Photosensitised regioselective [2+2]-cycloaddition of cinnamates and related alkenes

Article abstract of DOI:10.1039/c7cc06710k

An efficient method for the synthesis of substituted cyclobutanes from cinnamates, chalcones, and styrenes has been developed utilizing a visible-light triplet sensitisation mode. This reaction provides a diverse range of substituted cyclobutanes in high yields under mild conditions without the need of external additives. Good regioselectivity is obtained due to strong π-π-stacking of arene moieties, whereas diastereoselectivity relies on the electronic effects or ortho-substitution of the arene substrate. The utility of this transformation is demonstrated by the formal synthesis of the lignane natural product (±)-Tanegool.

Full text of DOI:10.1039/c7cc06710k

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COMMUNICATION
Photosensitised Regioselective [2+2]-Cycloaddition of Cinnamates
and related Alkenes
Received 00th January 20xx,
Accepted 00th January 20xx
Santosh K. Pagire, Asik Hossain, Lukas Traub, Sabine Kerres, and Oliver Reiser*
DOI: 10.1039/x0xx00000x
www.rsc.org/
HO
An efficient method for the synthesis of substituted cyclobutanes from
cinnamates, chalcones, and styrenes has been developed utilizing a visible-
light triplet sensitisation mode. This reaction provides a diverse range of
substituted cyclobutanes in high yields under mild conditions without the
need of external additives. Good regioselectivity is obtained due to strong
π-π-stacking of arene moieties, whereas diastereoselectivity relies on the
electronic effects or ortho-substitution of the arene substrate. The utility
of this transformation is demonstrated by the formal synthesis of the
lignane natural product (±)-Tanegool.
OH
HO
HO
O
O
MeO
MeO
HO
O
N
N
O
O
CO2H
CO2H
O
O
O
O
HO
HO
MeO
MeO
O
HO
OMe
Piperarborenine D
OH
HO
Truxinic acid
Sagerinic Acid
(cinnamate derivatives)
OH
MeO
MeO
OMe
Me
MeO
MeO
RO
HO
HO
Dimeric and strained cyclobutanes are prevalent structures
commonly encountered in natural products. They are found in
the plant kingdom, insects, and microbial species, many of
which possess a wide range of biological activities with
potential therapeutic applications.1 Cinnamic acid derived
dimers, such as truxinic acid, piperarborenine D, or Sagerinic
acid derivatives are prominent examples (figure 1).2 Moreover,
styrene-derived naturally occurring cyclobutanes such as
Endiandrin A, di-O-methylendiandrin A, Magnosalin (trans) or
Andamanicin (cis) are widely used as anti-inflammatory agents,
which potently bind to glucocorticoid receptors (GR).3
OMe
MeO
Me
O
O
Me
MeO
MeO
OMe
Me
MeO
RO
R = H,
OMe
Magnosalin
Andamanicin (cis)
(trans)
OH
Endiandrin A
R = OMe, di-O-methylendiandrin A
from Goniothalmus Thwaittesii
(styrene derivatives)
(chalcone derivative)
Figure
derivatives.
1 Representative naturally occurring head-to-head cyclobutanes
efficiently,11 being summarised in a recent review: Only if ren-
dered intramolecular and only if the reacting centers are spa-
tially close is a [2+2] photocycloaddition with cinnamates and
other β
-arylacrylic acid derivatives possible.4 Consequently, a
number of indirect approaches have been developed for such
Various synthetic methods have been developed for the syn-
thesis of four-membered carbocycles in an atom economic
manner.4,5 In general, the [2+2]-cycloaddition reaction of al-
kenes by thermal methods is rare,6 while photochemical
approaches under UV irradiation have long been established.7
Alternatively, visible-light photocatalysis has emerged for this
transformation.8 In particular, the group of Yoon has deve-
loped the visible-light synthesis of a wide range of cyclo-
butanes derivatives from olefins.9,10
substrates, requiring additional synthetic steps or additives:
Yoon and coworkers have introduced a redox auxiliary for α-β-
unsaturated carbonyl compounds, which upon photocyclo-
addition and subsequent cleavage affords cyclobutane carbox-
amides, esters, or thioesters.12 Beeler et al described a flow
technique for the dimerisation of cinnamates using thiourea
derived catalysts in combination with UV-light to afford ester-
substituted cyclobutanes.13
Despite the vast developments of photo mediated [2+2] cyclo-
addition reactions, surprisingly the intermolecular cycloaddi-
tion of simple cinnamates or styrenes was so far not achieved
Very recently, we have demonstrated that
α-bromocinna-
mates can be activated by direct electron transfer14 or by a
dual energy and electron transfer photocascade15 process.16
The later is believed to be initiated via a diradical species
through energy transfer from the excited photocatalyst, which
ultimately collapses to a vinyl radical upon bromine extrusion
in the presence of oxygen. In the absence of oxygen, however,
Institut für Organische Chemie, Universität Regensburg, Universitätsstr. 31, 93053
Regensburg, Germany. *E-mail: oliver.reiser@chemie.uni-regensburg.de
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
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J. Name., 2013, 00, 1-3 | 1
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Scheme 1. This work: Visible-light mediated [2+2]-cycloaddtions
Table 1 Synthesis of 2a and 3a: Catalyst screening and reaction
optimisationa
Visible-light (455 nm)
[Ir{dF(CF3)ppy}2(dtb-bpy)]PF6 (1 mol %)
rt, DMF
R1
R3
R3
R
R
R1
Reaction
Optimization
CO2Et
CO2Et
CO2Et
CO2Et
R3
CO2Et
R
Key features
Mild reaction conditions
Broad substrate scope
No additives
+
R1
(Table 1)
Cinnamates
Chalcones
Styrenes
30 examples
11-99% yields
1:1 - 99:1 d.r.
truxinate
β
(cis)
δ truxinate
(trans)
1a
3a
2a
only E/Z-isomerisation was observed, and, in particular, no
Photocatalyst
(1.0 mol %)
Yield
(%)b
63
d.r.
[2+2]-cycloadducts are formed. Thus, we questioned the utili- Entry
Atmosphere
(δ/β)c
9:1
9:1
9:1
-
sation of such diradicals for simple cinnamates, and indeed, we
01
[Ir{dF(CF3)ppy}2(dtb-bpy)]PF6
fac[Ir(ppy)3]
O2
O2
O2
O2
O2
N2
N2
N2
demonstrate here the feasibility of a triplet sensitisation
02
44
protocol for [2+2]-cycloadditions, which not only allows the
03
[Ir(ppy)2 (dtb-bpy)]PF6
[Cu(dap)2Cl]
18
synthesis of ester-substituted cyclobutanes but also of those
derived from chalcones and styrenes (Scheme 1).
04
05
traces
traces
96
[Ru(bpy)3Cl2]
-
The activation of cinnamates via electron transfer by typical
photocatalysts17 such as [Ru(bpy)3]Cl2] (bpy = 2,2’-bipyridine, –
0.81 V vs SCE)18 or [Ir{dF(CF3)ppy}2(dtb-bpy)]PF6 (dF(CF3)ppy =
06
07d,e
[Ir{dF(CF3)ppy}2(dtb-bpy)]PF6
[Ir{dF(CF3)ppy}2(dtb-bpy)]PF6
Rose bengal, 530 nm
9:1
NDf
-
78
08
-
09
10
No catalyst
N2
NRg
-
-
2-(2,4-difluorophenyl)-5-trifluoromethylpyridine, dtb-bpy
=
4,4’-di-tert-butyl-2,2’-dipyridyl, Ir-F, –0.89 V vs SCE)19 is ther-
modynamically unfavourable owing to their high reduction po-
tential (e.g. –1.79 V vs SCE for 1a).20 Thus, photoredox cata-
lyzed cycloadditions of these types of unsaturated carbonyl
[Ir{dF(CF3)ppy}2(dtb-bpy)]PF6
no light
N2
NRg
a
Reaction conditions: Ethyl cinnamate 1a (1.0 mmol), photocatalyst (1.0
mol %), dry DMF (2 mL), LED455, 72 h, LED455, room temperature. b Isolated
compound is more feasible by energy transfer.21 The efficiency yields. c Determined by crude 1H-NMR analysis. 0.5 mol % photocatalyst
d
used. e Reaction time was 84 h. f d.r. not determined. g No reaction.
of energy transfer depends on the excited state lifetime of the
photocatalyst, thus it is independent of the redox potentials of
exclusively the
δ-diastereomer 2c in 88% yield. Para-
the reacting substrates. Having these facts in mind, we
initiated our investigation by exploring [2+2]-photocyclo-
addition of ethyl cinnamate 1a in the presence of 1 mol % Ir-F
substituted cinnamates with donor (+I/+M) or weak acceptor
(–I/–M) groups afford the corresponding thermodynamically
favored all-trans substituted cyclobutanes in good yields and
diastereoselectivities (2d/3d to 2h/3h, Table 2). In contrast,
strong electron withdrawing substituents decrease the diaste-
reoselectivity to a great extent, presumably due to the desta-
bilisation of the radical species formed as intermediates (see
the mechanistic discussion). Substitution in ortho-position of
the arene dramatically enhances the diastereoselectivity (up to
20:1, Table 2, 2n/3n to 2p/3p). Relevant for naturally occurring
cyclobutanes (cf. Fig. 1), di- or tri-arylsubstituted cinnamates
can be employed, providing cyclobutanes 2l/3l and 2m/3m. In
(Τ
= 2300 ns19) with blue light (LED455) under an oxygen
atmosphere (Table 1, entry 1). Gratifyingly, only head-to-head
-truxinate, trans) 2a and ( -truxinate, cis) 3a isomers were
obtained in a 9:1 ratio and 63% yield. The use of neutral
fac[Ir(ppy)3] ( = 1900 ns, ppy = 2-phenylpyridine, entry 2) and
[Ir(ppy)2(dtb-bpy)]PF6 (T = 557 ns, ppy = 2-phenylpyridine,
entry 3) gave lower yields, while [Cu(dap)2Cl]22
= 270 ns,
dap 2,9-bis(para-anisyl)-1,10-phenanthroline) and
[Ru(bpy)3Cl2] ( = 1100 ns) did not provide any product under
(
δ
β
Τ
(Τ
=
Τ
the identical conditions (Table 1, entry 4, 5).
particular, the isolated δ-isomer (3l) has been shown to be a
crucial intermediate for the synthesis of lignane natural pro-
duct (±)-Tanegool.4,23
The best catalyst (Ir-F, Table 1, entry 1) was selected for
further optimisation: Pleasingly, the cycloaddition proceeded
much more efficiently under inert gas conditions (entry 6),
Furan, thiophene, and N-Boc-pyrrole substituted cinnamates
were also suitable substrates,4,24 giving rise to desired head-to-
giving rise to 2a/3a (9:1) in 96% yield. Reducing the catalyst
amount to 0.5 mol% (entry 7) gave a lower, but still respec-
table yield (78%). No reaction was observed in the presence of
the triplet sensitizer rose Bengal (entry 8), further control
experiments suggested the requirement of both, Ir-F and
visible light (entries 9, 10).
head cyclobutanes 2q-s
/3q-s in good yields, however with
moderate diastereoselectivity (~1.7:1). Interestingly, for the
first two substrates, the unexpected head-to-tail dimers 4q, 4r
could also be detected in small amounts (see 1H-NMR in the
ESI), while in the case of the pyrrole derivative, only the head-
Next, the scope of the reaction was studied (Table 2). Under
the optimised conditions, methyl cinnamate (1b) provided
2b/3b in 89% yield and 10:1 d.r., improving on a previous
report that yielded the desired cycloadduct in lower yields and
selectivity (60%; up to 4:1, Scheme 1a).13 Likewise, the
to-head dimerisation products 2s/3s were observed. A
limitation of our protocol was encountered for the indole
derivative 2t, which was obtained only in 11% yield (Table 2).
Due to a fast cis/trans isomerisation, thus causing relaxation of
the excited state, [2+2] photocycloaddition reactions of
chalcones are rare.25 Nevertheless, we were pleased to see
photodimerisation of β-methyl ethyl cinnamate (1c) provides
2 | J. Name., 2012, 00, 1-3
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Table 2 Scope for cyclobutanes.a
Scheme 2: [2+2] cycloaddition of styrenes
R1
Ar
Ar
R2
R2
R1
Standard Conditions
R2
R1
Ar
5
6
O2N
Me
Me
Me
Me
Me
2d/3d,
2e/3e,
2f/3f,
Ph
CO2R
CO2R
R1 = 3-Me,
91% (d.r. = 3:1)
89% (d.r. = 5.3:1)
83% (d.r. = 7:1)
Ph
Ph
CO2Et
R1 = 4- -Pr,
i
CO2Et
CO2Et
R1
R1
R1 = 4-OMe,
Me
Ph
CO2Et
2c,
88%
R
1 = 4-F, 2g/3g, 72% (d.r. = 6:1)
O2N
R1 = 4-Br, 2h/3h, 49%b (d.r. = 4:1)
R1 = 4-CN, 2i/3i, 85% (d.r. = 1.2:1)
R1 = 4-CO2Me, 2j/3j, 89% (d.r. = 1.5:1)
2k/3k,
, 88%
(trans:cis =
2a/3a
R = Et,
(d.r. = 9:1)
R = Me, 2b/3b, 89%
(d.r. = 10:1)
, 96%
6b
6d
6e
, 80%
(trans:cis =
6a
, 92%
(trans:cis =
2.57:1)
, 86%
6c
, 84%
(trans:cis =
3.96:1)
(δ isomer only)
(trans:cis =
5.19:1)
3.38:1)
2.44:1)
R1 = 4-NO2,
86% (d.r. = 1.3:1)
OMe
Cl
HO
MeO
R2
developed. Indeed, in all cases tested (Scheme 3), the desired cross
coupled products were obtained and isolated in pure form, how-
ever, no appreciable bias beyond the expected statistical
distribution towards the cross-coupled dimers was observed.
MeO
CO2Et
CO2Et
CO2Me
CO2Et
CO2Me
CO2Et
MeO
HO
R2
Cl
OMe
MeO
R2 = F, 2n/3n, 74% (d.r. = 5:1)
R2 = CN, 2o/3o, 63% (d.r. = 7.34:1)
2l/3l
, 65% (d.r. = 3:1)
2m/3m, 70% (d.r. = 6:1)
R2
=
Scheme 3: [2+2] cross-cycloaddition of cinnamates
Ph , 2p/3p, 63% (d.r. = 20:1)
Me
N
CO2Et
Ar1
Ar2
CO2Et
CO2Et
Ar1
Ar2
CO2Et
BocN
Standard Conditions
CO2Et
CO2Et
S
O
CO2Et
CO2Me
CO2Me
+
0.5 mmol of each cinnamate
CO2Et
S
CO2Et
CO2Et
11%
O
NBoc
N
MeO
2r/3r,
Me
77% (d.r. = 1.8:1)
2t,
2q/3q,
4q, 5% (head-to-tail) c
63% (d.r. = 1.7:1)
2s/3s, 54%
(d.r. = 1.4:1)
c
(δ isomer only)
4r
, 9% (head-to-tail)
CO2Et
CO2Et
CO2Et
CO2Et
CO2Et
R
O
O
Ph
O
O
CO2Et
Ph
Ph
Ph
MeO
NC
81% (total yield)
46% (total yield)
70% (total yield)
MeO2C
O
O
7c, 54% (d.r. = 1.75:1) [cross]
2f, 13%; 2i, 14% [homo]
7b, 32% (d.r. = 1.9:1) [cross]
2j, 14%; 2a, <5% [homo]
2u/3u,
(Intramolecular)
7a, 35% (d.r. = 1.9:1) [cross]
2f, 24%; 2a, 11% [homo]
76% (d.r. = 3:1)
R
=
R = H, 2v/3v, 80% (d.r. 3:1)
R = Cl, 2w/3w, 74% (d.r. = 3:1)
(X-ray: δ-isomer, 2v)
a
Scope for cyclobutanes: standard conditions:
Substrate 1 (1.0 mmol),
Following the rationale put forward by Haag et al for the pho-
todimerisation of cinnamates,28 we propose that the transfor-
mations described here proceed by energy transfer via
diradical formation (Figure 2).29
[Ir{dF(CF3)ppy}2(dtb-bpy)]PF6 (1.0 mol %), anhydrous DMF (2 mL), LED455, 72 h,
LED455, room temperature, the diastereomeric ratios were determined either by
b
crude 1H-NMR analysis or on the basis of yield of isolated products. Reaction
time was 96 h. c Head-to-tail products were detected by 1H-NMR analysis.
Figure 2: Proposed reaction mechanism
that chalcones also underwent clean [2+2]-cycloaddition under
the photochemical protocol developed, giving rise to the
R1
R
desired cyclobutanes (2v/3v and 2w/3w) in good yields. The δ-
R1
isomer of 2v was unambiguously characterised by single X-ray
crystallography. Unfortunately, the attempted cycloaddition of
corresponding sulfone, cyano, or nitro substituted alkenes only
led to the E/Z-isomerisation of the starting materials.
*
1
R
diradical species
(excited state)
Energy
Transfer
*
Ir(III)
Ir(III)
1
1
blue light
Next, we explored the intermolecular [2+2] dimerisation of
R
R
styrenes
5
by energy transfer,21 given the importance of the
R1
R1
R1
resulting cycloadducts for biologically active molecules (cf.
Figure 1).3 Intermolecular styrene cycloadditions by photo-
chemical alkene oxidation were reported under visible-light
conditions, but require electron rich systems.10,26 To our
delight (Scheme 2), a number of electronically unbiased
styrenes 5a,c-e, but also the electron deficient styrene 5b
strong π−π
stacking
R1
(head-to-head products)
R
R
A
2
provided the corresponding head-to-head cycloadducts
high yields under our conditions.
6 in
The photo-excitation of the Ir-catalyst forms the excited Ir*,
which transfers energy to the substrate to form the activated
diradical species *, followed by dimerisation with to give
rise to . In agreement with the experimental results, the
1
The selective synthesis of unsymmetrical cyclobutanes is
challenging and only a few general methods are known.27 We
questioned if two electronically differentiated cinnamates
would allow cross coupling under the reaction conditions
1
1
A
regioselectivity (head-to-head products) can be rationalized by
strong π−π stacking of the arene moieties. The stereoselec-
This journal is © The Royal Society of Chemistry 20xx
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ARTICLE
Journal Name
Yoon, Acc. Chem. Res., 2016, 49, 2307–2315; e) T. R. Blum, Z. D.
Miller, D. M. Bates, I. A. Guzei and T. P. Yoon, Science, 2016,
354, 1391–1395; f) J. Du, K. L. Skubi, D. M. Schultz and T. P.
Yoon, Science, 2014, 344, 392–396; g) M. A. Ischay, Z. Lu and T.
P. Yoon, J. Am. Chem. Soc., 2010, 132, 8572–8574; h) K. L.
Skubi, T. R. Blum and T. P. Yoon, Chem. Rev., 2016, 116, 10035–
10074; i) S. Lin, S. D. Lies, C. S. Gravatt and T. P. Yoon, Org.
Lett., 2017, 19, 368–371; j) M. A. Cismesia and T. P. Yoon,
Chem. Sci., 2015, 6, 5426–5434.
tivity is dependent on the stabilisation of the benzylic radicals
(Figure 2,
which consequently undergo slower ring closure to allow equi-
librating to the sterically most favourable all-trans
arrangements.
A), being more effective for electron rich substrates,
A
In summary, we have developed an effective strategy for the
photodimerisation of cinnamates, styrenes, and chalcones
which led to the synthesis of substituted cyclobutanes in good
to excellent yields with moderate to good diastereo-
selectivities under mild reaction conditions.
10 M. A. Ischay, M. S. Ament and T. P. Yoon, Chem. Sci., 2012, 3,
2807–2811.
11 a) S. Karthikeyan and V. Ramamurthy, J. Org. Chem., 2007, 72,
452–458; b) N. Nguyen, A. R. Clements and M. Pattabiraman,
New J. Chem., 2016, 40, 2433–2443.
12 E. L. Tyson, E. P. Farney and T. P. Yoon, Org. Lett., 2012, 14,
1110–1113.
Conflicts of interest
The authors declare no conflict of interest.
13 R. Telmesani, S. H. Park, T. Lynch-Colameta and A. B. Beeler,
Angew. Chem., Int. Ed., 2015, 54, 11521–11525.
14 a) S. Paria and O. Reiser, Adv. Synth. Catal., 2014, 356, 557–
562; b) S. Paria, V. Kais and O. Reiser, Adv. Synth. Catal., 2014,
356, 2853–2858; c) S. K. Pagire and O. Reiser, Green Chem.,
2017, 19, 1721–1725.
15 a) J. Xuan, X.-D. Xia, T.-T. Zeng, Z.-J. Feng, J.-R. Chen, L.-Q. Lu
and W.-J. Xiao, Angew. Chem., Int. Ed., 2014, 53, 5653–5656; b)
A. Hossain, S. K. Pagire and O. Reiser, Synlett, 2017, 28, 1707–
1714.
Acknowledgements
This work was supported by the DFG (RE 948/9-1 and GRK-
1626 Photocatalysis), DAAD (fellowship for S.K.P.), and the
Friedrich-Ebert-Stiftung (fellowship for S. K.). The authors
acknowledge Ms. B. Hischa and Dr. U. Chakraborty for single
crystal X-ray analysis.
16 S. K. Pagire, P. Kreitmeier and O. Reiser, Angew. Chem., Int. Ed.,
2017, 56, 10928–10932.
References
17 H. Roth, N. Romero and D. Nicewicz, Synlett, 2016, 27, 714–
723.
1
a) V. M. Dembitsky, J. Nat. Med., 2008, 62, 1–33; b) V. M.
Dembitsky, Phytomedicine, 2014, 21, 1559–1581; c) J. C.
Namyslo and D. E. Kaufmann, Chem. Rev., 2003, 103, 1485–
1538; d) A. Sergeiko, V. V. Poroikov, L. O. Hanus and V. M.
Dembitsky, Open Med. Chem. J., 2008, 2, 26–37.
a) R. D. Hartley, W. H. Morrison III, F. Balza and G. H. Neil
Towers, Phytochemistry, 1990, 29, 3699–3703; b) M. Krauze-
Baranowska, Acta Pol. Pharm., 2002, 59, 403–410.
R. A. Davis, A. R. Carroll, S. Duffy, V. M. Avery, G. P. Guymer, P.
I. Forster and R. J. Quinn, J. Nat. Prod., 2007, 70, 1118–1121.
S. Poplata, A. Troster, Y.-Q. Zou and T. Bach, Chem. Rev., 2016,
116, 9748–9815.
a) Y. Xu, M. L. Conner and M. K. Brown, Angew. Chem., Int. Ed.,
2015, 54, 11918–11928; b) M. B. Boxer and H. Yamamoto, Org.
Lett., 2005, 7, 3127–3129; c) G.-J. Duan, J.-B. Ling, W.-P. Wang,
Y.-C. Luo and P.-F. Xu, Chem. Commun., 2013, 49, 4625–4627;
d) K. Sakai, T. Kochi and F. Kakiuchi, Org. Lett., 2013, 15, 1024–
1027; e) F. Kleinbeck and F. D. Toste, J. Am. Chem. Soc., 2009,
131, 9178–9179; f) G. Alberti, A. Bernard, A. Frongia, P. Piras, F.
Secci and M. Spiga, Synlett, 2006, 2241–2245.
M. W. Smith and P. S. Baran, Science, 2015, 349, 925–926.
D. M. Schultz and T. P. Yoon, Science, 2014, 343, 1239176.
a) D. Menigaux, P. Belmont and E. Brachet, Eur. J. Org. Chem.,
2017, 2017, 2008–2055; b) N. Hoffmann, Eur. J. Org. Chem.,
2017, 2017, 1982–1992; c) M. H. Shaw, J. Twilton and D. W. C.
MacMillan, J. Org. Chem., 2016, 81, 6898–6926; d) O. Reiser,
Acc. Chem. Res., 2016, 49, 1990–1996; e) M. Majek and A.
Jacobi von Wangelin, Acc. Chem. Res., 2016, 49, 2316–2327; f)
M. D. Kärkäs, J. A. Porco and C. R. J. Stephenson, Chem. Rev.,
2016, 116, 9683–9747; g) D. Ravelli, S. Protti and M. Fagnoni,
Chem. Rev., 2016, 116, 9850–9913; h) J.-R. Chen, X.-Q. Hu, L.-Q.
Lu and W.-J. Xiao, Acc. Chem. Res., 2016, 49, 1911–1923; i) Y.-
Q. Zou, S.-W. Duan, X.-G. Meng, X.-Q. Hua, S. Gao, J.-R. Chen
and W.-J. Xiao, Tetrahedron 2012, 68, 6914-6919.
18 F. Teplý, Collect. Czech. Chem. Commun., 2011, 76, 859–917.
19 C. K. Prier, D. A. Rankic and D. W. C. MacMillan, Chem. Rev.,
2013, 113, 5322–5363.
20 I. Fussing, M. Gullu, O. Hammerich, A. Hussain, M. F. Nielsen, J.
H. P. Utley, J. Chem. Soc., Perkin Trans. 2, 1996, 649–658.
21 Z. Lu and T. P. Yoon, Angew. Chem., Int. Ed., 2012, 51, 10329–
10332.
22 a) D. B. Bagal, G. Kachkovskyi, M. Knorn, T. Rawner, B. M.
Bhanage and O. Reiser, Angew. Chem., Int. Ed., 2015, 54, 6999–
7002; b) M. Knorn, T. Rawner, R. Czerwieniec and O. Reiser,
ACS Catal., 2015, 5, 5186–5193; c) S. K. Pagire, S. Paria and O.
Reiser, Org. Lett., 2016, 18, 2106–2109; d) T. Rawner, M.
Knorn, E. Lutsker, A. Hossain and O. Reiser, J. Org. Chem., 2016,
81, 7139–7147; e) S. Paria and O. Reiser, ChemCatChem, 2014,
6, 2477–2483.
23 A. K. F. Albertson and J.-P. Lumb, Angew. Chem., Int. Ed., 2015,
54, 2204–2208.
24 M. D’Auria, G. Piancatelli, A. Vantaggi, J. Chem. Soc., Perkin
Trans. 1, 1990, 2999–3001.
25 F. Toda, K. Tanaka and M. Kato, J. Chem. Soc., Perkin Trans. 1,
1998, 1315–1318.
26 a) R. Li, B. C. Ma, W. Huang, L. Wang, Di Wang, H. Lu, K.
Landfester and K. A. I. Zhang, ACS Catal., 2017, 7, 3097–3101;
b) M. Riener and D. A. Nicewicz, Chem. Sci., 2013, 4, 2625–
2629.
2
3
4
5
6
7
8
27 a) R. Liu, M. Zhang, T. P. Wyche, G. N. Winston-McPherson, T.
S. Bugni and W. Tang, Angew. Chem., Int. Ed., 2012, 51, 7503–
7506; b) R. A. Panish, S. R. Chintala and J. M. Fox, Angew.
Chem., Int. Ed., 2016, 55, 4983–4987; c) J. He, Q. Shao, Q. Wu
and J.-Q. Yu, J. Am. Chem. Soc., 2017, 139, 3344–3347; d) W. R.
Gutekunst and P. S. Baran, J. Am. Chem. Soc., 2011, 133,
19076–19079; e) W. R. Gutekunst and P. S. Baran, J. Org.
Chem., 2014, 79, 2430–2452.
28 D. Haag and H.-D. Scharf, J. Org. Chem., 1996, 61, 6127–6135.
29 J. B. Metternich and R. Gilmour, J. Am. Chem. Soc., 2015, 137,
11254–11257.
9
a) T. P. Yoon, M. A. Ischay and J. Du, Nat. Chem., 2010, 2, 527–
532; b) M. A. Ischay, M. E. Anzovino, J. Du and T. P. Yoon, J.
Am. Chem. Soc., 2008, 130, 12886–12887; c) J. Du and T. P.
Yoon, J. Am. Chem. Soc., 2009, 131, 14604–14605; d) T. P.
4 | J. Name., 2012, 00, 1-3
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DOI: 10.1039/C7CC06710K
Communication
ChemComm
Table of contents entry:
A visible-light mediated, photocatalyzed strategy for the
efficient synthesis of substituted cyclobutanes from
cinnamates, styrenes, and chalcones is presented.
Visible-light (455 nm)
[Ir{dF(CF3)ppy}2(dtb-bpy)]PF6 (1 mol %)
rt, DMF
R1
R1
R3
R3
R
R
R1
R3
R
Key features
Mild reaction conditions
Broad substrate scope
No additives
Cinnamates
Chalcones
Styrenes
30 examples
11-99% yields
1:1 - 99:1 d.r.
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