Synthesis of Substituted Benzenes via Bi(OTf)3-Mediated Intramolecular Carbonyl Allylation of α-Prenyl or α-Geranyl β-Arylketosulfones

Article abstract of DOI:10.1021/acs.orglett.5b01461

Intramolecular carbonyl allylation of α-prenyl or α-geranyl β-arylketosulfones 5 in the presence of molecule sieves (MS) affords substituted benzenes 6-7 in moderate to good yields. The facile transformation proceeds by a synthetic sequence starting with the α-prenylation or α-geranylation of 1 and the Bi(OTf)₃-mediated annulation of 5 followed by a sequential desulfonative aromatization or then an intramolecular Friedel-Crafts alkylation. A plausible mechanism has been studied and proposed.

Full text of DOI:10.1021/acs.orglett.5b01461

Letter
pubs.acs.org/OrgLett
Synthesis of Substituted Benzenes via Bi(OTf) ‑Mediated
3
Intramolecular Carbonyl Allylation of α‑Prenyl or α‑Geranyl
β‑Arylketosulfones
Meng-Yang Chang,* Yu-Chieh Cheng, and Yi-Ju Lu
Department of Medicinal and Applied Chemistry, Kaohsiung Medical University, Kaohsiung 80708, Taiwan
*
S Supporting Information
ABSTRACT: Intramolecular carbonyl allylation of α-prenyl or α-geranyl β-arylketosulfones 5 in the presence of molecule sieves
(
MS) affords substituted benzenes 6−7 in moderate to good yields. The facile transformation proceeds by a synthetic sequence
starting with the α-prenylation or α-geranylation of 1 and the Bi(OTf) -mediated annulation of 5 followed by a sequential
3
desulfonative aromatization or then an intramolecular Friedel−Crafts alkylation. A plausible mechanism has been studied and
proposed.
i(OTf) as a Lewis acid has been used in a growing
catalyzed intramolecular hydroarylation of 1,3-dicarbonyl
3
1
B
number of synthetic applications, including Mukaiyama-
synthons with an α-allenyl or α-prenyl motif (see Scheme
2
3
4
5
5
type reaction, hydroamination, alkylation, benzannulation,
2). A novel catalytic Bi(OTf)
-mediated annulation route to
3
6
7
oxidation, and other reactions. For catalytic transformations,
the low toxicity of Bi(OTf) and its reasonably low cost make
Scheme 2. Bi(OTf)
3
-Mediated Hydroarylation by Dunach
3
this bismuth salt attractive. However, new Bi(OTf) -mediated
3
synthetic conversions that create a new C−C bond represent a
continuing need in the organic field. In continuation of our
investigations on the Bi(OTf) -mediated conversion of γ-
3
alkynones 2 (derived from α-propargylation of β-ketosulfones
8
9a
1
) into 2-arylfurans 3, the novel one-pot synthesis of
substituted benzenes 6 and tetralins 7 has been studied here via
the process of α-prenylation or α-geranylation of 1 with
bromides 4a or 4b, Bi(OTf) -mediated intramolecular carbonyl
3
allylation of 5 in MeNO , and sequential desulfonative
substituted benzenes has been developed via metal triflate
mediated reactions. Similarly, Narender et al. have also
2
9
aromatization or Friedel−Crafts alkylation (see Scheme 1).
Recently, Dunach et al. reported atom-economic synthetic
routes toward tetralins and benzosuberans via the Bi(OTf)3-
reported a synthesis of biaryls via the Al(III)-catalyzed domino
10
reaction of prenylated acetophenone. The construction of
substituted benzenes is of great interest because they constitute
11
useful building blocks in organic and medicinal chemistry.
Scheme 1. Synthetic Applications of 1
However, transition metal-mediated reactions are the most
popular route to such compounds among the existing methods,
12
especially Suzuki-Miyaura coupling or Reppe alkyne cyclo-
13
trimerization.
To explore the one-pot transformation from 5 to 6−7, α-
prenylation of 1a (R = Tol, Ar = Ph) with prenyl bromide (4a,
Received: May 19, 2015
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.5b01461
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
Y = Me) was first examined. In the presence of K CO , a
5a. Among the methods for allylic C−H activation, the S 2′
2
3
N
reaction of 1a with 4a afforded 5a in a 90% yield in boiling
acetone for 8 h. Furthermore, the use of various metal triflates
was investigated in the presence of MS for the intramolecular
annulation of 5a. Among the screened catalysts, which included
AgOTf, Mg(OTf) , Ni(OTf) , Sn(OTf) , Zn(OTf) , Fe(OTf) ,
electrophilic cross-coupling of allylpalladium species with
electron-rich molecules is a major pathway and has been used
15
for amination, oxidation, and alkylation. To the best of our
knowledge, no literature on Bi(III)-mediated intramolecular
allylic C−H cycloannulation of β-ketosulfones with an α-prenyl
or α-geranyl has been reported. With the optimized conditions
(Table 1, entry 12), we further explored the substrate scope of
the reaction, and the results are shown in Table 2.
2
2
2
2
3
Yb(OTf) , Sm(OTf) , Ga(OTf) , La(OTf) , Sc(OTf) , and
3
3
3
3
3
Bi(OTf) , only Bi(OTf) provided a 62% yield of m-
3
3
phenyltoluene (6a) along with a 15% yield of 8 in MeNO at
2
25 °C for 8 h (see Table 1, entry 1). Under these conditions,
a,b
Table 2. Synthesis of 6 and 7
a
Table 1. Reaction Conditions
b
yield (%)
6a/8
entry
catalyst (mol %), solvent (mL), temp (°C)
Bi(OTf) (2), MeNO (5), 25
1
2
3
4
5
6
7
8
9
62/15
3
2
c
c
BiBr (2), MeNO (5), 25
−/−
−/−
−/−
yield (%)
3
2
c
Bi O (2), MeNO (5), 25
2
3
2
entry
1, Ar =, R = ; 4a or 4b
5
6/7
c
Bi(OAc) (2), MeNO (5), 25
3
2
1
2
3
4
5
6
7
8
9
1a, Ph, Tol; 4a
5a, 90
5b, 92
5c, 89
5d, 88
5e, 84
5f, 83
5g, 86
5h, 86
5i, 87
5j, 84
5k, 89
5l, 82
6a, 86
6b, 82
6c, 80
6d, 82
6e, 78
6f, 76
6g, 80
6h, 85
6i, 85
6c, 82
6c, 82
7a, 78
7b, 73
7c, 75
7d, 76
7e, 77
7c, 73
Bi(OTf) (5), MeNO (5), 25
60/20
50/28
65/23
70/12
3
2
1b, 4-FC H , Tol; 4a
6
4
Bi(OTf) (2), MeNO (10), 25
3
2
1c, 4-MeOC H , Tol; 4a
6
4
Bi(OTf) (2), MeNO (5), 70
3
2
1d, 4-MeC H , Tol; 4a
d
6
4
Bi(OTf) (2), MeNO (5), 25
3
2
1e, 3-NO C H , Tol; 4a
c
2
6
4
Bi(OTf) (2), (CH Cl) (5), 25
−/−
−/−
−/−
3
2
2
1f, 4-NO C H , Tol; 4a
c
2
6
4
1
1
1
1
0
1
2
3
Bi(OTf) (2), benzene (5), 25
3
1g, 4-CF C H , Tol; 4a
c
3
6
4
Bi(OTf) (2), dioxane (5), 25
3
1h, 4-PhC H , Tol; 4a
e
6
4
Bi(OTf) (2), MeNO (5, dry), 25
86/−
28/61
3
2
1i, 2-naphthalene,Tol; 4a
1j, 4-MeOC H , Ph; 4a
f
Bi(OTf) (2), MeNO (5, wet), 25
3
2
10
11
12
13
14
15
16
17
6
4
a
b
The reactions were run on a 1.0 mmol scale with 5a for 8 h. Isolated
1k, 4-MeOC H , Me; 4a
c
d
e
f
6
4
yields. 5a was recovered. 40 h. MS (4 Å, 100 mg) was added. H O
2
1a, Ph, Tol; 4b
(
0.1 mL) was added.
1b, 4-FC H , Tol; 4b
5m, 86
5n, 87
5o, 84
5p, 86
5q, 82
6
4
1c, 4-MeOC H , Tol; 4b
6
4
1l, 4-PhC H , Me; 4b
6
4
the recovery of 5a only was observed for other metal triflates.
The use of other Bi(III) salts was examined for the synthesis of
1i, 2-naphthalene,Tol; 4b
1k, 4-MeOC H , Me; 4b
6
4
6
a. When 5a was treated with BiBr , Bi O or Bi(OAc) ,
3 2 3 3
a
The reactions were run on a 1.0 mmol scale with 1, K CO (2.9
mmol), 4a−b (1.05 mmol), acetone (10 mL), reflux, 8 h. The
reactions were run on a 1.0 mmol scale with 5, Bi(OTf) (0.02 mmol),
recovery of 5a was observed (entries 2−4). In comparison with
these Bi(III) salts, Bi(OTf) is a better catalyst for the
generation of 6a. With the use of Bi(OTf) as the catalyst,
variation of the equivalents, reaction concentration, solvents
and temperature was next studied. When 5 mol % of Bi(OTf)3
was used (entry 5), the yield and ratio of 6a and 8 were similar
to when 2 mol % was used. After decreasing the reaction
concentration (5 → 10, entry 6), the ratio of 6a to 8 was 2:1.
No obvious changes occurred at elevated temperature (25 →
2
3
b
3
3
3
c
MS (4 Å, 100 mg), MeNO (5 mL), 25 °C, 8 h. Isolated yield.
2
For the Ar and R groups of 1 (Ar = Ph, 4-FC H , 4-
MeOC H , 4-MeC H , 3-NO C H , 4-NO C H , 4-CF C H ,
4-PhC H , 2-naphthalene; R = 4-MeC H , Ph, Me), the phenyl
6
4
6
4
6
4
2
6
4
2
6
4
3
6
4
6
4
6
4
7
0, entry 7). Elongating the reaction time (8 → 40, entry 8)
increased the isolated ratio to 6:1. After changing the solvents
from MeNO to (CH Cl) , benzene or dioxane), a sluggish
ring, with both electron-withdrawing and electron-donating
substituents, was well tolerated, and provided the desired
products 5 and 6−7 in moderate to good yields. When using
1.05 equiv of prenyl bromide (4a) or geranyl bromide (4b),
5a−q were typically obtained in good yields (entries 1−17).
The one-pot intramolecular carbonyl allylation of 5a−q with
the combination of Bi(OTf) /MeNO /MS was also examined.
(
2
2
2
conversion was achieved (entries 9−11). Entry 12 shows that
the addition of molecular sieves increased the yield of 6a. In
contrast, the use of water generated 8 (61%) as the major
product along with 28% of 6a (entry 13). The structure of 8
3
2
14
was determined by single-crystal X-ray crystallography.
All entries showed that 6a−i and 7a−e were isolated in 76%−
86% and 73%−78% yields when Ar and R were aryl or alkyl
groups. Different substituents did not affect the procedure, and
the isolated yield was maintained. No obvious yield changes
were exhibited for the generation of 6a−i and 7a−e. The
structure of 7d was determined by single-crystal X-ray
The introduction of water caused a competition between
hydration (for 8 with a cyclohexane-1,3-diol skeleton) and
aromatization (for 6a with a benzene skeleton) during the
Bi(OTf) -mediated process. Overall, we envisioned that the
system of Bi(OTf) /MeNO /MS would provide an optimal
3
3
2
14
combination for the formation of 6a via C−H cycloallylation of
crystallography.
B
DOI: 10.1021/acs.orglett.5b01461
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
On the basis of the results, a possible reaction mechanism is
shown in Scheme 3. Mechanistically, the sequence initiates with
of D and the O-alkylation of K (Scheme 4). Through the
addition of H O (0.1 mL), the isolated yield of 9b was
2
Scheme 3. Possible Mechanism
Scheme 4. Bi(OTf) -Mediated Reaction of 5r
3
increased to 49% under wet conditions. However, attempts to
increase the reaction time (8 → 40 h) failed to afford 7. On the
basis of the isolation of 9a−b, we envision that the present
mechanism is reasonable to demonstrate Bi(OTf) -mediated
3
intramolecular carbonyl allylation of 5.
To examine the limitations of this Bi(OTf) -mediated route
Scheme 5), 5s−y were investigated. Bicyclic 10a (62%) and
3
(
Scheme 5. Bi(OTf) -Mediated Reactions of 5s−y
3
the formation of tertiary carbocation A by complexation of an
alkenyl motif of 5a with Bi(OTf) . Participation of a triflate
anion leads to a Hofmann intermediate B with an allylic
bismuth motif via abstraction of a less sterically hindered
3
tricyclic 10c (73%) were isolated, but no formation of 10b and
1
0d with the seven-membered ring was observed. A change of
the substituent from a sulfonyl to an aryl group gave none of
the desired skeleton via the intramolecular carbonyl allylation
of 5w−y. Only Friedel−Crafts cycloadducts 11a−c were
produced in 80%−85% yields. The results are consistent with
the Dunach reports. The structures of 9a−b and 11b were
determined by single-crystal X-ray crystallography. In
proton (E elimination). Protonation of B with in situ generated
2
16
HOTf gives C1. On the basis of the Felkin-Anh model, an
intramolecular nucleophilic addition of C2 by the methylene
group leads to an alternative tertiary alcohol intermediate via a
six-membered ring closure. Following debismuthation by the
5
14
triflate anion, D is obtained. After the Bi(OTf) -mediated
3
summary, we have developed a Bi(OTf) /MeNO /MS-
3
2
chelation of D (see blue symbols), a regioselective syn-
dehydration (deprotonated H , not H ) of the generated E
mediated intramolecular carbonyl allylation of 5 to generate
substituted benzenes 6−7 and 10−11 at 25 °C for 8 h.
Skeleton 5 was also provided in good yields via α-prenylation
and α-genarylation of 1. A plausible mechanism has been
proposed for these cyclization reactions. The structures of the
key products were confirmed by X-ray crystallography. Further
investigations regarding the synthetic application of β-
ketosulfones will be conducted and published.
a
b
forms the diene F via a six-membered chair conformation. The
addition of MS absorbs the resulting H O. Then, desulfonative
2
aromatization of F (removal of TolSO H) yields 6a (Y = Me).
2
When Y is a prenyl group, tertiary carbocation H can arise via
the Bi(OTf) -mediated attack in G. Next, an intramolecular
3
17
Friedel−Crafts alkylation of H generates I. Finally, after
dehydrogenative aromatization of I by the triflate anion, the
resulting HOTf continues the debismuthation from J to 7a. In
contrast (see red symbols), the isolation of 8 demonstrates that
wet MeNO2 promotes the conversion from D to K via
ASSOCIATED CONTENT
Supporting Information
Experimental data and scanned photocopies of H and 13C
■
*
S
1
5b
Bi(OTf) -mediated stereoselective hydration. According to
3
NMR spectral data. The Supporting Information is available
free of charge on the ACS Publications website at DOI:
the above experimental conditions and results (Tables 1 and 2),
the intramolecular carbonyl allylation of 1a demonstrates the
proposed mechanism.
1
0.1021/acs.orglett.5b01461.
When 5r was treated with the combination of Bi(OTf)3/
AUTHOR INFORMATION
Corresponding Author
MeNO /MS with a 4-nitrophenyl group, a decalin skeleton 9a
■
2
and a bridged skeleton 9b were obtained in 68% and 6% yields,
respectively, via the intramolecular Friedel−Crafts C-alkylation
*E-mail: mychang@kmu.edu.tw
C
DOI: 10.1021/acs.orglett.5b01461
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
Notes
(10) Narender, T.; Sarkar, S.; Rajendar, K.; Tiwari, S. Org. Lett. 2011,
3, 6140.
1
The authors declare no competing financial interest.
(
11) (a) Saito, S.; Yamamoto, Y. Chem. Rev. 2000, 100, 2901.
b) Hassan, J.; Sevignon, M.; Gozzi, C.; Schulz, E.; Lemaire, M. Chem.
Rev. 2002, 102, 1359. (c) Liu, J.-K. Chem. Rev. 2006, 106, 2209.
12) (a) Hassan, J.; Sevignon, M.; Gozzi, C.; Schulz, E.; Lemaire, M.
(
ACKNOWLEDGMENTS
■
(
The authors thank the Ministry of Science and Technology of
the Republic of China for financial support.
Chem. Rev. 2002, 102, 1359. (b) Schroter, S.; Stock, C.; Bach, T.
Tetrahedron 2005, 61, 2245. (c) Schnurch, M.; Flasik, R.; Khan, A. F.;
Spina, M.; Mihovilovic, M. D.; Stanetty, P. Eur. J. Org. Chem. 2006,
3
(
(
283. (d) Wang, R.; Manabe, K. Synthesis 2009, 1405.
13) (a) Varela, J. A.; Saa, C. Chem. Rev. 2003, 103, 3787.
b) Grotjahn, D. B. Transition Metal Alkyne Complexes: Transition
REFERENCES
■
(
1) (a) Le Roux, C.; Dubac, J. Synlett 2002, 181. (b) Leonard, N. M.;
Wieland, L. C.; Mohan, R. S. Tetrahedron 2002, 58, 8373. (c) Gaspard-
Iloughmane, H.; Le Roux, C. Eur. J. Org. Chem. 2004, 2517.
d) Gaspard-Iloughmane, H.; Le Roux, C. Eur. J. Org. Chem. 2004,
517. (e) Gaspard-Iloughmane, H.; Le Roux, C. Trends Org. Chem.
006, 11, 65. (f) Hua, R. Curr. Org. Synth. 2008, 5, 1. (g) Salvador, J.
A. R.; Pinto, R. M. A.; Silvestre, S. M. Curr. Org. Synth. 2009, 6, 426.
h) Salvador, J. A. R.; Pinto, R. M. A.; Silvestre, S. M. Mini-Rev. Org.
Chem. 2009, 6, 241. (i) Bothwell, J. M.; Krabbez, S. W.; Mohan, R. S.
Metal-Catalyzed Cyclotrimerization. In Comprehensive Organometallic
Chemistry II; Abel, E. W., Stone, F. G. A., Wilkinson, G., Hegedus, L.
S., Eds.; Pergamon: Oxford, U.K., 1995; Vol. 12, p 741. (c) Hilt, G.;
Vogler, T.; Hess, W.; Galbiati, F. Chem. Commun. 2005, 1474. (d) Xu,
L.; Yu, R.; Wang, Y.; Chen, J.; Yang, Z. J. Org. Chem. 2013, 78, 5744.
(
2
2
(
(
e) Vollhardt, K. P. C. Angew. Chem., Int. Ed. Engl. 1984, 23, 539.
f) Kotha, S.; Brahmachary, E.; Lahiri, K. Eur. J. Org. Chem. 2005,
(
4
2
(
741. (g) Gandon, V.; Aubert, C.; Malacria, M. Chem. Commun. 2006,
209.
14) CCDC 1057389 (7d), 1055718 (8), 1055717 (9a), 1401723
Chem. Soc. Rev. 2011, 40, 4649. (j) Ollevier, T. Org. Biomol. Chem.
2
(
7
013, 11, 2740.
2) (a) Ollevier, T.; Bouchard, J.-E.; Desyroy, V. J. Org. Chem. 2008,
3, 331. (b) Attanasi, O. A.; Favi, G.; Giorgi, G.; Mantellini, F.;
Karapetyan, V.; Langer, P. Tetrahedron 2009, 65, 5456.
3) (a) Qin, H.; Yamagiwa, N.; Matsunaga, S.; Shibasaki, M. Chem.
Asian J. 2007, 2, 150. (b) Mathia, F.; Szolcsanyi, P. Org. Biomol. Chem.
012, 10, 2830. (c) Komeyama, K.; Kouya, Y.; Ohama, Y.; Takaki, K.
Chem. Commun. 2011, 47, 5031.
4) (a) Anzalone, P. W.; Baru, A. R.; Danielson, E. R.; Hayes, P. D.;
Nguyen, M.-P.; Panico, A. F.; Smith, R. C.; Mohan, R. S. J. Org. Chem.
005, 70, 2091. (b) Rubenbauer, P.; Herdtweck, E.; Strassner, T.;
Bach, T. Angew. Chem., Int. Ed. 2008, 47, 10106. (c) Rueping, M.;
Nachtsheim, B. J.; Kuenkel, A. Org. Lett. 2007, 9, 825.
5) (a) Lemiere, G.; Cacciuttolo, B.; Belhassen, E.; Dunach, E. Org.
Lett. 2012, 14, 2750. (b) Cacciuttolo, B.; Poulain-Martini, S.; Fontaine-
Vive, F.; Abdo, M. A. H.; El-Kashef, H.; Dunach, E. Eur. J. Org. Chem.
014, 7458. (c) Cacciuttolo, B.; Poulain-Martini, S.; Dunach, E. Eur. J.
Org. Chem. 2011, 3710. (d) Cacciuttolo, B.; Ondet, P.; Poulain-
Martini, S.; Lemiere, G.; Dunach, E. Org. Chem. Front. 2014, 1, 765.
(
9b), and 1062664 (11b), contain the supplementary crystallographic
data for this paper. This data can be obtained free of charge via www.
ccdc.cam.ac.uk/conts/retrieving.html (or from the CCDC, 12 Union
Road, Cambridge CB2 1EZ, U.K.; fax: 44-1223-336033; e-mail:
deposit@ccdc.cam.ac.uk).
(
2
(
15) (a) Lin, S.; Song, C.-X.; Cai, G.-X.; Wang, W.-H.; Shi, Z.-J. J.
Am. Chem. Soc. 2008, 130, 12901. (b) Reed, S. A.; White, M. C. J. Am.
Chem. Soc. 2008, 130, 3316. (c) Delcamp, J. H.; White, M. C. J. Am.
Chem. Soc. 2006, 128, 15076. (d) Chen, M. S.; Prabagaran, N.; Labenz,
N. A.; White, M. C. J. Am. Chem. Soc. 2005, 127, 6970. (e) Chen, M.
S.; White, M. C. J. Am. Chem. Soc. 2004, 126, 1346.
(
2
(
16) (a) Mengel, A.; Reser, O. Chem. Rev. 1999, 99, 1191. (b) Gung,
(
B. W. Tetrahedron 1996, 52, 5263. (c) Ager, D. J.; East, M. B.
Tetrahedron 1992, 48, 2803.
(
Tetrahedron Lett. 2013, 54, 4330. For AgOTf, see: (b) Youn, S. W.;
Pastine, S. J.; Sames, D. Org. Lett. 2004, 6, 581. For In(OTf) , see:
17) For Bi(OTf) , see: (a) Nammalwar, B.; Bunce, R. A.
3
2
3
(c) Xie, K.; Wang, S.; Li, P.; Li, X.; Yang, Z.; An, X.; Guo, C.-C.; Tan,
(
6) (a) Bonvin, Y.; Callens, E.; Larrosa, I.; Henderson, D. A.;
Oldham, J.; Burton, A. J.; Barrett, A. G. M. Org. Lett. 2005, 7, 4549.
b) Vatele, J.-M. Synlett 2008, 1785. (c) Barnych, B.; Vatele, J.-M.
Synlett 2011, 2048.
7) (a) Godeau, J.; Olivero, S.; Antoniotti, S.; Dunach, E. Org. Lett.
011, 13, 3320. (b) Kelly, B. D.; Allen, J. M.; Tundel, R. E.; Lambert,
Z. Tetrahedron Lett. 2010, 51, 4466.
(
̀
(
2
T. H. Org. Lett. 2009, 11, 1381. (c) Komeyama, K.; Takahashi, K.;
Takaki, K. Org. Lett. 2008, 10, 5119. (d) Murai, M.; Hosokawa, N.;
Roy, D.; Takai, K. Org. Lett. 2014, 16, 4134. (e) Murai, M.; Origuchi,
K.; Takai, K. Org. Lett. 2014, 16, 3828. (f) Jaratjaroonphong, J.;
Tuengpanya, S.; Ruengsangtongkul, S. J. Org. Chem. 2015, 80, 559.
(
(
g) Yun, J.; Park, J.; Kim, J.; Lee, K. Tetrahedron Lett. 2015, 56, 1045.
h) Ono, F.; Ishikura, Y.; Tada, Y.; Endo, M.; Sato, T. Synlett 2008,
2
365. (i) Diaf, I.; Lemiere, G.; Dunach, E. Angew. Chem., Int. Ed. 2014,
5
3, 4177. (j) Ondet, P.; Joffrin, A.; Diaf, I.; Lemiere, G.; Dunach, E.
Org. Lett. 2015, 17, 1002.
8) (a) Pospisil, J.; Sato, H. J. Org. Chem. 2011, 76, 2269. (b) Tsui, G.
C.; Glenadel, Q.; Lau, C.; Lautens, M. Org. Lett. 2011, 13, 208.
c) Sreedhar, B.; Rawat, V. S. Synlett 2012, 23, 413. (d) Lu, Q.; Zhang,
J.; Zhao, G.; Qi, Y.; Wang, H.; Lei, W. J. Am. Chem. Soc. 2013, 135,
1481. (e) Tang, X.; Huang, L.; Xu, Y.; Yang, J.; Wu, W.; Jiang, H.
(
(
1
Angew. Chem., Int. Ed. 2014, 53, 4205. (f) Chawla, R.; Singh, A. K.;
Yadav, L. D. S. Eur. J. Org. Chem. 2014, 10, 2032. (g) Singh, A. K.;
Chawla, R.; Yadav, L. D. S. Tetrahedron Lett. 2014, 55, 4742. (h) Shi,
X.; Ren, X.; Ren, Z.; Li, J.; Wang, Y.; Yang, S.; Gu, J.; Gao, Q.; Huang,
G. Eur. J. Org. Chem. 2014, 10, 5083. (i) Xuan, J.; Feng, Z.-J.; Chen, J.-
R.; Lu, L.-Q.; Xiao, W.-J. Chem.Eur. J. 2014, 20, 3045.
(
9) (a) Chang, M.-Y.; Cheng, Y.-J.; Lu, Y.-R. Org. Lett. 2015, 17,
1
264. (b) Chang, M.-Y.; Chen, Y.-C.; Chan, C.-K.; Huang, G. G.
Tetrahedron 2015, 71, 2095.
D
DOI: 10.1021/acs.orglett.5b01461
Org. Lett. XXXX, XXX, XXX−XXX