Rhodium(I)-Catalyzed [2+2+2] Cycloaddition between Allene, Alkyne, and Imine via a Strained Azarhodacycle Intermediate

Article abstract of DOI:10.1002/adsc.201500417

The rhodium(I)-catalyzed intramolecular [2+2+2] cycloaddition between allenes, alkynes, and imines has been developed. This cyclization proceeds via a strained azarhodacycle, giving a 5,7-fused cyclic amide or a tricyclic product containing an 8-azabicyclo[3.2.1]octane skeleton in high yield.

Full text of DOI:10.1002/adsc.201500417

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DOI: 10.1002/adsc.201500417
Very Important Publication
Rhodium(I)-Catalyzed [2+2+2] Cycloaddition between Allene,
Alkyne, and Imine via a Strained Azarhodacycle Intermediate
Yoshihiro Oonishi,a,* Yoshio Hato,a,b and Yoshihiro Satoa,c,*
a
Faculty of Pharmaceutical Sciences, Hokkaido University, Sapporo 060-0812, Japan
Fax: (+81)-11-706-3722; e-mail: oonishi@pharm.hokudai.ac.jp or biyo@pharm.hokudai.ac.jp
Shionogi Innovation Center for Drug Discovery, Shionogi & Co., Ltd., Sapporo 001-0021, Japan
ACT-C, Japan Science and Technology Agency (JST), Sapporo 060-0812, Japan
b
c
Received: April 28, 2015; Revised: July 11, 2015; Published online: October 13, 2015
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201500417.
Abstract: The rhodium(I)-catalyzed intramolecular
[2+2+2] cycloaddition between allenes, alkynes,
and imines has been developed. This cyclization
proceeds via a strained azarhodacycle, giving a 5,7-
fused cyclic amide or a tricyclic product containing
an 8-azabicyclo[3.2.1]octane skeleton in high yield.
tion proceeds through the unusual insertion of a C=O
double bond into rhodacycle intermediate Ia, which
might be the pathway via a highly strained transition
state, producing the metallacycle intermediate IIa. We
envisaged that if a C=N double bond could be utilized
in the [2+2+2] cyclization instead of a C=O double
bond, nitrogen-containing heterocycles would be ob-
tained through an azarhodacycle intermediate IIb
(Scheme 2).
Keywords: alkynes; allenes; [2+2+2] cycloaddition;
imines; rhodium
Initially, [2+2+2] cycloaddition using various C=N
double bonds was tested (Scheme 3). The reaction of
allene-yne 3a having an oxime moiety in a tether
under the optimal conditions previously reported by
Transition metal-catalyzed [2+2+2] cycloadditions in- us {i.e., 10 mol% [Rh(dpbbz)]ClO4, dichloroethane,
volving carbon-heteroatom multiple bonds as a com- 808C}[5] did not afford the desired bicyclic compound
ponent should be one of most straightforward strat- 4a at all but produced 5-membered cyclic compounds
egies for the synthesis of complicated heterocycles in 6a and 7a in 74% and 3% yields, respectively. The
a one-pot procedure.[1] There are a plethora of reports compound 6a would be produced through oxidative
on transition metal-catalyzed [2+2+2] cycloadditions cycloaddition of the allene and alkyne moieties to the
ꢀ
of two C-C multiple bonds with a C N triple bond Rh(I) complex followed by b-hydride elimination
such as a nitrile to afford pyridine or dihydropyridyne from Ib and reductive elimination, while 7a was
derivatives [Scheme 1, Eq. (1)].[1] On the other hand, formed from 6a through elimination of the benzyl al-
[2+2+2] cycloadditions in which the C=N double cohol.[7] The result suggests that the C=N double
bonds such as imines[2,3] or oximes[4] were employed bond of the oxime could not be inserted into the C
À
remain rare [Scheme 1, Eq. (2)].
We have recently reported
Rh bond of rhodacycle intermediate Ib. When the
a
Rh(I)-catalyzed substrate 3b having a p-toluenesulfinyl imine was
[2+2+2] cyclization between allenes, alkynes, and al- tested in the reaction, the desired [2+2+2] product 4b
dehydes, giving bicyclo[5.3.0]decane or 8-oxabicy- was obtained in 33% yield as an almost 1:1 diastereo-
clo[3.2.1]octane derivatives (2 or 3) in good to high mixture and the yield of 5-membered ring 7b was sup-
yields (Scheme 2).[5,6] Notably, this [2+2+2] cycloaddi- pressed to 2%.[8–10] Furthermore, the cyclization of 3c
having a tert-butylsulfinyl imine under the same con-
ditions afforded the cyclic compound 4c in 69%
yield.[11] These results indicate that the nature of a C=
N double bond greatly influences the reactivity
toward [2+2+2] cycloaddition.
Next, the cyclization of 3c using various ligands was
investigated, and the results are summarized in
Table 1. The cycloaddition using dppe proceeded
smoothly, giving the desired cyclic compound 4c in
59% yield (entry 2). When dppp was employed in this
Scheme 1. Cycloaddition involving C-N multiple bonds.
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Scheme 2. [2+2+2] Cycloaddition through the unusual insertion of a C=X bond.
Table 1. Screening of Catalysts.
Entry
Catalyst[a]
Yield [%][b]
1
2
3
4
5
6
[Rh(dppbz)]ClO4
[Rh(dppe)]ClO4
[Rh(dppp)]ClO4[c]
[Rh(dppp)]ClO4
[Rh(dppb)]ClO4
[Rh(BINAP)]ClO4
69
59
76
74
9
[d]
–
[a]
[Rh(ligand)]ClO4 was generated from [Rh(ligand)(nbd)]-
ClO4 and H2 in ClCH2CH2Cl.
Almost a 1:1 diastereomeric mixture of 4c was obtained.
5 mol% [Rh(dppp)]ClO4 were used.
[b]
[c]
[d]
A complex mixture was obtained.
[Rh(BINAP)]ClO4 were not effective for this cycload-
dition (entries 5 and 6).
Having established the optimal conditions, the
scope and limitations of the cyclization were exam-
ined (Table 2). The cyclization of 3d and 3e, having
a TMS or an ester at the terminus of the alkyne, pro-
ceeded smoothly, giving 4d and 4e in 64% and 65%
yields, respectively. The substrate 3f, having no sub-
stituent on the terminus of the alkyne, is also applica-
ble in this cyclization, giving the bicyclic amide 4f in
Scheme 3. Effect of the substituent on the C=N double
bond.
reaction, the yield of 4c was improved to 76% 41% yield. On the other hand, the cyclizations of 4g
(entry 3), in which case the catalyst loading could be and 4h, having a phenyl group and a chloride atom at
reduced to 5 mol%, thereby giving 4c in 74% yield the terminus, were sluggish and the yields of the
(entry 4). On the other hand, [Rh(dppb)]ClO4 and cyclic compounds were modest or low. In these cases,
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Rhodium(I)-Catalyzed [2+2+2] Cycloaddition
Table 2. Cyclization of various substrates.[a]
Table 3. Cyclization through direct reductive elimination
from IIb.
Entry
Catalyst[a]
Time [h]
Yield [%][b]
1
2
3
4
5
6
7
[Rh(dppp)]ClO4
[Rh(dppe)]ClO4
[Rh(dppb)]ClO4
[Rh(dppbz)]ClO4
[Rh(BINAP)]ClO4
[Rh(BIPHEP)]ClO4
3
4
3
2
3
3
1
33
24
44
55
74
75
84
[c]
[Rh(BINAP)]ClO4
[a]
[Rh(ligand)]ClO4 was generated from [Rh(nbd)2]ClO4,
ligand, and H2 in ClCH2CH2Cl.
[b]
[c]
Almost a 1:1 diastereomeric mixture of 5i was obtained.
3i was recovered in 49% (entry 1) and 31% (entry 2).
5 mol% [Rh(BINAP)]ClO4 were used. [Rh(BINAP)]-
ClO4 was generated from [Rh(BINAP)(nbd)]ClO4 and
H2 in ClCH2CH2Cl.
duced to 5 mol% without significant loss of the yield
of 5i (entry 7).
[a]
Next, the cyclization of various substrates having
no hydrogen atom at the b-position of the sulfinyli-
mine moiety was examined (Table 4). Allene-ynes 3j
and 3k, having ester and no substituent at the termi-
nus of the alkyne, gave the corresponding cyclic com-
pounds 5j and 5k in 84% and 69% yields, respectively.
The cyclization of 3l–3n using [Rh(BINAP)]ClO4
of showed low yields. In these cases, the use of
Almost a 1:1 mixture of diastereoisomers of 4 was ob-
tained except for 4d and 4g (4d: dr=4.9/1, 4g: 2.9/1, see
the Supporting Information).
The yields when using 10 mol% [Rh(dppbz)]ClO4 are
[b]
shown in parentheses.
the
use
of
[Rh(dppbz)]ClO4
instead
[Rh(dppp)]ClO4 improved the yields of 4g and 4h to [Rh(dppbz)]ClO4 instead of [Rh(BINAP)]ClO4 could
61% and 72% yields, respectively. slightly improve the yields of cyclic compounds, and
Next, we investigated the [2+2+2] cyclization of 5l–5n were obtained in 43%, 44%, and 12% yields, re-
a substrate having no hydrogen atom at the b-position spectively.
of the sulfinylimine moiety, which was expected to
Finally, the cyclization of 1,6-allenyne 3o instead of
proceed through the direct reductive elimination from 1,5-allenynes 3a–3n, having no substituents at the b-
azarhodacycle intermediate IIb, producing 8-azabicy- position of the sulfinylimine moiety in the substrate,
clo[3.2.1]octane derivatives 5 (Scheme 2). Unfortu- was investigated (Scheme 4). Interestingly, it was
nately, the cyclization of 3i with 10 mol% found that the use of [Rh(dppbz)]ClO4 afforded the
[Rh(dppp)]ClO4 provided the desired cyclic com- bicyclic amide 4o and 8-azabicyclo[3.2.1]octane 5o in
pound 5i in only 33% yield as an almost 1:1 diastereo- 31% and 29% yields, respectively, with high diaste-
mixture (Table 3, entry 1).[12] Thus, screening of Rh(I) reoselectivities (dr= >20/1). This result suggests that
complexes was reinvestigated in this reaction system. the diastereomers of 3o originating from both the
The use of cationic Rh(I)-dppe and Rh(I)-dppb af- axial chirality of the allene moiety and the chiral
forded 5i in 24% and 44% yields, respectively (en- center of the sulfur atom show different reactivities
tries 2 and 3). When dppbz was used as a ligand, the that would influence the course of reaction for the
yield was slightly improved to 55% (entry 4). On the formation of 4o and 5o.
other hand, reactions using biaryl ligands BINAP and
To obtain an insight into the above-mentioned dia-
BIPHEP proceeded smoothly, giving the azacyclic stereoselectivities, the substrate 3o was prepared from
compound 5i in 74% and 75% yields, respectively racemic allene-aldehyde 8[13] and (S)-tert-butylsulfina-
(entries 5 and 6). Additionally, it was found that the mide, and the resulting diastereomers (S,S)-3o (98%
catalyst loading of [Rh(BINAP)]ClO4 could be re- de) and (R,S)-3o (97% de) were separated by prepa-
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Table 4. Cyclization of various substrates.[a]
Scheme 5. Preparation of (S,S)-3o and (R,S)-3o.
axial chirality of the allene moiety was transferred to
the cyclized product (Scheme 6).[5] Thus, in this cycli-
zation, cyclized products (S,S)-4o and (S,S)-5o should
be produced from (S,S)-3o via (S,S)-III, while (R,S)-
4o and (R,S)-5o should be formed from (R,S)-3o. In
the cyclization of (S,S)-3o or (R,S)-3o with
[Rh(dppbz)]ClO4, however, only two cyclic com-
pounds (R,S)-4o and (S,S)-5o were obtained in almost
the same yields as shown in Table 5, indicating that
racemization of the allene moiety in (S,S)-3o or
(R,S)-3o would occur under the reaction condi-
tions.[16,17] That means, the formation of bicyclic rho-
dacycle intermediate (S,S)-III or (R,S)-III from 1,6-al-
lenyne (S,S)-3o or (R,S)-3o, their rhodacycles having
a 6–5 fused ring system, is relatively slower than that
from 1,5-allenynes 3a–3n, resulting in competition be-
tween the enantiospecific cyclization from (S,S)-3o or
(R,S)-3o producing chiral cyclized products 4o and 5o
and racemization of the allene moiety in 3o. Howev-
er, the reason why the cyclization via rhodacycle in-
termediate (S,S)-IV or (R,S)-IV stereospecifically af-
fords (S,S)-5o or (R,S)-4o, respectively, is still unclear.
In conclusion, we have succeeded in the develop-
ment of an Rh(I)-catalyzed [2+2+2] cycloaddition of
allene-ynes with tethered imines through a highly
strained azarhodacycle intermediate IIb. b-Hydride
[a]
Almost a 1:1 mixture of diastereoisomers of 5 was ob-
tained.
The yields when using 10 mol% [Rh(dppbz)]ClO4 are
shown in parentheses.
[b]
Scheme 4. Cyclization of 3o using [Rh(dppbz)]ClO4.
rative chiral HPLC (Scheme 5). Then each of the dia- elimination from azarhodacycle IIb followed by re-
stereomers was subjected to the above-mentioned ductive elimination afforded 5,7-fused cyclic amides
conditions (Table 5). Surprisingly, it was found that in high yields, while reductive elimination from IIb
there was no apparent difference of reactivity be- gave 8-azabicyclo[3.2.1]octane derivatives in moder-
tween the diastereomers (S,S)-3o and (R,S)-3o, giving ate to high yields. Furthermore, on the basis of mech-
cyclic compounds (R,S)-4o and (S,S)-5o, respectively, anistic studies, it was found that the cyclization of 1,6-
in almost the same yields. In these reactions, the dia- allenyne with a tethered sulfinylimine proceeded
stereomers (S,S)-4o and (R,S)-5o were not detected at through racemization of the allene moiety in the sub-
all (entries 1 and 2).[14,15]
strate and that stereochemistry of the substrate affect-
On the basis of the results of these studies, a possi- ed the reaction course. Further studies to determine
ble reaction mechanism is depicted in Scheme 6. the scope and limitations of the cycloaddition and its
From our previous study on the Rh(I)-catalyzed cycli- application to the synthesis of natural products are in
zation of allene-ynes with a tethered aldehyde, the progress.
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Rhodium(I)-Catalyzed [2+2+2] Cycloaddition
Table 5. Cyclizations of (S,S)-3o and (R,S)-3o.[a]
Entry
Substrate
Yields [%]
(S,S)-4o
(R,S)-4o
(S,S)-5o
(R,S)-5o
1
2
(S,S)-3o
(R,S)-3o
–
–
22
24
19
14
–
–
[a]
[Rh(dppbz)]ClO4 was generated from [Rh(dppbz)(nbd)]ClO4 and H2 in ClCH2CH2Cl.
Scheme 6. Possible reaction mechanism.
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[4] For examples of Rh(I)-catalyzed [2+2+2] cycloaddition
reactions using an oxime as one component, see: a) F.
Xu, C. X. Wang, D. P. Wang, X. C. Li, B. S. Wan, Chem.
Eur. J. 2013, 19, 2252; b) F. Xu, C. X. Wang, H. L.
Wang, X. C. Li, B. S. Wan, Green Chem. 2015, 17, 799.
[5] Y. Oonishi, T. Yokoe, A. Hosotani, Y. Sato, Angew.
Chem. 2014, 126, 1153; Angew. Chem. Int. Ed. 2014, 53,
1135.
[6] For our recent study of different types of Rh(I)-cata-
lyzed [2+2+2] cycloadditions of allene-ynes with C=O
bonds, see: Y. Oonishi, Y. Kitano, Y. Sato, Tetrahedron
2013, 69, 7713.
[7] For selected examples of Rh(I)-catalyzed cycloisomeri-
zation of allene-ynes to give similar cyclic compounds,
see: a) K. M. Brummond, H. Chen, P. Sill, L. You, J.
Am. Chem. Soc. 2002, 124, 15186; b) T. Shibata, Y.
Takesue, S. Kadowaki, K. Takagi, Synlett 2003, 268;
c) C. Mukai, F. Inagaki, T. Yoshida, S. Kitagaki, Tetra-
hedron Lett. 2004, 45, 4117.
Experimental Section
General Procedure for Cyclization Using
[Rh(ligand)]ClO4
[18]
A
solution of [Rh(ligand)(nbd)]ClO4
(0.0150 mmol,
10 mol% to a substrate) in degassed (a freeze-pump up-
thaw cycle was conducted) ClCH2CH2Cl (0.58 mL: 0.026M
to Rh) was stirred under an H2 atmosphere at room temper-
ature for 1 h. Then the reaction mixture was degassed, and
the reaction vessel was flushed with argon gas. To the mix-
ture, was added a solution of substrate (0.150 mmol) in de-
gassed ClCH2CH2Cl (0.92 mL) and the reaction mixture was
stirred at the indicated temperature for the indicated time.
After removal of the solvent, the residue was purified by
silica gel column chromatography to give the product.
Acknowledgements
[8] A 1:1 diastereomixture of allene-yne 3, having a
sulfinylimine in the tether was used as substrate.
[9] For selected examples of Rh(I)-catalyzed intramolecu-
lar cycloaddition to give similar bicyclic compounds in-
cluding 7-membered rings: [5+2] cycloaddition of vi-
nylcyclopropane, see: a) P. A. Wender, H. Takahashi, B.
Witulski, J. Am. Chem. Soc. 1995, 117, 4720; b) P. A.
Wender, L. O. Haustedt, J. Lim, J. A. Love, T. J. Wil-
liams, J.-Y. Yoon, J. Am. Chem. Soc. 2006, 128, 6302;
[5+2] cycloaddition of allenylcyclopropane, see: c) F.
Inagaki, K. Sugikubo, Y. Miyashita, C. Mukai, Angew.
Chem. 2010, 122, 2252; Angew. Chem. Int. Ed. 2010, 49,
2206; [5+2] cycloaddition of 3-acyloxy-1,4-enyne, see:
d) X.-Z. Shu, S. Huang, D. Shu, I. A. Guzei, W. Tang,
Angew. Chem. 2011, 123, 8303; Angew. Chem. Int. Ed.
2011, 50, 8153; e) X.-Z. Shu, X. Li, D. Shu, S. Huang,
C. M. Schienebeck, X. Zhou, P. J. Robichaux, W. Tang,
J. Am. Chem. Soc. 2012, 134, 5211 and see also ref.[4]
[10] For selected examples of Rh(I)-catalyzed cyclization to
give 7-membered carbocyclic rings, see: a) Y. Sato, Y.
Oonishi, M. Mori, Angew. Chem. 2002, 114, 1266;
Angew. Chem. Int. Ed. 2002, 41, 1218; b) Y. Oonishi,
M. Mori, Y. Sato, Synthesis 2007, 2323; c) C. Aïssa, A.
Fürstner, J. Am. Chem. Soc. 2007, 129, 14836; d) D.
CrØpin, C. Tugny, J. H. Murray, C. Aïssa, Chem.
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Dr. Yasunori Yamamoto in Hokkaido University is greatly
acknowledged for X-ray crystallographic analysis. This work
was financially supported by Grants-in-Aid for Scientific Re-
search (B) (No. 26293001) and Grants-in-Aid for Scientific
Research (C) (No. 2646000104) from the Japan Society for
the Promotion of Science (JSPS) and also by a Grant-in-Aid
for Scientific Research on Innovative Areas “Molecular Acti-
vation Directed toward Straightforward Synthesis” (No.
23105501) from the Ministry of Education, Culture, Sports,
Science and Technology, Japan.
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[11] The structure of 4c was unambiguously determined by
X-ray analysis after chemical transformation. CCDC
1052420 contains the supplementary crystallographic
data. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Also see the Sup-
porting Information.
[12] The structure of 5i was unambiguously determined by
X-ray analysis after chemical transformation. CCDC
1052421 contains the supplementary crystallographic
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Rhodium(I)-Catalyzed [2+2+2] Cycloaddition
data. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Also see the Sup-
porting Information).
[16] At this stage, the mechanism of racemization of the
allene moiety is not clear.
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52, 10630.
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[13] Y. Oonishi, A. Hosotani, Y. Sato, J. Am. Chem. Soc.
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[14] The absolute configuration of (R,S)-4o was determined
by the Mosher method after desulfination followed by
reaction with MTPACl (see the Supporting Informa-
tion).
[15] The absolute configuration of (S,S)-5o was unambigu-
ously determined by X-ray analysis after chemical
transformation. CCDC 1052422 contains the supple-
mentary crystallographic data. These data can be ob-
tained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif. Also see the Supporting Information).
nich,
Organometallics
1988,
7,
936;
for
[Rh(dppbz)(nbd)]ClO4, see: c) S. H. Bergens, P.
Noheda, J. Whelan, B. Bosnich, J. Am. Chem. Soc.
1992, 114, 2128.
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