Manganese(III)-mediated oxidative annulation of vinylidenecyclopropanes with 1,3-dicarbonyl compounds

Article abstract of DOI:10.1016/j.tet.2011.06.109

Manganese(III)-mediated oxidative annulation of vinylidenecyclopropanes with 1,3-dicarbonyl compounds in acetonitrile/acetic acid produces the corresponding functionalized dihydrofuran derivatives in moderate to good yields under mild conditions. The subs

Full text of DOI:10.1016/j.tet.2011.06.109

Tetrahedron 67 (2011) 7139e7142
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Manganese(III)-mediated oxidative annulation of vinylidenecyclopropanes with
1,3-dicarbonyl compounds
*
Wei Yuan, Yin Wei, Min Shi
State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 354 Fenglin Road, Shanghai 200032, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 21 April 2011
Received in revised form 28 June 2011
Accepted 29 June 2011
Available online 29 July 2011
Manganese(III)-mediated oxidative annulation of vinylidenecyclopropanes with 1,3-dicarbonyl com-
pounds in acetonitrile/acetic acid produces the corresponding functionalized dihydrofuran derivatives in
moderate to good yields under mild conditions. The substrate scope has been examined and a plausible
reaction mechanism has been also proposed on the basis of experimental results and previous literature.
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
Manganese(III)
Vinylidenecyclopropanes
1,3-Dicarbonyl compounds
Radical
Annulation
Dihydrofuran
1. Introduction
also applied to the construction of complex natural and biologically
active compounds.6 In this aspect, the oxidative addition of acetic
Vinylidenecyclopropanes (VDCPs) 1, which have highly
strained cyclopropyl group connected with an allene moiety and
yet are thermally stable and reactive substances in organic
chemistry, are versatile intermediates in organic synthesis.1 Thus
far, many novel and useful transformations of these interesting
highly strained small ring molecules have been disclosed by many
organic chemists. For example, it has been demonstrated that
VDCPs 1 are able to react with diverse nucleophiles, such as al-
cohols, amines or carboxylic acids, and other reactants, such as
aldehydes or imines in the presence of Lewis acids/Brønsted acids/
transition metals to produce a variety of interesting products.2e4
Many of these reactions are initiated by the electrophilic addi-
tions of the corresponding in situ generated active species to the
electron-rich VDCPs. Moreover, several examples based on the
radical species initiated reactions of VDCPs have been also ex-
plored recently.2d,5
acid to alkenes in the presence of 2.0 equiv of Mn(OAc)3 in AcOH
under reflux to give -lactones was first reported in 1968 by Heiba
g
and Dessau7a,c as well as Bush and Finkbeiner,7b respectively
(Scheme 1, Eq. 1). Over the past 40 years, the use of Mn(OAc)3 to
oxidatively initiate free-radical reactions of mono and 1,3-
dicarbonyl compounds with other reactants has been widely
reviewed with an emphasis on the synthetic applications.6e,8,9 In
our previous work, we have also investigated the reactions be-
tween methylenecyclopropanes (MCPs) and 1,3-dicarbonyl com-
pounds to produce the corresponding dihydrofuran derivatives
through a mechanism of Mn(OAc)3 induced free-radical oxidative
process (Scheme 1, Eq. 2).10 However, among all these reports, there
is no any example involving the reaction between 1,3-dicarbonyl
compound and VDCP mediated by Mn(OAc)3. We envisaged that
VDCPs 1 having a highly strained cyclopropane ring connected with
an allene moiety would be also suitable substrates in the reaction
with 1,3-dicarbonyl compounds if using Mn(OAc)3 as a promoter
(Scheme 1, Eq. 3). In this paper, we wish to disclose that
manganese(III)-mediated oxidative annulation of VDCPs with 1,3-
dicarbonyl compounds can proceed smoothly in acetonitrile/ace-
tic acid to produce the corresponding functionalized dihydrofuran
derivatives in moderate to good yields under mild conditions,
subsequently enriching the chemistry of Mn(III)-mediated oxida-
tive free-radical reactions.
Mn(III)-mediated oxidative free-radical reactions have been
extensively developed during the past two decades, which have
been proven to be an extremely valuable method in numerous
regio-, chemo-, and stereoselective carbonecarbon bond forma-
tions both in inter- and intramolecular reactions, and have been
* Corresponding author. Tel.: þ86 21 54925137; fax: þ86 21 64166128; e-mail
address: Mshi@mail.sioc.ac.cn (M. Shi).
0040-4020/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2011.06.109

7140
W. Yuan et al. / Tetrahedron 67 (2011) 7139e7142
Table 2
Substrate scope of the reactions between VDCPs 1 and cyclohexane-1,3-dione in the
presence of Mn(OAc)3$2H2O
O
Ar1
Ar2
O
O
Mn(OAc)3.2H2O (2.0 equiv)
CH3CN, HOAc (5.0 equiv), 60 oC, 6 h
.
1
+
Ar1
Ar2
O
3.0 equiv
2
Entrya
Ar1/Ar2
Yield (%)b
2
1
2
3
4
5
6
7
8
p-FC6H4/p-FC6H4, 1b
p-CIC6H4/p-CIC6H4, 1c
p-CIC6H4/C6H5, 1d
p-BrC6H4/p-BrC6H4, 1e
o-CH3C6H4/C6H5, 1f
p-CH3C6H4/C6H5, 1g
p-CH3C6H4/p-CH3C6H4, 1h
p-CH3OC6H4/P-CH3OC6H4, 1i
2b, 65
2c, 64
2d, 75
2e, 59
2f, 60
2g, 58
2h, 72
2i, 68
Scheme 1. Mn(III)-mediated oxidative free-radical reactions.
Initial assays were carried out by using VDCP 1a and cyclohex-
ane-1,3-dione as the substrates. To our delight, the reaction of VDCP
1a with cyclohexane-1,3-dione proceeded smoothly in HOAc
within 12 h at room temperature (20 ꢀC) to give the corresponding
dihydrofuran derivative 2a in 43% yield (Table 1, entry 1). Next, we
attempted to optimize the reaction conditions and the results of
these experiments are summarized in Table 1. Using acetonitrile
(CH3CN) as the solvent afforded 2a in 45% yield upon extending the
reaction time to 48 h (Table 1, entry 2) and moreover, using ace-
tonitrile (CH3CN) as the solvent combined with HOAc (2.0 equiv)
produced 2a in 54% yield within 12 h (Table 1, entry 3). Further
increasing the employed amount of HOAc did not improve the yield
of 2a (Table 1, entries 4 and 5). The examination of solvent effects
revealed that acetonitrile is the suitable solvent in this reaction
compared with other solvents, such as N,N-dimethylformamide
(DMF), tetrahydrofuran (THF) and toluene (Table 1, entries 6e8).
Upon raising the reaction temperature to 60 ꢀC and reducing the
reaction time to 6 h, we found that the corresponding dihydrofuran
derivative 2a could be obtained in 67% yield in the presence of
5.0 equiv of HOAc (Table 1, entry 10).
a
VDCP 1, cyclohexane-1,3-dione (3.0 equiv) and Mn(OAc)3$2H2O (2.0 equiv)
were added into a flask under argon, and then, HOAc (5.0 equiv) was injected into
the flask. Reactions were carried out in CH3CN at 60 ꢀC within 6 h under argon.
b
Isolated yields.
2bei in moderate to good yields under mild conditions. As for
VDCPs 1bee bearing electron-withdrawing groups on their aro-
matic rings of Ar1 and Ar2, the corresponding products 2bee could
be obtained in 59e75% yields (Table 2, entries 1e4). Meanwhile,
introducing electron-donating groups onto aromatic rings of Ar1
and Ar2 could also afford the corresponding dihydrofuran de-
rivatives 2fei in moderate to good yields, suggesting that the
electronic property on the aromatic rings has litter influence in this
reaction (Table 2, entries 5e8).
Using dimedone as the 1,3-dicarbonyl compound to replace
cyclohexane-1,3-dione, the reactions with VDCPs 1 also proceeded
efficiently to afford the corresponding dihydrofuran derivatives 3 in
good to high yields under the standard conditions. The results have
been summarized in Table 3. As can be seen from Table 3, the
corresponding dihydrofuran derivatives 3aei could be obtained in
64e92% yields whether they have electron-withdrawing or
electron-donating groups on their aromatic rings of Ar1 and Ar2
(Table 3, entries 1e8). The structure of 3a was unambiguously de-
termined by X-ray diffraction. Its ORTEP drawing is shown in Fig. 1
and its CIF data are presented in the Supplementary data.11
Under this optimized reaction conditions, we next set out to
explore the substrate scope of this transformation and the results of
these experiments are summarized in Table 2. As shown in Table 2,
a variety of VDCPs 1 could react with cyclohexane-1,3-dione
smoothly to give the corresponding dihydrofuran derivatives
Table 1
Optimization of the reaction conditions between VDCP 1a and cyclohexane-1,3-
dione in the presence of Mn(OAc)3$2H2O
O
Table 3
C6H5
C6H5
O
O
Reactions of VDCPs 1 with dimedone in the presence of Mn(OAc)3$2H2O
Mn(OAc)3.2H2O (2.0 equiv)
.
1a
+
C6H5
C6H5
solvent, HOAc (x equiv), temp, y h
O
O
2a
Ar1
Ar2
O
+
O
3.0 equiv
Mn(OAc)3.2H2O (2.0 equiv)
CH3CN, HOAc (5.0 equiv), 60 oC, 6 h
Ar1
Ar2
.
1
Entrya
Solvent
x
y (h)
Temp (ꢀC)
Yield(%)b
O
3
3.0 equiv
2a
Entrya
Ar1/Ar2
Yield(%)b
1
2
3
4
5
6
7
8
9
HOAc
12
48
12
12
12
12
12
12
12
6
rt
rt
rt
rt
rt
rt
rt
rt
60
60
43
45
54
53
54
24
30
23
63
67
CH3CN
CH3CN
CH3CN
CH3CN
Toluene
DMF
THF
CH3CN
CH3CN
d
3
2.0
5.0
10
5.0
5.0
5.0
5.0
5.0
1
2
3
4
5
6
7
8
C6H5/C6H5, 1a
3a, 83
3b, 64
3c, 85
3d, 72
3e, 65
3g, 75
3h, 92
3i, 81
p-FC6H4/p-FC6H4, 1b
p-CIC6H4/p-CIC6H4, 1c
p-CIC6H4/C6H5, 1d
p-BrC6H4/p-BrC6H4, 1e
p-CH3C6H4/C6H5, 1g
p-CH3C6H4/p-CH3C6H4, 1h
p-CH3OC6H4/p-CH3OC6H4, 1i
10
a
VDCP 1, cyclohexane-1,3-dione (3.0equiv) and Mn(OAc)3$2H2O (2.0equiv) were
added into a flask under argon, and then, HOAc (x equiv) was injected into the flask
under certain conditions. Reactions were carried out in the employed solvent at
different temperature within y h under argon.
a
VDCP 1, dimedone (3.0 equiv) and Mn(OAc)3$2H2O (2.0 equiv) were added into
a flask under argon, and then, HOAc (5.0 equiv) was injected into the flask. Reactions
were carried out in CH3CN at 60 ꢀC within 6 h under argon.
b
b
Isolated yields.
Isolated yields.

W. Yuan et al. / Tetrahedron 67 (2011) 7139e7142
7141
formation of dihydrofuran derivative 2 or 3 has been outlined in
Scheme 4 using VDCP 1 as the reaction model. The reaction of 1,3-
dicarbonyl compound with Mn(OAc)3$2H2O affords a Mn(III)-
enolate A, which rapidly undergoes electron loss to the oxo-
centered Mn(III) metal complex to give the radical intermediate
B. Then, the radical intermediate B adds to the double bond of VDCP
1 to furnish the corresponding radical intermediate C.6g The oxi-
dation of 1,3-dicarbonyl compound to give radical intermediate C
has been considered as the rate determining step.6g This radical
intermediate is stabilized by two aromatic groups of VDCP 1.12
Therefore, it is further oxidized by another molecule of
Mn(OAc)3$2H2O (2.0 equiv of Mn(OAc)3$2H2O in the reaction sys-
tem) to produce the corresponding cationic intermediate D, which
is also stabilized by the corresponding aromatic rings. At any sense,
this cationic intermediate D is more stable than the radical in-
termediate C because it is exactly a long-lived cyclopropylcarbinyl
cation through the delocalization and resonance effects, providing
a driving force for the transformation of intermediate C to in-
termediate D.13 The intramolecular attack of the oxygen atom at the
carbonyl group gives the oxonium cation E, which undergoes
deprotonation to produce the corresponding [3þ2] annulation
product 2 or 3.
Fig. 1. ORTEP Drawing of 3a.
To further examine the substrate scope, we employed several
other 1,3-dicarbonyl compounds in the reaction with VDCP 1a
under the standard conditions and the results of these experiments
have been shown in Scheme 2. A brief screening of several 1,3-
dicarbonyl compounds revealed that pentane-2,4-dione could
also react with VDCP 1a as well as VDCP 1i to produce the corre-
sponding dihydrofuran derivatives 4 and 5 in 31% and 22% yields,
respectively (Scheme 2, Eq. 1 and Eq. 2). Using other 1,3-dicarbonyl
compounds, such as cyclopentane-1,3-dione, ethyl 3-oxobutanoate,
ethyl 3-oxo-3-phenylpropanoate, 2,2-dimethyl-1,3-dioxane-4,6-
dione, and 1,3-diphenylpropane-1,3-dione as the reactants, either
no reactions occurred or none of the corresponding dihydrofuran
derivatives 6 was formed (Scheme 3). In addition, VDCP 1i did not
react with these 1,3-dicarbonyl compounds either. Moreover, as for
VDCP substrates bearing aromatic substituent on their cyclopro-
panes, the reactions with cyclohexane-1,3-dione or dimedone gave
complex product mixtures under the standard conditions.
Scheme 4. A plausible reaction mechanism for the formation of 2 or 3.
In conclusion, we have explored a novel transformation of
VDCPs 1 with 1,3-dicarbonyl compounds in the presence of
Mn(OAc)3$2H2O under mild conditions, affording the correspond-
ing dihydrofuran derivatives in moderate to good yields and sub-
sequently enriching the chemistry of Mn(III)-mediated oxidative
free-radical reactions. Moreover, a plausible reaction mechanism
has been proposed in this paper, that is, based on our experimental
results and previous literature. Efforts are in progress to further
elucidate the mechanistic details of this reaction and to determine
its scope and limitations.
Scheme 2. Further screening of pentane-2,4-dione with VDCP’s 1a and 1i in the
presence of Mn(OAc)3$2H2O.
Acknowledgements
We thank the Shanghai Municipal Committee of Science and
Technology (08dj1400100-2), National Basic Research Program of
China (973)-2009CB825300, and the National Natural Science
Foundation of China (21072206, 20472096, 20872162, 20672127,
20821002, and 20732008) are greatly acknowledged.
Scheme 3. Further screening of other 1,3-dicarbonyl compounds with VDCP’s 1a and
1i in the presence of Mn(OAc)3$2H2O.
Supplementary data
On the basis of above results and previous investigations on
Mn(III)-mediated reactions,2d,5,10 a plausible mechanism for the
Supplementary data related to this article can be found online at
doi:10.1016/j.tet.2011.06.109.

7142
W. Yuan et al. / Tetrahedron 67 (2011) 7139e7142
Wang, F.-J.; Qi, M.-H.; Shao, L.-X.; Shi, M. Organometallics 2009, 28, 1569e1574;
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11. The crystal data of 3a have been deposited in CCDC with number 814690.
Empirical Formula: C29H32O2; Formula Weight: 412.53; Crystal Color, Habit:
colorless; Crystal System: monoclinic; Lattice Type: primitive; Crystal size: 0.
ꢀ
3
ꢀ
ꢀ
ꢀ
30ꢁ0.20ꢁ0.15; Lattice Parameters: a¼9.210(4) A, b¼13.927(6) A, c¼18.349(8) A,
ꢀ
a
¼90ꢀ,
b
¼92.566(9)ꢀ,
g
¼90 , V¼2351.2(18) A ; Space group: P2(1)/c; Z¼4;
Dcalcd¼1.165 g/cm3; F000¼888; Final R indices [I>2
(I)]: R1¼0.0572; wR2¼0.
s
1850.
12. (a) Kochi, J. K.; Krusic, P. J.; Eaton, D. R. J. Am. Soc. Chem. 1969, 91, 877e1879; (b)
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with, A. L. J.; Bowry, V. W. J. Am. Soc. Chem. 1994, 116, 2710e2716; (e) Masnovi,
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