close

Вход

Забыли?

вход по аккаунту

?

C7QO00891K

код для вставкиСкачать
View Article Online
View Journal
organic
chemistry
frontiers
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: C. Peter, P.
Geoffroy and M. Miesch, Org. Chem. Front., 2017, DOI: 10.1039/C7QO00891K.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Volume 3 | Number 1 | January 2016
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
ORGANIC
CHEMISTRY
FRONTIERS
http://rsc.li/frontiers-organic
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
rsc.li/frontiers-organic
Please do
not adjustFrontiers
margins
Organic
Chemistry
Page 1 of 5
View Article Online
DOI: 10.1039/C7QO00891K
Journal Name
ARTICLE
Highly diastereoselective access to polyfunctionalized 1,3oxazines promoted by Brønsted/Lewis acids
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
a
a
Clovis Peter , Philippe Geoffroy and Michel Miesch
a*
The Brønsted/Lewis acid catalyzed reaction of pyrrolidone, piperidone and isoindolinone derivatives tethered to α,β unsaturated ketones or aldehydes afforded exclusively in high diastereoselectivities and yields polyfunctionalized 1,3oxazines.
Introduction
The reactivity of N-acyliminium ions with nucleophiles
represents one of the most powerful method for the
1
formation of C-C and C-heteroatom bonds. Among the diverse
methodologies reported in the literature, some studies dealing
with the reactivity of pyrrolidones/piperidones tethered to
activated olefins were reported. Particularly, halo-Michael
aldol (HMA) and Morita-Baylis-Hillman (MBH) reactions
allowed
an
access
to
a
large
variety
of
indolizidinones/pyrrolizidinones/azepinones as it was reported
2
3
4
5
by Taber (R=OMe), Aggarwal, Tamura and Figueredo (R=H).
Nevertheless, it clearly came out from these literature data
that the reactivity of α,β-unsaturated ketones tethered to Nsubstituted heterocyclic derivatives was not documented apart
the results reported by Figueredo et al.5 Being already involved
in studies concerning HMA and MBH reactions of
cycloalkanones (-diones) tethered to α,β-unsaturated
ketones,6 we became interested in the reactivity of α,βunsaturated ketones tethered to α-alkyloxyamides.
Herein we disclose a highly diastereoselective synthesis of
polyfunctionalized 1,3-oxazines via Brønsted or Lewis acids
catalyzed reactions starting from α,β-unsaturated ketones
tethered to different heterocycles, the formation of
indolizidinones, pyrrolizidinones and azepinones being never
observed (Scheme 1).
Scheme 1. Reactivity of N-substituted heterocycles tethered to
activated olefins toward Lewis/Brønsted acids
Results and discussion
We started our studies using our reaction conditions
previously developed for HMA and MBH reactions of
cycloalkanones (-diones) tethered to α,β-unsaturated
ketones.6
At atmospheric pressure, no reaction took place when nBu3P or PPh3 were added to compound 1a. At high pressure (9
kbar) or in the presence of TiCl4, decomposition occurred took
place. Thereafter, the MBH reaction was carried out in the
presence of TMSOTf/Me2S, reaction conditions which were
already used to achieve efficient inter and intramolecular MBH
reactions.7 The formation of the expected MBH product 3
occurred in a poor yield, this being in good accordance with
the previous results reported by Figueredo et al..5 Finally, to
activate the MBH reaction, a Lewis acid, ie BF3·Et2O, was added
to the reaction mixture after addition of n-Bu3P. A complex
mixture of compounds was obtained from which it was
possible to isolate a very low amount of 1,3-oxazine 2a (yield:
~7%). These preliminary results prompted us to investigate the
reaction conditions allowing the formation of 1,3-oxazines, this
being, to best of our knowledge, not yet reported (Scheme 2).
J. Name., 2013, 00, 1-3 | 1
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins
Organic Chemistry Frontiers Accepted Manuscript
Published on 26 October 2017. Downloaded by University of Newcastle on 26/10/2017 07:01:16.
1
2
3
4
5
6
7
8
9
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
Please do
not adjustFrontiers
margins
Organic
Chemistry
Page 2 of 5
View Article Online
DOI: 10.1039/C7QO00891K
Journal Name
Scheme 2. HMA and MBH reactions starting from compound
1a
Thus, in the presence of 1 equiv BF3·Et2O, a highly
diastereoselective reaction occurred affording exclusively 1,3oxazine 2a in high yield. The structure of the latter was
secured by X-ray analysis (Scheme 3).8
Scheme 3. Lewis acid catalyzed reaction leading to 1,3-oxazine
2a
entry
acid (equiv)
R
solvent
yield
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
BF3·Et2O (0.1)
BF3·Et2O (0.2)
BF3·Et2O (0.5)
BF3·Et2O (1.0)
BF3·Et2O (1.0)
BF3·Et2O (1.0)
TiCl4 (1.0)
FeCl3 (1.0)
SnCl2 (1.0)
InCl3 (1.0)
ZnCl2 (1.0)
Me3Al or MgCl2 (1.0)
CeCl3·7 H2O (1.0)
p-TsOH·H2O (0.2)
p-TsOH·H2O (0.5)
p-TsOH·H2O (1.0)
p-TsOH anhydrous (0.5)
CSA (1.0)
Tf2NH (1.0)
p-TsOH·H2O (0.5)
p-TsOH·H2O (0.5)
Et
Et
Et
Et
Et
Et
Et
Et
Et
Et
Et
Et
Et
Et
Et
Et
Et
Et
Et
OBn
OTBS
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
toluene
CH3CN
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
65%
75%
95%
85%
16%
29%
b
41%
62%
11%
49%
c
c
d
69%
83%
80%
82%
e
41%
f
39%
93%
81%
a
Next, a set of reaction parameters was examined including
solvents and different Brønsted/Lewis acids, the reaction
taking always place at room temperature. When the reaction
was carried out in the presence of distilled BF3·Et2O in dry
dichloromethane, compound 2a was isolated, the highest yield
being obtained with 50 mol% BF3·Et2O (entries 1-4). In
acetonitrile or in toluene the yields decreased (entries 5-6).
Different Lewis acids were utilized but either decomposition
occurred (entry 7) or the yields were moderate (entries 8-11)
or starting material was recovered (entries 12-13). Using
Brønsted acids instead of Lewis acids, we noticed that the
addition of p-TsOH monohydrate (p-TsOH·H2O) to compound
1a led readily to 1,3-oxazine 2a (entries 14-16). Moreover, the
reaction time was shorter compared to the previous reactions,
the best being to run the reaction in the presence of 50 mol%
p-TsOH·H2O during 7 h at room temperature. It has also to be
noted that the formation of compound 2a took also readily
place in the presence of 50 mol% anhydrous p-TsOH.9 Thus,
the presence or absence of water does not influence the
progress of the reaction (entry 17). In the presence of CSA
(entry 18) or Tf2NH (entry 19), the yields were moderate and
starting material was recovered. 1,3-oxazine 2a was also
formed starting respectively from compounds 1k and 1l
bearing respectively a 5-OTBS or a 5-OBn group (entries 2021). Finally, when compound 2a was submitted to the same
reaction conditions (p-TsOH·H2O, 7h, 25 °C), no changes
occurred indicating that 2a is the most thermodynamically
stable compound.
All reactions were carried out with distilled solvents and reactants, the
work-up of the reactions was achieved with a saturated aqueous NH4Cl
solution; reaction time: 24 h for Lewis acids (entries 1-13); 7 h for Brønsted
acids (entries 14-21). bdecomposition. cstarting material (sm) was recovered.
d
17% sm was recovered. e28% sm was recovered. f56% sm was recovered.
Consequently, it clearly came out from our reaction
parameters studies, that the formation of 1,3-oxazine 2a was
most easily achieved in the presence of 50 mol% p-TsOH·H2 O
in dichloromethane, this reaction condition being highly
convenient and easy-to-run.
The scope and limitations of our reaction were then
investigated. Starting from pyrrolidone, piperidone and
isoindolinone derivatives 1a-j,10 the diastereoselective
formation of 1,3-oxazines 2a-j always took place smoothly
even if the tether was bearing an aldehyde (Scheme 4).
Scheme 4. Brønsted acid catalyzed reactions leading to
pyrrolo, piperido and isoindolo-1,3-oxazines 2a-j
Table 1. Reaction conditions optimization leading to-1,3oxazine 2aa
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins
Organic Chemistry Frontiers Accepted Manuscript
Published on 26 October 2017. Downloaded by University of Newcastle on 26/10/2017 07:01:16.
1
2
3
4
5
6
7
8
9
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
ARTICLE
Please do
not adjustFrontiers
margins
Organic
Chemistry
Page 3 of 5
View Article Online
DOI: 10.1039/C7QO00891K
Journal Name
ARTICLE
It was mentioned that 1,3-oxazines can be obtained by acid
catalyzed reactions of heterocycles (ie pyrrolidone etc…) Ntethered to an alkanol or an acetal moiety as pro-nucleophiles
or to unactivated olefins. However, to the best of our
knowledge, no reports disclosed the access of 1,3-oxazines
11-15
starting from activated olefins tethered to heterocycles.
To set-up an asymmetric synthesis of 1,3-oxazine
derivatives, we started from diethyl (L)-tartrate which was
transformed into the pyrrolidone (+)-4 according to literature
16
procedures. However, the protection of the 5-hydroxyl group
as an ethyl ether 4a did not take place using usual reaction
conditions (p-TsOH·H2O, EtOH). Nevertheless, after protection
of the hydroxyl group as a TBS ether, the resulting pyrrolidone
(+)-5 was readily obtained. The α,β-unsaturated ketones were
installed via a Grubbs cross metathesis reaction, affording the
expected pyrrolidones (+)-6-(+)-8. After treatment with 50
mol% p-TsOH·H2O, the corresponding 1,3-oxazines (+)-9-(+)-11
were isolated as a mixture of diastereomers.17 Otherwise,
when TBAF was added to pyrrolidones (+)-6-(+)-8, the
formation of the corresponding alcoolate A took place. The
latter underwent a stereoseselective oxa-Michael addition to
the electrophilic double bond to yield 1,3-oxazines (+)-9a-(+)11a (Scheme 5).18
directly undergo an oxa-Michael addition to the α,βunsaturated ketone to give oxonium 14. The stereochemical
outcome of the reaction was rationalized on the basis of the
intermediates depicted in scheme 6 where the nucleophilic
addition of the alcohol occured through a chair-like transition
state in which the propanone substituent is in the equatorial
position. Moreover, when the reaction was carried out starting
from compound 1l (R=OBn), the quantitative recovery of
benzyl alcohol took place. Thus, it’s reasonable to invoke two
different routes leading to the corresponding 1,3-oxazines
either via the N-acyliminium ion or via the direct formation of
oxonium 14 (Scheme 6).
Scheme 6. Proposed mechanism for the formation of 1,3oxazine 2a
R=Et, TBS, Bn
O
12
+ ROH
O
R
Brønsted/Lewis acid
O
O
N
O
R
13
O
14
direct
oxa-Michael
O
O
R
work-up (NH4Cl sat)
N
O
O
O
2a
(L)-diethyl tartrate
O
O
O
p-TsOH—H2O R
X
EtOH
R
R
N
R
OEt
4a
R1
R
N
imidazole
90%
R
OTBS (+)-5
O
O
TBAF
1
R
N
R
TBSCl
N
OH (+)-4
O
Grubbs II
O
O
1a
N
N
O
Scheme 5. Formation of 1,3-oxazines(+) – 9 - (+) - 11
R=OBn
N
O
OTBS
(+)-6 R1=CH3 87%
(+)-7 R1=Ph 64%
(+)-8 R1=p-OMeC6H4 76%
N
R
THF
0 °C
5 min
R
R
O
R
H2
R1
A
(+)-9a (R1=CH3 72%)
(+)-10a (R1=Ph 63% )
(+)-11a (R1=p-OMeC6H4 66% )
p-TsOH—H2O
(50 mol%)
CH2Cl2, 25 °C, 7 h
O
O
For the formation of the two isomers (+)-9a and (+)-9b, it
could be suggested that the first intermediate of the reaction
is the N-acyliminium ion 15. Thereafter, the latter could be in
equilibrium with the two pyrrolidone isomers 16 and (+)-6 that
evolve via a direct oxa-Michael reaction to give the oxonium
derivatives 17/18. Finally, after hydrolysis, 1,3-oxazines (+)-9a
and (+)-9b were obtained (Scheme 7).
Scheme 7. Proposed mechanism: direct oxa-Michael for the
formation of 1,3-oxazine (+)-9a and (+)-9b
O
N
O
+
R1
R
H'2
N
O
R1
R H1
R H'1
1
(+)-9a + (+)-9b [R =CH3 83% (dr= 1.2 : 1)]
(+)-10a + (+)-10b [R1=Ph 75% (dr= 1.2 : 1)]
(+)-11a + (+)-11b [R1=p-OMeC6H4 66% (dr= 1.05 : 1)]
O
O
To explain our results, the following mechanism proposal
could be suggested. It was reasonable to postulate that the
addition of Brønsted/Lewis acids (50 mol%) to pyrrolidone 1a
induces the formation of N-acyliminium ion 12. Thereafter,
two different pathways can be considered. First, the alcohol
which is formed in situ, evolves through a 1,4-oxa-Michael
addition19 toward to the α,β-unsaturated ketone to give
intermediate 13. The latter undergoes an addition to the Nacyliminium intermediate affording oxonium cation 14. The
latter led to pyrrolo-1,3-oxazine 2a after hydrolysis of the
reaction mixture with a saturated aqueous NH4Cl solution.
Second, it cannot be excluded that the starting material 1a,
which is in equilibrium with the N-acyliminium ion 12, could
As above, it cannot be excluded that 1,4-addition of silanol
to the electrophilic double bond took place, leading to
intermediates 19/20. The latter underwent an intramolecular
addition to the N-acyliminium ion to give the corresponding
oxonium derivatives 21/22 which, after hydrolysis, afforded
20
1,3-oxazines (+)-9a and (+)-9b (Scheme 8).
J. Name., 2013, 00, 1-3 | 3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins
Organic Chemistry Frontiers Accepted Manuscript
Published on 26 October 2017. Downloaded by University of Newcastle on 26/10/2017 07:01:16.
1
2
3
4
5
6
7
8
9
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
Please do
not adjustFrontiers
margins
Organic
Chemistry
Page 4 of 5
View Article Online
DOI: 10.1039/C7QO00891K
Journal Name
Scheme 8. Proposed mechanism: 1,4 addition of alcohol
leading to the formation of 1,3-oxazine (+)-9a and (+)-9b
2
3
R=TBS
O
O
N
1,4-oxa-Michael
2
2
O
OR
O
N
BnO
BnO
OBn
(+)-6
OR
2
BnO
OBn
O
OR
+
OBn
O
N
5
BnO
OBn
20
19
15
O
(+)-9a + (+)-9b
NH4Cl sat
O
BnO
N
22
H
O
R
H
OBn
4
2
N
O
+ ROH
O
6
O
+
O
N
O
H
BnO
21
H
R
7
OBn
It should be emphasized that 1,3-oxazines derivatives show
a wide range of biological activities21 and that 1,3-oxazine
scaffolds were found in bioactive natural products like the
araguspongin/xestospongin alkaloids22 and sinensilactam.23
Therefore, the development of new strategies giving access to
these scaffolds are of interest (Figure 1).
8
9
10
Figure 1. 1,3-oxazines scaffolds present in natural products.
11
12
13
14
Conclusions
In summary, we have set up an easy to run Brønsted/Lewis
acid catalyzed reaction starting from pyrrolidones, piperidones
and
isoindolinones
tethered
to
α,β-unsaturated
ketones/aldehydes and affording exclusively in high
diastereoselectivities and yields 1,3-oxazines. Further
explorations of the reactivity of the latter as well as synthetic
applications are in progress and will be reported in due course.
15
16
17
Conflicts of interest
“There are no conflicts to declare”.
18
Acknowledgements
Support for this work was provided by CNRS and the Université
de Strasbourg. CP thanks MRT for financial support. The
authors thank Dr. Jennifer Wytko for the preparation of the
manuscript.
19
Notes and references
1
(a) A. Daïch, A. Ghinet and B. Rigo in: Comprehensive
Organic Synthesis 2nd edition (Eds: G. A. Molander, P.
Knochel), Oxford, UK, Elsevier, 2014,vol. 2, chapter 2.17, 682;
(b) P. Wu and T. E. Nielsen, Chem. Rev., 2017, 117, 7811.
20
D. F. Taber, R. S. Hoerrner and M. D. Hagen, J. Org. Chem.,
1991, 56, 1287.
E. L. Myers, J. G. de Vries and V. K. Aggarwal, Angew. Chem.
Int. Ed., 2007, 46, 1893.
(a) H. Kurasaki, I. Okamoto, N. Morita and O. Tamura, Chem.
Eur. J., 2009, 15, 12754; (b) H. Kurasaki, I. Okamoto, N.
Morita and O. Tamura, Org. Lett., 2009, 11, 1179.
J. Alonso-Fernandez, C. Benaiges, E. Casas, R. Alibés, P.
Bayon, F. Busqué, A. Alvarez-Larena and M. Figueredo,
Tetrahedron, 2016, 72, 3500.
(a) B. Ressault, A. Jaunet, P. Geoffroy, S. Goudedranche and
M. Miesch, Org. Lett., 2012, 14, 366. (b) Y. Wang, A. Jaunet,
P. Geoffroy and M. Miesch, Org. Lett., 2013, 15, 6198.
T. Kataoka and H. Kinoshita, Eur. J. Org. Chem., 2005, 45. (b)
S. Uehira, Z. Han, H. Shinokubo and K. Oshima, Org. Lett.,
1999, 1, 1383; (c) K. Yagi, T. Turitani, H. Shinokubo and K.
Oshima, Org. Lett., 2002, 4, 3111; (d) Z. Han, S. Uehira, H.
Shinokubo and K. Oshima, J. Org. Chem., 2001, 66, 7854.
The structure of compound 2a was secured by X-ray analysis
CCDC 1469808.
Anhydrous p-TsOH was obtained by drying under high
vacuum (100 °C, 0.01 mmHg) commercially available pTsOH·H2O.
For the synthesis of compounds 1a-1j see supporting
informations.
J. Dijkink and W. N. Speckamp, Tetrahedron Lett., 1975, 46,
4047; (b) Review: W. N.,Speckamp and M. J. Moolenaar,
Tetrahedron, 2000, 56, 3817.
(a) K. Indukuri, R. Unnava, M. J. Deka and A. K. Saikia, J. Org.
Chem., 2013, 78, 10629. (b) A. K Saikia,. K. Indukuri and J.
Das, Org. Biomol. Chem., 2014, 12, 7026.
(a) J. Sikoraiova, S. Marchalin, A. Daïch and B. Decroix,
Tetrahedron Lett., 2002, 43, 4747. (b) P. Pigeon, J. Sikoraiova,
S. Marchalin and B. Decroix, Heterocycles, 2002, 56, 129.
(a) D. Koley, K. Srinivas, Y Krishna and A. Gupta, RSC Adv.,
2014, 4, 3934. (b) D. Koley, Y Krishna, Y. Srinivas, A. A Khan
and R. Kant, Angew. Chem. Int. Ed., 2014, 53, 13196. (c) K.
Srinivas, N. Singh, D. Das and D. Koley, Org. Lett., 2017, 19,
274; (d) N. Liu, H-Y. Wang, W. Zhang, Z-H. Jia, I. A. Guzei, HD. Xu and W. Tang, Chirality, 2013, 25, 805.
B. P. Wijnberg and W. N. Speckamp, Tetrahedron Lett., 1981,
22, 5079.
W. Thaharn, T. Bootwicha, D. Soorukram, C. Kuhakarn, S.
Prabpai, P. Kongsaeree, P. Tuchinda, V. Reutrakul, and M.
Pohmakotr, J. Org. Chem., 2012, 77, 8465.
The analysis of the NMR spectra of compounds 9a/9b
revealed that the coupling constant between H1 /H2 and
H’1/H’2 was respectively 3.0 Hz and 5.1 Hz. Therefore the
relationship between H1/H2 is cis and trans for H’1/H’2. This
clearly indicated that the configuration of the carbon located
at the ring junction (α to the nitrogen) was inverted. Thus,
the formation of the N-acyliminium 15 took place leading to
a mixture of two diastereomers (+)-6 and 16.
The treatment of compound 1k with TBAF afforded 1,3oxazine 2a in 86% yield, the latter resulting from an oxaMichael addition.
(a) C. F. Nising and S. Bräse, Chem. Soc. Rev., 2012, 41 ,988;
(b) As mentioned by Nising and Bräse, the major drawbacks
of an oxa-Michael addition are reversibility of the alcohol
addition as well as the poor nucleophilicity of the employed
alcohols: here, the exclusive formation of 1,3-oxazines
clearly indicate again that the latter are the most
thermodynamically stable compounds.
(a)The acidic treatment of compound 6 could also induce a
deprotection of the TBS ether leading to the corresponding
hydroxyl derivative which evolves according to the same
pathways indicated in schemes 7 and 8; (b) we were unable
to isolate compound 02 bearing a free 5-hydroxyl group (5-
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins
Organic Chemistry Frontiers Accepted Manuscript
Published on 26 October 2017. Downloaded by University of Newcastle on 26/10/2017 07:01:16.
1
2
3
4
5
6
7
8
9
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
ARTICLE
Please do
not adjustFrontiers
margins
Organic
Chemistry
Page 5 of 5
View Article Online
DOI: 10.1039/C7QO00891K
Journal Name
ARTICLE
OH instead of 5-OEt; see ESI). However, starting from diethyl
tartrate, it was possible to isolate compound 6a bearing a
free 5-hydroxyl group and the p-TsOH treatment gave the
corresponding 1,3-oxazine in high yield (83%; 5:1)
21 B. P. Mathew, A. Kumar, S. Sharma, P. K Shukla and M. Nath,
Eur. J. Med. Chem., 2010, 45, 1502.
22 (a) Y. Venkateswarlu, and M. Venkata Rami Reddy, J. Nat.
Prod., 1994, 57, 1283. (b) K. Y. Orabi, K. A. El Sayed, M. T
Hamann,. D. C. Dunbar, M. S. Al-Said, T. Higa and M. Kelly, J.
Nat. Prod., 2002, 65, 1782. (c) S-S. Moon, J. B. MacMillan, M.
M. Olmstead, T. A .Ta, I. N. Pessah and T. F. Molinsky, J. Nat.
Prod., 2002, 65, 249. (d) T. Oka, K. Sato, M. Hori, H. Ozaki and
H. Karaki, Br. J. Pharmacol., 2000, 130, 650.
23 Q. Luo, L. Tian, L. Di, Y-M. Yan, X-Y. Wei, X-F. Wang and Y-X.
Cheng, Org. Lett., 2015, 17, 1565
Organic Chemistry Frontiers Accepted Manuscript
Published on 26 October 2017. Downloaded by University of Newcastle on 26/10/2017 07:01:16.
1
2
3
4
5
6
7
8
9
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
J. Name., 2013, 00, 1-3 | 5
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins
Документ
Категория
Без категории
Просмотров
2
Размер файла
642 Кб
Теги
c7qo00891k
1/--страниц
Пожаловаться на содержимое документа