Rhodium(I)-catalyzed intramolecular [5+2] cycloaddition reactions of alkynes and allenylcyclopropanes: Construction of bicyclo[5.4.0]undecatrienes and bicyclo[5.5.0]dodecatrienes

Full text of DOI:10.1002/anie.200906994

Communications
DOI: 10.1002/anie.200906994
[5+2] Cycloaddition
Rhodium(I)-Catalyzed Intramolecular [5+2] Cycloaddition Reactions
of Alkynes and Allenylcyclopropanes: Construction of Bicyclo-
[5.4.0]undecatrienes and Bicyclo[5.5.0]dodecatrienes**
Fuyuhiko Inagaki, Katsuya Sugikubo, Yusuke Miyashita, and Chisato Mukai*
Highly strained cyclopropane derivatives have served as
useful and powerful C3 building blocks[1] for the construction
of various ring systems, and the metal-catalyzed cleavage of
the activated carbon-carbon s bond of the cyclopropane
ring[2,3] must be one of the most attractive methods from a
synthetic point of view. Of particular interest is the RhI-
catalyzed [5+2] cycloaddition of vinylcyclopropanes[3–5] with
carbon–carbon p-components for the efficient formation of
seven-membered compounds. In 1995, Wender et al. reported
the first example[3a] of the RhI-catalyzed [5+2] cycloaddition
reaction of vinylcyclopropanes with alkynes to provide
bicyclo[5.3.0]decadienes.[3c,g,j] This method[3,4] was successfully
applied to the [5+2] cycloaddition reactions of allenes[3e,f,h] as
well as alkenes[3b,d,g,j,4a] as an alternative carbon–carbon
p-counterpart. In sharp contrast to the extensive investigation
of vinylcyclopropanes,[2b,c,e,3–5] very few examples[6] of the ring-
closing reaction of allenylcyclopropane, which is regarded as
an alkylidene homologue of vinylcyclopropane, have been
reported. Two representative examples are shown in
Scheme 1; one involves the RhI-catalyzed cycloisomeriza-
Our continuing interest in the field of the [{RhCl(CO)2}2]-
and [{RhCl(CO)dppp}2]-catalyzed cycloaddition reactions of
phenylsulfonylallenes[7] prompted us to investigate the intra-
molecular cycloaddition reaction between phenylsulfonylal-
lenes that contain a cyclopropyl group at the allene terminus
and alkynes. Herein, we describe the preliminary results of
the RhI-catalyzed ring-closing reaction of alkyne-allenylcy-
clopropane derivatives for the facile preparation of the
bicyclo[5.4.0]undecatrienes and bicyclo[5.5.0]dodecatrienes.
Our initial evaluation of the RhI-catalyzed [5+2] cycloaddi-
tion of an alkyne-allenylcyclopropane derivative focused on
the preparation of the bicyclo[5.4.0]undecatriene framework.
Treatment of N-Ts derivative 1, which possesses a terminal
alkyne group, with 10 mol% of [{RhCl(CO)2}2] in toluene at
808C under a nitrogen atmosphere for 2 h produced the
desired bicyclo[5.4.0]undecatriene derivative 2 in 66% yield
(Table 1, entry 1).[8] This ring-closing reaction even occurred
at room temperature to give 2 in 57% yield, although a more
prolonged reaction time (24 h) was required (Table 1,
entry 2). It is noteworthy that these results are in sharp
contrast to those obtained for the [{RhCl(CO)2}2]-catalyzed
[5+2] cycloaddition of alkyne-vinylcyclopropanes,[3c] in which
an internal alkyne consistently and efficiently afforded the
corresponding ring-closed products, whereas no [5+2] cyclo-
Table 1: Rhodium(I)-catalyzed [5+2] cycloaddition reaction of 1.[a]
Scheme 1. Metal-catalyzed ring-closing reaction of allenylcyclopro-
panes.
tion[6b] of allenylcyclopropanes into a-alkylidenecyclopen-
tenes, and the other is the formation of the a-alkylidene-3-
cyclohexen-1-one frameworks by the IrI-catalyzed carbon-
ylative [5+1] ring-closing reaction[6c] of allenylcyclopropanes.
Entry
RhI catalyst
Solvent
T [8C]
t [h]
Yield [%][b]
1
2
3
4
5
6
7
8
9
[{RhCl(CO)2}2]
[{RhCl(CO)2}2]
[{RhCl(CO)dppp}2]
[{RhCl(CO)dppp}2]
[{RhCl(CO)2}2]
[{RhCl(CO)2}2]
[{RhCl(CO)2}2]
[{RhCl(CO)2}2]
[{RhCl(CO)dppp}2]
[{RhCl(CO)dppp}2]
[{RhCl(CO)dppp}2]
[{RhCl(CO)dppp}2]
toluene
toluene
toluene
toluene
dioxane
dioxane
DCE
80
RT
80
RT
80
RT
80
RT
80
RT
80
RT
2
24
0.2
1
0.3
1.5
1
30
1
11
0.5
3
66
57
90
88
64
55
80
66
72
n.r.[c]
69
79
[*] Dr. F. Inagaki, K. Sugikubo, Y. Miyashita, Prof. Dr. C. Mukai
Division of Pharmaceutical Sciences, Graduate School of Natural
Science and Technology, Kanazawa University
Kakuma-machi, Kanazawa 920-1192 (Japan)
Fax: (+81)76-234-4410
DCE
dioxane
dioxane
DCE
10
11
12
E-mail: cmukai@kenroku.kanazawa-u.ac.jp
Homepage: http://www.p.kanazawa-u.ac.jp/~yakuzou/
indexen.html
DCE
[**] This work was supported by a Grant-in-Aid for Scientific Research
from the Ministry of Education, Culture, Sports, Science, and
Technology (Japan), for which we are thankful.
[a] Reaction conditions: 0.1m solution of alkyne-allenylcyclopropane 1
was treated with the RhI catalyst (10 mol%) under
nitrogen
atmosphere. [b] Yield of isolated product. [c] n.r.=no reaction. DCE=
dichloroethane, dppp=1,3-bis(diphenylphosphino)propane, Ts=4-tol-
uenesulfonyl.
a
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.200906994.
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Table 2: Rhodium(I)-catalyzed [5+2] cycloaddition reaction of 3.[a]
addition product was formed when
a terminal alkyne was employed.[9]
Other catalysts were tested, such as
[RhCl(PPh3)3],
(PPh3)2],
[{RhCl(CO)dppp}2],
[RhCl(CO)-
[{RhCl(cod)}2],
[Rh-
(C10H8)cod]+BF4À, and [Rh(CO)-
(dppp)2]+ClÀ, with or without a
silver salt; however, much lower
yields or no reaction at all was
observed in all cases, apart from
[{RhCl(CO)dppp}2]. Indeed, the
Entry
Substrate
RhI cat.
T [8C], t [h]
Product (yield [%])[b]
addition of compound
1
to
1
3a
A
A
80, 0.5
RT, 3
4a (86)
4a (87)
10 mol% [{RhCl(CO)dppp}2] in
toluene at 808C for 10 min afforded
2 in a higher yield (90%; Table 1,
entry 3). Similarly, a satisfactory
yield was obtained when the reac-
tion was performed at room tem-
perature for 1 h (Table 1, entry 4).
Therefore, [{RhCl(CO)2}2] and
[{RhCl(CO)dppp}2] were found to
be suitable catalysts for our pur-
pose. Next, we examined two sol-
vents, dioxane and dichloroethane,
both of which are frequently
employed in rhodium-catalyzed
reactions.[3] Dichloroethane fur-
nished higher yields in the
[{RhCl(CO)2}2]-catalyzed reaction
(Table 1, entries 7 and 8), although
[{RhCl(CO)dppp}2]/toluene
2
3
3b
A
A
80, 0.2
RT, 6
4b (80)
4b (76)
3c
A
A
80, 0.2
RT, 1
4c (83)
4c (64)
4
3d
3e
3 f
B
B
80, 1
RT, 24
4d (53)
5d (12)
5d (28)
4d (10)[c]
(Table 1, entries 3 and 4) was supe-
rior to both dioxane and dichloro-
ethane (Table 1, entries 9–12).
The [5+2] cycloaddition of sev-
eral substrates that contain a termi-
nal triple bond was examined using
the complementary and inter-
changeable use of two sets of con-
ditions: [{RhCl(CO)2}2]/dichloro-
ethane and [{RhCl(CO)dppp}2]/tol-
uene (Table 2). Treatment of 3a
with [{RhCl(CO)2}2] afforded the
corresponding ring-closed product
4a in satisfactory yields at both
808C and at room temperature
(Table 2, entry 1). Bis(phenylsul-
fonyl) derivative 3b and dimethyl
acetal derivative 3c showed similar
behavior to 3a under the
5[d]
A
A
80, 0.2
RT, 1
4e (65)
4e (51)
6
B
B
80, 1
4 f (52)
4 f (60)
5 f (trace)
5 f (19)
RT, 24[e]
[a] Reaction conditions: 0.1m solution of alkyne-allenylcyclopropane 3 was treated with 10 mol% of
[{RhCl(CO)2}2] in dichloroethane or with 10 mol% of [{RhCl(CO)dppp}2] in toluene under a nitrogen
atmosphere. [b] Yield of isolated product. [c] Compound 3d was recovered in 35% yield. [d] Reaction
was performed in 0.05m solution of toluene in the presence of 20 mol% of [{RhCl(CO)2}2]. [e] Reaction
was carried out in 0.05m solution.
[{RhCl(CO)2}2] conditions to furnish 4b and 4c in high
yields (Table 2, entries 2 and 3). In the case of malononitrile
derivative 3d, the [5+2] product 4d was formed in moderate
two reaction conditions (Table 2, entry 5). A slightly lower
yield of 4e (compared with those of 4a–c) might be largely
due to a loss of the bis(substituent) effect.[11] Oxygen analogue
4 f was obtained in moderate yields with [{RhCl(CO)dppp}2]
(Table 2, entry 6). Therefore, the results in Tables 1 and 2 may
be summarized as follows: 1) judicial choice of two catalysts
consistently and complementarily afforded the corresponding
[5+2] products 4 (and 2) in moderate to high yields; and
yield (53%) with the formation of a cyclopentene derivative
[10]
by-product 5d
when exposed to [{RhCl(CO)dppp}2]
(Table 2, entry 4). Compound 3e, which contained a simple
methylene tether between two reaction centers, provided the
corresponding [5+2] product 4e in 65% or 51% yields for the
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Table 3: Rhodium(I)-catalyzed [5+2] cycloaddition reaction of 7.[a]
2) [{RhCl(CO)2}2] usually produced better results than those
Product (yield [%])[b]
with [{RhCl(CO)dppp}2], although this depends on the
substrate.
Entry Substrate
T [8C], t [h]
There are two plausible mechanisms for the production of
the [5+2] product 4, based on the previously proposed
mechanism for the metal-catalyzed [5+2] cycloaddition of
vinylcyclopropanes containing p-p multiple bonds
(Scheme 2).[3,4] Path a involves the initial production of a
1
2
3
4
7a
80, 0.2
RT, 1
8a (76)
8a (75)
7b
80, 0.2
RT, 1
8b (59)
8b (67)
7c (Z=CO2Me) 80, 0.2
8c (89)
8c (81)
RT, 1
7d (Z=CO2Me) 80, 0.5
8d (58)
8d (50)
9d (25)
9d (9)
RT, 24
Scheme 2. A plausible mechanism for the formation of 4, 5, and 6
from 3.
[a] Reaction conditions: 0.1m solution of alkyne-allenylcyclopropane 7
was treated with 10 mol% of [{RhCl(CO)2}2] in dichloroethane under a
nitrogen atmosphere. [b] Yield of isolated product. TMS=trimethylsilyl.
rhodacyclohexene intermediate I from the RhI-catalyzed
cycloisomerization reaction between a cyclopropane ring
and the distal double bond of an allenyl moiety.[6b,c] The
bicyclo[5.4.0] derivatives 8a and 8c in satisfactory yields
(Table 3, entries 1 and 3). The terminal TMS compounds 7b
and 7d furnished their corresponding [5+2] cycloaddition
products 8b and 8d, respectively, in lower yields compared to
those of 8a and 8c (Table 3, entries 2 and 4). In the case of 7d,
the formation of cyclopentene derivative 9d, which is
structurally similar to 5d and 5 f (Table 2), was observed
(Table 3, entry 4). The alternative [{RhCl(CO)dppp}2] cata-
lyst was not as effective in the transformation of 7 into 8.
Our next objective was the application of the alkyne-
allenylcyclopropane ring-closing reaction to the construction
of the larger-sized bicyclo[5.5.0]dodecatriene to preliminarily
confirm the scope of this procedure (Scheme 3). Exposure of
one-carbon homologated substrate 10 to a catalytic amount of
[{RhCl(CO)2}2] under the standard condition provided the
desired bicyclo[5.5.0]derivative 11 in low yields (22–32%).
III
À
insertion reaction of the Csp2 Rh bond into the triple bond
of I would lead to rhodabicyclo[6.4.0]dodecatriene interme-
diate II. Reductive elimination of RhIII from intermediate II
should then provide 4. Isolation of cyclopentene derivative
5
[6b] would strongly rationalize the intermediacy of I (path a).
Reductive elimination, instead of the insertion reaction of I,
would result in the formation of 5. The other possible reaction
pathway is indicated by path b. The oxidative addition
reaction of the RhI catalyst to an alkyne group and the
distal double bond of the allenyl moiety would initially form
the rhodabicyclo[4.3.0]nonadiene intermediate III, which
might be susceptible to a ring expansion assisted by the
release of the ring strain in the cyclopropane ring to generate
the eight-membered intermediate II. Path b, via intermedia-
te III, might be indirectly supported by the fact that a
carbonylative [2+2+1] product 6 was obtained as a by-
product together with 2, when 1 was reacted under a carbon
monoxide atmosphere instead of nitrogen.[12] Thus, it seems
that both reaction pathways are feasible for this [5+2] ring-
closing reaction, depending on the reaction conditions.
Changing
the
catalyst
from
[{RhCl(CO)2}2]
to
[{RhCl(CO)dppp}2] produced a significant improvement to
furnish 11 in 63% yield along with the formation of 12 (17%).
[{RhCl(CO)dppp}2] was also effective for nitrogen-atom-
containing substrate 13. Indeed, 14 was obtained in 74% yield
together with 15 (4%) when heated in toluene for two hours.
Finally, it was shown that having a phenylsulfonyl
substituent on the allenyl moiety was not essential for the
efficient [5+2] ring-closing reactions of the alkyne-allenylcy-
clopropane derivatives. Furthermore, treatment of 16 with
Next, we examined the RhI-catalyzed [5+2] cycloaddition
reaction between an allenylcyclopropane and internal alkyne
groups (Table 3). Treatment of N-Ts derivative 7a and
malonate derivative 7c, both of which contain a 2-heptynyl
residue, with a catalytic amount of [{RhCl(CO)2}2] provided
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Scheme 4. Ring-closing reaction of methyl-substituted allene 16.
In summary, we have developed a RhI-catalyzed intra-
molecular [5+2] cycloisomerization reaction between alkyne
and allenylcyclopropane functionalities under mild condi-
tions, which leads to the facile formation of the bicyclo-
[5.4.0]undecatriene frameworks. Judicious choice of the RhI
catalyst, [{RhCl(CO)2}2] or [{RhCl(CO)dppp}2], consistently
afforded the desired products in satisfactory yields. This
method was successfully applied to the construction of larger
bicyclo[5.5.0]dodecatriene skeletons. Further investigation
into the scope and limitations of this method, as well as its
applications in the synthesis of natural products, are now
underway.
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Received: December 12, 2009
Published online: February 19, 2010
Keywords: allenes · bicyclic compounds · cycloaddition ·
.
cyclopropanes · rhodium
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Communications
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[12] Compound 6 (13%) was formed along with 2 (48%) when a
solution of 1 was heated in toluene at 1008C in the presence of
10 mol% of [{RhCl(CO)2}2] under 10 atm of CO for 1 h.
[13] A small amount of a by-product was obtained,
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[8] The reaction of 1 with 5 mol% of [{RhCl(CO)2}2] produced 2 in
37% yield. Thus, we used 10 mol% of RhI catalyst for the next
investigation.
the structure of which may be assigned as 18
1
from its H NMR and IR spectra. The forma-
[9] A successful example of [{RhCl(CO)2}2]-catalyzed [5+2] cyclo-
addition between the terminal alkyne and (E)-2-(1-ethoxycy-
clopropyl)vinyl moieties was reported; see Ref. [3g].
[10] The Z configuration of 5 was determined by NOE experiments
in which enhancement between Ha and Hb was observed.
tion of 18 could be rationalized in terms of
participation of carbon monoxide derived
from the [{RhCl(CO)2}2] catalyst.
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