Design of Planar Chiral Phosphoric Acids with a [2.2]Paracyclophanyl Backbone as Organocatalysts for the Highly Enantioselective Aza-Friedel-Crafts Reaction

Article abstract of DOI:10.1021/acs.orglett.9b01127

A new type of robust planar chiral phosphoric acid bearing a [2.2]paracyclophane scaffold was synthesized and shown to be an optimal catalyst in asymmetric aza-Friedel-Crafts reactions for the first synthesis of enantioenriched styryl indolylmethanamine d

Full text of DOI:10.1021/acs.orglett.9b01127

Letter
pubs.acs.org/OrgLett
Cite This: Org. Lett. XXXX, XXX, XXX−XXX
Design of Planar Chiral Phosphoric Acids with a
[2.2]Paracyclophanyl Backbone as Organocatalysts for the Highly
Enantioselective Aza-Friedel−Crafts Reaction
En Xie, Shaoying Huang, and Xufeng Lin*
Department of Chemistry, Zhejiang University, Hangzhou 310027, China
S
* Supporting Information
ABSTRACT: A new type of robust planar chiral phosphoric
acid bearing a [2.2]paracyclophane scaffold was synthesized
and shown to be an optimal catalyst in asymmetric aza-
Friedel−Crafts reactions for the first synthesis of enantioen-
riched styryl indolylmethanamine derivatives in good yields
with excellent enantioselectivities (93−>99% ee) under 0.5−1
mol % catalyst loading.
Planar chirality plays an important role in asymmetric
symmetric phosphoric acid catalysis represents a sub-
Astantial scientific contribution and has enabled numerous catalysis, especially disubstituted ferrocene or substituted
[2.2]paracyclophanes [PCPs].3 Recently, remarkable contri-
organic transformations in a highly enantioselective fashion
butions have been achieved in the development of planar chiral
phosphoric acids. Enders reported the first synthesis planar
chiral phosphoric acid derived from [2.2]paracyclophane
(Figure 1, 5).4 However, the new catalyst was evaluated in
enantioselective aza-Friedel−Crafts reactions and Mannich-
type reactions to give only ee values of up to 38%. Betzer and
Marinetti disclosed the first series of planar chiral phosphoric
acids with a paracyclophane backbone tethered by either a
1,1′-ferrocenediyl or a 1,8-biphenylenediyl unit (Figure 1, 6
and 7) giving promising levels of enantioselectivity in
organocatalytic asymmetric aza-Friedel−Crafts reaction and
H-transfer reduction.5 However, the synthetic approach to
access these enantiomerically enriched catalysts 6 and 7 must
utilize chiral HPLC preparative chromatography or diaster-
eomers separation. In addition, acid 6 displayed only moderate
thermal stability, giving partial decomposition at 60 °C.
Despite these notable advances, developing new planar chiral
phosphoric acids with excellent catalytic activities and readily
accessible architectures is still highly valuable and desirable.
Our group reported the first synthesis and application of
SPINOL-derived phosphoric acids (Figure 1, 4), denoted as
SPAs, which proved to be highly efficient in asymmetric
catalysis and received increasing attention.1l,2d,6 As a
continuation of our work on the design and application of
novel chiral catalysts,2d,7 herein we describe a new type of
robust planar chiral phosphoric acids bearing a [2.2]-
since Akiyama, Terada, and co-workers reported BINOL-based
chiral phosphoric acids in 2004.1 The backbone of the chiral
catalysts had a remarkable influence on their catalytic
performance in many cases. Alongside new catalytic reactions,
a variety of structurally diverse chiral phosphoric acids, mainly
derived from centrally chiral TADDOL and axially chiral diols
like H8−BINOL, VAPOL, SPINOL, and others, have been
developed (Figure 1, 1−4).2 Despite a growing focus toward
efforts on new asymmetric reactions and new catalytic
strategies, the development of chiral phosphoric acids bearing
novel frameworks with excellent catalytic activities is still highly
valuable and very challenging in a diverse range of asymmetric
transformations.
Received: March 31, 2019
Figure 1. Chiral phosphoric acids.
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.9b01127
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Organic Letters
Letter
paracyclophane scaffold (Figure 1, 8, denoted as PPAs),
starting from commercially available starting materials (Rp)-
4,12-dibromo[2.2]paracyclophane, and demonstrate that
planar chiral PPAs can serve as highly efficient enantioselective
strong Brønsted acid organocatalysts.
Six planar chiral phosphoric acids bearing a [2.2]-
paracyclophane scaffold 8a−f were prepared, and their
syntheses are outlined in Scheme 1. The synthetic procedure
under reflux for 12 h and did not show any decomposition and
epimerization, displaying good thermal stability.
The catalytic enantioselective aza-Friedel−Crafts reaction of
indoles with imines is the most versatile method to achieve the
synthesis of enantiopure 3-indolylmethanamine derivatives,
which are distributed in natural products having significant
biological activities.9 Therefore, extensive effort has been
devoted to this research field, and some excellent chiral
organocatalysts10 and chiral metal salt catalysts11 have been
developed over the past decade. Despite these notable
advances, to the best of our knowledge, cinnamaldehyde-
derived N-tosylimines have not been used in these catalytic
asymmeteric aza-Friedel−Crafts reactions. To evaluate the
effectiveness of planar chiral PPAs as enantioselective Brønsted
acid catalysts, we examined their performance in the first
asymmetric aza-Friedel−Crafts reaction for the efficient
synthesis of various enantioenriched styryl indolylmethan-
amine derivatives.
a
Scheme 1. Synthesis of Planar Chiral Phosphoric Acids
As shown in Table 1, we began with identification of the best
catalyst using cinnamaldehyde-derived N-tosylimine 13a as a
model substrate and indole 14a as a nucleophile in the
presence of a catalytic planar chiral phosphoric acid. We
observed that 1 mol % of (Rp)-8a catalyzed smoothly the
reaction in toluene in the presence of 4 Å MS at −40 °C in 2 h
a
Yields are given for G = CH3.
a
Table 1. Reaction Optimization
starts with the Suzuki coupling reaction between (Rp)-4,12-
dibromo[2.2]paracyclophane (9) and the corresponding
arylboron reagents, which feature a Me-protected hydroxyl
function in their meta position and a G substituent in their
para position. The desired compound (Rp)-10b (R = Me) was
obtained in 75% yield and subsequently demethylated with
BBr3 in DCM to give the key [2.2]paracyclophane-based
bisphenol (Rp)-11b (R = Me) in quantitative yield. The
conversion of the bisphenol to the corresponding phosphoric
acid was first tested with the typical POCl3-based method.2d
However, no desired product of cyclization was obtained when
bisphenol (Rp)-11b was treated with POCl3 in the presence of
pyridine. The cyclization reaction of bisphenol (Rp)-11b with
phosphorodiamidite (i-Pr2N)2PO(CH2)2CN in the presence
of 1H-tetrazole,5a,8 followed by oxidation of the resulting
phosphite with tert-butyl hydroperoxide, afforded the corre-
sponding cyclic phosphate (Rp)-12b (R = Me) in 60% yield
over two steps. Removal of the cyanoethyl substituent of
phosphates (Rp)-12 under basic conditions (DBU) afforded
the desired planar chiral phosphoric acids 8a−f in good yields.
The X-ray crystal structure of (Rp)-12b is shown in Figure 2.
The dihedral angle between the two phenyl planes of bisphenol
in (Rp)-12b is 23.46°, and the distance between the two
oxygen atoms of bisphenol is 2.504 Å, indicating that the
corresponding phosphoric acid may have a unique chiral
cavity, which could be beneficial for certain asymmetric
transformations. The sample of (Rp)-8b was heated in toluene
b
c
entry
catalyst
solvent
temp (°C)
yield (%)
ee (%)
1
2
3
4
5
6
(Rp)-8a
(Rp)-8b
(Rp)-8c
(Rp)-8d
(Rp)-8e
(Rp)-8f
(Rp)-8d
(Rp)-8d
(Rp)-8d
(Rp)-8d
(Rp)-8d
(Rp)-8d
(Rp)-8d
(R)-1a
(R)-1b
(R)-1c
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
m-xylene
CH2Cl2
THF
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
−40
−40
−40
−40
−40
−40
−40
−40
−40
−40
−40
−20
0
−20
−20
−20
−20
−20
−20
80
79
85
90
95
80
91
85
90
89
nr
92
55
89
86
trace
87
90
80
4
31
26
99
97
50
98
98
97
95
d
7
e
8
9
10
11
12
13
14
15
16
17
18
19
99
97
81
69
(R)-1d
(S)-4a
(S)-4b
71
71
66
a
Reaction conditions: 13a (0.25 mmol), 14a (0.25 mmol), catalyst (1
mol %), and 4 Å MS (75 mg) in 2.5 mL of solvent under N2 for 2 h.
Isolated yields. Determined by chiral HPLC analysis. Without the
b
c
d
e
use of 4 Å MS. With catalyst (0.5 mol %).
Figure 2. X-ray crystal structure of (Rp)-12b.
B
DOI: 10.1021/acs.orglett.9b01127
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Organic Letters
Letter
to give the desired product 15aa in good yield but poor
enantioselecitvity (entry 1). In terms of further catalyst
screening, PPAs (Rp)-8d and (Rp)-8e were found to induce
excellent enantioselectivity in this reaction (entries 2−6). The
adduct 15aa could be obtained in 90% yield and 99%
enantiomeric excess (ee) in the case of using of 1 mol % of
(Rp)-8d as a catalyst at −40 °C (entry 4). Removal of 4 Å MS
or reducing the loading of catalyst (Rp)-8d to 0.5 mol % hardly
compromised enantioselectivity (98% ee, entries 7 and 8).
Furthermore, the reaction solvents and the temperature were
screened, and the optimal results (15aa in 92% yield and 99%
ee) could be delivered with 1 mol % of (Rp)-8d at −20 °C in
toluene (entry 12). As a comparison, we examined the known
privileged chiral phosphoric acid catalysts 1a−d and 4a,b in
the model reaction to show a dramatic decrease of the reaction
enantioselectivity (entries 14−19).
deficient indoles gave high yields and excellent enantioselec-
tivities (15ab, 15ae−ag, and 15ai). Moreover, the absolute
configuration (S) of the stereogenic center in product 15 was
determined by X-ray crystallographic analysis of a single crystal
of 15ba.
To test the practicality of the current catalytic system, a
gram-scale reaction was achieved under the optimized reaction
conditions. As shown in Scheme 3, the reaction of 13f with
Scheme 3. Gram-Scale Experiment
With the optimized reaction conditions in hand, we then
evaluated the substrate scope of the asymmetric aza-Friedel−
Crafts reaction between cinnamaldehyde-derived N-tosyli-
mines and indoles. The results are summarized in Scheme 2.
indole 14a in the presence of 1 mol % of PPA (Rp)-8d was
carried out on a 2.5 mmol scale of 13f. The desired product
15fa was obtained in 98% yield (1.181 g) with 96% ee.
Scheme 2. Substrate Scope for Reaction of Indoles with N-
Finally, we expanded the investigation of our new catalytic
system to the asymmetric aza-Friedel−Crafts reaction between
aromatic aldehyde-derived N-tosylimines and indoles. The
reaction of N-tosyl phenyl aldimine with indole was initially
examined, and a concise screening of PPAs and reaction
conditions was carried out again. Gratifyingly, the reaction
proceeded smoothly to give the desired product 17aa in 99%
yield with 96% ee using 2 mol % of (Rp)-8e as a catalyst in
toluene in the presence of 4 Å MS at −20 °C in 2 h, as shown
in Scheme 4. It is interesting to note that this result compares
quite favorably with BINOL-phosphoric acid catalyst, which at
10 mol % loading was reported to catalyze the same reaction in
toluene at −60 °C for 30 min to furnish 17aa in 83% yield and
98% ee,10c while SPINOL−phosphoric acid catalyst was
reported to catalyze the same reaction in toluene at −60 °C
for 36 h with 10 mol % loading to afford 17aa in 80% yield and
96% ee.2d Subsequently, diverse aromatic aldehyde-derived N-
tosylimines 16 and indoles 14 were evaluated to define the
reaction scope. We observed that the PPA (Rp)-8e catalyzed
aza-Friedel−Crafts reaction of N-tosyl aryl aldimines with
indole was found to be general with N-tosyl aryl aldimines
bearing different either electron-donating groups or electron-
withdrawing groups as substituents. In all cases, almost
quantitative yields and excellent enantioselectivities could be
achieved (17aa−ka, all 99% yields, 92−99% ee). We then
examined several substituted indoles and found that 2-
methylindole provided slightly lower enantioselectivity
(17db, 87% ee) compared to those bearing 4,7-substituted
indoles (17dc−de and 17ee−ek, 91−99% ee), probably
because of steric hindrance. In addition, we were pleased to
find that N-tosylaldimine-derived 2-naphthaldehyde and
heteroaryl 2-thiophenyl aldehyde could also be successfully
employed to afford the corresponding products in good yields
with excellent enantioselectivities (17la, 97% ee; 17ma, 94%
ee) under similar reaction conditions. In the case of an
aliphatic aldehyde derived imine, high yield but only moderate
enantioselectivity were obtained (17na, 95% yield, 77% ee).
In summary, we have developed a novel class of robust
planar chiral phosphoric acids bearing a [2.2]paracyclophane
scaffold which combines the features of easy accessibility,
conformational rigidity, good thermal stability, and fascinating
catalyst efficiency. Their advantageous catalytic performance
a
Tosylvinylaldimines
a
Reaction conditions: 13 (0.25 mmol), 14 (0.25 mmol), (Rp)-8d (1
mol %), and 4 Å MS (75 mg) in 2.5 mL of toluene under N2 at −20
°C for 2 h. At −40 °C for 12 h. One mol % of (Rp)-8e was used at
−40 °C for 12 h.
b
c
We first investigated the substituent effects of cinnamaldehyde-
derived N-tosylimines 13. As a result, the substituent and its
position of 13 had almost no effect on the enantioselectivity,
and the corresponding products were obtained in good yield
and with excellent enantioselectivity (15aa−ga, 60−95% yield,
93 to >99% ee). In addition, a substrate with a heteroaromatic
structure was also compatible under the same conditions, and
the corresponding products 15ia was obtained with high
enantioselectivity (97% ee). We next examined the scope of
indoles 14. In all cases, both electron-rich and electron-
C
DOI: 10.1021/acs.orglett.9b01127
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Letter
Scheme 4. Substrate Scope for Reaction of Indoles with N-
Tosylarylaldimines
AUTHOR INFORMATION
■
a
Corresponding Author
*E-mail: lxfok@zju.edu.cn.
ORCID
Xufeng Lin: 0000-0003-4611-0507
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
We thank the National Natural Science Foundation of China
(21572200) for financial support.
■
REFERENCES
■
(1) For pioneering works on chiral phosphoric acid catalysis, see:
(a) Akiyama, T.; Itoh, J.; Yokota, K.; Fuchibe, K. Angew. Chem., Int.
Ed. 2004, 43, 1566−1568. (b) Uraguchi, D.; Terada, M. J. Am. Chem.
Soc. 2004, 126, 5356−5357 For reviews, see: . (c) Akiyama, T.; Itoh,
J.; Fuchibe, K. Adv. Synth. Catal. 2006, 348, 999−1010. (d) Akiyama,
T. Chem. Rev. 2007, 107, 5744−5758. (e) Terada, M. Chem. Commun.
2008, 4097−4112. (f) Adair, G.; Mukherjee, S.; List, B. Aldrichimica
Acta 2008, 41, 31−39. (g) You, S.-L.; Cai, Q.; Zeng, M. Chem. Soc.
Rev. 2009, 38, 2190−2201. (h) Terada, M. Synthesis 2010, 2010,
1929−1982. (i) Rueping, M.; Kuenkel, A.; Atodiresei, I. Chem. Soc.
Rev. 2011, 40, 4539−4549. (j) Yu, J.; Shi, F.; Gong, L.-Z. Acc. Chem.
Res. 2011, 44, 1156−1171. (k) Parmar, D.; Sugiono, E.; Raja, S.;
Rueping, M. Chem. Rev. 2014, 114, 9047−9153. (l) Rahman, A.; Lin,
X. F. Org. Biomol. Chem. 2018, 16, 4753−4777.
(2) (a) Rowland, G. B.; Zhang, H.; Rowland, E. B.;
Chennamadhavuni, S.; Wang, Y.; Antilla, J. C. J. Am. Chem. Soc.
2005, 127, 15696−15697. (b) Akiyama, T.; Saitoh, Y.; Morita, H.;
Fuchibe, K. Adv. Synth. Catal. 2005, 347, 1523−1526. (c) Chen, X.-
H.; Xu, X.-Y.; Liu, H.; Cun, L.-F.; Gong, L.-Z. J. Am. Chem. Soc. 2006,
128, 14802−14803. (d) Xu, F.; Huang, D.; Han, C.; Shen, W.; Lin, X.
a
Reaction conditions: 16 (0.125 mmol), 14 (0.125 mmol), (Rp)-8e
(2 mol %), and 4 Å MS (38 mg) in 1.25 mL of toluene under N2 at
−20 °C for 12 h. At −40 °C
b
̌
́
F.; Wang, Y. G. J. Org. Chem. 2010, 75, 8677−8680. (e) Coric, I.;
Mu
̈
ller, S.; List, B. J. Am. Chem. Soc. 2010, 132, 17370−17373.
has been demonstrated to make them the optimal catalysts in
asymmetric aza-Friedel−Crafts reactions with the first syn-
thesis of enantioenriched styryl indolylmethanamine deriva-
tives in good yields with excellent enantioselectivities (93−
>99% ee) under 0.5−1 mol % catalyst loading. The new
catalytic system was also successfully expanded to aromatic
aldehyde-derived N-tosylimines, affording the corresponding
aryl indolylmethanamines with excellent enantioselectivities
(up to 99% ee). Further investigations for more effective planar
chiral phosphoric acids bearing a [2.2]paracyclophane scaffold
as well as expansion of their other challenging applications in
asymmetric catalysis are underway in our laboratory.
(f) Chen, X.-H.; Zhang, W.-Q.; Gong, L.-Z. J. Am. Chem. Soc. 2008,
130, 5652−5653. (g) Wang, Y.-Z.; Liu, W.; Ren, W.-L.; Shi, Y.-A. Org.
Lett. 2015, 17, 4976−4979.
(3) (a) Dai, L.-X., Hou, X.-L., Eds. Chiral Ferrocenes in Asymmetric
Catalysis; Wiley-VCH: New York, 2010. (b) Dai, L.-X.; Tu, T.; You,
S.-L.; Deng, W.-P.; Hou, X.-L. Acc. Chem. Res. 2003, 36, 659−667.
(c) Wu, X.-W.; Sun, W.; Hou, X.-L. Chin. J. Org. Chem. 2003, 23,
906−913. (d) Gibson, S. E.; Knight, J. D. Org. Biomol. Chem. 2003, 1,
1256−1269. (e) Pye, P. J.; Rossen, K.; Reamer, R. A.; Tsou, N. N.;
Volante, R. P.; Reider, P. J. J. Am. Chem. Soc. 1997, 119, 6207−6208.
(4) Enders, D.; Ludwig, M.; Raabe, G. Chirality 2012, 24, 215−222.
(5) (a) Stemper, J.; Isaac, K.; Duret, V.; Retailleau, P.; Voituriez, A.;
Betzer, J.-F.; Marinetti, A. Chem. Commun. 2013, 49, 6084−6086.
(b) Stemper, J.; Isaac, K.; Pastor, J.; Frison, G.; Retailleau, P.;
Voituriez, A.; Betzer, J.-F.; Marinetti, A. Adv. Synth. Catal. 2013, 355,
3613−3624. (c) Isaac, K.; Stemper, J.; Servajean, V.; Retailleau, P.;
Pastor, J.; Frison, G.; Kaupmees, K.; Leito, I.; Betzer, J.-F.; Marinetti,
A. J. Org. Chem. 2014, 79, 9639−9646.
(6) For selected examples by this group, see: (a) Huang, D.; Li, X.;
Xu, F.; Li, L.; Lin, X. F. ACS Catal. 2013, 3, 2244−2247. (b) Shen, X.
M.; Wang, Y. G.; Wu, T. D.; Mao, Z. J.; Lin, X. F. Chem. - Eur. J. 2015,
21, 9039−9043. (c) Lou, H. Q.; Wang, Y. T.; Jin, E. Z.; Lin, X. F. J.
Org. Chem. 2016, 81, 2019−2026. (d) Xie, E.; Rahman, A.; Lin, X. F.
Org. Chem. Front. 2017, 4, 1407−1410. (e) Luo, J.; Zhang, T.; Wang,
L.; Liao, G.; Yao, Q. J.; Wu, Y. J.; Zhan, B. B.; Lan, Y.; Lin, X. F.; Shi,
B. F. Angew. Chem., Int. Ed. 2019, DOI: 10.1002/anie.201902126.
For recent examples by other groups, see: (f) Wang, F.-L.; Dong, X.-
Y.; Lin, J.-S.; Zeng, Y.; Jiao, G.-Y.; Gu, Q.-S.; Guo, X.-Q.; Ma, C.-L.;
Liu, X.-Y. Chem. 2017, 3, 979−990. (g) Qian, D.; Chen, M.;
Bissember, A.-C.; Sun, J. Angew. Chem., Int. Ed. 2018, 57, 3763−3766.
(h) Qi, L.-W.; Mao, J.-H.; Zhang, J.; Tan, B. Nat. Chem. 2018, 10,
ASSOCIATED CONTENT
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* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.or-
glett.9b01127.
Experimental procedures, spectral data for all new
compounds (PDF)
Accession Codes
CCDC 1904580−1904581 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
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DOI: 10.1021/acs.orglett.9b01127
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58−64. (i) Li, J.-T.; Kong, M.; Qiao, B.-K.; Lee, R.; Zhao, X.-W.;
Jiang, Z.-Y. Nat. Commun. 2018, 9, 2445−2453. (j) Zhang, J.; Yu, P.-
Y.; Li, S.-Y.; Sun, H.; Xiang, S.-H.; Wang, J.; Houk, K. N.; Tan, B.
Science 2018, 361, 8707−8715. (k) Lin, J.-S.; Li, T.-T.; Liu, J.-R.; Jiao,
G.-Y.; Gu, Q.-S.; Cheng, J.-T.; Guo, Y.-L.; Hong, X.; Liu, X.-Y. J. Am.
Chem. Soc. 2019, 141, 1074−1083.
(7) (a) Gu, H.-R.; Han, Z.; Xie, H. J.; Lin, X. F. Org. Lett. 2018, 20,
6544−6549. (b) Sun, W. Y.; Gu, H. R.; Lin, X. F. J. Org. Chem. 2018,
83, 4034−4043. (c) Shan, H. Y.; Zhou, Q. X.; Yu, J. L.; Zhang, S. Q.;
Hong, X.; Lin, X. F. J. Org. Chem. 2018, 83, 11873−11885.
(8) Bannwarth, W.; Trzeciak, A. Helv. Chim. Acta 1987, 70, 175−
186.
(9) For reviews on asymmetric aza-Friedel−Crafts reaction, see:
(a) Bandini, M.; Melloni, A.; Umani-Ronchi, A. Angew. Chem., Int. Ed.
2004, 43, 550−556. (b) Poulsen, T. B.; Jorgensen, K. A. Chem. Rev.
2008, 108, 2903−2915. (c) Bandini, M.; Eichholzer, A. Angew. Chem.,
Int. Ed. 2009, 48, 9608−9644. (d) You, S.-L.; Cai, Q.; Zeng, M. Chem.
́
Soc. Rev. 2009, 38, 2190−2201. (e) Reid, J. P.; Simon, L.; Goodman,
J. M. Acc. Chem. Res. 2016, 49, 1029−1041. For recent examples, see:
(f) Li, G.; Rowland, G. B.; Rowland, E. B.; Antilla, J. C. Org. Lett.
2007, 9, 4065−4068. (g) Husmann, R.; Sugiono, E.; Mersmann, S.;
Raabe, G.; Rueping, M.; Bolm, C. Org. Lett. 2011, 13, 1044−1047.
(h) Zhang, K.-F.; Nie, J.; Guo, R.; Zheng, Y.; Ma, J.-A. Adv. Synth.
Catal. 2013, 355, 3497−3502. (i) Wang, S.-G.; You, S.-L. Angew.
Chem., Int. Ed. 2014, 53, 2194−2197. (j) Kano, T.; Takechi, R.;
Kobayashi, R.; Maruoka, K. Org. Biomol. Chem. 2014, 12, 724−727.
(10) (a) Wang, Y.-Q.; Song, J.; Hong, R.; Li, H.; Deng, L. J. J. Am.
Chem. Soc. 2006, 128, 8156−8157. (b) Terada, M.; Sorimachi, K. J.
Am. Chem. Soc. 2007, 129, 292−293. (c) Kang, Q.; Zhao, Z.-A.; You,
S.-L. J. Am. Chem. Soc. 2007, 129, 1484−1485. (d) Terada, M.;
Yokoyama, S.; Sorimachi, K.; Uraguchi, D. Adv. Synth. Catal. 2007,
349, 1863−1867. (e) Rowland, G. B.; Rowland, E. B.; Liang, Y.;
Perman, J. A.; Antilla, J. C. Org. Lett. 2007, 9, 2609−2611. (f) Zhang,
G.-W.; Wang, L.; Nie, J.; Ma, J.-A. Adv. Synth. Catal. 2008, 350,
1457−1463. (g) Qiu, H.; Li, M.; Jiang, L.-Q.; Lv, F.-P.; Zan, L.; Zhai,
C.-W.; Doyle, M. P.; Hu, W.-H. Nat. Chem. 2012, 4, 733−738. (h) Li,
X. J.; Chen, D.; Gu, H. R.; Lin, X. F. Chem. Commun. 2014, 50, 7538−
7541. (i) Wang, L.; Rahman, A.; Lin, X. F. Org. Biomol. Chem. 2017,
15, 6033−6041. (j) Rahman, A.; Xie, E.; Lin, X. F. Org. Biomol. Chem.
2018, 16, 1367−1374. (k) Hatano, M.; Mochizuki, T.; Nishikawa, K.;
Ishihara, K. ACS Catal. 2018, 8, 349−353.
(11) (a) Wang, B.-L.; Li, N.-K.; Zhang, J.-X.; Liu, G.-G.; Liu, T.;
Shen, Q.; Wang, X.-W. Org. Biomol. Chem. 2011, 9, 2614−2617.
(b) Takizawa, S.; Arteaga, F. A.; Yoshida, Y.; Kodera, J.; Nagata, Y.;
Sasai, H. DaltonTrans 2013, 42, 11787−11790. (c) Kumari, P.; Bera,
P.-K.; Khan, N.-U.-H.; Kureshy, R.-I.; Abdi, S.-H.-R.; Bajaj, H.-C.
Catal. Sci. Technol. 2014, 4, 563−568. (d) Zou, K.; Ye, J.; Wu, X.-Y.
Tetrahedron 2015, 71, 7869−7873. (e) Arai, T.; Kakino, J. Angew.
Chem., Int. Ed. 2016, 55, 15263−15267. (f) Kim, M.-J.; Xue, L.; Liu,
Y.; Paladhi, S.; Park, S.-J.; Yan, H.; Song, C.-E. Adv. Synth. Catal.
2017, 359, 811−823.
E
DOI: 10.1021/acs.orglett.9b01127
Org. Lett. XXXX, XXX, XXX−XXX