Fe2(CO)9-mediated [5+1] cycloaddition of vinylcyclopropanes and CO for the synthesis of α, β-cyclohexenones

Article abstract of DOI:10.1016/j.tet.2016.01.046

A Fe₂(CO)₉-mediated [5+1] cycloaddition of vinylcyclopropanes (VCPs) and CO to α, β-cyclohexenones has been developed. The reaction can tolerate aryl and aliphatic groups at the α-position of VCPs, while VCP substrates with vinyl or alkynyl substitutions are not suitable ones. In addition, this reaction can also be used to synthesize bicyclic rings if an aryl group is attached to the vinyl moiety of the substrate. Compared to the Fe(CO)₅-mediated [5+1] reaction, the use of cheap and safe Fe₂(CO)₉ and abandoning the photo-irradiation conditions are the two major advantages of the present method.

Full text of DOI:10.1016/j.tet.2016.01.046

Tetrahedron xxx (2016) 1e4
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Fe2(CO)9-mediated [5þ1] cycloaddition of vinylcyclopropanes and
CO for the synthesis of a, b-cyclohexenones
*
Cheng-Hang Liu, Zhe Zhuang, Sritama Bose, Zhi-Xiang Yu
Beijing National Laboratory for Molecular Sciences (BNLMS), Key Laboratory of Bioorganic Chemistry and Molecular Engineering, College of Chemistry,
Peking University, Beijing 100871, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A Fe2(CO)9-mediated [5þ1] cycloaddition of vinylcyclopropanes (VCPs) and CO to
a
,
b
-cyclohexenones
Received 7 December 2015
Received in revised form 22 January 2016
Accepted 26 January 2016
Available online xxx
has been developed. The reaction can tolerate aryl and aliphatic groups at the
a-position of VCPs, while
VCP substrates with vinyl or alkynyl substitutions are not suitable ones. In addition, this reaction can also
be used to synthesize bicyclic rings if an aryl group is attached to the vinyl moiety of the substrate.
Compared to the Fe(CO)5-mediated [5þ1] reaction, the use of cheap and safe Fe2(CO)9 and abandoning
the photo-irradiation conditions are the two major advantages of the present method.
Ó 2016 Elsevier Ltd. All rights reserved.
Keywords:
Fe2(CO)9
5þ1
Cycloaddition
Vinylcyclopropane
CO
1. Introduction
more advantageous in terms of costs and sustainability. In 2005, de
Meijere’s group reported that Co2(CO)8 can mediate stoichiomet-
During the last 100 years, many reactions and strategies to
synthesize the ubiquitously found six-membered carbocycles have
been discovered and developed. Among them, the most widely
used reaction is the DielseAlder reaction between dienes and
dienophiles.1 But the DielseAlder reaction and other existing
methods could be inefficient to reach six-membered carbocycles
that have substitution patterns and stereochemistries unmatched
with the requirements of the known reactions and methods. Con-
sequently, it is significant to develop new reactions and methods to
access six-membered carbocycles, which can power the arsenal of
synthetic chemists so that the synthesis of the target molecules
could have more chances to reach ideal synthesis.2
rically or catalytically (under CO balloon pressure) [5þ1] cycload-
dition under mild conditions (usually at room temperature).4a In
their work, the rather special vinylcyclopropanes (VCPs), in which
the double bond of VCP is part of a methylenecyclopropane (MCP),
show higher reactivity due to the enhanced nucleophilicity of the
MCP moiety. Iwasawa’s group also reported the Co2(CO)8-mediated
[5þ1]
transformation
of
allenylcyclopropanols
to 1,4-
hydroquinones, where formation of the aromatic compounds
could be the driving force for the success of this reaction.7
Transition metal-mediated or -catalyzed [5þ1] cycloadditions of
vinylcyclopropanes/allenylcyclopropanes and CO has emerged re-
cently as alternative approaches to the synthesis of six-membered
cyclohexenones.3 The efficiency of these reactions towards the
construction of important skeletons with six-membered carbo-
cycles has been demonstrated by several groups. Typically, high-
price noble metals such as Rh4,5 and Ir6 play the leading role in
the [5þ1] cycloadditions (Scheme 1a). Replacing these expensive
and potentially toxic metals by inexpensive, earth-abundant, en-
vironmentally benign, and less toxic metals like Co and Fe would be
Scheme 1. (a) Our group’s Rh-catalyzed [5þ1] cycloaddition. (b) Iron-mediated photo-
[5þ1] cycloaddition. (c) This work.
* Corresponding author. E-mail address: yuzx@pku.edu.cn (Z.-X. Yu).
http://dx.doi.org/10.1016/j.tet.2016.01.046
0040-4020/Ó 2016 Elsevier Ltd. All rights reserved.
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C.-H. Liu et al. / Tetrahedron xxx (2016) 1e4
In contrast, cheap iron-mediated photo-[5þ1] reaction of VCPs
a transformation under the balloon-pressured CO gas had no ben-
efit for the [5þ1] reaction (Table 1, entries 16e18). Very similar
result was obtained when Fe3(CO)12 (instead of Fe2(CO)9) was used
under the same reaction conditions (Table 1, entry 19). Therefore,
we chose the reaction conditions in entry 6 of Table 1 as the optimal
conditions for Fe-mediated [5þ1] reaction.
and CO has a broad reaction scope.8,9 The iron-mediated [5þ1]
cycloaddition was originally developed by Sarel’s group,10 in which
they used Fe(CO)5 or Fe2(CO)9 under ultraviolet irradiation condi-
tion.11,12 After that, Taber’s group further advanced photo-
irradiated and iron-mediated [5þ1] cycloaddition13aec and ap-
plied such a methodology to the total synthesis of natural
products13def (Scheme 1b). However, a limitation in both the
original and modified iron-mediated [5þ1] cycloadditions is that
the reaction had to be carried out by photoirradiation, which is
difficult for reaction scale-up. Another drawback of the photo-
irradiated and iron-mediated [5þ1] cycloadditions is the use of
toxic and volatile Fe(CO)5. Therefore, we were interested in de-
veloping a new iron-mediated [5þ1] reaction of VCPs and CO that
needs neither difficultly handled Fe(CO)5 nor photoirradiation
conditions.
Table 1
Optimization of the reaction conditions
Entrya
Solvent
T (ꢀC)
t (h)
Yield (%)b
1
2
3
4
5
6
7
8
iPrOH
nPrOH
tamylOH
tBuOH
tBuOH
tBuOH
HFIP
THF
DME
Dioxane
CPME
Toluene
DCE
90
90
90
90
90
90
60
60
90
90
90
90
90
Reflux
90
90
90
90
90
1
4
4
4
7
12
3
4
4
8
53c
62d
49
65
70
80
3
58
32
58
41
44
59
13e
df
76
64
34
79
We noticed that Fe2(CO)9 is a cheap14 and much easily handled
solid. Fe2(CO)9 is also regarded as precursor of Fe(CO)4,15a which is
the active species in the Fe(CO)5-mediated photo-[5þ1] reaction.
We also found that stoichiometrical Fe2(CO)9 has been used in the
carbonylation reactions such as PausoneKhand reaction15,16 and
[4þ1] cycloaddition of allenyl imines and CO17 under
photoirradiation-free conditions. Therefore, we hypothesized that
the original photo-irradiated Fe(CO)5-mediated [5þ1] reaction of
VCPs and CO could be advanced to a Fe2(CO)9-mediated [5þ1] re-
action without photoirradiation.18 We report here our realization of
such a Fe2(CO)9-mediated thermal [5þ1] cycloaddition for the
9
10
11
12
13
14
15
16g
17h
18h,i
19j
5
6
7
3
MeCN
DMF
construction of a, b-cyclohexenones (Scheme 1c).
6
tBuOH
tBuOH
tBuOH
tBuOH
12
12
12
12
2. Results and discussion
We first screened the reaction conditions using the easily ac-
cessible VCP 1a as the standard substrate and Fe2(CO)9 as the me-
diator without using photoirradiation. The [5þ1] reaction can give
a
The reaction was performed in 0.3 mmol scale and 2 mL solvent was used.
Isolated yields.
b
c
d
e
f
Byproduct 4a can be detected by 1H NMR.
Byproduct 5a can be detected by 1H NMR.
Large amount of the substrate 1a remained.
Complex mixture.
both unconjugated and conjugated cyclohexenones. To obtain a, b-
cyclohexenone 2a exclusively, after the accomplishment of the
[5þ1] cycloaddition, DBU was added to the reaction solution and
stirred at room temperature for 30 min to realize the complete
isomerization. Initially, the reaction was performed using iPrOH as
solvent and stirred at 90 ꢀC for 1 h. The desired product 2a was
isolated in a moderate yield and a byproduct 4a was detected (Table
1, entry 1). Alcohol 4a is the reductive product of the unconjugated
intermediate 3a and may be formed by the iron-catalyzed hydro-
gen transfer from iPrOH.19 Apart from the reductive byproduct 4a,
some unidentified byproducts with low polarity similar to the
substrate 1a, were also observed from the TLC plate. We proposed
that such low-polar byproducts might originate from the heat-
induced rearrangement of VCP 1a.20 When nPrOH was used as
the solvent, the reaction yield was increased to 62%, together with
a byproduct, ketal 5a, which can be isolated (Table 1, entry 2). To
avoid the formation of byproducts 4a and 5a, we chose tertiary
alcohols such as tamylOH (tert-amyl alcohol) and tBuOH as the
solvents, finding that the yield could be increased to 65% when the
g
h
i
0.5 equiv Fe2(CO)9 was used.
0.2 equiv Fe2(CO)9 was used.
The reaction was performed under the CO atmosphere (1 atm).
1 equiv Fe3(CO)12 was used instead of Fe2(CO)9.
j
The reaction scope of the iron-mediated [5þ1] cycloaddition
under the optimal reaction conditions was studied (Table 2 and
Fig. 1). It was found that the electronic properties of the sub-
stitutions in the benzene rings of aryl-substituted VCPs had little
effect on the yields of the [5þ1] reactions (Table 2, 2beg). Besides
the phenyl group, both electron-withdrawing and -donating
groups gave good yields. The position of the substitutions on the
aryl ring of the substrate had limited effect on the outcome of the
reaction. We found that para-, meta- and ortho-methoxy
substituted substrates gave similar yields (Table 2, 2gei). We also
tried the naphthyl-substituted substrates 1j and 1k, finding that the
corresponding products 2j and 2k were obtained in moderate
yields. In addition, heterocyclic aryl substituted substrate 1l could
also give the cyclohexenone product in a good yield when it was
subjected to the iron-mediated [5þ1] reaction.
t
reaction was performed in BuOH (Table 1, entry 4). Further pro-
longing the reaction time led to the increase of the reaction yield of
the desired product 2a to 80%, accompanied by a trace amount of
low-polar rearrangement product (Table 1, entry 6). We also
screened several other solvents such as HFIP (hexa-
fluoroisopropanol), ethers, toluene, DCE and acetonitrile (Table 1,
entries 7e15). HFIP and acetonitrile were found to be inefficient for
the present transformation as only a trace amount of target [5þ1]
product could be isolated in these reaction systems. In ether sol-
vents, the transformation was slow and some other unidentified
byproducts were observed. The [5þ1] reaction performed in tolu-
ene or DCE only gave moderate yields. We also observed that, re-
ducing the equivalent of Fe2(CO)9 or carrying out such
Apart from the aryl substituted substrates, alkyl substituted VCP
substrates were also synthesized and tested for the present [5þ1]
cycloaddition reaction (Table 2, 2mep). Moderate yields could be
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C.-H. Liu et al. / Tetrahedron xxx (2016) 1e4
3
Table 2
Scope of the [5þ1] reaction
moiety and subjected it to the [5þ1] reaction. To our delight, the
corresponding bicyclic product 2x could be isolated in 60% yield
(Scheme 2). This result implied that the Fe2(CO)9-mediated [5þ1]
reaction could be used to synthesize some structurally complicated
skeletons.
Scheme 2. [5þ1] reaction of bicyclic compound 1x.
3. Conclusion
In conclusion, we have developed an efficient photoirradiation-
free Fe2(CO)9-mediated [5þ1] cycloaddition to synthesize conju-
gated cyclohexenones from vinylcyclopropanes and CO. The re-
action tolerates aryl and aliphatic groups at the a-position of VCPs,
while VCP substrates with vinyl or alkynyl substitutions are not
suitable substrates. Bicyclic ring can also be synthesized for VCP
with an aryl substitution in the vinyl moiety (see 1x). Although the
substrate scope of Fe2(CO)9-mediated [5þ1] cycloaddition, com-
pared to the photo-irradiated Fe(CO)5-mediated [5þ1] reaction, is
not satisfactory, the use of cheap and safe Fe2(CO)9 and abandoning
the photo-irradiation conditions are the two major advantages of
the present method.
4. Experimental section
4.1. General information
Fig. 1. Some unsuccessful substrates.
Synthetic reagents were purchased from Acros, Aldrich, and Alfa
Aesar and used without further purification unless otherwise in-
dicated. Analytical pure tBuOH was used directly. Fe2(CO)9 was
stored in glove box at ꢁ20 ꢀC and weighted in the glovebox. NMR
spectra were measured on Bruker ARX 400 (1H at 400 MHz, 13C at
101 MHz) nuclear magnetic resonance spectrometers. 1H NMR
spectra are reported relative to Me4Si (0.00 ppm). Data for 13C NMR
are reported relative to residual solvent peak (CDCl3: 77.0 ppm).
Infrared spectra were recorded on Bruker Tensor 27 fourier trans-
form infrared spectrometer (FTIR) and were reported in wave-
numbers (cmꢁ1). High-resolution mass spectra (HRMS) were
recorded on Bruker Apex IV FTMS mass spectrometer (ESI) and
Micromass U.K. GCT GCeMS mass spectrometer (EI).
achieved and more byproducts could be observed from the TLC
plate compared to those from the reactions of the aryl substituted
substrates. For substrate 1p with a TSNH substituent, we had to use
para-toluenesulfonic acid monohydrate instead of DBU to get the
final isomerization cyclohexenone product 2p after finishing the
[5þ1] cycloaddition (when DBU was used, 2p decomposed).4b The
desired product 2p was isolated in 42% yield under the acidic
conditions.
Furthermore, we synthesized the vinyl and alkynyl substituted
VCP substrates 1q and 1r, which had never been applied in pre-
viously reported [5þ1] cycloadditions. To our disappointment, both
compounds 1q and 1r were not suitable substrates for the present
iron-mediated [5þ1] reaction: complex mixtures were obtained
under the standard reaction conditions, which might have origi-
nated from the side-reactions of tricarbonyl iron coordinated sub-
strates (via the diene or ene-yne moieties as the ligands).
Compound 1s was not a suitable substrate either. For VCP sub-
strates 1t and 1u with internal alkenes, only trace products could
4.2. Typical procedure for the [5D1] cycloaddition of (1-
cyclopropylvinyl)benzene (1a) to 3-phenyl-cyclohex-2-enone
(2a)
A solution of 1a (44.5 mg, 0.30 mmol) and Fe2(CO)9 (109 mg,
t
0.30 mmol) in BuOH (2 mL) was stirred under an argon atmo-
t
sphere at 90 ꢀC for 12 h. After the accomplishment of the [5þ1]
cycloaddition reaction, the reaction mixture was cooled to room
temperature and then filtered through a short silica gel eluting with
DCM. The filtrate was concentrated and a DCM solution of DBU
(45 mg, 0.3 mmol in 2 mL DCM) was added. The mixture was stirred
at room temperature for 30 min and then concentrated. The crude
mixture was submitted to flash column chromatography on silica
gel (eluted with PE/EA 20:1 then 10:1) to afford the corresponding
product 2a as a white solid (42.6 mg, 80% reaction yield).
be obtained after heating the reactions for 24 h in BuOH solution.
The corresponding cyclohexenone product 2u (from 1u’s [5þ1]
reaction) could be isolated in 8% yield.21,22 Both substrates 1v and
1w failed to give the desired [5þ1] cycloadducts with a bicyclic
skeleton, because these two substrates slowly decomposed under
the optimized reaction conditions.23
Considering the importance of the substitutions at the a-posi-
tion of VCPs for the [5þ1] reactions, we synthesized bicyclic com-
pound 1x with a 4-methoxylphenyl group attached to the vinyl
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C.-H. Liu et al. / Tetrahedron xxx (2016) 1e4
2. (a) Hendrickson, J. B. J. Am. Chem. Soc. 1975, 97, 5784; (b) Gaich, T.; Baran, P. S. J.
The second run of this reaction using 44.0 mg 1a gave 40.7 mg
Org. Chem. 2010, 75, 4657; (c) Wender, P. A.; Verma, V. A.; Paxton, T. J.; Pillow, T.
S. Acc. Chem. Res. 2008, 41, 40; (d) Yu, Z.-X.; Liang, Y. In Organic Chemistry-
breakthroughs and Perspectives; Ding, K., Dai, L., Eds.; Wiley-VCH: Weinheim,
Germany, 2012; pp 561e601.
3. For a review of transition metal-catalyzed or -mediated [5þ1] cycloadditions,
see: (a) Khusnutdinov, R. I.; Dzhemilev, U. M. J. Organomet. Chem. 1994, 471,
1; (b) Fu, X.-F.; Yu, Z.-X. In Methods and Applications of Cycloaddition Reactions
in Organic Syntheses; Nishiwaki, N., Ed.; Wiley-VCH: Weinheim, Germany,
2014; pp 551e564; (c) Gao, Y.; Fu, X.-F.; Yu, Z.-X. Top. Curr. Chem. 2014, 346,
195.
2a, with a reaction yield of 78%. Therefore, the average yield of two
runs for this substrate was 79%, which is given in Table 2.
2a: White solid. 1H NMR (400 MHz, CDCl3):
d 7.56e7.50 (m, 2H),
7.43e7.38 (m, 3H), 6.42 (t, J¼1.3 Hz, 1H), 2.79e2.74 (m, 2H),
2.51e2.45 (m, 2H), 2.19e2.11 (m, 2H). The 1H NMR spectrum is
consistent with the literature.4b
The similar procedure was used for the [5þ1] cycloaddition re-
actions of 1be1p and 1x. For substrates 1j and 1x, the reaction
system was stirred at 90 ꢀC for 24 h. For substrate 1j, after filtration,
para-toluenesulfonic acid monohydrate was added instead of DBU
and the mixture was stirred at room temperature for 2 h.
4. For Rh-catalyzed [5þ1] reactions of vinylcyclopropanes and CO, see: (a) Kur-
ahashi, T.; de Meijere, A. Synlett 2005, 2619; (b) Jiang, G.-J.; Fu, X.-F.; Li, Q.; Yu,
Z.-X. Org. Lett. 2012, 14, 692.
5. For Rh-catalyzed [5þ1] reaction of allenylcyclopropanes and CO, see: (a)
Shu, D.; Li, X.; Zhang, M.; Robichaux, P. J.; Tang, W. Angew. Chem., Int. Ed.
2011, 50, 1346; (b) Shu, D.; Li, X.; Zhang, M.; Robichaux, P. J.; Guzei, I. A.;
Tang, W. J. Org. Chem. 2012, 77, 6463; (c) Zhang, M.; Tang, W. Org. Lett. 2012,
50, 3756.
6. For Ir-catalyzed [5þ1] reaction of allenylcyclopropanes and CO, see: Murakami,
M.; Itami, K.; Ubukat, M.; Tsuji, I.; Ito, Y. J. Org. Chem. 1998, 63, 4.
7. (a) Iwasawa, N.; Owada, Y.; Matsuo, T. Chem. Lett. 1995, 115; (b) Owada, Y.;
Matsuo, T.; Iwasawa, N. Tetrahedron 1997, 53, 11069.
8. For a review of iron-catalyzed organic reactions, see: (a) Bauer, E. B. Curr. Org.
Chem. 2008, 12, 1341; (b) Bolm, C.; Legros, J.; Paih, L.; Zani, L. Chem. Rev. 2004,
104, 6217; (c) Bauer, I.; Knolker, H.-J. Chem. Rev. 2015, 115, 3170; (d) Klein, J. E.
M. N.; Plietker, B. Org. Biomol. Chem. 2013, 11, 1271.
4.3. 4-(4-Methoxylphenyl)-4a,5,6,7,8,8a-hexahydronaph-
thalen-2(1H)-one (2x)
First run: 69.3 mg 1x was converted to 47.1 mg 2x, with a yield of
60%. Second run: 67.5 mg 1x was converted to 46.2 mg 2x, with
a yield of 61%. Therefore, the average yield of two runs for this
substrate was 60%.
The ratio of two isomers (2.3:1, see Scheme 2) was determined
by the integral of 1H NMR of vinyl hydrogen. Pure products trans-
2x and cis-2x could be obtained by preparative thin layer chro-
matography. The relative configuration was assigned on compari-
son by analogy with the chemical shifts of similar compound.23
9. For selected examples of iron-catalyzed CꢁC bond activations of VCPs, see: (a)
€
Sherry, B. D.; Furstner, A. Chem. Commun. 2009, 7116; (b) Dieskau, A. P.; Holz-
warth, M. S.; Plietker, B. J. Am. Chem. Soc. 2012, 134, 5048.
10. (a) Ben-Shoshan, R.; Sarel, S. Chem. Commun. 1969, 883; (b) Victor, R.; Ben-
Shoshan, R.; Sarel, S. Tetrahedron Lett. 1970, 49, 4253; (c) Sarel, S. Acc. Chem. Res.
1978, 11, 204; (d) Aumann, R. J. Am. Chem. Soc. 1974, 96, 2631 Also see Ref. 3a.
11. Thermal [5þ1] reactions using Fe(CO)5 were also reported when ceric ammo-
nium nitrate (CAN) and high temperature (150 ꢀC) was used, see: (a) Schulze,
M. M.; Gockel, U. Tetrahedron Lett. 1996, 37, 357; (b) Schulze, M. M.; Gockel, U. J.
Organomet. Chem. 1996, 525, 155.
trans-2x: Colorless oil, 1H NMR (400 MHz, CDCl3)
d 7.19 (d,
J¼8.7 Hz, 2H), 6.91 (d, J¼8.7 Hz, 2H), 6.03 (d, J¼2.1 Hz, 1H), 3.83 (s,
3H), 2.56e2.47 (m, 1H), 2.42 (dd, J¼16.1, 3.6 Hz, 1H), 2.29 (dd,
J¼16.1, 14.1 Hz, 1H), 2.03e1.95 (m, 1H), 1.92e1.74 (m, 4H), 1.45e1.24
12. For preliminary mechanistic study of iron-mediated [5þ1] reactions of VCPs
(m, 3H), 0.90e0.79 (m, 1H). 13C NMR (101 MHz, CDCl3)
d 199.5,
and CO, see ref. 10d and 11b.
13. (a) Taber, D. F.; Kanai, K.; Jiang, Q.; Bui, G. J. Am. Chem. Soc. 2000, 122, 6807;
(b) Taber, D. F.; Joshi, P. V.; Kanai, K. J. Org. Chem. 2004, 69, 2268; (c) Taber, D.
F.; Guo, P.; Guo, N. J. Am. Chem. Soc. 2010, 132, 11179; (d) Taber, D. F.; Bui, G.;
Chen, B. J. Org. Chem. 2001, 66, 3423; (e) Taber, D. F.; Sheth, R. B. J. Org. Chem.
2008, 73, 8030; (f) Taber, D. F.; Sheth, R. B.; Tian, W. J. Org. Chem. 2009, 74,
2433.
165.2, 159.9, 131.3, 128.0, 127.6, 113.7, 55.3, 44.8, 43.8, 41.6, 33.2,
30.7, 26.9, 25.7. IR (KBr):
y 2925, 2855, 2247, 1659, 1606, 1511, 1446,
1332, 1244, 1179, 1034, 832 cmꢁ1. HRMS (ESI) calcd for C17H21O2
(MþHþ): 257.1536. Found: 257.1541.
cis-2x: Colorless oil, 1H NMR (400 MHz, CDCl3)
d 7.52 (d,
14. Enthaler, S.; Junge, K.; Beller, M. Angew. Chem., Int. Ed. 2008, 47, 3317.
15. (a) Williams, D. R.; Shah, A. A.; Mazumder, S.; Baik, M.-H. Chem. Sci. 2013, 4,
238; (b) Williams, D. R.; Shah, A. A. J. Am. Chem. Soc. 2014, 136, 8829.
16. For Fe2(CO)9 catalyzed hetero-PausoneKhand-type [2þ2þ1] cycloaddition, see:
J¼8.8 Hz, 2H), 6.93 (d, J¼8.8 Hz, 2H), 6.30 (s, 3H), 3.85 (s, 1H),
2.93e2.85 (m, 1H), 2.70 (dd, J¼16.6,14.7 Hz, 1H), 2.55e2.44 (m, 1H),
2.23 (dd, J¼16.9, 4.1 Hz, 1H), 1.80e1.57 (m, 5H), 1.52e1.30 (m, 3H).
€
(a) Imhof, W.; Gobel, A. J. Mol. Catal. A: Chem. 2003, 197, 15; (b) Imhof, W.;
13C NMR (101 MHz, CDCl3)
d 200.8, 164.4, 161.2, 129.8, 128.1, 123.0,
€
€
Anders, E.; Gobel, A.; Gorls, H. Chem.dEur. J. 2003, 9, 1166; (c) Imhof, W.; An-
ders, E. Chem.dEur. J. 2004, 10, 5717.
114.2, 55.4, 39.3, 37.5, 33.6, 30.4, 27.2, 25.9, 20.4. IR (KBr):
y 2930,
17. Sigman, M. S.; Eaton, B. E. J. Org. Chem. 1994, 59, 7488.
18. Fe2(CO)9-mediated ring-opening process of VCPs has been reported and Fe-
2853, 2247, 1656, 1600, 1512, 1256, 1231, 1182, 1033, 836 cmꢁ1
.
HRMS (ESI) calcd for C17H21O2 (MþHþ): 257.1536. Found: 257.1539.
carbonyl complexes containing both
p-allyl and s-components could be iso-
lated, see: (a) Aumann, R. Angew. Chem., Int. Ed. 1971, 10, 188; (b) Moriarty, R.
M.; Yeh, C.-L. J. Am. Chem. Soc. 1971, 93, 6709; (c) Moriarty, R. M.; Yeh, C.-L.;
Chen, K.-N. Tetrahedron Lett. 1972, 13, 5325; (d) Sarel, S.; Ben-Shoshan, R.;
Kirson, B. Isr. J. Chem. 1972, 10, 787.
Acknowledgments
19. Similar reaction has been reported using Fe3(CO)12, see: Yu, S.; Shen, W.; Li, Y.;
Dong, Z.; Xu, Y.; Li, Q.; Zhang, J.; Gao, J. Adv. Synth. Catal. 2012, 354, 818.
20. (a) Sarel, S.; Ben-Shoshan, R.; Kirson, B. J. Am. Chem. Soc. 1965, 87, 2517 Also see
Ref. 11a.
We thank the Natural Science Foundation of China (21232001),
and the National Basic Research Program of China-973 Program
(2011CB808600) for financial support.
21. The 1H NMR spectroscopy is consistent with the literature: Jin, T.; Yamamoto, Y.
Org. Lett. 2007, 9, 5259.
Supplementary data
22. Low yield of 1u compared to 1a was also reported by Schulze in the Fe(CO)5/
CAN-mediated [5þ1] reaction, showing that VCP substrates with internal al-
kene were not good for the [5þ1] reaction, see ref. 11a.
Supplementary data associated with this article can be found in
the online version, at http://dx.doi.org/10.1016/j.tet.2016.01.046.
23. For substrate 1w, after stirred for 1 h, 18% [5þ1] cycloadduct 2w product could
be detected according to the 1H NMR (1,3,5-trimethoxybenzene as internal
standard substance). The 1H NMR spectroscopy of 2w is consistent with the
literature: Kim, W. H.; Lee, J. H.; Danishefsky, S. J. J. Am. Chem. Soc. 2009, 131,
12576.
References and notes
1. (a) Nicolaou, K. C.; Snyder, S. A.; Montagnon, T.; Vassilikogiannakis, G. Angew.
Chem., Int. Ed. 2002, 41, 1668; (b) Funel, J.-A.; Abele, S. Angew. Chem., Int. Ed.
2013, 52, 3822.
Please cite this article in press as: Liu, C.-H.; et al., Tetrahedron (2016), http://dx.doi.org/10.1016/j.tet.2016.01.046