), 1.56-1.67 (3 H, m), 1.27-1.54 (4 H,
1
3
m), 1.42 (9 H, s), 0.92 (3 H, t, J = 7.5 Hz); C NMR (100 MHz, CDCl
3
) δ ppm: 200.7, 173.3,
-1
1
3
C
55.3, 146.4, 130.5, 79.9, 53.2, 52.2, 42.1, 32.5, 32.1, 28.3, 27.6, 24.8, 17.7, 13.8; IR (cm ),
+
357, 1750, 1718, 1671, 1516, 1437, 1369, 1247, 1167; m/z (ES+) found MH : 342.2269,
18 5
H32NO
requires 342.2280.
1
,12-Dibenzyl (2S,6E/Z,11S)-2,11-bis(([(tert-butoxy) carbonyl] amino))dodec-6-enedioate
(16)
General procedure B, using benzyl (2S)-2-([(tert-butoxy)carbonyl]amino)hept-6-enoate 10
nd
(110 mg, 0.33 mmol, 1 eq.) as the starting material and Grubbs 2 generation catalyst (14
D
mg, 0.016 mmol, 5 mmol%), gave compound 16 (104 mg, 0.163 mmol, 98%) as an oil [α] -
1
1
7
4
.3 (c 1.5, CHCl
3
); R
f
= 0.3 (20% EtOAc in petroleum ether); H NMR (400 MHz,CDCl
3
) δ ppm:
.29-7.40 (10 H, m), 5.25-5.36 (2 H, m), 5.21 (2 H, d, J = 12.5 Hz), 5.12 (2 H, d, J = 12.5 Hz),
.99-5.01 (2 H, m), 4.27-4.43 (2 H, m), 1.87-2.08 (4 H, m), 1.72-1.86 (2 H, m), 1.54-1.71 (2 H,
13
m), 1.19-1.52 (4 H, m), 1.44 (18 H, s); C NMR (100 MHz, CDCl ) δ ppm: 172.8, 155.4, 135.5,
3
-
1
1
30.1, 128.6, 128.4, 128.3, 79.8, 66.9, 53.5, 32.5, 31.9, 28.3, 25.0; IR (cm ), 3370, 1745,
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2
3
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5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
+
1717, 1501, 1459, 1250, 1163; m/z (ES+) found MH : 639.3638, C36
H
51
N
2
O
8
requires
6
39.3645.
General Procedure C: Hydrogenation of cross-metathesis product
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
A two-necked round bottomed flask with magnetic stirrer bar was fitted with a rubber
septum and three-way tap, and was flame-dried under vacuum and back-filled with nitrogen
three times. The flask was allowed to cool, and palladium on carbon (10% w/w) (amount
specified in each experiment) was added to the flask which was evacuated and back-filled
with nitrogen three times. Then nitrogen gas line was replaced with balloon of hydrogen
gas, and the cross-metathesis product (1 eq.) was added to the flask as a solution in EtOAc
(7 mL) via syringe. The flask was evacuated until the reaction mixture began to boil, and
then back-filled with hydrogen gas. This procedure was repeated three more times, and the
reaction stirred at room temperature for 1 day. To remove the catalyst the mixture was
filtered through Celite® and then washed with EtOAc. The filtrate and washings were
combined, and the solvent was removed under reduced pressure.
Methyl (2S)-2-([(tert-butoxy)carbonyl]amino)-7-oxooctanoate (17a)
General procedure C using 13a (105 mg, 0.368 mmol, 1 eq.) and 10% w/w palladium on
carbon (20 mg) gave methyl (2S)-2-([(tert-butoxy)carbonyl]amino)-7-oxooctanoate 17a (100
mg, 0.348 mmol, 94%) as a colorless oil. [α]
D
+15.8 (c 0.95, CHCl
3 f
); R = 0.31 (40% EtOAc in
1
petroleum ether); H NMR (400 MHz, CDCl
3
) δ ppm: 5.02 (1 H, d, J = 8.1 Hz), 4.23-4.34 (1 H,
m), 3.74 (3 H, s), 2.43 (2 H, t, J = 7.2 Hz), 2.13 (3 H, s), 1.73-1.87 (1 H, m), 1.52-1.68 (3 H, m),
13
1.44 (9 H, s), 1.22-1.40 (2 H, m); C NMR (100 MHz, CDCl ) δ ppm: 208.6, 173.3, 155.4, 79.8,
3
-
1
5
1
3.3, 52.3, 43.3, 32.5, 29.8, 28.3, 24.8, 23.2; IR (cm ), 3370, 1749, 1715, 1516, 1439, 1364,
+
250, 1169; m/z (ES+) found MNa : 310.1618, C14
H
25NO
5
Na requires 310.1630.
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8
9
Methyl (2S)-2-([(tert-butoxy)carbonyl]amino)-7-oxononanoate (17b)
General procedure C using 13b (58 mg, 0.194 mmol, 1 eq.) and 10% w/w palladium on
carbon (10 mg) gave methyl (2S)-2-([(tert-butoxy)carbonyl]amino)-7-oxononanoate 17b (58
mg, 0.193 mmol, 99%) as a colorless oil. [α] +16.0 (c 1, CHCl ); R = 0.22 (20% EtOAc in
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
D
3
f
1
petroleum ether); H NMR (400 MHz, CDCl
3
) δ ppm: 5.03 (1 H, d, J = 8.1 Hz), 4.21-4.31 (1 H,
m), 3.70 (3 H, s), 2.34-2.43 (4 H, m), 1.69-1.84 (1 H, m), 1.50-1.66 (3 H, m), 1.42 (9 H, s),
1
3
1
1
.22-1.37 (2 H, m), 1.02 (3 H, t, J = 7.3 Hz); C NMR (100 MHz, CDCl ) δ ppm: 211.3, 173.3,
3
-1
55.4, 79.8, 53.3, 52.2, 41.9, 35.9, 32.6, 28.3, 24.9, 23.3, 7.8; IR (cm ), 3360, 1751, 1712,
+
1519, 1455, 1370, 1256, 1167; m/z (ES+) found: MH 302.1955, C15
H
28NO
5
requires
3
02.1967.
Methyl (2S)-2-([(tert-butoxy)carbonyl]amino)-7-oxodecanoate (17c)
General procedure C using 13c (89 mg, 0.284 mmol, 1 eq.) and 10% w/w palladium on
carbon (40 mg) gave methyl (2S)-2-([(tert-butoxy)carbonyl]amino)-7-oxodecanoate 17c (88
mg, 0.279 mmol, 98%) as colorless oil. [α]
D
+15.0 (c 2, CHCl
3 f
); R = 0.46 (30% EtOAc in
1
petroleum ether); H NMR (400 MHz, CDCl
3
) δ ppm: 5.01 (1 H, d, J = 8.1 Hz), 4.23-4.34 (1 H,
m), 3.73 (3 H, s), 2.39 (2 H, t, J = 7.3 Hz), 2.36 (2 H, t, J = 7.3 Hz), 1.71-1.87 (1 H, m), 1.51-1.67
1
3
(
5 H, m), 1.44 (9 H, s), 1.24-1.39 (2 H, m), 0.91 (3 H, t, J = 7.3 Hz); C NMR (100 MHz, CDCl
3
)
δ ppm: 210.8, 173.3, 155.4, 79.8, 53.3, 52.2, 44.7, 42.3, 32.6, 28.3, 24.9, 23.3, 17.3, 13.7; IR
-1
+
(
cm ), 3370, 1749, 1715, 1514, 1454, 1367, 1250, 1170; m/z (ES+) found MH : 316.2134,
requires 316.2124.
(2S)-2-([(tert-Butoxy)carbonyl]amino)-8-oxononanoic acid (18a)
16 5
C H30NO
1
7
General procedure C using 14a (50 mg, 0.133 mmol, 1 eq.) and 10% w/w palladium on
carbon (25 mg) gave (2S)-2-([(tert-butoxy)carbonyl]amino)-8-oxononanoic acid 18a (34 mg,
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7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0.12 mmol 90%) as a colorless oil. [α]
D
+5.0 (c 1.0, CHCl
3 f
); R = 0.17 (EtOAc : petroleum ether
1
:
acetic acid, 5 : 5 : 0.1 mL); H NMR (400 MHz, CDCl
3
) δ ppm: 5.02 (1 H, d, J = 7.8 Hz), 4.25-
4
1
.35 (1 H, m), 2.44 (2 H, t, J = 7.3 Hz), 2.14 (3 H, s), 1.79-1.93 (1 H, m), 1.63-1.74 (1 H, m),
1
3
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
.58 (2 H, quint., J = 7.5 Hz), 1.27-1.48 (4 H, m), 1.45 (9 H, s); C NMR (100 MHz, CDCl ) δ
3
-1
ppm: 209.6, 176.9, 155.6, 80.1, 53.3, 43.5, 32.3, 29.8, 28.6, 28.3, 25.0, 23.4. IR (cm ), 3340,
+
1730, 1700, 1658, 1520, 1390, 1368, 1252, 1167; m/z (ES+) found MH : 288.1806, C14
H26NO
5
1
requires 288.1811. In the H NMR the carboxylic acid proton was not observed due,
presumably, to its broadness.
1
3,14,17,18
(2S)-2-([(tert-Butoxy)carbonyl]amino)-8-oxodecanoic acid (18b)
General procedure C using 14b (52 mg, 0.134 mmol, 1 eq.) and 10% w/w palladium on
carbon (23 mg) gave (2S)-2-([(tert-butoxy)carbonyl]amino)-8-oxodecanoic acid 18b (35 mg,
0
D 3 f
.12 mmol, 89%) as a colorless oil. [α] -37.2 (c 0.94, CHCl ); R = 0.28 (EtOAc : petroleum
1
ether : acetic acid, 5 : 5 : 0.1 mL); H NMR (400 MHz, CDCl ) δ ppm: 5.02 (1 H, d, J = 8.0 Hz),
3
4
.24-4.35 (1 H, m), 2.42 (2 H, q, J = 7.3 Hz), 2.41 (2 H, t, J = 7.3 Hz), 1.79-1.92 (1 H, m), 1.63-
1.74 (1 H, m), 1.58 (2 H, quint., J = 7.3 Hz), 1.27-1.48 (4 H, m), 1.45 (9 H, s), 1.05 (3 H, t, J =
1
3
7
2
3
.3 Hz); C NMR (100 MHz, CDCl ) δ ppm: 212.1, 176.9, 155.6, 80.2, 53.3, 42.1, 35.9, 32.2,
-1
8.7, 28.3, 25.1, 23.5, 7.8; IR (cm ), 3322, 1735, 1713, 1681, 1510, 1460, 1395, 1249, 1166;
+
m/z (ES+) found MH : 302.1953, C15
H
28NO
5
requires 302.1967.
(2S)-2-([(tert-Butoxy)carbonyl]amino)-8-oxoundecanoic acid (18c)
General procedure C using 14c (82 mg, 0.2 mmol, 1 eq.) and 10% w/w palladium on carbon
(37 mg) gave (2S)-2-([(tert-butoxy)carbonyl]amino)-8-oxoundecanoic acid 18c (62 mg, 0.196
mmol, 98%) as a colorless oil. [α]
D
-16.0 (c 0.5, CHCl
3
); R
f
= 0.25 (EtOAc : petroleum ether :
1
acetic acid, 5 : 5 : 0.1 mL); H NMR (400 MHz, CDCl
3
) δ ppm: 5.03 (1 H, d, J = 8.1 Hz), 4.24-
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7
8
9
4.35 (1 H, m), 2.40 (2 H, t, J = 7.8 Hz), 2.38 (2 H, t, J = 7.5 Hz), 1.77-1.93 (1 H, m), 1.52-1.74 (5
13
3
H, m), 1.24-1.51 (4 H, m), 1.45 (9 H, s), 0.91 (3 H, t, J = 7.4 Hz); C NMR (100 MHz, CDCl ) δ
ppm: 211.6, 176.9, 155.6, 80.2, 53.3, 44.7, 42.5, 32.2, 28.7, 28.3, 25.1, 23.4, 17.3, 13.7; IR
-1
+
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(
cm ), 3346, 1717, 1701, 1688, 1511, 1453, 1366, 1243, 1159; m/z (ES+) found MH :
1
3
16.2119, C16
H
30NO
5
requires 316.2124. In the H NMR the carboxylic acid proton was not
observed due, presumably, to its broadness.
Methyl (2S)-2-([(tert-butoxy)carbonyl]amino)-9-oxodecanoate (19a)
General procedure C using 15a (50 mg, 0.159 mmol, 1 eq.) and 10% w/w palladium on
carbon (25 mg) gave methyl (2S)-2-([(tert-butoxy)carbonyl]amino)-9-oxodecanoate 19a
(
47.5 mg, 0.15 mmol, 94%) as a colorless oil. [α] +10.9 (c 1.1, CHCl ); R = 0.17 (20% EtOAc in
D 3 f
1
petroleum ether); H NMR (500 MHz, CDCl
3
) δ ppm: 4.99 (1 H, br.d, J = 7.7 Hz), 4.22-4.32 (1
H, m), 3.72 (3 H, s), 2.39 (2 H, t, J = 7.4 Hz), 2.12 (3 H, s), 1.69-1.82 (1 H, m), 1.51-1.65 (3 H,
1
3
m), 1.43 (9 H, s), 1.22-1.37 (6 H, m); C NMR (125 MHz, CDCl ) δ ppm: 209.1, 173.4, 155.3,
3
-1
7
9.8, 53.3, 52.1, 43.6, 32.6, 29.8, 28.9, 28.8, 28.3, 25.0, 23.6; IR (cm ), 3365, 1745, 1712,
+
1516, 1438, 1370, 1249, 1164; m/z (ES+) found MH : 316.2137, C16
H
30NO
5
requires
1
3
16.2124. In the H NMR the carboxylic acid proton was not observed due, presumably, to
its broadness.
Methyl (2S)-2-([(tert-butoxy)carbonyl]amino)-9-oxoundecanoate (19b)
General procedure C using 15b (49 mg, 0.15 mmol, 1 eq.) and 10% w/w palladium on carbon
17 mg) gave methyl (2S)-2-([(tert-butoxy)carbonyl]amino)-9-oxoundecanoate 19b (49 mg,
0.148 mmol, 99%) as a colorless oil. [α] +19.3 (c 0.68, CHCl ); R = 0.27 (20% EtOAc in
(
D
3
f
1
3
petroleum ether); H NMR (400 MHz, CDCl ) δ ppm: 5.00 (1 H, br.d, J = 8.1 Hz), 4.22-4.31 (1
H, m), 3.72 (3 H, s, OCH
3
), 2.34-2.44 (4 H, m), 1.69-1.82 (1 H, m), 1.49-1.65 (3 H, m), 1.43 (9
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2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
1
3
H, s), 1.20-1.37 (6 H, m), 1.03 (3 H, t, J = 7.3 Hz); C NMR (100 MHz, CDCl
3
) δ ppm: 211.7,
-1
1
3
73.4, 155.3, 79.8, 53.3, 52.2, 42.2, 35.8, 32.7, 28.9 (2 C), 28.3, 25.1, 23.7, 7.8; IR (cm ),
+
367, 1746, 1711, 1704, 1518, 1455, 1364, 1168; m/z (ES+) found MH : 330.2290, C17H32NO
5
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
requires 330.2280.
Methyl (2S)-2-([(tert-butoxy)carbonyl]amino)-9-oxododecanoate (19c)
General procedure C using 15c (44 mg, 0.129 mmol, 1 eq.) and 10% w/w palladium on
carbon (17 mg) gave methyl (2S)-2-([(tert-butoxy)carbonyl]amino)-9-oxododecanoate 19c
(
44 mg, 0.128 mmol, 99%) as a colorless oil. [α]
D
+14.1 (c 0.85, CHCl
3 f
); R = 0.57 (30% EtOAc
1
in petroleum ether); H NMR (400 MHz, CDCl
3
) δ ppm: 5.00 (1 H, br.d, J = 8.3 Hz), 4.23-4.33
(1 H, m), 3.73 (3 H, s), 2.37 (2 H, t, J = 7.3 Hz), 2.36 (2 H, t, J = 7.3 Hz), 1.69-1.85 (1 H, m),
13
1
.49-1.67 (5 H, m), 1.44 (9 H, s), 1.21-1.37 (6 H, m), 0.90 (3 H, t, J = 7.5 Hz); C NMR (100
MHz, CDCl ) δ ppm: 211.4, 173.4, 155.4, 79.8, 53.4, 52.2, 44.7, 42.7, 32.7, 28.9 (2 C), 28.3,
3
-1
25.1, 23.6, 17.3, 13.7; IR (cm ), 3370, 1749, 1713, 1692, 1520, 1462, 1247, 1172; m/z (ES+)
+
found MH : 344.2437, C18
H
34NO
5
requires 344.2437.
General Procedure D: Intramolecular aza-Michael reactions
The cross-metathesis product 13 (1 eq.) was dissolved in CH
in Et O (1 M, 0.6 mol%) was added. After 19 h stirring the resulting solution was
concentrated under reduced pressure to give the product.
2 2
Cl (2 mL) and a solution of HCl
2
1
-tert-Butyl 2-methyl (2S,5R)-5-(2-oxopropyl)pyrrolidine-1,2-dicarboxylate (20a) & 1-tert-
butyl 2-methyl (2S,5S)-5-(2-oxopropyl)pyrrolidine-1,2-dicarboxylate (20b)
General procedure D using methyl (2S,5E)-2-([(tert-butoxy)carbonyl]amino)-7-oxooct-5-
-4
2
enoate 13a (32 mg, 0.112 mmol, 1 eq.) and 1 M HCl/Et O (6.6 × 10 mmol, 0.66 µL, 0.6
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mol%) in CH
2
Cl
2
(2 mL), after 19 h stirring at r.t. gave the title compounds 20a/b (32 mg,
0
.11 mmol, 100%), as an oil, in a ratio of (0.04 cis 20a, t
r
11.82 min: 0.96 trans 20b, t
r
11.67
1
min) based on GC and H NMR. [α]
D
-54.0 (c 1, CHCl
3
); R = 0.19 (20% EtOAc in petroleum
f
1
o
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
ether); H NMR (500 MHz, DMSO 100 C) δ ppm: 4.14-4.23 (2 H, m), 3.65 (3 H, s), 2.85 (1 H,
br.d, J = 16.2 Hz), 2.53 (1 H, dd, J = 16.2 and 9.7 Hz), 2.17-2.29 (1 H, m), 2.09 (3 H, s), 1.95-
13
2.06 (1 H, m), 1.78-1.85 (1 H, m), 1.55-1.64 (1 H, m), 1.36 (9 H, s); C NMR (125 MHz,
DMSO) δ ppm: 207.5 (207.4), 173.5 (173.0), 153.1 (153.4), 79.5 (79.8), 59.4 (59.1), 54.1
-
1
(
53.9), 52.3 (52.2), 47.2 (48.1), 30.6 (30.7), 28.6 (29.3), 28.3 (28.4), 27.9 (27.1); IR (cm ),
+
1752, 1703, 1396, 1210, 1165, 1126; m/z (ES+) found MH : 286.1661, C14
H
24NO
5
requires
13
2
86.1654. In the C NMR the signals due to the minor rotamer are in parentheses.
1
-tert-Butyl 2-methyl (2S,5R)-5-(2-oxobutyl)pyrrolidine-1,2-dicarboxylate (21a) & 1-tert-
butyl 2-methyl (2S,5S)-5-(2-oxobutyl)pyrrolidine-1,2-dicarboxylate (21b)
General procedure D using methyl (2S,5E)-2-([(tert-butoxy)carbonyl]amino)-7-oxonon-5-
-4
enoate 13b (30 mg, 0.1 mmol, 1 eq.) and 1 M HCl/Et O (6 × 10 mmol, 0.6 µL, 0.6 mol%) in
2
2 2
CH Cl (2 mL), after 19 h stirring at r.t. gave the title compounds 21a/b (30 mg, 100%) as a
solid, in a ratio of (0.02 cis , t
r
17.69 min: 0.98 trans, , t
r
17.40 min) based on GC of the crude
o
1
product, mp 52-54 C; [α] -50.5 (c 0.46, CHCl ); R = 0.22 (20% EtOAc in petroleum ether); H
D
3
f
o
NMR (500 MHz, DMSO 100 C) δ ppm: 4.22-4.16 (2 H, m), 3.65 (3 H, s), 2.84 (1 H, br.dd, J =
1
1
6.0 and 3 Hz), 2.52 (1 H, dd, J = 16.0 and 9.2 Hz), 2.41 (2 H, q, J = 7.4 Hz), 2.19-2.31 (1 H, m),
.96-2.08 (1 H, m), 1.78-1.85 (1 H, m), 1.55-1.63 (1 H, m), 1.36 (9 H, s), 0.96 (3 H, t, J = 7.3);
C NMR (125 MHz, DMSO) δ ppm: 209.9 (209.8), 173.5 (173.0), 153.1 (153.4), 79.5 (79.7),
9.4 (59.1), 54.2 (54.0), 52.3 (52.2), 46.0 (46.7), 35.8 (35.9), 28.6 (29.3), 28.3 (28.4), 27.9
1
3
5
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1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
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4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
-
1
(27.1), 7.94 (7.98); IR (cm ), 1745, 1705, 1396, 1366, 1212, 1175, 1123; m/z (ES+) found
+
13
MH : 300.1818, C15
5
H26NO requires 300.1811. In the C NMR signals due to the minor
rotamer are in parentheses.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1-tert-Butyl 2-methyl (2S,5R)-5-(2-oxopentyl)pyrrolidine-1,2-dicarboxylate (22a) & 1-tert-
Butyl 2-methyl (2S,5S)-5-(2-oxopentyl)pyrrolidine-1,2-dicarboxylate (22b)
General procedure D using methyl (2S,5E)-2-([(tert-butoxy)carbonyl]amino)-7-oxodec-5-
-4
enoate 13c (49 mg, 0.16 mmol, 1 eq.) and 1 M HCl/Et O (9 × 10 mmol, 0.9 µL, 0.6 mol%) in
2
CH
2 2
Cl (2 mL), after 19 h stirring at r.t. gave the title compounds 22a/b (49 mg, 0.16 mmol,
1
00%), as an oil, in a ratio of (0.02 cis, t
r
25.62 min: 0.98 trans, t
r
25.14 min) based on GC of
1
the crude product; [α] -56.0 (c 1.25, CHCl ); R = 0.18 (15% EtOAc in petroleum ether); H
D
3
f
o
NMR (500 MHz, DMSO 100 C) δ ppm: 4.15-4.22 (2 H, m), 3.65 (3 H, s), 2.84 (1 H, br.d, J =
1
6.1 Hz), 2.52 (1 H, dd, J = 16.1 and 9.5 Hz), 2.38 (2 H, t, J = 7.3 Hz), 2.19-2.30 (1 H, m), 1.96-
2.07 (1 H, m), 1.78-1.86 (1 H, m), 1.56-1.64 (1 H, m), 1.52 (2 H, sextet, J = 7.3 Hz), 1.36 (9 H,
13
s), 0.87 (3 H, t, J =7.4 Hz); C NMR (125 MHz, DMSO) δ ppm: 209.1 (209.0), 173.0 (172.6),
1
52.6 (152.9), 79.1 (79.3), 58.9 (58.7), 53.7 (53.5), 51.8 (51.7), 45.8 (46.6), 44.2 (44.3), 28.2
-1
(28.8), 27.8 (27.9), 27.5 (26.6), 16.5 (16.6), 13.5 (13.4); IR (cm ), 1751, 1699, 1392, 1258,
+
13
1
085, 1020, 795; m/z (ES+) found MH : 314.1982, C16
5
H28NO requires 314.1967. In the C
NMR signals due to the minor rotamer are in parentheses.
General procedure E: Boc deprotection of pyrrolidines 20b, 21b and 22b
2 2
The N-Boc protected compound was dissolved in CH Cl (4 mL). Neat TFA (50 eq.) relative to
the substrate was added and the reaction followed by TLC until the starting material has
disappeared. The solvent and excess TFA was then removed under reduced pressure to give
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the TFA salts. The salts were not sufficiently thermally stable for melting points to be
determined.
(2S,5S)-2-(Methoxycarbonyl)-5-(2-oxopropyl)pyrrolidin-1-ium trifluoroacetate (23)
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
General procedure E using 20b (88 mg, 0.31 mmol, 1 eq.) and TFA (1.2 mL, 15.5 mmol, 50
eq.) gave (2S, 5S)-2-(methoxycarbonyl)-5-(2-oxopropyl)pyrrolidin-1-ium trifluoroacetate 23
(
D 3 f
94 mg, 0.31 mmol, 100%) as a solid, mp decomp.; [α] -10.0 (c 1, CHCl ); R = 0.075 (20%
1
CHCl , 30% petroleum ether and 50% acetonitrile), H NMR (400 MHz, CDCl ) δ ppm: 4.48-
3
3
4
2
.75 (1 H, m), 3.94-4.08 (1 H, m), 3.86 (3 H, s), 3.18-3.37 (1 H, m), 2.93-3.13 (1 H, m), 2.53-
1
3
.67 (1 H, m), 2.19-2.36 (1 H, m), 2.22 (3 H, s), 2.04-2.18 (1 H, m), 1.85-2.00 (1 H, m); C
-1
NMR (100 MHz, CDCl ) δ ppm: 206.8, 169.7, 58.8, 57.1, 53.7, 44.1, 29.8, 29.5, 27.8; IR (cm ),
3
+
3
425, 1751, 1715, 1676, 1445, 1366, 1245, 1185; m/z (ES+) found M : 186.1125, C
9
H
16NO
3
1
requires 186.1130. In the H NMR there are additional signals in the low field range due to
the two acidic NH protons, and trace residual CF
depending on conditions.
3 2
CO H. The chemical shifts are very variable
(2S,5S)-2-(Methoxycarbonyl)-5-(2-oxobutyl)pyrrolidin-1-ium trifluoroacetate (24)
General procedure E using 21b (43 mg, 0.144 mmol, 1 eq.) and TFA (0.55 mL, 7.2 mmol, 50
eq.) gave (2S,5S)-2-(methoxycarbonyl)-5-(2-oxobutyl)pyrrolidin-1-ium trifluoroacetate 24
(
(
45 mg, 0.143 mmol, 99% yield) as a solid, mp decomp.; [α]
D
-6.1 (c 1.15, CHCl
3
); R
f
= 0.125
1
20% CHCl
3
, 30% petroleum ether and 50% acetonitrile); H NMR (400 MHz, CDCl
3
) δ ppm:
4
2
.55-4.80 (1 H, m), 3.92-4.04 (1 H, m), 3.88 (3 H, s), 3.22-3.38 (1 H, m), 2.93-3.08 (1 H, m),
.60-2.72 (1 H, m), 2.41-2.59 (2 H, m), 2.21-2.35 (1 H, m), 2.05-2.18 (1 H, m), 1.91-2.05 (1 H,
1
3
3
m), 1.08 (3 H, t, J = 7.1 Hz); C NMR (100 MHz, CDCl ) δ ppm: 209.2, 169.7, 58.7, 56.9, 53.7,
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1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
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4
5
5
5
5
5
5
5
5
5
5
6
-
1
43.1, 35.7, 30.1, 27.9, 7.3; IR (cm ), 1752, 1715, 1674, 1446, 1246, 1203, 1176; m/z (ES+)
+
1
3
found M : 200.1293, C10H18NO requires 200.1287. In the H NMR there are additional
signals in the low field range due to the two acidic NH protons, and trace residual CF
The chemical shifts are very variable depending on conditions.
3 2
CO H.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(
2S,5S)-2-(Methoxycarbonyl)-5-(2-oxopentyl)pyrrolidin-1-ium trifluoroacetate (25)
General procedure E using 22b (98 mg, 0.313 mmol, 1 eq.) and TFA (1.2 mL, 15.6 mmol, 50
eq.) gave (2S, 5S)-2-(methoxycarbonyl)-5-(2-oxopentyl) pyrrolidin-1-ium trifluoroacetate 25
(
100 mg, 0.31 mmol, 99% yield) as a solid, mp decomp.; [α]
D
-2.0 (c 1, CHCl
3
); R
f
= 0.15 (20%
1
CHCl
3
, 30% petroleum ether and 50% acetonitrile); H NMR (400 MHz, CDCl
3
) δ ppm: 4.62 (1
H, t, J = 7.8 Hz), 3.89-4.04 (1 H, m), 3.87 (3 H, s), 3.29 (1 H, dd, J = 18.7 and 9.1 Hz), 2.97 (1 H,
dd, J = 18.7 and 3.8 Hz), 2.56-2.67 (1 H, m), 2.35-2.55 (2 H, m), 2.20-2.34 (1 H, m), 2.03-2.16
1
3
(
1 H, m), 1.87-2.02 (1 H, m), 1.62 (2 H, sextet, J = 7.3 Hz), 0.92 (3 H, t, J = 7.3 Hz); C NMR
(100 MHz, CDCl
3
) δ ppm: 208.9, 169.7, 58.8, 57.2, 53.8, 44.4, 43.2, 29.9, 27.8, 16.8, 13.4; IR
-1
+
(
cm ), 1749, 1715, 1674, 1446, 1246, 1203, 1176; m/z (ES+) found M : 214.1439, C11
H
20NO
3
1
requires 214.1443. In the H NMR there are additional signals in the low field range due to
the two acidic NH protons, and trace residual CF
depending on conditions.
3 2
CO H. The chemical shifts are very variable
Acknowledgements
We thank the Kurdistan Regional Government for support (NS), and EPSRC for an equipment
grant (EP/L026872/1), and Dr V. Gulati for developing the iodine activation protocol for use in
copper-catalyzed allylation reactions.
Supporting Information
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Details for the X-ray structure determinations of compounds 21b, 23, 24 and 25, and a
1
13
combined cif file; H and C NMR spectra for 4, 5, 9-11, 13a-c, 14a-c, 15a-c, 16, 17a-c, 18a-c,
1
9a-c, 20b, 21b, 22b, and 23-25; GC Traces for 20a/20b, 21a/21b, and 22a/22b. This
10
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information is available free of charge via the Internet at http://pubs.acs.org.
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