Stereoselective Cascade Reactions of Donor–Acceptor Cyclopropanes with m-N,N-Dialkylaminophenyl α,β-Unsaturated Carbonyls: Diastereoselective Synthesis of cis- and trans-Tetralins

Article abstract of DOI:10.1002/adsc.201600416

The ytterbium(III) triflate [Yb(OTf)₃]-catalyzed diastereoselective cascade reaction of m-N,N-dimethylaminophenyl α,β-unsaturated carbonyls with cyclopropane 1,1-diesters under mild reaction conditions afforded highly substituted cis- and trans-tetralins. The reaction of m-N,N-dimethylaminophenyl α,β-unsaturated ketones with cyclopropane 1,1-diesters provided tetralins with a trans orientation of the 1,4-substitutents on the cyclohexyl ring; cis-tetralins were obtained from m-N,N-dimethylaminophenyl substituted methylidenemalonates with high diastereoselectivities. (Figure presented.).

Full text of DOI:10.1002/adsc.201600416

UPDATES
DOI: 10.1002/adsc.201600416
Stereoselective Cascade Reactions of Donor–Acceptor Cyclopro-
panes with m-N,N-Dialkylaminophenyl a,b-Unsaturated Carbon-
yls: Diastereoselective Synthesis of cis- and trans-Tetralins
Seunghui Sina and Sung-Gon Kima,*
a
Department of Chemistry, Kyonggi University, 154-42, Gwanggyosan-ro, Yeongtong-gu, Suwon 16227, Republic of Korea
Fax : (+82)-31-253-1165; phone: (+82)-31-249-9631; e-mail: sgkim123@kyonggi.ac.kr
Received: April 19, 2016; Revised: May 17, 2016; Published online: && &&, 0000
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201600416.
Abstract: The ytterbium(III) triflate [Yb(OTf)3]-
catalyzed diastereoselective cascade reaction of m-
N,N-dimethylaminophenyl a,b-unsaturated carbon-
yls with cyclopropane 1,1-diesters under mild reac-
tion conditions afforded highly substituted cis- and
trans-tetralins. The reaction of m-N,N-dimethylami-
nophenyl a,b-unsaturated ketones with cyclopro-
pane 1,1-diesters provided tetralins with a trans ori-
entation of the 1,4-substitutents on the cyclohexyl
ring; cis-tetralins were obtained from m-N,N-dime-
thylaminophenyl substituted methylidenemalonates
with high diastereoselectivities.
However, only a few papers have reported the one-
pot synthesis of the 1-aryltetralin skeleton.[6] Herein,
we report the development of a short, one-pot diaste-
reoselective synthesis of cis- and trans-tetralins by the
Lewis acid-catalyzed Friedel–Crafts/Michael addition
cascade reaction of m-N,N-dimethylaminophenyl a,b-
unsaturated carbonyls with donor–acceptor (D–A) cy-
clopropanes.
D–A cyclopropanes with donor and acceptor sub-
stituents at the vicinal position have recently become
popular and powerful building blocks in organic syn-
thesis for the construction of various acyclic and
cyclic compounds.[7] Owing to their special features
and immense reactivity, they have been deployed in
numerous synthetic methodologies and are widely
used in organic synthesis. The common transforma-
tion of D–A cyclopropanes is a ring-opening reaction,
providing access to 1,3-bifunctionalized compounds.[8]
Keywords: cascade reactions; donor–acceptor cyclo-
propanes; Friedel–Crafts reaction; Michael addi-
tion; tetralins
Tetralin is a well-known privileged scaffold commonly
encountered in several biologically active natural
products and synthetic pharmaceutical compounds.[1]
In particular, the 1-aryltetralin skeleton belongs to
a class of lignans found in natural cyclolignans and
synthetic derivatives with a broad spectrum of biolog-
ical activities including antimalarial, antifungal, anti-
bacterial, anti-inflammatory, antitumor, anti-HIV, and
antidepressant activities (Figure 1).[2] For example,
sertraline (Zoloft) is primarily used to treat depres-
sion due to its selective inhibition of the reuptake of
human synaptosomal serotonin.[3] Podophyllotoxin
(Condylox) is applied to the skin as a topical treat-
ment for external genital warts, and its synthetic de-
rivatives such as etoposide and teniposide are type II
topoisomerase targeting anticancer drugs used for the
treatment of lung cancer, leukemia, lymphomas, and
genital tumors.[4] In view of their potent biological ac-
tivities and unique structural features, several synthet-
Figure 1. Biologically active compounds containing the aryl-
ic approaches have been developed for aryltetralins.[5] tetralin scaffold.
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Table 1. Optimization of the reaction conditions.[a]
Scheme 1. Lewis acid-catalyzed reaction of donor-acceptor
cylopropanes with electron-enriched arenes.
The cycloadditions of D–A cyclopropanes with
dienes, dipolarophiles, or 1,3-dipoles, which have at-
tracted much interest, afford various highly function-
alized carbo- and heterocyclic compounds.[9]
Recently, we developed a Friedel–Crafts type ring-
opening reaction of D–A cyclopropanes with elec-
tron-enriched benzenes including N,N-dialkylaniline
providing a valuable method for the synthesis of 1,1-
diarylalkane derivatives (Scheme 1a).[10] N,N-Dialkyl-
[a]
Unless otherwise specified, the reactions were carried
out in solvent (0.2M) with 1a (0.10 mmol), 2a
(0.12 mmol), 4ꢁ molecular sieve (20 mg), and Lewis acid
(20 mol%).
ACHTUNGTRENNUNGaniline acts as a good nucleophile without any deacti-
vation or decomposition by Lewis acids such as
Yb(OTf)3, which was used as the catalyst in this Frie-
del–Crafts reaction. In the present study, we further
advanced this ring-opening strategy to achieve the
stereoselective Friedel–Crafts type ring-opening/intra-
molecular Michael addition cascade reaction of D–A
cyclopropanes with m-N,N-dimethylaminophenyl a,b-
[b]
Isolated yield after chromatographic purification.
[c]
[d]
1
Determined by H NMR analysis.
10 mol% Lewis acid was used.
unsaturated carbonyl compounds leading to the for- and stereoselectivity of the reaction. The best results
mation of the corresponding tetralin derivatives were obtained with CHCl3. Moreover, 10 mol%
(Scheme 1b).[11]
Yb(OTf)3 was sufficient to catalyze the reaction with-
Based on these considerations, we began our stud- out significantly affecting the yield, reaction time, or
ies on the cascade reaction of m-(N,N-dimethylanilin- diastereoselectivity (entry 14).
yl)-a,b-unsaturated phenyl ketone 1a with dimethyl 2-
With the optimized reaction conditions in hand
phenylcyclopropane-1,1-dicarboxylate 2a as the model [1 equiv. of 1, 1.2 equiv. of 2, and 10 mol% catalyst
substrates using 20 mol% Sc(OTf)3 as the catalyst in Yb(OTf)3 in CHCl3], the substrate scope and general-
CHCl3 at 608C. To our delight, the desired tetralin ity of the reaction were investigated (Table 2). Firstly,
compound 3a was produced in a 78% yield and with diverse D–A cyclopropanes 2 were investigated to ex-
good diastereoselectivity (8:1 dr) (Table 1, entry 1). amine the generality of this cascade reaction with m-
To optimize the reaction conditions for maximum (N,N-dimethylanilinyl)-a,b-unsaturated phenyl ketone
yield, higher diastereoselectivity, and a shorter reac- 1a, and the results are shown in Table 2.
tion time, several Lewis acid catalysts such as
In general, the reactions of all the substrates
Ni(ClO)4, Cu(OTf)2, Zn(OTf)2, Sm(OTf)3, and smoothly afforded the corresponding tetralins in mod-
Yb(OTf)3 were screened (entries 2–6). The Yb(OTf)3- erate to good yields (51–89%). The reactions of the
catalyzed reaction afforded the product in an excel- diethyl and dibenzyl ester compounds resulted in
lent yield (85%) and with a high diastereoselectivity slightly decreased yields and diastereoselectivities
(12:1 dr) in a shorter reaction time (entry 6). To fur- (Table 2, 3b and 3c). The cyclopropanes with elec-
ther optimize the reaction efficiency, various solvents tron-donating groups (Me/OMe) on the phenyl ring
were examined in the Yb(OTf)3-catalyzed reaction were more reactive than those with an unsubstituted
(entries 7–13). The reaction medium was found to phenyl group, producing the corresponding 1,4-disub-
have substantial impact on the conversion efficiency stituted tetralins 3d, 3e, and 3f, respectively, in good
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Table 2. Substrate scope of D-A cyclopropnes in the Frie-
Table 3. Substrate scope of the m-N,N-dimethylaminophen-
yl-a,b-unsaturated ketones in the Friedel–Crafts/Michael ad-
dition cascade reaction.[a]
del–Crafts/Michael addition cascade reaction.[a]
[a]
All of the reactions were carried out in CHCl3 (0.2M)
with 1a (0.10 mmol), 2 (0.12 mmol), 4ꢁ molecular sieve
(20 mg), and Yb(OTf)3 (10 mol%). Isolated yields are
shown.
[a]
All of the reactions were carried out in CHCl3 (0.2M)
with 1 (0.10 mmol), 2a (0.12 mmol), 4ꢁ molecular sieve
(20 mg), and Yb(OTf)3 (10 mol%). Isolated yields are
shown.
yields and with high diastereoselectivities. Halogen
substituents in the 4-position of the benzene ring in
D–A cyclopropane did not affect the reactivity or ste-
reoselectivity; halo-substituted analogs 3g–i were ob-
tained in good yields from the corresponding D–A cy- results are shown in Table 3. In the case of the R3
clopropanes 1g–i. Moreover, cyclopropane 1j with group, the reactions proceeded well with electron-do-
a styryl substituent provided the corresponding prod- nating (3m and 3n) and electron-withdrawing (3o–3s)
uct 3j in moderate yield, and the diastereoselectivity substituents. Notably, the ortho-chloro substituent on
in this case was the lowest in the series. Notably, 1- the phenyl R3 group afforded the corresponding prod-
heteroaryl-substituted tetralins 3k and 3l were also uct in a better reactivity and with a higher diastereo-
obtained when the corresponding D–A cyclopropanes selectivity than the meta- or para-chloro substituents
2k and l bearing thienyl and furanyl groups, respec- (3s vs. 3q and 3r). When a heteroaryl group was intro-
tively, were reacted with substrate 1a.
duced at the R3 position, the reactions showed good
Next, the scope of m-N,N-dimethylaminophenyl- stereocontrol and produced the corresponding prod-
a,b-unsaturated ketones 1 was investigated, and the ucts 3t and 3u in good yields. Furthermore, the reac-
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Scheme 2. Proposed mechanism of the reaction and origin of diastereoselectivity.
tions of aliphatic a,b-unsaturated ketones with a bulki- laminophenyl-a,b-unsaturated ketone (see the Sup-
er group, such as tert-butyl and cyclopropyl, proceed- porting Information for details).
ed smoothly to afford the corresponding products 3v
and 3w with good stereoselectivities, even though the actions of D–A cyclopropanes
yield of product 3v decreased slightly. dimethylaminophenyl-substituted methylidenemalo-
Encouraged by these MM2 results, the cascade re-
2
with m-N,N-
AHCTUNGTRENNUNG
The relative configuration of product 3w was found nate 4a were subsequently investigated under the
to be trans by single-crystal X-ray diffraction analysis; same optimized reaction conditions. As shown in
those of the others in this series were assigned by Table 4, the reaction products, tetralin tetraesters,
analogy.[12]
were obtained in moderate to good yields. As expect-
Based on the experimental results, the mechanism ed, the relative stereochemistry was found to be cis
of this reaction is depicted in Scheme 2. The Lewis by the single-crystal X-ray diffraction data of 5f.[12]
acid activates D–A cyclopropane 2a generating com- With an increase in the sterically bulky benzyl ester
plex A. Subsequent Friedel–Crafts type attack of the group in D–A cyclopropane, the diastereoselectivity
m-(N,N-dimethylanilinyl)-a,b-unsaturated
phenyl increased, whereas the yield decreased slightly (5c).
ketone 1a at the benzylic position provides ring-open- The reactions tolerated cyclopropanes with electron-
ing complex B. This intermediate B undergoes cycli- donating or electron-withdrawing groups, and the de-
zation via the attack of the generated enolate on mal- sired products 5d–5i were obtained in good yields
onate, producing the corresponding tetralin. To align (62–88%) and with high diastereoselectivities (8:1 to
itself in the proper position for the intramolecular Mi- 16:1 dr). When styryl-cyclopropane 1j was reacted
chael addition, intermediate B can adopt two differ- with 4a, the corresponding product 5j was obtained in
ent conformations C and D. Conformer D suffers a moderate yield and with a high diastereoselectivity.
from a severe eclipsing interaction of the phenyl 1-Heteroaryl-substituted tetralins 5k and 5l were also
group with the malonyl methyl ester group, whereas obtained, even though the yield and diastereoselectiv-
conformer C experiences a less eclipsing interaction ity were low in the case of 5k (48%, 2:1 dr).
from its phenyl and ester moieties. The more stable
conformer C is preferred over D providing product 3a cient protocol for the synthesis of 1,4-substituted tet-
with a trans configuration of the 1,4-substituents. ralins via the reactions of m-N,N-dimethylaminophen-
In conclusion, we have developed a simple and effi-
Interestingly, from examining the models and rough yl-a,b-unsaturated carbonyls with D–A cyclopropanes
MM2 calculations of the intermediates to better un- in a cascade fashion. This method selectively provides
derstand the mechanism, the D-type conformer was both 1,4-substituted cis and trans tetralins depending
found to be more stable than the C-type conformer on the m-N,N-dimethylaminophenyl-a,b-unsaturated
when m-N,N-dimethylaminophenyl-substituted meth- carbonyls used. The reaction of m-N,N-dimethylami-
ylidenemalonate was used instead of m-N,N-dimethy- nophenyl-a,b-unsaturated ketones with D–A cyclo-
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Table 4. Friedel–Crafts/Michael addition cascade reaction of
m-N,N-dimethylaminophenyl methylidenemalonate 4a with
D–A cyclopropanes 2.[a]
Experimental Section
General Procedure for the Friedel–Crafts/Michael
Addition Cascade Reaction of D–A Cyclopropanes
with m-N,N-Dimethylaminophenyl a,b-Unsaturated
Carbonyls
To a solution of m-N,N-dimethylaminophenyl-a,b-unsaturat-
ed carbonyl 1 or 4a (0.10 mmol, 1.0 equiv.), Yb(OTf)3
(0.020 mmol, 20 mol%), and 4ꢁ molecular sieve in CHCl3
(0.5 mL) was added D–A cyclopropane
2 (0.12 mmol,
1.2 equiv.). The resulting mixture was stirred at 608C until
complete consumption of m-N,N-dimethylaminophenyl-a,b-
unsaturated carbonyl 1 or 4a was observed as determined by
TLC. The resulting mixture was cooled to room temperature
and was quenched with saturated NaHCO3 solution. The
mixture was extracted with CH2Cl2. The combined organic
layer were washed with brine, dried over anhydrous MgSO4,
and concentrated under vacuum. The crude residue was pu-
rified by flash column chromatography with EtOAc/hexanes
as the eluent to afford the desired tetralin compound 3or 5.
Acknowledgements
This research was supported by the Nanomaterial Technology
Development Program through the National Research Foun-
dation of Korea (NRF) funded by the Ministry of Science,
ICT and Future Planning (NRF-2012M3A7B4049645) and
the Basic Science Research Program through NRF funded by
the Ministry of Education (NRF-2013R1A1A2009850).
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Stereoselective Cascade Reactions of Donor–Acceptor
Cyclopropanes with m-N,N-Dialkylaminophenyl a,b-
Unsaturated Carbonyls: Diastereoselective Synthesis of cis-
and trans-Tetralins
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Adv. Synth. Catal. 2016, 358, 1 – 7
Seunghui Sin, Sung-Gon Kim*
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