Gorlos-Phos for palladium-catalyzed borylation of aryl chlorides

Article abstract of DOI:10.1039/c4ob00293h

Using a readily available form of the mono-phosphine ligand, Gorlos-Phos·HBF₄, Pd-catalyzed borylation of aryl chlorides afforded aryl boronates in high yields. A variety of functional groups are well compatible with this palladium catalyzed borylation reaction. This journal is the Partner Organisations 2014.

Full text of DOI:10.1039/c4ob00293h

Organic &
Biomolecular Chemistry
View Article Online
View Journal | View Issue
PAPER
Gorlos-Phos for palladium-catalyzed borylation of
aryl chlorides†
Cite this: Org. Biomol. Chem., 2014,
12, 3604
Pengbin Li, Chunling Fu and Shengming Ma*
Received 8th February 2014,
Accepted 20th March 2014
Using a readily available form of the mono-phosphine ligand, Gorlos-Phos·HBF4, Pd-catalyzed borylation
of aryl chlorides afforded aryl boronates in high yields. A variety of functional groups are well compatible
with this palladium catalyzed borylation reaction.
DOI: 10.1039/c4ob00293h
www.rsc.org/obc
phino for the borylation reaction of aryl chlorides.10 Thus, devel-
opment of practical and highly efficient readily available ligands
Introduction
Aryl boronic acids and their derivatives play important roles in for such a transformation is still highly desirable. Recently we
organic synthesis, especially in metal-catalyzed cross-coupling have developed readily available mono-phosphines LB-Phos,
reactions, due to their air-stability, low-toxicity and functional Zheda-Phos, and Gorlos-Phos.11 They have been proven to be
group compatibility.1 When an aryl lithium or Grignard efficient in the palladium-catalyzed C–Cl bond based Suzuki
reagent was used for preparation of aryl boronic derivatives, coupling reactions,11a–c amination reactions,11d and α-arylation
the harsh conditions limited the scope seriously. On one of acetone.11e In this paper, we wish to report the application of
hand, the development of transition metal-catalyzed borylation those phosphines in C–Cl activation-based borylation reaction.
of aryl halides and direct C–H activation borylation reaction in
the last decade provides an efficient alternative to aryl boronic
derivatives with various functional groups.2 On the other
Results and discussion
hand, the huge demand for various aryl boronic derivatives
Using p-chloroanisole (1a) and B2pin2 as the model substrates
requires a highly efficient, yet cheap enough synthetic protocol
for the catalyzed-borylation reaction, we first screened these
and obviously aryl chlorides are ideal substrates for the boryla-
above mentioned phosphines developed by our group.
tion reaction, which show great advantages in terms of atom-
economy, cost, and availability.3 The sterically bulky and elec-
Pd(OAc)2/LB-Phos·HBF4 did catalyze the borylation reaction of
1a using KOAc (2.0 equiv.) as the base with 77% yield of 2a and
tron-rich phosphine ligands are the key to the success of C–Cl
activation reaction.4 Some notable phosphine ligands in bory-
9% recovery of 1a. While Zheda-phos was used instead, 90%
recovery of 1a was achieved. Interestingly, the readily available
lation of aryl chlorides are listed as follows: the pioneering
11d
Gorlos-Phos·HBF4
gave a better result with 84% yield of 2a,
work on Pd-catalyzed borylation of aryl chlorides was reported
by Miyaura and coworkers in 2001 with PCy3 as a ligand;5 in
2007, Buchwald and coworkers reported a method using SPhos
or XPhos as a ligand with 1 mol% loading of [Pd2dba3] in
10 min to 5 h;6 in 2010, Molander reported a direct route to
aryl boronic acid by Pd-catalyzed borylation of aryl chlorides
with tetrahydroxydiboron using XPhos as a ligand giving
facile access to diverse boronic acids;7,8 it is impressive that
Sawamura’s silica-supported phosphine silica-SMAP is
efficient in borylation of sterically demanding aryl chlorides;9
Kwong’s indole-based phosphine PPh2-Andole-Phos is the only
efficient ligand bearing a –PPh2 moiety instead of dialkylphos-
though still 5% of 1a was recovered (Scheme 1).
Laboratory of Molecular Recognition and Synthesis, Department of Chemistry,
Zhejiang University, Hangzhou 310027, Zhejiang, P. R. China.
E-mail: masm@mail.sioc.ac.cn; Fax: (+86)21-6416-7510
†Electronic supplementary information (ESI) available. See DOI: 10.1039/
c4ob00293h
Scheme 1
3604 | Org. Biomol. Chem., 2014, 12, 3604–3610
This journal is © The Royal Society of Chemistry 2014

View Article Online
Organic & Biomolecular Chemistry
Paper
Reducing the loading of Gorlos-Phos·HBF4 would decrease in yields of 89% and 92% (Table 2, entries 8 and 9). Base sen-
the yield of 2a sharply to 49% (Table 1, entry 1). In contrast, sitive functional groups, such as –COMe, –CHO, –COOMe,
further optimizing the ratio of Pd(OAc)2/Gorlos-Phos·HBF4 to –CONH2, –NHCOMe, and –OH, were well tolerated under this
1/4 could reduce the loading of Pd(OAc)2 to 1 mol% (Table 1, set of mild reaction conditions (Table 2, entries 10–15). And
entries 2 and 3). Strong bases like K2CO3 and K3PO4 would even p-chlorobenzoic acid could be directly transformed into
lead to the formation of a symmetric biaryl compound as a borate with a yield of 74% in 3.0 h (Table 2, entry 16).
byproduct (Table 1, entries 4 and 5). Finally, we found that
improving the concentration of 1a from 0.2 M to 0.5 M would
a
shorten the reaction time to 2.5 h and improve the yield of 2a
to 98% (Table 1, entry 6). Compared to DMSO and toluene,
dioxane is a better solvent (Table 1, entries 6–8).
Table 2 Borylation reaction of aryl chlorides with B2pin2
Table 1 Borylation reaction of p-chloroanisole (1a)a
Entry
1
Time/h
Yield of 2b/%
1
2
3
4
4-MeOC6H4 (1a)
3-MeOC6H4 (1b)
2-MeC6H4 (1c)
1-Naphthyl (1d)
4-tBuC6H4 (1e)
4-MeCOC6H4 (1f)
4-NCC6H4 (1g)
4-MeSO2C6H4 (1h)
4-O2NC6H4 (1i)
3-MeCOC6H4 (1j)
2-OCHC6H4 (1k)
4-MeO2CCH2OC6H4 (1l)
4-H2NCOC6H4 (1m)
4-MeCONHC6H4 (1n)
4-HOC6H4 (1o)
2.5
1.0
7.5
2.0
2.5
5.0
3.0
1.0
1.0
1.0
1.0
1.5
1.5
1.0
2.5
3.0
90 (2a)
91 (2b)
82 (2c)
92 (2d)
80 (2e)
81 (2f)
87 (2g)
89 (2h)
92 (2i)
88 (2j)
89 (2k)
79 (2l)
81 (2m)
92 (2n)
76 (2o)
74 (2p)
5
6c
7c
8
9
10
11
12
13
14
15
16
Pd/ligand/
(mol%/mol%)
Yield
Recovery
Entry
Time/h
of 2ab/%
of 1ab/%
1
2
3
3/4.5
1/3
1/4
1/4
1/4
1/4
1/4
1/4
5.0
9.5
17
17
17
2.5
2.5
2.5
49
81
91
71
62
98
18
61
32
8
8
—
—
—
67
11
4-HOOCC6H4 (1p)
4c
5d
6e
7f
8g
a Reaction conditions: aryl chloride (1.0 mmol), B2pin2 (1.2 mmol),
Pd(OAc)2 (0.01 mmol), Gorlos-Phos·HBF4 (0.04 mmol), and KOAc
(3.0 mmol) in 2.0 mL of dioxane at 110 °C. b Isolated yield. c 1.02
equiv. of B2pin2 were used.
a Reaction conditions: aryl chloride (0.4–1.0 mmol, 0.2 M), B2pin2 (1.2
equiv.), Pd(OAc)2 (1 mol%), Gorlos-Phos·HBF4 (4 mol%), and KOAc
(3.0 equiv.) in dioxane at 110 °C. b Determined by 1H-NMR analysis.
c 3.0 equiv. of K2CO3 were used as the base here and 29% yield of 4,4′-
dimethoxybiphenyl was detected. d 3.0 equiv. of K3PO4 were used as
the base here and 37% yield of 4,4′-dimethoxybiphenyl was detected.
e The concentration of 1a was 0.5 M here. f DMSO was used as a solvent
here. g Toluene was used as a solvent instead here.
It is noted that the borylation of heteroaryl chlorides such
as 7-chloro-2-methylquinoline and 3-thienyl chloride also
occurred smoothly to produce 2q12 and 2r5 in 84% and 49%
yields (Scheme 2).
With the optimized conditions in hand (Table 1, entry 6),
we explored the scope of aryl chlorides in the borylation reac-
tion. The Pd(OAc)2/Gorlos-Phos·HBF4 system demonstrated
very high activity on borylation reaction of differently substi-
tuted aryl chlorides. Electron-donating group-substituted aryl
chlorides such as p-chloroanisole, m-chloroanisole, 1-chlo-
ronaphthalene, and p-chloro-tert-butylbenzene could be trans-
formed into the corresponding borate products smoothly
within 1.0–2.5 h with excellent yields (Table 2, entries 1–2 and
4–5). It took 7.5 h for complete conversion with o-chloroto-
luene probably due to its steric factor (Table 2, entry 3). The
equivalent of B2pin2 could be reduced to 1.02 equivalents
without any drop in the yield but with a longer reaction time
(Table 2, entries 6–7). The borylation reaction of the electron-
deficient 4-chlorophenyl methylsulfone and 4-chloronitroben-
zene could be completed within 1.0 h to afford borate products
Scheme 2 Borylation reaction of heteroaryl chlorides with B2pin2.
It is found that the highly sterically hindered substrate,
2-chloro-m-xylene 1s, is hard to convert when B2pin2 was used
as a boron source. Luckily, the application of commercially
available less steric demanding bis(neophentylglycolato)-
diboron 313 afforded borate 4 in 52% yield (Scheme 3).
This journal is © The Royal Society of Chemistry 2014
Org. Biomol. Chem., 2014, 12, 3604–3610 | 3605

View Article Online
Paper
Organic & Biomolecular Chemistry
Experimental
General information
1H and 13C NMR spectra were recorded in CDCl3 on the instru-
ment operated at 300 and 75 MHz, respectively. Chemical
shifts (δ) are given in parts per million (ppm) with the residual
peak of CHCl3 at 7.260 ppm or TMS at 0.000 ppm as the
internal standard. Infrared spectra were recorded for thin
films of pure samples on sodium chloride plates for liquid
samples or in the form of KBr discs for solid samples. Mass
and HRMS spectra were recorded in EI mode. Thin layer
chromatography was performed on pre-coated glass-back
plates and visualized with UV light at 254 nm. Flash column
chromatography was performed with silica gel (10–40 μm).
Commercially available aryl chlorides, B2pin2, and KOAc were
used directly. Dioxane and toluene used in the experiment
were refluxed in the presence of sodium using diphenyl ketone
as an indicator and distilled right before use. DMSO was
refluxed in the presence of CaH2 overnight and distilled right
before use. CH2Br2 was used as the internal standard for
1H NMR analysis (Tables 1 and 2).
Scheme 3 Palladium-catalyzed borylation of the highly steric hindered
substrate 1s.
In order to show the practicality,
a 10 mmol scale
Typical procedure
reaction of 4-chlorotoluene 1t was conducted. The loading
of the Pd-catalyst could be reduced further to 0.1 mol%
affording 2t in 83% yield in 22 h; product 2p (∼12 g) could
be easily obtained by simple recrystallization right after the
borylation with a yield of 74% (see also entry 16 of Table 2,
Scheme 4).
(1) Synthesis of 2-(4-methoxyphenyl)-4,4,5,5-tetramethyl-
1,3,2-dioxaborolane (2a).5 To a flame-dried and nitrogen filled
Schlenk vessel were added Pd(OAc)2 (2.3 mg, 0.01 mmol),
Gorlos-Phos·HBF4 (19.0 mg, 0.04 mmol), KOAc (294.7 mg,
3.0 mmol), and bis(pinacolato)diboron (305.9 mg, 1.2 mmol).
The Schlenk vessel was evacuated and backfilled with nitrogen
two times. Then 1a (141.8 mg, 1.0 mmol) and 2.0 mL of
dioxane were added (if the aryl chloride is a solid, it should be
added before evacuation). The vessel was heated at 110 °C with
a preheated oil bath. After 2.5 h, the reaction was complete as
monitored by GC. The reaction mixture was diluted with
10 mL of ethyl acetate and filtered through a short column of
silica gel (eluent: 2 × 10 mL of ethyl acetate). Evaporation and
purification by chromatography (eluent: petroleum ether–ethyl
acetate = 10/1) on a short silica gel column (10 cm, ∅ 2 cm)
afforded 2a (209.9 mg, 90%) as a liquid: 1H NMR (300 MHz,
CDCl3) δ 7.77 (d, J = 8.7 Hz, 2H, ArH), 6.91 (d, J = 8.4 Hz, 2H,
ArH), 3.82 (s, 3H, OCH3), 1.34 (s, 12H, 4 × CH3); 13C NMR
(75 MHz, CDCl3) δ 162.1, 136.5, 113.3, 83.8, 55.0, 24.8; IR
(neat) v (cm−1) 2978, 2934, 2838, 1605, 1570, 1518, 1466, 1410,
1397, 1362, 1318, 1278, 1248, 1214, 1175, 1144, 1092, 1031,
1011; MS (70 eV, EI) m/z (%): 235 (M+ + 1, 13.01), 234
(M+, 95.13), 134 (100).
Scheme 4 1 g scale and 10 g scale reactions.
The following compounds were prepared by this procedure.
(2) 2-(3-Methoxyphenyl)-4,4,5,5-tetramethyl-1,3,2-dioxa-
borolane (2b).5 The reaction of 1b (143.6 mg, 1.0 mmol),
Pd(OAc)2 (2.3 mg, 0.01 mmol), Gorlos-Phos·HBF4 (19.2 mg,
0.04 mmol), B2pin2 (305.8 mg, 1.2 mmol), and KOAc
(295.3 mg, 3.0 mmol) in 2.0 mL of dioxane at 110 °C under
nitrogen afforded 2b (214.2 mg, 91%) as a liquid (eluent: pet-
roleum ether–ethyl acetate = 10/1): H NMR (300 MHz, CDCl3)
δ 7.41 (d, J = 7.2 Hz, 1H, ArH), 7.37–7.22 (m, 2H, ArH),
7.05–6.97 (m, 1H, ArH), 3.83 (s, 3H, ArCH3), 1.34 (s, 12H, 4 ×
Conclusions
In summary, we have developed the Pd-catalyzed borylation
reaction of a variety of electron-rich and electron-deficient
group-substituted aryl chlorides under mild conditions using
the readily available Gorlos-phos, affording aryl boronates with
much synthetically active functionality. Even the steric
demanding 2,6-disubstituted aryl chlorides and heteroaryl
chlorides work. Further studies in this area are being con-
ducted by our group.
1
3606 | Org. Biomol. Chem., 2014, 12, 3604–3610
This journal is © The Royal Society of Chemistry 2014

View Article Online
Organic & Biomolecular Chemistry
Paper
CH3); 13C NMR (75 MHz, CDCl3) δ 159.0, 128.9, 127.1, 118.7, 84.2, 26.7, 24.8; IR (KBr) v (cm−1) 2990, 2932, 1682, 1560, 1508,
117.9, 83.8, 55.2, 24.8; IR (neat) v (cm−1) 2978, 2935, 2834, 1398, 1360, 1326, 1267, 1212, 1144, 1107, 1094, 1066, 1017; MS
1599, 1576, 1491, 1450, 1424, 1386, 1356, 1317, 1270, 1240, (70 eV, EI) m/z (%): 247 (M+ + 1, 3.91), 246 (M+, 24.84), 231
1227, 1145, 1102, 1073, 1046; MS (70 eV, EI) m/z (%): 235 (100).
(M+ + 1, 5.72), 234 (M+, 39.61), 134 (100).
(7) 4-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)benzo-nitrile
(3) 4,4,5,5-Tetramethyl-2-o-tolyl-1,3,2-dioxaborolane (2c).5 The (2g).5 The reaction of 1g (137.8 mg, 1.0 mmol), Pd(OAc)2
reaction of 1c (125.8 mg, 1.0 mmol), Pd(OAc)2 (2.2 mg, (2.3 mg, 0.01 mmol), Gorlos-Phos·HBF4 (19.3 mg, 0.04 mmol),
0.01 mmol), Gorlos-Phos·HBF4 (19.2 mg, 0.04 mmol), B2pin2 B2pin2 (259.4 mg, 1.02 mmol), and KOAc (295.3 mg, 3.0 mmol)
(305.5 mg, 1.2 mmol), and KOAc (295.6 mg, 3.0 mmol) in in 2.0 mL of dioxane at 110 °C under nitrogen afforded 2g
2.0 mL of dioxane at 110 °C under nitrogen afforded 2c (200.6 mg, 87%) as a solid (eluent: petroleum ether–ethyl
1
(177.1 mg, 82%) as a liquid (eluent: petroleum ether–ethyl acetate = 10/1): m.p. 94–95 °C (n-hexane); H NMR (300 MHz,
acetate = 10/1): 1H NMR (300 MHz, CDCl3) δ 7.68 (d, J = 6.9 Hz, CDCl3) δ 7.88 (d, J = 8.1 Hz, 2H, ArH), 7.64 (d, J = 8.1 Hz, 2H,
1H, ArH), 7.22 (t, J = 7.2 Hz, 2H, ArH), 7.12–6.97 (m, 2H, ArH), ArH), 1.35 (s, 12H, 4 × CH3); 13C NMR (75 MHz, CDCl3) δ
2.45 (s, 3H, ArCH3), 1.24 (s, 12H, 4 × CH3); 13C NMR (75 MHz, 135.0, 131.0, 118.8, 114.4, 84.4, 24.8; IR (KBr) v (cm−1) 3003,
CDCl3) δ 144.8, 135.8, 130.8, 129.7, 124.7, 83.3, 24.8, 22.2; IR 2976, 2932, 2228, 1611, 1508, 1399, 1359, 1334, 1272, 1210,
(neat) v (cm−1) 3053, 2978, 2930, 1601, 1566, 1490, 1441, 1424, 1143, 1089, 1021; MS (70 eV, EI) m/z (%): 230 (M+ + 1, 2.01),
1381, 1347, 1312, 1265, 1146, 1124, 1110, 1073, 1043; MS 229 (M+, 13.99), 143 (100).
(70 eV, EI) m/z (%): 219 (M+ + 1, 6.10), 218 (M+, 46.98), 161 (100).
(8) 4,4,5,5-Tetramethyl-2-(4-(methylsulfonyl)phenyl)-1,3,2-
(4) 4,4,5,5-Tetramethyl-2-(naphthalen-1-yl)-1,3,2-dioxa-boro- dioxaborolane (2h).15 The reaction of 1h (191.0 mg,
lane (2d).5 The reaction of 1d (162.3 mg, 1.0 mmol), Pd(OAc)2 1.0 mmol), Pd(OAc)2 (2.1 mg, 0.01 mmol), Gorlos-Phos·HBF4
(2.2 mg, 0.01 mmol), Gorlos-Phos·HBF4 (19.1 mg, 0.04 mmol), (19.2 mg, 0.04 mmol), B2pin2 (303.5 mg, 1.2 mmol), and KOAc
B2pin2 (305.1 mg, 1.2 mmol), and KOAc (294.3 mg, 3.0 mmol) (296.7 mg, 3.0 mmol) in 2.0 mL of dioxane at 110 °C under
in 2.0 mL of dioxane at 110 °C under nitrogen afforded 2d5 nitrogen afforded 2h (252.3 mg, 89%) as a solid (eluent:
(232.4 mg, 92%) as a solid (eluent: petroleum ether–ethyl petroleum ether–ethyl acetate
= 20/1): m.p. 160–161 °C
acetate = 20/1): m.p. 56–57 °C (n-hexane); H NMR (300 MHz, (n-hexane); 1H NMR (300 MHz, CDCl3) δ 7.98 (d, J = 8.1 Hz,
CDCl3) δ 8.80 (d, J = 8.4 Hz, 1H, ArH), 8.11 (d, J = 6.3 Hz, 1H, 2H, ArH), 7.91 (d, J = 8.1 Hz, 2H, ArH), 3.03 (s, 3H, CH3),
ArH), 7.96 (d, J = 8.4 Hz, 1H, ArH), 7.85 (d, J = 8.4 Hz, 1H, 1.34 (s, 12H, 4 × CH3); 13C NMR (75 MHz, CDCl3) δ 142.5,
ArH), 7.63–7.39 (m, 3H, ArH), 1.44 (s, 12H, 4 × CH3); 13C NMR 135.5, 126.2, 84.5, 44.3, 24.8; IR (KBr) v (cm−1) 2977, 2932,
(75 MHz, CDCl3) δ 136.9, 135.6, 133.2, 131.6, 128.4, 128.3, 1605, 1492, 1396, 1362, 1333, 1301, 1271, 1156, 1143, 1095,
126.3, 125.5, 124.9, 83.7, 24.9; IR (KBr) v (cm−1) 3043, 2978, 1079; MS (70 eV, EI) m/z (%): 283 (M+ + 1, 2.69), 282
2929, 1577, 1508, 1463, 1436, 1414, 1405, 1371, 1339, 1298, (M+, 13.13), 196 (100).
1
1257, 1207, 1147, 1135, 1111, 1059, 1023, 1006; MS (70 eV, EI)
(9) 4,4,5,5-Tetramethyl-2-(4-nitrophenyl)-1,3,2-dioxaborolane
m/z (%): 255 (M+ + 1, 14.99), 254 (M+, 90.06), 154 (100).
(2i).5 The reaction of 1i (156.0 mg, 1.0 mmol), Pd(OAc)2
(5) 2-(4-t-Butylphenyl)-4,4,5,5-tetramethyl-1,3,2-dioxa-boro- (2.3 mg, 0.01 mmol), Gorlos-Phos·HBF4 (19.1 mg, 0.04 mmol),
lane (2e).14 The reaction of 1e (169.3 mg, 1.0 mmol), Pd(OAc)2 B2pin2 (304.7 mg, 1.2 mmol), and KOAc (294.6 mg, 3.0 mmol)
(2.3 mg, 0.01 mmol), Gorlos-Phos·HBF4 (19.1 mg, 0.04 mmol), in 2.0 mL of dioxane at 110 °C under nitrogen afforded 2i
B2pin2 (304.4 mg, 1.2 mmol), and KOAc (294.6 mg, 3.0 mmol) (226.4 mg, 92%) as a solid (eluent: petroleum ether–ethyl
in 2.0 mL of dioxane at 110 °C under nitrogen afforded 2e acetate = 10/1): m.p. 107–108 °C (n-hexane–ethyl ether); 1H
(208.8 mg, 80%) as a solid (eluent: petroleum ether–ethyl NMR (300 MHz, CDCl3) δ 8.18 (d, J = 8.4 Hz, 2H, ArH), 7.95 (d,
acetate = 10/1): m.p. 137–138 °C (n-hexane) 1H NMR (300 MHz, J = 8.1 Hz, 2H, ArH), 1.36 (s, 12H, 4 × CH3); 13C NMR (75 MHz,
CDCl3) δ 7.77 (d, J = 8.4 Hz, 2H, ArH), 7.42 (d, J = 8.4 Hz, 2H, CDCl3) δ 149.8, 135.6, 122.4, 84.6, 24.8; IR (KBr) v (cm−1) 2991,
ArH), 1.34 (s, 12H, 4 × CH3), 1.33(s, 9H, C(CH3)3); 13C NMR 2976, 2933, 1599, 1520, 1397, 1363, 1350, 1307, 1276, 1147,
(75 MHz, CDCl3) δ 154.5, 134.7, 124.7, 83.6, 34.9, 31.2, 24.8; IR 1088, 1012; MS (70 eV, EI) m/z (%): 250 (M+ + 1, 1.13), 249
(KBr) v (cm−1) 2968, 2868, 1612, 1472, 1400, 1364, 1326, 1270, (M+, 7.99), 234 (100).
1212, 1144, 1118, 1084, 1021. MS (70 eV, EI) m/z (%): 261
(10) 1-(3-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)-phenyl)-
(M+ + 1, 2.50), 260 (M+, 15.36), 245 (100).
ethanone (2j).14 The reaction of 1j (155.7 mg, 1.0 mmol),
(6) 1-(4-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)-phenyl)- Pd(OAc)2 (2.3 mg, 0.01 mmol), Gorlos-Phos·HBF4 (19.2 mg,
ethanone (2f).10 The reaction of 1f (154.6 mg, 1.0 mmol), 0.04 mmol), B2pin2 (306.4 mg, 1.2 mmol), and KOAc
Pd(OAc)2 (2.3 mg, 0.01 mmol), Gorlos-Phos·HBF4 (19.1 mg, (295.6 mg, 3.0 mmol) in 2.0 mL of dioxane at 110 °C under
0.04 mmol), B2pin2 (260.2 mg, 1.02 mmol), and KOAc nitrogen afforded 2j (217.0 mg, 88%) as a liquid (eluent: pet-
1
(296.3 mg, 3.0 mmol) in 2.0 mL of dioxane at 110 °C under roleum ether–ethyl acetate = 10/1): H NMR (300 MHz, CDCl3)
nitrogen afforded 2f (200.3 mg, 81%) as a solid (eluent: pet- δ 8.35 (s, 1H, ArH), 8.03 (d, J = 8.1 Hz, 1H, ArH), 7.97 (d, J =
roleum ether–ethyl acetate = 10/1): m.p. 63–64 °C (n-hexane); 7.2 Hz, 1H, ArH), 7.45 (t, J = 7.7 Hz, 1H, ArH), 2.61 (s, 3H,
1H NMR (300 MHz, CDCl3) δ 7.93 (d, J = 8.1 Hz, 2H, ArH), 7.88 CH3), 1.34 (s, 12H, 4 × CH3); 13C NMR (75 MHz, CDCl3) δ
(d, J = 7.8 Hz, 2H, ArH), 2.61 (s, 3H, CH3), 1.35 (s, 12H, 4 × 198.4, 139.4, 136.5, 134.8, 130.8, 128.0, 84.1, 26.7, 24.8; IR
CH3); 13C NMR (75 MHz, CDCl3) δ 198.4, 138.9, 134.9, 127.3, (neat) v (cm−1) 2974, 2929, 1687, 1599, 1485, 1417, 1358, 1324,
This journal is © The Royal Society of Chemistry 2014
Org. Biomol. Chem., 2014, 12, 3604–3610 | 3607

View Article Online
Paper
Organic & Biomolecular Chemistry
1275, 1250, 1144, 1072; MS (70 eV, EI) m/z (%): 247 (M+ + 1, 5/1/1). The impurity in this product was removed by washing
3.26), 246 (M+, 17.15), 231 (100).
with 10 mL n-hexane to afford 240.5 mg (92%) of the pure
(11) 2-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)benz- product 2n: m.p. 157–158 °C (n-hexane–ethyl acetate); 1H NMR
aldehyde (2k).16 The reaction of 1k (139.9 mg, 1.0 mmol), (300 MHz, CDCl3) δ 7.94 (bs, 1H, NH), 7.74 (d, J = 8.1 Hz, 2H,
Pd(OAc)2 (2.3 mg, 0.01 mmol), Gorlos-Phos·HBF4 (19.0 mg, ArH), 7.53 (d, J = 7.8 Hz, 2H, ArH), 2.15 (s, 3H, CH3), 1.32 (s,
0.04 mmol), B2pin2 (304.7 mg, 1.2 mmol), and KOAc 12H, 4 × CH3); 13C NMR (75 MHz, CDCl3) δ 168.7, 140.7, 135.7,
(294.8 mg, 3.0 mmol) in 2.0 mL of dioxane at 110 °C under 118.6, 83.7, 24.8, 24.6; IR (KBr) v (cm−1) 3312, 3271, 3183,
nitrogen afforded 2k (204.3 mg, 89%) as a liquid (eluent: pet- 3108, 3057, 2979, 2931, 1673, 1598, 1535, 1400, 1360, 1321,
1
roleum ether–ethyl acetate = 20/1); H NMR (300 MHz, CDCl3) 1290, 1258, 1141, 1092, 1019; MS (70 eV, EI) m/z (%): 262
δ 10.53 (s, 1H, CHO), 7.99–7.91 (m, 1H, ArH), 7.89–7.78 (M+ + 1, 9.55), 261 (M+, 65.57), 119 (100).
(m, 1H, ArH), 7.64–7.47 (m, 2H, ArH), 1.38 (s, 12H, 4 × CH3);
(15) 4-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)phenol
13C NMR (75 MHz, CDCl3) δ 194.6, 141.2, 135.4, 132.9, 130.7, (2o).6 The reaction of 1o (127.7 mg, 0.99 mmol), Pd(OAc)2
127.8, 84.3, 24.8; IR (neat) v (cm−1) 2975, 2932, 1697, 1593, (2.3 mg, 0.01 mmol), Gorlos-Phos·HBF4 (19.2 mg, 0.04 mmol),
1567, 1489, 1441, 1380, 1347, 1325, 1258, 1202, 1144, 1111, B2pin2 (305.9 mg, 1.2 mmol), and KOAc (297.1 mg, 3.0 mmol)
1068, 1036; MS (70 eV, EI) m/z (%):217 (M+ − CH3, 10.61), 174 in 2.0 mL of dioxane at 110 °C under nitrogen afforded 2o
(100).
(166.0 mg, 76%) as a solid (eluent: petroleum ether–ethyl
(12) Methyl 2-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)- acetate = 10/1): m.p. 109–110 °C (n-hexane–ethyl acetate); 1H
phenoxy)acetate (2l). The reaction of 1l (200.6 mg, 1.0 mmol), NMR (300 MHz, CDCl3) δ 7.70 (d, J = 8.4 Hz, 2H, ArH), 6.82 (d,
Pd(OAc)2 (2.3 mg, 0.01 mmol), Gorlos-Phos·HBF4 (19.1 mg, J = 8.4 Hz, 2H, ArH), 5.85–5.53 (bs, 1H, OH), 1.34 (s, 12H, 4 ×
0.04 mmol), B2pin2 (305.3 mg, 1.2 mmol), and KOAc CH3); 13C NMR (75 MHz, CDCl3) δ 158.4, 136.8, 114.9, 83.7,
(295.9 mg, 3.0 mmol) in 2.0 mL of dioxane at 110 °C under 24.8; IR (KBr) v (cm−1) 3319, 2985, 2941, 1608, 1579, 1430,
nitrogen afforded 2l (229.7 mg, 79%) as a liquid (eluent: pet- 1401, 1393, 1383, 1373, 1360, 1309, 1273, 1263, 1218, 1170,
1
roleum ether–ethyl acetate = 10/1); H NMR (300 MHz, CDCl3) 1141, 1096, 1080; MS (70 eV, EI) m/z (%): 221 (M+ + 1, 5.04),
δ 7.75 (d, J = 8.7 Hz, 2H, ArH), 6.89 (d, J = 8.7 Hz, ArH), 4.66 (s, 220 (M+, 32.19), 121 (100).
2H, CH2), 3.79 (s, 3H, CH3), 1.32 (s, 12H, 4 × CH3); 13C NMR
(16) 2-Methyl-7-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-
(75 MHz, CDCl3) δ 169.2, 160.2, 136.6, 113.8, 83.6, 64.9, yl)quinoline (2q).12 The reaction of 1q (177.1 mg, 1.0 mmol),
52.2, 24.8; IR (neat) v (cm−1) 2978, 1759, 1604, 1573, 1515, Pd(OAc)2 (2.2 mg, 0.01 mmol), Gorlos-Phos·HBF4 (19.1 mg,
1437, 1394, 1361, 1317, 1291, 1205, 1142, 1093, 1079, 1012; MS 0.04 mmol), B2pin2 (302.9 mg, 1.2 mmol), and KOAc
(70 eV, EI) m/z (%): 293 (M+ + 1, 11.81), 292 (M+, 62.87), (296.6 mg, 3.0 mmol) in 2.0 mL of dioxane at 110 °C under
133 (100). HRMS Cacld for C15H21BO5 (M+): 292.1482, Found nitrogen afforded 2q (225.3 mg, 84%) as a solid (eluent: pet-
292.1481.
roleum ether–ethyl acetate–pyridine
=
5/1/0.05): m.p.
(13) 4-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)-benz- 105–107 °C (n-hexane); 1H NMR (300 MHz, CDCl3) δ 8.55 (s,
amide (2m).17 The reaction of 1m (155.4 mg, 1.0 mmol), 1H, ArH), 7.99 (d, J = 8.1 Hz, 2H, ArH), 7.83 (d, J = 8.1 Hz, 1H,
Pd(OAc)2 (2.3 mg, 0.01 mmol), Gorlos-Phos·HBF4 (19.2 mg, ArH), 7.73 (d, J = 8.1 Hz, 1H, ArH), 7.26 (d, J = 8.7 Hz, 1H,
0.04 mmol), B2pin2 (305.4 mg, 1.2 mmol), and KOAc ArH), 2.73 (s, 3H, CH3), 1.37 (s, 12H, 4 × CH3); 13C NMR
(296.7 mg, 3.0 mmol) in 2.0 mL of dioxane at 110 °C under (75 MHz, CDCl3) δ 158.7, 147.2, 136.6, 135.8, 130.1, 128.1,
nitrogen afforded 2m (200.7 mg, 81%) as a solid (eluent: pet- 126.5, 122.6, 83.9, 25.3, 24.8; IR (KBr) v (cm−1) 3051, 2979,
roleum ether–ethyl acetate = 5/1 (300 mL), then petroleum 2929, 1604, 1554, 1508, 1449, 1409, 1382, 1356, 1329, 1296,
ether–ethyl acetate = 1/1): m.p. 178–180 °C (ethyl acetate– 1273, 1216, 1166, 1143, 1131, 1113, 1075; MS (70 eV, EI) m/z
dichloromethane); 1H NMR (300 MHz, CDCl3) δ 7.84 (d, J = (%): 270 (M+ + 1, 8.97), 269 (M+, 57.26), 268 (100).
7.8 Hz, 2H, ArH), 7.78 (d, J = 8.1 Hz, 2H, ArH), 6.76 (s, 1H, one
(17) 4,4,5,5-Tetramethyl-2-(thien-3-yl)-1,3,2-dioxaborolane
proton of NH2), 6.55 (s, 1H, one proton of NH2), 1.32 (s, (2r).5 The reaction of 1r (118.9 mg, 1.0 mmol), Pd(OAc)2
12H, 4 × CH3); 13C NMR (75 MHz, CDCl3) δ 169.9, 135.6, (2.3 mg, 0.01 mmol), Gorlos-Phos·HBF4 (19.2 mg, 0.04 mmol),
134.8, 126.4, 84.1, 24.8; IR (KBr) v (cm−1) 3484, 3411, B2pin2 (304.2 mg, 1.2 mmol), and KOAc (296.7 mg, 3.0 mmol)
3352, 3289, 3188, 2985, 2938, 1671, 1604, 1555, 1510, in 2.0 mL of dioxane at 110 °C under nitrogen afforded 2r
1358, 1328, 1273, 1211, 1168, 1143, 1111, 1086, 1018; MS (102.2 mg, 49%) as a solid (eluent: petroleum ether–ethyl
1
(70 eV, EI) m/z (%): 248 (M+ + 1, 3.40), 247 (M+, 21.44), acetate = 20/1): m.p. 76–78 °C (n-hexane); H NMR (300 MHz,
148 (100).
CDCl3) δ 7.92 (dd, J1 = 2.7 Hz, J2 = 0.9 Hz, 1H, ArH), 7.41 (dd,
(14) N-(4-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)-phenyl)- J1 = 4.8 Hz, J2 = 1.2 Hz, 1H, ArH), 7.7.34 (dd, J1 = 4.8 Hz, J2 =
acetamide (2n).8d The reaction of 1n (170.6 mg, 1.0 mmol), 2.7 Hz, 1H, ArH), 1.34 (s, 12H, 4 × CH3); 13C NMR (75 MHz,
Pd(OAc)2 (2.3 mg, 0.01 mmol), Gorlos-Phos·HBF4 (19.1 mg, CDCl3) δ 136.4, 132.0, 125.3, 83.6, 24.8; IR (KBr) v (cm−1) 3083,
0.04 mmol), B2pin2 (304.7 mg, 1.2 mmol), and KOAc 2980, 2929, 1519, 1412, 1389, 1372, 1341, 1312, 1264, 1211,
(294.8 mg, 3.0 mmol) in 2.0 mL of dioxane at 110 °C under 1200, 1166, 1139, 1111, 1089; MS (70 eV, EI) m/z (%): 211
nitrogen afforded 2n (261.1 mg) as a solid after chromato- (M+ + 1, 5.6), 210 (M+, 43.19), 124 (100).
graphic separation (eluent: petroleum ether–ethyl acetate =
(18) Synthesis of 2-(2,6-dimethylphenyl)-5,5-dimethyl-
5/1, then petroleum ether–ethyl acetate–dichloromethane = 1,3,2-dioxaborinane (4).18 The reaction of Pd(OAc)2 (2.1 mg,
3608 | Org. Biomol. Chem., 2014, 12, 3604–3610
This journal is © The Royal Society of Chemistry 2014

View Article Online
Organic & Biomolecular Chemistry
Paper
0.01 mmol), Gorlos-Phos·HBF4 (19.2 mg, 0.04 mmol), KOAc tored by TLC. The resulting mixture was quenched with
(292.3 mg, 3.0 mmol), bis(neophentyl glycolato)diboron 100 mL of H2O, extracted with ethyl acetate (100 mL × 3),
(338.2 mg, 1.5 mmol), 1s (140.9 mg, 1.0 mmol), and 2.0 mL of washed with 100 mL of brine, and dried over anhydrous
dioxane afforeded 4 (113.3 mg, 52%) as a solid (petroleum Na2SO4. Filtration, evaporation and purification by recrystalli-
1
ether–ethyl acetate = 10/1). m.p. 47–49 °C (n-hexane): H NMR zation three times (n-hexane and ethyl acetate) afforded 2p
(300 MHz, CDCl3) δ 7.12 (t, J = 7.5 Hz, 1H, ArH), 6.96 (d, J = (5.7863 g + 5.0512 g + 1.0850 g = 11.9225 g, 74%) as a solid: 1H
7.2 Hz, 2H, ArH), 3.81 (s, 4H, 2 × CH2), 2.41 (s, 6H, 2 × CH3), NMR (300 MHz, CDCl3) δ 10.61 (bs, 1H, COOH) 8.10 (d, J =
1.12 (s, 6H, 2 × CH3); 13C NMR (75 MHz, CDCl3) δ 140.4, 128.4, 8.1 Hz, 2H, ArH), 7.91 (d, J = 8.1 Hz, 2H, ArH), 1.37 (s, 12H,
126.3, 72.2, 31.6, 22.2; IR (KBr) v (cm−1) 3051, 3012, 2967, 4 × CH3); 13C NMR (75 MHz, CDCl3) δ 172.2, 134.7, 131.4,
2929, 2872, 1596, 1476, 1457, 1414, 1376, 1327, 1297, 1249, 129.2, 84.2, 24.8.
1219, 1129, 1091, 1029; MS (70 eV, EI) m/z (%): 219 (M+ + 1,
16.23), 218 (M+, 100).
(19) 10 mmol scale reaction of 1t – synthesis of 4,4,5,5-
Acknowledgements
tetramethyl-2-p-tolyl-1,3,2-dioxaborolane (2t).5 The reaction of
Financial support from the National Natural Science Foun-
Pd(OAc)2 (2.3 mg, 0.01 mmol), Gorlos-Phos·HBF4 (19.1 mg,
dation of China (21172192) and the National Basic Research
0.04 mmol), KOAc (2.9380 g, 30.0 mmol), B2pin2 (3.047 g,
Program of China (2011CB808700) are greatly appreciated.
12.0 mmol), 1t (1.2679 g, 10.0 mmol) and 20 mL of dioxane
Shengming Ma is a Qiu Shi Adjunct Professor at Zhejiang Uni-
afforded 2t (1.8114 mg, 83%) as a liquid (eluent: petroleum
versity. We thank Bukeyan Miao in our group for reproducing
1
ether–ethyl acetate = 20/1); H NMR (300 MHz, CDCl3) δ 7.74
the results of 2i, 2o and 2r.
(d, J = 7.5 Hz, 2H, ArH), 7.21 (d, J = 8.1 Hz, 2H, ArH), 2.39 (s,
3H, CH3), 1.36 (s, 12H, 4 × CH3); 13C NMR (75 MHz, CDCl3) δ
141.3, 134.8, 128.4, 83.5, 24.8, 21.7; IR (neat) v (cm−1) 3047,
Notes and references
2978, 2926, 1614, 1518, 1481, 1465, 1446, 1398, 1360, 1318,
1304, 1266, 1213, 1183, 1145, 1106, 1089; MS (70 eV, EI)
m/z (%): 219 (M+ + 1, 4.78), 218 (M+, 33.83), 119 (100).
1 D. G. Hall, Boronic Acids: Preparation and Applications in
Organic Synthesis, Medicine and Materials, Wiley-VCH, Wein-
heim, Germany, 2nd edn, 2011, vol. 1 and 2.
Synthesis of 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-
benzoic acid (2p).19 To a flame-dried and nitrogen filled
Schlenk vessel were added Pd(OAc)2 (2.3 mg, 0.01 mmol),
Gorlos-Phos·HBF4 (19.0 mg, 0.04 mmol), KOAc (295.6 mg,
3.0 mmol), B2pin2 (305.6 mg, 1.2 mmol), and 1p (156.1 mg,
1.0 mmol). The Schlenk vessel was evacuated and backfilled
with nitrogen two times. Then 2.0 mL of dioxane were added.
The vessel was heated with a preheated oil bath at 110 °C.
After 3.0 h, the reaction was complete as monitored by TLC.
The reaction mixture was quenched with 10 mL of H2O,
extracted with ethyl acetate (10 mL × 3), washed with 20 mL of
brine, and dried over anhydrous Na2SO4. Filtration, evapor-
ation and purification by chromatography (eluent: petroleum
ether–ethyl acetate = 10/1) on a short silica gel column (10 cm,
∅ 2 cm) afforded 2p (182.8 mg, 74%) as a solid: m.p.
227–228 °C (n-hexane–ethyl acetate); 1H NMR (300 MHz,
CDCl3) δ 10.9 (bs, 1H, COOH), 8.10 (d, J = 8.1 Hz, 2H, ArH),
7.91 (d, J = 8.1 Hz, 2H, ArH), 1.37 (s, 12H, 4 × CH3); 13C NMR
(75 MHz, CDCl3) δ 172.2, 134.8, 131.5, 129.2, 84.3, 24.9; IR
(KBr) v (cm−1) 2982, 2667, 2542, 1686, 1560, 1510, 1425, 1400,
1362, 1329, 1270, 1145, 1126, 1088, 1018; MS (70 eV, EI)
m/z (%): 248 (M+, 23.34), 149 (100).
65 mmol scale reaction of 1p. To a flame-dried and nitro-
gen filled 500 mL Schlenk vessel were added Pd(OAc)2
(14.7 mg, 0.066 mmol), Gorlos-Phos·HBF4 (124.3 mg,
0.260 mmol), KOAc (19.1170 g, 195.1 mmol), bis(pinacolato)
diboron (19.8142 g, 78.0 mmol), and 1p (10.1814 g, 65 mmol).
The Schlenk vessel was evacuated and backfilled with nitrogen
two times. Then 260 mL of dioxane were added. The resulting
mixture was stirred vigorously and heated with a preheated oil
bath at 110 °C. After 40 h, the reaction was complete as moni-
2 For a review on the transition metal-catalyzed borylation of
aryl halides, see: (a) W. K. Chow, O. Y. Yuen, P. Y. Choy,
C. M. So, C. P. Lau, W. T. Wong and F. Y. Kwong, RSC Adv.,
2013, 3, 12518. For the recent reviews on the transition
metal-catalyzed borylation reaction by C–H activation, see:
(b) I. A. I. Mkhalid, J. H. Barnard, T. B. Marder,
J. M. Murphy and J. F. Hartwig, Chem. Rev., 2010, 110, 890;
(c) J. F. Hartwig, Acc. Chem. Res., 2012, 45, 864.
3 V. V. Grushin and H. Alper, Chem. Rev., 1994, 94, 1047.
4 For the reviews, see: (a) A. F. Littke and G. C. Fu, Angew.
Chem., Int. Ed., 2002, 41, 4176; (b) D. S. Surry and
S. L. Buchwald, Angew. Chem., Int. Ed., 2008, 47, 6338;
(c) R. Martin and S. L. Buchwald, Acc. Chem. Res., 2008, 41,
1461.
5 T. Ishiyama, K. Ishida and N. Miyaura, Tetrahedron, 2001,
57, 9813.
6 K. L. Billingsley, T. E. Barder and S. L. Buchwald, Angew.
Chem., Int. Ed., 2007, 46, 5359.
7 (a) G. A. Molander, S. L. J. Trice and S. D. Dreher, J. Am.
Chem. Soc., 2010, 132, 17701; (b) G. A. Molander,
S. L. J. Trice, S. M. Kennedy, S. D. Dreher and M. T. Tudge,
J. Am. Chem. Soc., 2012, 134, 11667.
8 For selected samples of Ni catalyzed borylation reaction of
aryl chlorides, see: (a) B. M. Rosen, C. Huang and
V. Percec, Org. Lett., 2008, 10, 2597; (b) C. Moldoveanu,
D. A. Wilson, C. J. Wilson, P. Leowanawat, A. M. Resmerita,
C. Liu, B. M. Rosen and V. Percec, J. Org. Chem., 2010, 75,
5438; (c) P. Leowanawat, A. M. Resmerita, C. Moldoveanu,
C. Liu, N. Zhang, D. A. Wilson, L. M. Hoang, B. M. Rosen
and V. Percec, J. Org. Chem., 2010, 75, 7822;
This journal is © The Royal Society of Chemistry 2014
Org. Biomol. Chem., 2014, 12, 3604–3610 | 3609

View Article Online
Paper
Organic & Biomolecular Chemistry
(d) T. Yamamoto, T. Morita, J. Takagi and T. Yamakawa,
Chem., 2013, 11, 98; (d) B. Lü, P. Li, C. Fu, L. Xue, Z. Lin
and S. Ma, Adv. Synth. Catal., 2011, 353, 100; (e) P. Li,
B. Lü, C. Fu and S. Ma, Adv. Synth. Catal., 2013, 355,
1255. Patents filed (CN201210146220.6 and PCT/CN2012/
078129), 2012.
Org. Lett., 2011, 13, 5766; (e) A. S. Dudnik and G. C. Fu,
J. Am. Chem. Soc., 2012, 134, 10693; (f) G. A. Molander,
L. N. Cavalcanti and C. García-García, J. Org. Chem., 2013,
78, 6427. For Ni catalyzed borylation of aryl mesylates, tosy-
lates, or carbamates, see: (g) D. A. Wilson, C. J. Wilson, 12 P. Zhang, M. Zou, A. L. Rodriguez, P. J. Conn and
C. Moldoveanu, A. M. Resmerita, P. Corcoran, L. M. Hoang, A. H. Newman, Bioorg. Med. Chem., 2010, 18, 3026.
B. M. Rosen and V. Percec, J. Am. Chem. Soc., 2010, 132, 13 H. Fang, G. Kaur, J. Yan and B. Wang, Tetrahedron Lett.,
1800; (h) K. Huang, D. G. Yu, S. F. Zheng, Z. H. Wu and
Z. J. Shi, Chem. – Eur. J., 2011, 17, 786.
2005, 46, 1671.
14 C. Zhu and M. Yamane, Org. Lett., 2012, 14, 4560.
9 S. Kawamorita, H. Ohmiya, T. Iwai and M. Sawamura, 15 Y. Yamamoto, Adv. Synth. Catal., 2010, 352, 478.
Angew. Chem., Int. Ed., 2011, 50, 8363.
10 (a) W. K. Chow, O. Y. Yuen, C. M. So, W. T. Wong and
16 F. Wienhold, D. Claes, K. Graczyk and W. Maison, Syn-
thesis, 2011, 4059.
F. Y. Kwong, J. Org. Chem., 2012, 77, 3543; (b) T. Iwai, 17 F. Mo, Y. Jiang, D. Qiu, Y. Zhang and J. Wang, Angew.
T. Harada, R. Tanaka and M. Sawamura, Chem. Lett., 2014,
DOI: 10.1246/cl.131161.
11 (a) B. Lü, C. Fu and S. Ma, Tetrahedron Lett., 2010, 51,
Chem., Int. Ed., 2010, 49, 1846.
18 M. Schnürch, M. Holzweber, M. D. Mihovilovic and
P. Stanetty, Green Chem., 2007, 9, 139.
1284; (b) B. Lü, C. Fu and S. Ma, Chem. – Eur. J., 2010, 19 D. Qiu, L. Jin, Z. Zheng, H. Meng, F. Mo, X. Wang, Y. Zhang
16, 6434; (c) P. Li, B. Lü, C. Fu and S. Ma, Org. Biomol. and J. Wang, J. Org. Chem., 2013, 78, 1923.
3610 | Org. Biomol. Chem., 2014, 12, 3604–3610
This journal is © The Royal Society of Chemistry 2014