Rhodium-catalyzed asymmetric formal olefination or cycloaddition: 1,3-dicarbonyl compounds reacting with 1,6-diynes or 1,6-enynes

Article abstract of DOI:10.1002/anie.201007727

A cationic rhodium(I) complex catalyzes the title reaction of 1,6-diynes through a [2+2+2] cycloaddition and subsequent electrocyclic ring opening (see scheme; cod=1,5-cyclooctadiene, H₈-binap=2,2′- bis(diphenylphosphino)-5,5′,6,6′,7,7′,8,8′-octahydro-1, 1′-binaphthyl). The asymmetric intramolecular [2+2+2] cycloaddition of 1,3-dicarbonyl compounds with 1,6-enynes was also accomplished. Copyright

Full text of DOI:10.1002/anie.201007727

DOI: 10.1002/anie.201007727
Asymmetric Catalysis
Rhodium-Catalyzed Asymmetric Formal Olefination or Cycloaddition:
1,3-Dicarbonyl Compounds Reacting with 1,6-Diynes or 1,6-Enynes**
Takeshi Suda, Keiichi Noguchi, and Ken Tanaka*
Transition-metal-catalyzed asymmetric hydrogenation of
enolizable b-ketoesters leading to b-hydroxyesters is a
useful method for the one-step construction of two consec-
utive stereocenters.[1–3] In this reaction, the ketone carbonyl
group is enantioselectively reduced with hydrogen through
and diastereoselectivity.[13,14] We report herein the cationic
rhodium(I)/H8-binap or segphos complex as a catalyst for the
asymmetric formal olefination and cycloaddition of 1,3-
dicarbonyl compounds with 1,6-diynes and 1,6-enynes,
respectively, which construct one or three stereocenters with
high diastereo- and enantioselectivity.[15]
À
À
C H/O H bond formation (Scheme 1). In contrast, asym-
We first investigated the reaction of b-ketoester 2a
(1.1 equiv) with sulfonamide-linked 1,6-diyne 1a in the
presence of
a cationic rhodium(I)/(R)-binap complex
(5 mol%). Gratifyingly, the reaction proceeded at room
temperature for only 1 hour to give a-methyl-b,g-unsaturated
ester 3aa with moderate yield and enantioselectivity presum-
ably through [2+2+2] cycloaddition and subsequent electro-
cyclic ring opening[16] (Table 1, entry 1). After screening biaryl
À
À
Scheme 1. Transition-metal-catalyzed asymmetric C H/O H versus
Table 1: Screening of ligands for rhodium-catalyzed asymmetric inter-
molecular reaction of 1,6-diyne 1a and b-ketoester 2a.[a]
=
À
À
C C or C C/C O bond-forming reactions of enolizable b-ketoesters.
metric olefination or cycloaddition of the ketone carbonyl
=
À
À
group of b-ketoesters through C C or C C/C O bond
formation would furnish chiral b,g-unsaturated esters or b-
alkoxyesters in a single step (Scheme 1).[4] Despite potential
synthetic utility of such reactions, no report has been found in
the literature to date. In 2007 our research group reported
that a cationic rhodium(I)/H8-binap complex[5,6] is a highly
active and versatile catalyst for the [2+2+2] cycloaddition[7]
of 1,2-dicarbonyl compounds with 1,6-diynes.[8–12] After this
report, we succeeded using the cationic rhodium(I)/H8-binap
complex as a catalyst in the asymmetric [2+2+2] cyclo-
addition of 1,2-dicarbonyl compounds with 1,6-enynes,
thereby constructing two stereocenters with high enantio-
Entry
Ligand
2a [equiv]
Yield [%][b] (E/Z)
ee [%][c]
1
2
3
4
5
(R)-binap
1.1
1.1
1.1
2.0
2.0
69 (1:7)
66 (1:7)
61 (1:5)
83 (1:6)
97 (1:7)
61 (S)
70 (S)
92 (S)
94 (S)
96 (S)
(R)-H8-binap
(R)-segphos
(R)-segphos
(R)-H8-binap
[a] In all entries, complete conversions of 1a were observed. [b] Yield of
isolated product. [c] The ee value and absolute configuration of a major
olefin geometric isomer. (R)-binap=(R)-2,2’-bis(diphenylphosphino)-
[*] T. Suda, Prof. Dr. K. Tanaka
Department of Applied Chemistry, Graduate School of Engineering
Tokyo University of Agriculture and Technology
Koganei, Tokyo 184-8588 (Japan)
1,1’-binaphthyl,
5,5’,6,6’,7,7’,8,8’-octahydro-1,1’-binaphthyl,
(R)-H8-binap=(R)-2,2’-bis(diphenylphosphino)-
cod=1,5-cyclooctadiene,
(R)-segphos=(R)-5,5’-bis(diphenylphosphino)-4,4’-bi-1,3-benzodioxole.
Fax: (+81)42-388-7037
E-mail: tanaka-k@cc.tuat.ac.jp
Homepage: http://www.tuat.ac.jp/~tanaka-k/
Prof. Dr. K. Noguchi
Instrumentation Analysis Center, Tokyo University of Agriculture
and Technology, Koganei, Tokyo 184-8588 (Japan)
bisphosphine ligands (entries 1–3), the use of (R)-segphos
furnished 3aa with the highest ee value, but the yield was still
moderate (entry 3). The use of excess 2a (2.0 equiv) in the
reaction using (R)-segphos increased the product yield along
with slight improvement of the product ee value (entry 4).
Significant improvement of both the product yield and
ee value using excess 2a was observed in the reaction using
(R)-H8-binap, which furnished 3aa with the highest yield and
ee value (entry 5). The absolute configuration of the major
[**] This work was supported partly by Grants-in-Aid for Scientific
Research (Nos. 20675002 and 20·8746) from MEXT (Japan). We are
grateful to Takasago International Corporation for the gift of H8-
binap, segphos, and xyl-segphos, and Umicore for generous
support in supplying a rhodium complex.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201007727.
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4475

Communications
product (À)-(Z)-3aa was determined to be S by derivatization
were required in cases of 1d and 1e (entries 4 and 5). With
respect to 1,3-dicarbonyl compounds, both aryl-substituted b-
ketoesters 2a and 2b (entries 1 and 6) and 1,3-diketone 2c
(entry 7) reacted with 1a to give the formal olefination
products with high yields and ee values. However, the
reactions of both methyl-substituted b-ketoester 2d
(entry 8) and 1,3-diketone 2e (entry 9) with 1a proceeded
in lower yields because of the formation of the homo-
[2+2+2]-cycloaddition products of 1a, although the ee values
were high. The formation of chloro- or fluoro-substituted
stereocenters (entries 10–13) other
into the known (R)-2-benzoyl-1-propanol.[17]
The generality of the asymmetric intermolecular formal
olefination of 1,3-dicarbonyl compounds with 1,6-diynes was
then examined by using the cationic rhodium(I)/(R)-H8-binap
complex as a catalyst at room temperature (Table 2).[16] With
respect to 1,6-diynes, a variety of symmetrical and unsym-
metrical internal 1,6-diynes (1a–e; entries 1–5) could be
employed for this reaction, although a moderate ee value
was observed in the case of 1c (entry 3) and slow additions
than methyl-substituted ones was
Table 2: Rhodium-catalyzed asymmetric intermolecular formal olefination of 1,3-dicarbonyl compounds
also possible, although the lower
enantioselectivity was observed.
Next, the asymmetric [2+2+2]
cycloaddition of b-ketoester 2a with
sulfonamide-linked 1,6-enyne 4 was
attempted, and was expected to
furnish the bicyclic chiral ester 5
possessing three stereocenters
(Scheme 2). However, no reaction
was observed at room temperature,
and the homo-[2+2+2] cycloaddi-
tion of 1,6-enyne 4 proceeded at
808C.
with 1,6-diynes.[a]
Entry
1
2
t [h] Yield [%][b]
ee [%][c]
1
1a (Z=NSO2Ar,[d] R1 =R2 =Me) 2a
1
1
(S)-3aa: 97 (E/Z=1:7) 96
2
1b (Z=NTs, R1 =R2 =Me)
1c (Z=C(CO2Bn)2,
2a
2a
3ba: 95 (E/Z=1:8)
95
59
3[e]
16 3ca: 72 (E/Z=1:7)
R1 =R2 =Me)
4[f]
5[f]
1d (Z=NTs, R1 =R2 =Et)
2a
3
3da: 24 (E/Z=1:>20) 99
1e (Z=NTs, R1 =Ph, R2 =Me) 2a
16 3ea: 62 (E/
99
Z=1:>20)[g]
Thus, an asymmetric intramo-
lecular [2+2+2] cycloaddition of a
b-ketoester with a 1,6-enyne was
investigated as shown in Table 3.[18]
Fortunately, the reaction of sub-
strate 6a, in which the 1,6-enyne
and a-methyl-b-ketoester moieties
are connected with a benzene ring,
in the presence of the cationic
6
7
1a
1a
2b
2c
1
3ab: 89 (E/Z=1:1)
95 (E), 95 (Z)
rhodium(I)/(S)-binap
complex
1
1
3ac: >99 (E/Z=1:4)
3ad: 38 (E/Z=1:6)
99
(10 mol%) proceeded at 808C to
give the desired cycloaddition prod-
uct 7a in good yield with excellent
diastereoselectivity, although the
enantioselectivity was moderate
(entry 1). After screening biaryl
bisphosphine ligands (entries 1–3),
the use of (S)-segphos furnished 7a
with the highest yield and ee value
(entry 3). As increasing the steric
bulk on the phosphorus [(S)-xyl-
segphos] decreased both the yield
and ee value (entry 4), (S)-segphos
was selected as the best ligand.
8
9
1a
1a
2d (R=OEt)
2e (R=Me)
94
16 3ae: 54 (E/Z=1:2)
94 (E), 93 (Z)
10
11
1a
1a
2 f (R=Ph)
2g (R=Me)
2g (R=Me)
1
1
3af: 96 (E/Z=1:3)
3ag: 50 (E/Z=1:>20) 84
79
12[e] 1c
16 3cg: 71 (E/Z=1:>20) 74
The generality of this asymmet-
ric intramolecular [2+2+2] cyclo-
addition of 1,3-dicarbonyl com-
pounds with 1,6-enynes was then
examined by using the cationic
rhodium(I)/(S)-segphos complex as
a catalyst at 808C (Table 4). With
respect to the 1,3-dicarbonyl moi-
eties, both acetyl (6a; entry 1) and
benzoyl esters (6b; entry 2) could
13[e] 1c
2h
16 3ch: 65 (E/Z=1:10)
67
[a] Reactions conditions: [Rh(cod)2]BF4 (5 mol%), (R)-H8-binap (5 mol%), 1a–e (1 equiv), 2a–h
(2 equiv) in CH2Cl2 at room temperature. Structure of the major olefin geometry isomer was described.
[b] Yield of isolated product. [c] The ee value of the major olefin geometric isomer. [d] Ar=4-BrC6H4.
[e] Ligand: (S)-segphos (entry 3). Ligand: (R)-segphos (entries 12 and 13). [f] 1 was added to 2a and the
Rh catalyst over 2 h. [g] The regioisomer was generated in approximately 10%, although this compound
could not be isolated in a pure form. Bn=benzyl, Ts=4-toluenesulfonyl.
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Table 4: Rhodium-catalyzed asymmetric intramolecular cycloaddition of
1,3-dicarbonyl compounds with 1,6-enynes.[a]
Entry
6
t
Yield [%][b]
ee
[h]
[%]
Scheme 2. Rhodium-catalyzed intermolecular reaction of 1,6-enyne 4
and b-ketoester 2a.
1
2
6a (Z=NTs, R=Me)
6b (Z=NTs, R=Ph)
16 (+)-7a: 94,
16 (3aR,5aR,6R)-(À)-7b[c]:
95
16 (À)-7c: 98
86
87
Table 3: Screening of ligands for rhodium-catalyzed asymmetric intra-
molecular reaction of 6a.
3
4
6c (Z=C(CO2Me)2,
R=Me)
6d (Z=C(CO2Me)2, R=Ph) 24 (À)-7d: 94
88
74
Entry
Ligand
Conv. [%][a]
Yield [%][b]
ee [%]
5[d]
6e
16 (+)-7e: 68
85
1
2
3
4
(S)-binap
90
100
100
59
72
87
94
43
61 (+)
45 (+)
86 (+)
60 (+)
(S)-H8-binap
(S)-segphos
(S)-xyl-segphos
[a] Determined by 1H NMR analysis. [b] Yield of isolated product. xyl-
segphos=5,5’-bis[di(3,5-dimethylphenyl)phosphino]-4,4’-bi-1,3-benzo-
dioxole.
6
7
6 f (R=OMe)
6g (R=Cl)
16 (+)-7 f: 80
80
84
16 (+)-7g[c]: 90
equally be employed to give tetracyclic esters 7a and 7b,
respectively in high yields with good ee values. This observa-
tion is in sharp contrast to the reactions of entries 1 and 8 in
Table 2 that exhibited significantly different reactivity. Not
only b-ketoesters but also 1,3-diketone 6e could participate in
this reaction, although the product yield decreased (entry 5).
With respect to the 1,6-enyne moieties, not only sulfonamide-
linked 1,6-enynes but also malonate-linked 1,6-enynes 6c and
6d could be employed (entries 3 and 4). With respect to the
tethers between the 1,6-enyne and 2-methylene-1,3-dicarbon-
yl moieties, not only the phenyl group but also the methoxy-
phenyl (6 f; entry 6) and chlorophenyl (6g; entry 7) groups
could be employed to give tetracyclic esters 7 f and 7g,
respectively, in high yields with good ee values. Furthermore,
tricyclic ester 7h could also be obtained with high ee value,
although a high catalyst loading was required (entry 8).
Importantly, the present asymmetric intramolecular [2+2+2]
cycloaddition of 1,3-dicarbonyl compounds with 1,6-enynes is
highly diastereoselective. Other diastereomers were detected
8[e]
6h
24 (+)-7h: 59
92
[a] Reaction conditions: [Rh(cod)2]BF4 (10 mol%), (S)-segphos
(10 mol%), 6a–h in (CH2Cl)2, 808C. [b] Yield of isolated product.
[c] The relative and absolute configuration of (À)-7b was determined to
be 3aR,5aR,6R by the X-ray crystallographic analysis of the corresponding
4-bromobenzoyl ester (À)-8.[17,19] The relative configuration of (Æ)-7g
was also confirmed by the X-ray crystallographic analysis of the
corresponding 4-bromobenzoyl ester (Æ)-9.[17,19] [d] Ligand: (S)-binap.
[e] Catalyst: 20 mol%.
1
in at least less than 5% yields by H NMR analysis of the
crude reaction mixture.
Possible mechanisms for the selective formation of (S)-
3aa and (3aR,5aR,6R)-7b using (R)-H8-binap and (S)-seg-
phos ligands are shown in Schemes 3 and 5, respectively,
although the precise mechanisms cannot be concluded at the
present stage. The reaction of 1a and 2a with the cationic
rhodium(I)/(R)-H8-binap complex furnishes intermediate A
through coordination of the ester carbonyl group to rhodium.
Scheme 3. Possible mechanism for cationic rhodium(I)/(R)-H8-binap-
catalyzed selective formation of (S)-3aa.
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Communications
Reductive elimination of rhodium and subsequent electro-
between the intermolecular reaction of 1,3-dicarbonyl com-
pounds with 1,6-diynes and the intramolecular reaction of 1,3-
dicarbonyl compounds with 1,6-enynes. Thus for comparison,
the intramolecular reaction of a 1,3-dicarbonyl compound
with a 1,6-diyne, not a 1,6-enyne, was examined. Interestingly,
the reaction of substrate 10 proceeded to give almost racemic
product 11, although the product yield was high (Scheme 6).
cyclic ring-opening furnishes (S)-3aa. The formation of
intermediate A’, which would furnish (R)-3aa, is unfavorable
because of the steric interaction between the equatorial
phenyl group on the phosphorus atom of (R)-H8-binap and
the methyl group derived from 1a.
Indeed, the reactions of sterically more demanding
internal diynes 1d,e and 2a furnished products 3da and
3ea, respectively, with higher ee values than 3ba (Table 2,
entries 4 and 5 versus entry 2). In contrast, the reaction of
sterically less demanding terminal diyne 1e[20] and 2a
furnished almost racemic product 3 fa (Scheme 4).
Scheme 6. Rhodium-catalyzed intramolecular cycloaddition of 1,3-di-
carbonyl compound with 1,6-diyne.
In conclusion, we have developed the cationic rhodium(I)/
(R)-H8-binap complex as a catalyst for the asymmetric
intermolecular formal olefination of enolizable 1,3-dicarbon-
yl compounds with 1,6-diynes by [2+2+2] cycloaddition and
subsequent electrocyclic ring opening. The asymmetric intra-
molecular [2+2+2] cycloaddition of 1,3-dicarbonyl com-
pounds with 1,6-enynes was also accomplished by using a
cationic rhodium(I)/(S)-segphos complex as a catalyst. Future
work will focus on the synthetic application of this method-
ology.[21]
Scheme 4. Rhodium-catalyzed asymmetric intramolecular cycloaddition
of 1,3-dicarbonyl compound with 1,6-diyne.
As shown in Scheme 5, the reaction of 6b with the cationic
rhodium(I)/(S)-segphos complex furnishes intermediate B, in
which one chiral center is constructed enantioselectively.
Indeed, this observed enantioface selection is consistent with
our previously reported rhodium-catalyzed asymmetric inter-
molecular [2+2+2] cycloaddition of 1,2-dicarbonyl com-
pounds with 1,6-enynes.[13] Subsequent ketone carbonyl
group insertion and coordination of the ester carbonyl
group to rhodium are able to furnish two intermediates, C
and C’, in which two additional chiral centers are constructed
diastereoselectively. However, the formation of the inter-
mediate C’, which furnishes (3aR,5aS,6S)-7b, would be
unfavorable because of the steric interaction between the
axial phenyl group on the phosphorus atom of (S)-segphos
and the ethoxy group derived from 6b. Thus, reductive
elimination of rhodium from the intermediate C furnishes
(3aR,5aR,6R)-7b.
Received: December 9, 2010
Revised: February 28, 2011
Published online: April 7, 2011
Keywords: asymmetric catalysis · cycloaddition · enynes ·
.
olefination · rhodium
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À
À
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[15] We have recently reported the rhodium-catalyzed [2+2+2]
cycloaddition of a 1,6-diyne with acetylacetone and methyl
acetoacetate. See: Ref. [8c].
[16] The product olefin geometry is determined primarily through
thermodynamic control of the electrocyclic ring-opening reac-
tion. However, the other relies on the influence of the cationic
rhodium(I) complex or silica gel during the reaction or the
product isolation, respectively. For thermodynamic control of
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[18] For the rhodium-catalyzed enantio- and diastereoselective
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[19] CCDC 803849 [(3aR,5aR,6R)-(À)-8] and 811124 [(Æ )-9] contain
the supplementary crystallographic data for this paper. These
data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif.
[20] Although the reaction of a tosylamide-linked terminal 1,6-diyne
and 2a was also examined, the corresponding formal olefination
product was not obtained at all because of the rapid homo-
[2+2+2] cycloaddition of the diyne.
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