Cobalt porphyrin catalyzed [3+2] cycloaddition of cyclopropanes and carbonyl compounds

Article abstract of DOI:10.1055/s-0034-1378394

A cobalt porphyrin efficiently catalyzed the formal [3+2] cycloaddition of alkyl-/aryl-substituted cyclopropanes and carbonyl compounds such as aldehydes and ketones to afford the corresponding substituted tetrahydrofurans. The use of the cobalt porphyrin complex as a Lewis acid to catalyze the reaction via the electrophilic activation of cyclopropanes was demonstrated. The high functional-group tolerance and robustness of the catalyst were also demonstrated. Further, the potential utility of the catalyst was demonstrated by performing the cycloaddition of cyclic ketones and cyclopropanes to afford spiro tetrahydrofurans. Georg Thieme Verlag Stuttgart · New York.

Full text of DOI:10.1055/s-0034-1378394

LETTER
▌2005
lCettoerbalt Porphyrin Catalyzed [3+2] Cycloaddition of Cyclopropanes and
Carbonyl Compounds
[3+2] Cycloaddition
Takahiro Shiba,a Daiki Kuroda,a Takuya Kurahashi,*a,b Seijiro Matsubara*a
a
Department of Material Chemistry, Graduate School of Engineering, Kyoto University, Kyoto 615-8510, Japan
Fax +81(75)3832438; E-mail: kurahashi.takuya.2c@kyoto-u.ac.jp; E-mail: matsubara.seijiro.2e@kyoto-u.ac.jp
b
JST, ACT-C, 4-1-8 Honcho, Kawaguchi, Saitama, 332-0012, Japan
Received: 19.05.2014; Accepted after revision: 09.06.2014
cloadduct 3aa in 82% yield and with a diastereomeric ra-
tio of 20:1 (Table 1, entry 1).
Abstract: A cobalt porphyrin efficiently catalyzed the formal [3+2]
cycloaddition of alkyl-/aryl-substituted cyclopropanes and carbonyl
compounds such as aldehydes and ketones to afford the correspond-
ing substituted tetrahydrofurans. The use of the cobalt porphyrin
complex as a Lewis acid to catalyze the reaction via the electrophil-
ic activation of cyclopropanes was demonstrated. The high func-
tional-group tolerance and robustness of the catalyst were also
demonstrated. Further, the potential utility of the catalyst was
demonstrated by performing the cycloaddition of cyclic ketones and
cyclopropanes to afford spiro tetrahydrofurans.
Table 1 Metalloporphyrin-Catalyzed [3+2] Cycloaddition of Cyclo-
propane 1a and Aldehyde 2a To Afford Tetrahydrofuran 3aa
Ph
X–
N
N
Ph
M+
Ph
N
N
Key words: aldehydes, catalysis, cycloaddition, furans, ketones
Ph
MeO2C CO2Me
Ph
metalloporphyrin catalyst
[M(TPP)]X (2 mol%)
MeO2C
Ph
CO2Me
+
O
Efficient synthesis of tetrahydrofurans is one of the most
important research topics in organic synthesis because
they are privileged scaffolds in many natural products and
bioactive compounds.1–3 Among various synthetic meth-
ods, Lewis acid catalyzed [3+2] cycloadditions have
emerged as one of the most powerful tools for the synthe-
sis of tetrahydrofurans in the last decades; cycloadditions
of malonate-derived cyclopropanes and aldehydes cata-
lyzed by Lewis acids such as Sc(OTf)3, SnCl4, and MgI2
have been reported.4–8 Herein, we report the cobalt por-
phyrin catalyzed regio- and stereoselective intermolecular
[3+2] cycloaddition of cyclopropanes with carbonyl com-
pounds. The cycloaddition of cyclopropanes and ketones
catalyzed by cobalt porphyrin to afford the corresponding
substituted tetrahydrofurans was achieved.
Ph
H
O
solvent, 4 h
Ph
1a
2a
3aa
Entry Catalyst
Solvent
Temp (°C) Yield (%)a,b
1
2
[Co(TPP)]SbF6
[Fe(TPP)]SbF6
[Mn(TPP)]SbF6
[Cr(TPP)]SbF6
[Co(TPP)]Cl
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
CH2Cl2
toluene
THF
60
60
60
60
60
60
60
60
60
60
55
50
55
55
55
82 (20:1)
<1
3
<1
4
<1
5
<1
6
[Co(TPP)]OTf
[Co(TPP)]BF4
[Co(TPP)]PF6
[Co(TPP)]TFPB
NaTFPB
<1
7
<1
Porphyrins have emerged as useful ligands for Lewis acid
catalysts in organic reactions that are difficult to perform
using other ligands.9 One of the distinct properties of por-
phyrin ligands can be attributed to their characteristic
structure; metals can be rigidly coordinated in the porphy-
rin plane, thus stabilizing the high-valent Lewis acidic
metal center. During our study on metalloporphyrin-cata-
lyzed organic reactions, we found that a cobalt porphyrin
efficiently catalyzes the [3+2] cycloaddition of malonate-
derived cyclopropanes with aldehydes to afford the corre-
sponding substituted tetrahydrofurans in high yields re-
gio- and stereoselectively (Table 1).10,11 The reaction of
cyclopropane 1a with benzaldehyde (2a) catalyzed by 2
mol% [Co(TPP)]SbF6 (TPP: meso-tetraphenylporphyrin)
in 1,2-dichloroethane at 60 °C for four hours afforded cy-
8
<1
9
99 (13:1)
<1
10
11
12
13
14
15
[Co(TPP)]TFPB
[Co(TPP)]TFPB
[Co(TPP)]TFPB
[Co(TPP)]TFPB
[Co(TPP)]TFPB
99 (20:1)
49 (20:1)
99 (20:1)
82 (20:1)
<1
a Isolated yields.
b Ratios of diastereomers.
Among
various
metalloporphyrins,
such
as
SYNLETT 2014, 25, 2005–2008
Advanced online publication: 04.08.2014
DOI: 10.1055/s-0034-1378394; Art ID: st-2014-u0436-l
© Georg Thieme Verlag Stuttgart · New York
[Fe(TPP)]SbF6, [Mn(TPP)]SbF6, and [Cr(TPP)]SbF6,
only [Co(TPP)]SbF6 catalyzed the cycloaddition (Table 1,
entries 1–4). We also examined the effect of counteran-
0
9
3
6
-
5
2
1
4
1
4
3
7
-
2
0
9
6

2006
T. Shiba et al.
LETTER
–
–
ions such as Cl–, OTf–, BF4 , and PF6 , which act as axial in 61% yield (Table 3, entry 2), and the reactions of ani-
ligands, on the cationic nature of Co3+ (Table 1, entries 5– saldehydes 2c and 2d afforded the corresponding tetrahy-
8). When tetrakis[3,5-bis(trifluoromethyl)phenyl]borate drofurans 3ac and 3ad in 91% and 95% yields,
(TFPB) was used as the counteranion, 3aa was obtained respectively (Table 3, entries 3 and 4).13 However, the re-
in 99% isolated yield (Table 1, entry 9). The reaction action with o-anisaldehyde failed, probably because of the
failed when the sodium salt of TFPB (NaTFPB) was used steric hindrance or coordination of the ortho-methoxy
as the catalyst (Table 1, entry 10). Further, 3aa was ob- moiety to the cobalt porphyrin. Benzaldehydes, contain-
tained diastereoselectively in 99% yield when the reaction ing functional groups such as bromo, fluoro, acetyl, and
was performed at a lower reaction temperature (Table 1, acetoxy, afforded the corresponding tetrahydrofurans 3
entry 11). Among the reaction solvents examined, nonpo- diastereoselectively (Table 3, entries 5–8). Furyl and thie-
lar solvents such as dichloromethane and toluene were nyl substituents were also tolerated under the reaction
suitable for the reaction, whereas polar solvents such as conditions to afford the corresponding substituted tetrahy-
tetrahydrofuran resulted in poor yields (Table 1, entries drofurans (Table 3, entries 9–11). Furthermore, cyclopro-
13–15).
pane 1a also underwent reaction with aliphatic aldehydes
to afford the corresponding tetrahydrofurans 3; the reac-
tion of cyclohexanecarboaldehyde 2l with 1a afforded 3al
in 77% yield (Table 3, entry 12). Notably, the reaction of
cyclopropanecarboaldehyde 2m with 1a afforded 3am in
excellent yield (Table 3, entry 13).
To determine the substrate scope of this cycloaddition, we
carried out the reactions of various malonate-derived cy-
clopropanes 1 with benzaldehyde (2a) under the opti-
mized reaction conditions (Table 2). The reactions of aryl-
substituted cyclopropanes such as 1b, 1c, and 1d with 2a
afforded the corresponding substituted tetrahydrofurans
(Table 2, entries 2–4).12 The reaction of cyclopropane 1e,
with a 2-furyl moiety, with 2a afforded 3ea (Table 2, entry
5). The reaction of vinyl cyclopropane 1f with 2a afforded
vinyl-substituted tetrahydrofuran 3fa in excellent yield
(Table 2, entry 6). The reaction of cyclopropane 1g, con-
taining a phthalimide moiety, with 2a afforded 3ga in
61% yield (Table 2, entry 7). The reaction of gem-dimeth-
yl-substituted cyclopropane 1h with 2a afforded 3ha in
68% yield (Table 2, entry 8).
Table 3 Cobalt Porphyrin Catalyzed [3+2] Cycloaddition of Cyclo-
propane 1a and Aldehydes 2
MeO2C CO2Me
MeO2C
Ph
CO2Me
+
O
[Co(TPP)]TFPB (2 mol%)
DCE, 55 °C, 4 h
R3
R3
H
O
Ph
1a
2
3
Entry
2
R3
Ph
314
Yield (%)a,b
1
2
2a
2b
2c
2d
2e
2f
3aa
99 (20:1)
61 (20:1)
91 (2:1)c
95 (10:1)
80 (20:1)
88 (20:1)
41 (20:1)
90 (20:1)c
80 (3:1)
Table 2 Cobalt Porphyrin Catalyzed [3+2] Cycloaddition of Cyclo-
propanes 1 and Benzaldehyde (2a)
4-MeC6H4
4-MeOC6H4
3-MeOC6H4
4-BrC6H4
4-FC6H4
3ab
3ac
3ad
3ae
3af
3
MeO2C CO2Me
MeO2C
R1
CO2Me
+
O
[Co(TPP)]TFPB (2 mol%)
DCE, 55 °C, 4 h
4
Ph
Ph
H
O
5
R1
2a
R2
R2
1
6
3
7
2g
2h
2i
4-AcC6H4
4-AcOC6H4
2-furyl
3ag
3ah
3ai
Entry
1
R1
Ph
R2
3
Yield (%)a,b
8
1
2
3
4
5
6
7
8
1a
1b
1c
1d
1e
1f
H
3aa
3ba
3ca
3da
3ea
3fa
99 (20:1)
92 (13:1)
69 (17:1)
60 (2:1)
30 (3:1)
90 (2:1)
61 (10:1)
68
9
4-MeC6H4
2-MeC6H4
4-MeOC6H4
2-furyl
H
10
11
12
13
2j
3-furyl
3aj
70 (20:1)
42 (20:1)
77 (20:1)
99 (10:1)
H
2k
2l
2-thienyl
3ak
3al
H
cyclohexyl
cyclopropyl
H
2m
3am
vinyl
H
a Isolated yields.
1g
1h
PhthNc
H
3ga
3ha
b Ratios of diastereomers.
c Reaction temperature: 70 °C.
Me
Me
a Isolated yields.
b Ratios of diastereomers.
c PhthN: phthalimido.
The cobalt porphyrin catalyzed cycloaddition of cyclo-
propane 1a with acetone 2n afforded gem-dimethyl-sub-
stituted tetrahydrofuran 3an in 73% yield with prolonged
reaction time (Scheme 1). The reaction is also applicable
to the synthesis of spiro tetrahydrofurans from cyclic ke-
tones. For example, the reaction of 1a with cyclopenta-
We next examined the cycloaddition of 1a with diverse al-
dehydes 2, and the results are summarized in Table 3. The
reaction of tolualdehyde 2b afforded tetrahydrofuran 3ab
Synlett 2014, 25, 2005–2008
© Georg Thieme Verlag Stuttgart · New York

LETTER
[3+2] Cycloaddition
2007
MeO2C CO2Me
R4
R3
MeO2C
Ph
CO2Me
O
[Co(TPP)]TFPB (2 mol%)
DCE, 55 °C, 4 h
+
R3
R4
O
1a
2
Ph
3
MeO2C CO2Me
MeO2C CO2Me
MeO2C CO2Me
MeO2C CO2Me
O
O
O
O
Ph
Ph
Ph
Ph
3an
3ao
82%
3ap
42%
3aq
37%
73% (12 h)
54% [12 h, Sc(OTf)3]
65% [Sc(OTf)3]
Scheme 1 Cobalt porphyrin catalyzed [3+2] cycloaddition of cyclopropane 1a and ketones 2
none 2o in the presence of cobalt porphyrin catalyst opment of an asymmetric variant of the reaction with chi-
afforded spiro tetrahydrofuran 3ao in 82% yield. It was ral cobalt porphyrins are under way.
found that the reaction of 1a with 2n and 2o with Sc(OTf)3
in place of cobalt porphyrin catalyst afforded cycload-
ducts in moderate yields. These results clearly highlight
Acknowledgment
This work was supported by JST, ACT-C and Grants-in-Aid from
the Ministry of Education, Culture, Sports, Science and Technolo-
gy, Japan. T.K. acknowledges the Asahi Glass Foundation, the
Uehara Memorial Foundation, Tokuyama Science Foundation, and
Kurata Memorial Hitachi Science and Technology Foundation. We
thank Rigaku Corporation for the valuable help in X-ray crystal
structural analysis.
the excellent reactivity of the cobalt porphyrin for the
cycloaddition of cyclopropanes with carbonyl compounds
compared to other Lewis acid catalysts. The cycloaddition
with cyclohexanone 2p and cycloheptanone 2q also
afforded the corresponding spiro tetrahydrofurans 3ap
and 3aq.
The cycloaddition of optically active cyclopropane 1a
(99% ee) with 2a afforded tetrahydrofuran 3aa with 77%
enantiomeric excess (Scheme 2). However, optically ac-
tive cyclopropane 1a gradually racemized in the presence
of cobalt catalyst, indicating that the Lewis acidic cobalt
porphyrin catalyst initially facilitates the ring opening of
the cyclopropane to generate a cationic intermediate,
which reacts with 2a to afford tetrahydrofuran by stepwise
reaction mechanism.13
Supporting Information for this article is available online
at
http://www.thieme-connect.com/products/ejournals/journal/
10.1055/s-00000083.SunogIpimrfiantoSuIpg
n
fonirtat
ori
References and Notes
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MeO2C CO2Me
MeO2C
CO2Me
O
[Co(TPP)]TFPB (2 mol%)
H
DCE, 55 °C, 4 h
Ph
+
Ph
O
Ph
2a
Ph
3aa 99% (77% ee)
1a (99% ee)
racemization of chiral 1a under the reaction conditions
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MeO2C
Ph
CO2Me
MeO2C
Ph
CO2Me
[Co(TPP)]TFPB (2 mol%)
DCE, 55 °C, 4 h
1a (99% ee)
1a 91% (66% ee)
Scheme 2 Cobalt porphyrin catalyzed [3+2] cycloaddition of chiral
cyclopropane 1a and benzaldehyde (2a)
In summary, an efficient access to tetrahydrofuran deriv-
atives was developed by a cobalt porphyrin catalyzed
[3+2] cycloaddition of malonate-derived cyclopropanes
and aldehydes. The use of the cobalt porphyrin catalyst
also allows ketones to react with cyclopropanes. Efforts to
expand the substrate scope of the reaction and the devel-
© Georg Thieme Verlag Stuttgart · New York
Synlett 2014, 25, 2005–2008

2008
T. Shiba et al.
LETTER
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(Table 2, entry 4) and 3ac (Table 3, entry 3) with low
diasteroselectivity. These reactions proceed in high
diasteroselectivity at initial stage, however, epimerization
occurs upon completion of the reaction probably because
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by stabilizing benzylic cation intermediate. For
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(14) General Procedure for the [3+2] Cycloaddition
The reaction was performed in a 15 mL sealed tube equipped
with a Teflon-coated magnetic stirrer bar. An aldehyde 2
(0.15 mmol) was added to a solution of cyclopropane 1 (0.1
mmol) and [Co(TPP)]TFPB (3.1 mg, 4 μmol) in DCE (1 mL)
in a dry box. The sealed tube was taken outside the dry box
and heated at 55 °C for the indicated time under argon
atmosphere. The resulting reaction mixture was cooled to
ambient temperature and filtered through a silica gel pad,
concentrated in vacuo. The residue was purified by flash
silica gel column chromatography (20 g, 2 × 15 cm; hexane–
EtOAc, 5:1) to give the products 3.
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