One-pot formylation and dimerization of p-alkyl phenols using DCMT-activated DMSO

Article abstract of DOI:10.1080/00397911.2011.590916

Dimerization and formylation of p-alkyl-substituted phenols have been successfully achieved in one pot, using 2,4-dichloro-6-methoxy[1,3,5]triazine (DCMT)-activated dimethylsulfoxide. Similarly, the d5-labeled products have been prepared in high selectivity. To the best of our knowledge, the products are of new skeletons, which have not been reported to date. A plausible mechanism is proposed based on the experiments. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397911.2011.590916

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One-Pot Formylation and Dimerization
of p-Alkyl Phenols Using DCMT-Activated
DMSO
Guobiao Chu a , Zhifang Yu a , Feng Gao a & Chunbao Li a
a Department of Chemistry, College of Science, Tianjin University,
Tianjin, China
Accepted author version posted online: 01 Feb 2012. Version of
record first published: 05 Sep 2012
To cite this article: Guobiao Chu, Zhifang Yu, Feng Gao & Chunbao Li (2013): One-Pot Formylation
and Dimerization of p-Alkyl Phenols Using DCMT-Activated DMSO, Synthetic Communications: An
International Journal for Rapid Communication of Synthetic Organic Chemistry, 43:1, 44-51
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Synthetic Communications1, 43: 44–51, 2013
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2011.590916
ONE-POT FORMYLATION AND DIMERIZATION OF
p-ALKYL PHENOLS USING DCMT-ACTIVATED DMSO
Guobiao Chu, Zhifang Yu, Feng Gao, and Chunbao Li
Department of Chemistry, College of Science, Tianjin University,
Tianjin, China
GRAPHICAL ABSTRACT
Abstract Dimerization and formylation of p-alkyl-substituted phenols have been success-
fully achieved in one pot, using 2,4-dichloro-6-methoxy[1,3,5]triazine (DCMT)-activated
dimethylsulfoxide. Similarly, the d5-labeled products have been prepared in high selectivity.
To the best of our knowledge, the products are of new skeletons, which have not been
reported to date. A plausible mechanism is proposed based on the experiments.
Keywords 2,4-Dichloro-6-methoxy[1,3,5]triazine; dimerization; DMSO; formylation;
phenols
INTRODUCTION
Cyanuric chloride (CC) and its derivatives have been reported as efficient
reagents in synthesis.[1] Recently there has been a considerable growth of interest
in the use of CC and its derivatives in the processes involving functional group trans-
formations; notable examples include activation of carboxylic acids,[2] preparation of
sulfonyl and alkyl chlorides,[3] selective protection of primary alcohols by a formyl
residue,[4] catalysis of the Beckmann rearrangement,[5] deprotection of 1,3-dithioace-
tals and 1,3-oxathiolanes to their corresponding carbonyl compounds,[6] activation
of dimethylsulfoxide (DMSO) in the Swern oxidation,[7] conversion of formamides
to isonitriles,[8] and catalysis of FriedelꢀCrafts acylations.[9] We have reported the
Received March 11, 2011.
Address correspondence to Zhifang Yu, Department of Chemistry, College of Science, Tianjin
University, Tianjin 300072, China. E-mail: zfyu@tju.edu.cn
44

DIMERIZATION AND FORMYLATION OF PHENOLS
45
Scheme 1.
preparation of methylene acetal[10] and methylenebisaminde[11] using 2,4-dichloro-6-
methoxy[1,3,5]triazine (DCMT)–activated DMSO (Scheme 1).
RESULTS AND DISCUSSION
In an attempted synthesis of bis(p-tolyloxy)methane from p-cresol using
DCMT-activated DMSO, we discovered the rather surprising formation of
2-((2-hydroxy-5-methylbenzyloxy)methoxy)-5-methylbenzaldehyde (Table 1) when
the reaction temperature was elevated to 110 ꢁC. Therefore, we started optimizing
the reaction conditions for this interesting new product. No product was observed
when the reaction was carried out at lower temperature (Table 1, entry 6) or without
DCMT (Table 1, entry 1). The reaction was performed in various solutions, such as
Table 1. Optimization of the reaction of p-cresol and DCMT-activated DMSOa
Entry
DCMT (equiv)
T (ꢁC)
Yield (%)b
1
2
3
4
5
6
0
110
110
110
110
110
90
Trace
10
26
0.6
1.2
1.5
2
36
35
1.5
Trace
aReaction conditions: p-cresol (500 mg, 1 equiv.), DMSO (10 mL), 90–110 ꢁC.
bIsolated yields.

46
G. CHU ET AL.
toluene, xylene, and DMSO, and DMSO gave the best result. Decreasing the amount
of the DCMT resulted in reduced yield, while increasing the amount to 2 equiv. did
not make the reaction system complicated and the yield was not notably changed.
Under these optimized conditions, the scope of p-substituted phenols were
investigated (Table 2). Altogether seven p-substituted phenols have been successfully
transformed into the dimerized aldehydes. In a typical precedure, p-cresol and
DCMT (1.5 equiv.) were heated in 10 mL DMSO at 110 ꢁC for 6 h followed by usual
workup to get the products. However, no reaction took place for phenols bearing
electron withdrawing groups (Table 2, entries 8 and 9). It is obvious that only alkyl-
and alkoxy-substituted phenols are capable of reacting with DCMT-activated
DMSO to produce the desired products. The yields range from 35% to 58% and
the reaction durations from 4 h to 6 h. The dimerized phenolic aldehydes are of
new skeletons, not known in the literature. In one pot, we have realized formyl-
ation and dimerization of phenols. Formylation reactions represented[12] by the
Gatermann–Koch reaction, the Friedel–Crafts reaction, and the Vilsmeier–Haack
reaction are important organic reactions. Our procedure not only formylates the
phenols as the known reactions do but also dimerizes the phenols. Although
the yields of the reactions are poor, this reaction has provided a simple route to
the multifunctional group products. It is noteworthy that the products possess two
active functional groups, which could be used for further transformations.
When the reaction was carried out in DMSO-d6 (99.9%), d5-labeled products
were obtained (Table 3). The reaction conditions and the yields of these reactions
1
were similar to the reactions in DMSO. HNMR indicates that deuterated formyl
Table 2. Reaction of p-substituted phenols and DCMT-activated DMSOa
Entry
R
Compound
Time (h)
Yield (%)b
1
2
3
4
5
6
7
8
9
-CH3
-OCH3
-C(CH3)3
2a
2b
2c
2d
2e
2f
6
4
36
35
4
56
58
-C(CH3)2CH2CH3
Cyclohexyl
n-C9H19
4
6
47
52
5
-CH2COOCH3
-NO2
-COCH3
2g
2h
2i
6
45
Trace
Trace
12
12
aReaction conditions: p-substituted phenol (500 mg, 1 equiv.), DCMT (1.5 equiv.),
DMSO (10 mL), 110 ꢁC.
bIsolated yields.

DIMERIZATION AND FORMYLATION OF PHENOLS
47
a
Table 3. Reaction of p-substituted phenols and DCMT-activated DMSO-d6
Entry
R
Compound
Time (h)
Yield (%)b
1
2
3
4
-CH3
-OCH3
2a0
2b0
2d0
2g0
6
4
4
6
37
39
55
48
-C(CH3)2CH2CH3
-CH2COOCH3
aReaction conditions: p-substituted phenol (500 mg, 1 equiv.), DCMT (1.5 equiv.),
DMSO-d6 (10 mL), 110 ꢁC.
bIsolated yields.
Scheme 2.

48
G. CHU ET AL.
and methylene groups of the products originate from DMSO-d6. According to
1HNMR, the deuterations are highly regioselective and the nonlabeled products
are not detected. The reaction has fully utilized the DMSO-d6 in building the CD2
and deuterated formyl (CDO) groups. In the literature,[13] only the deuterated hydro-
gen atoms of DMSO-d6 have been used in building the labeled products. Deuterated
compounds are useful in the studies of metabolism and movement of drugs and toxic
substances in humans and animals, and reaction mechanisms.[14] We have provided a
convenient route to d5-labeled compounds from the inexpensive DMSO-d6 in one pot.
On the basis of these experiments, a plausible mechanism is proposed
(Scheme 2). Reacting with DCMT, DMSO yields intermediate II via intermediate
I. Addition of intermediate II to both the phenolic ring and the phenolic hydroxyl
generate thioester III. The bisulfide is a good nucleophile to form sulfonium salt IV
with DCMT or 4-chloro-6-methoxy-1,3,5-triazin-2-ol (CMT). On the other hand,
formaldehyde formed from the thermal decomposition of DMSO[15] hydroxymethy-
lates the phenol in the presence of HCl, leading to V. This hydroxymethylated pro-
duct can polymerize with another phenol in the presence of HCl, which may
account for the moderate yields of the reactions. Nucleophilic attack of V on sulfo-
nium IV leads to intermediate VI, which is in equilibrium with VII. After aqueous
workup, VI hydrolyzed into the final product VIII. This mechanism is supported by
the d5-labeled products from the reaction run in DMSO-d6 (Table 3). It is further
supported by the fact that phenols substituted with electron-withdrawing groups
cannot afford desired products (Table 2, entries 8 and 9). The reason is that these
phenols are not electron-rich enough to react with II, which is not sufficiently
electrophilic.
CONCLUSION
In conclusion, we have demonstrated that the dimerization and formylation
of p-alkyl-substituted phenols can be performed in one pot. Similarly, the d5-labeled
products have been prepared with the same procedure when DMSO-d6 was used.
The procedure reported herein is operationally simple and requires inexpensive
reagents. A plausible mechanism of the reaction is proposed and supported by
the experiments. Further study into the synthetic applications is ongoing in our
laboratory.
EXPERIMENTAL
All of the chemicals were obtained from commercial sources or prepared
1
according to standard methods. The HNMR (500 MHz) and 13CNMR (125 MHz)
spectra were recorded on a Varian Oxford 500 spectrometer. The 1HNMR
(400 MHz) and 13CNMR (100 MHz) spectra were recorded on a Bruker AM-400
spectrometer. Chemical shifts (d) are reported relative to tetramethylsilane (TMS)
(1H) or CDCl3 (13C). Mass spectra [electrospray ionization (ESI)] were obtained on
a Finnigan LCQ Advantage MAX spectrometer. Elemental analyses for C and H
were performed on a Yanaco CHNCORNER MF-3 elemental analyzer, and the
analytical results were within ꢂ0.4% of the theoretical values.

DIMERIZATION AND FORMYLATION OF PHENOLS
49
Typical Experimental Procedure
The procedure for the reaction of DMCT-activated DMSO and p-cresol (Table 2,
entry 1) is representative for all p-substituted phenols. p-Cresol (500mg, 4.63 mmol) was
added to the solution of DCMT (1250mg, 6.94mmol) in dryDMSO (5 mL). The mixture
was stirred at 110ꢁC and monitored by TLC until completion (6 h). Then, it was neutra-
lized with saturated aqueous NaHCO3 (20 mL) and extracted with CH2Cl2 (3 ꢃ 10 mL).
The extract was washed with water (5ꢃ 5 mL) and dried over anhydrous Na2SO4. The
solvent was concentrated in vacuo to give the crude product, which was further purified
by silica-gel column chromatography (PE=EA ¼ 30=1) to afford 2-((2-hydroxy-
5-methylbenzyloxy)methoxy)-5-methylbenzaldehyde (2a) (238 mg, yield 36%).
Compound 2a
1H NMR (CDCl3, 500 MHz) d 10.85 (s, 1H), 9.85 (s, 1H), 7.33–7.35 (m, 2H),
6.97 (dd, J ¼ 7.6 Hz, J ¼ 8.3 Hz, 1H), 6.90 (d, J ¼ 2.0 Hz, 1H), 6.77 (m, 2H), 5.22 (s,
2H), 4.87 (s, 2H), 2.34 (s, 3H), 2.27 (s, 3H); 13C NMR (CDCl3, 125 MHz): d 196.8,
159.8, 150.7, 138.3, 133.6, 130.8, 129.4, 128.8, 125.6, 121.2, 120.6, 117.6, 116.8, 91.5,
66.4, 20.9, 20.5; MS (ESI): m=z (%) ¼ 325 [M þ K]þ (100): Anal. calcd. for C17H18O4:
C, 71.31; H, 6.34. Found: C, 71.74; H, 6.10.
2-((2-Hydroxy-5-methoxybenzyloxy)methoxy)-5-
methoxybenzaldehyde (2b)
1H NMR (CDCl3, 500 MHz) d 10.66 (s, 1H), 9.86 (s, 1H), 7.15 (dd, J ¼ 3.1 Hz,
J ¼ 9.1 Hz, 1H), 7.01 (d, J ¼ 3.1 Hz, 1H), 6.94 (d, J ¼ 9.1 Hz, 1H), 6.82 (d, J ¼ 8.9 Hz,
1H), 6.74 (dd, J ¼ 2.9 Hz, J ¼ 8.9 Hz, 1H), 6.50 (d, J ¼ 2.9 Hz, 1H), 5.20 (s, 2H), 4.88
(s, 2H), 3.82 (s, 1H), 3.75 (s, 3H); 13C NMR (CDCl3, 125 MHz): d 196.4, 156.3,
154.3, 152.9, 146.8, 1(m, 2H), 6.817.15 (m, 4H), 5.24 (s, 2H), 4.91 (s, 2H), 25.5,
122.0, 120.3, 118.9, 117.8, 115.4, 114.2, 109.9, 91.4, 66.4, 56.2, 55.9; MS (ESI):
m=z 318.3(%) ¼ 341 [M þNa]þ (100): Anal. calcd. for C17H18O6: C, 64.14; H,
5.70. Found: C, 64.32; H, 5.92.
5-tert-Butyl-2-((5-tert-butyl-2-hydroxybenzyloxy)methoxy)
benzaldehyde (2c)
1H NMR (CDCl3, 500 MHz) d 10.88 (s, 1H), 9.90 (s, 1H), 7.60 (dd, J ¼ 2.5 Hz,
J ¼ 8.7 Hz, 1H), 7.52 (d, J ¼ 2.5 Hz, 1H), 7.20 (dd, J ¼ 2.4 Hz, J ¼ 8.6 Hz, 1H), 6.96
(m, 2H), 6.83 (d, J ¼ 8.6 Hz, 1H), 5.24 (s, 2H), 4.92 (s, 2H), 1.34 (s, 9H), 1.29 (s,
9H); 13C NMR (CDCl3, 125 MHz): d 197.1, 159.7, 150.6, 144.3, 143.0, 134.9,
130.0, 125.3, 121.9, 120.7, 120.2, 117.5, 116.4, 91.4, 66.7, 34.5, 34.3, 31.8, 31.4; MS
(ESI): m=z (%)þ ¼ 409 [M þK] (100): Anal. calcd. for C23H30O4: C, 74.56; H,
8.16. Found: C, 74.74; H, 8.10.
2-((2-Hydroxy-5-tert-pentylbenzyloxy)methoxy)-5-tert-
pentylbenzaldehyde (2d)
1H NMR (CDCl3, 500 MHz) d 10.87 (s, 1H), 9.89 (s, 1H), 7.52 (dd, J ¼ 2.2 Hz,
J ¼ 8.7 Hz, 1H), 7.46 (d, J ¼ 2.2 Hz, 1H), 7.13 (dd, J ¼ 2.2 Hz, J ¼ 8.6 Hz, 1H), 6.95

50
G. CHU ET AL.
(d, J ¼ 8.7 Hz, 1H), 6.89 (d, J ¼ 2.2 Hz, 1H), 6.82 (d, J ¼ 8.6 Hz, 1H), 5.24 (s, 2H),
4.91 (s, 2H), 1.62 (m, 4H), 1.29 (s, 6H), 1.24 (s, 6H), 0.69 (m, 6H); 13C NMR (CDCl3,
125 MHz): d 197.1, 159.6, 150.5, 142.6, 141.2, 135.4, 130.9, 125.9, 122.6, 120.6, 120.3,
117.4, 116.4, 91.5, 66.7, 37.6, 37.5, 37.1, 36.9, 28.8, 28.6, 9.36, 9.29; MS (ESI): m=z
(%) ¼ 437 [M þ K]þ (100): Anal. calcd. for C25H34O4: C, 75.34; H, 8.60. Found: C,
74.98; H, 8.79.
2-((2-Hydroxy-5-nonylbenzyloxy)methoxy)-5-nonylbenzaldehyde (2e)
1H NMR (CDCl3, 500 MHz) d 10.88 (s, 1H), 9.89 (s, 1H), 7.39–7.53 (m, 2H),
6.81–7.15 (m, 4H), 5.24 (s, 2H), 4.91 (s, 2H), 0.66–1.71 (m, 38H); 13C NMR (CDCl3,
125 MHz): d 197.2, 159.6, 150.3, 143.8, 142.4, 135.5, 131.0, 126.6, 126.0, 122.7, 120.4,
117.2, 116.2, 91.5, 66.8, 41.6, 40.6, 31.6, 31.0, 30.9, 30.1, 30.0, 29.4, 25.7, 24.9, 24.6,
23.7, 23.1, 22.2, 21.6, 20.2, 14.7, 14.3; MS (ESI): m=z (%) ¼ 534 [M þNa]þ (100):
Anal. calcd. for C33H50O4: C, 77.60; H, 9.87. Found: C, 77.84; H, 9.60.
5-Cyclohexyl-2-((5-cyclohexyl-2-hydroxybenzyloxy)methoxy)
benzaldehyde (2f)
1H NMR (CDCl3, 400 MHz) d 10.87 (s, 1H), 9.89 (s, 1H), 7.38–7.42 (m, 2H),
6.81–7.05 (m, 4H), 5.24 (s, 2H), 4.91 (s, 2H), 2.40–2.51 (m, 2H), 1.74–1.88 (m, 10H),
1.23–1.47 (m, 10H); 13C NMR (CDCl3, 100 MHz): d 196.7, 159.8, 150.7, 141.1,
139.6, 136.1, 131.2, 126.4, 123.1, 120.9, 120.4, 117.4, 116.5, 91.2, 66.3, 43.9, 43.3,
34.7, 34.5, 26.9, 26.8, 26.1, 26.0; MS (ESI): m=z (%) ¼ 446 [M þNa]þ (100): Anal.
calcd. for C33H50O4: C, 76.74; H, 8.11. Found: C, 76.34; H, 8.40.
Methyl-2-(3-formyl-4-((2-hydroxy-5-(2-methoxy-2-oxoethyl)
benzyloxy)methoxy)phenyl)acetate (2g)
1H NMR (CDCl3, 500 MHz) d 10.95 (s, 1H), 9.88 (s, 1H), 7.48 (d, J ¼ 2.1 Hz, 1H),
7.45 (dd, J ¼ 2.2 Hz, J ¼ 8.5 Hz, 1H), 7.06 (dd, J ¼ 2.2 Hz, J ¼ 8.4 Hz, 1H), 6.97 (d,
J ¼ 8.5 Hz, 1H), 6.88 (d, J ¼ 2.2 Hz, 1H), 6.83 (d, J ¼ 8.4 Hz, 1H), 5.23 (s, 2H), 4.89
(s, 2H), 3.71 (s, 3H), 3.69 (s, 3H), 3.62 (s, 2H), 3.54 (s, 2H); 13C NMR (CDCl3,
100 MHz): d 196.6, 172.3, 171.7, 160.9, 151.8, 140.4, 138.1, 134.2, 128.9, 125.9, 125.4,
121.4, 120.5, 118.0, 117.1, 91.3, 66.2, 52.2, 52.1, 40.4, 39.8; MS (ESI): m=z (%) ¼ 441
[M þ K]þ (100): Anal. calcd. for C21H22O8: C, 62.68; H, 5.51. Found: C, 62.84; H, 5.40.
2-((2-Hydroxy-5-methylbenzyloxy)methoxy)-5-methylbenzaldehyde-
D5 (2a’)
1H NMR (CDCl3, 500 MHz) d 10.85 (s, 1H), 7.33–7.35 (m, 2H), 6.97 (dd,
J ¼ 7.6 Hz, J ¼ 8.3 Hz, 1H), 6.90 (m, 1H), 6.77 (m, 2H), 2.34 (s, 3H), 2.27 (s, 3H);
MS (ESI): m=z (%) ¼ 330 [M þ K]þ (100).
2-((2-Hydroxy-5-methoxybenzyloxy)methoxy)-5-
methoxybenzaldehyde-D5 (2b’)
1H NMR (CDCl3, 500 MHz) d 10.66 (s, 1H), 7.15 (dd, J ¼ 3.1 Hz, J ¼ 9.1 Hz,
1H), 7.01 (d, J ¼ 3.1 Hz, 1H), 6.94 (d, J ¼ 9.1 Hz, 1H), 6.82 (d, J ¼ 8.9 Hz, 1H),

DIMERIZATION AND FORMYLATION OF PHENOLS
51
6.74 (dd, J ¼ 2.9 Hz, J ¼ 8.9 Hz, 1H), 6.50 (d, J ¼ 2.9 Hz, 1H), 3.82 (s, 3H), 3.75 (s,
3H); MS (ESI): m=z (%) ¼ 346 [M þ Na]þ (100).
2-((2-Hydroxy-5-tert-Pentylbenzyloxy)methoxy)-
5-tert-pentylbenzaldehyde-d5 (2d’)
1H NMR (CDCl3, 400 MHz) d 10.92 (s, 1H), 7.55 (d, J ¼ 8.7 Hz, 1H), 7.53 (s,
1H), 7.15 (d, J ¼ 8.7 Hz, 1H), 6.96 (d, J ¼ 8.4 Hz, 1H), 6.91 (s, 1H), 6.83(d,
J ¼ 8.4 Hz, 1H), 1.62 (m, 4H), 1.29 (s, 6H), 1.24 (s, 6H), 0.69 (m, 6H); MS (ESI):
m=z (%) ¼ 426 [M þ Na]þ (100).
Methyl-2-(3-formyl-4-((2-hydroxy-5-(2-methoxy-
2-oxoethyl)benzyloxy)methoxy)phenyl)acetate-D5 (2g’)
1H NMR (CDCl3, 500 MHz) d 10.99 (s, 1H), 7.50 (s, 1H), 7.45 (d, J ¼ 8.5 Hz,
1H), 7.09 (d, J ¼ 8.4 Hz, 1H), 6.99 (d, J ¼ 8.5 Hz, 1H), 6.90 (s, 1H), 6.85 (d,
J ¼ 8.4 Hz, 1H), 3.72 (s, 3H), 3.70 (s, 3H), 3.64 (s, 2H), 3.56 (s, 2H); MS (ESI):
m=z (%) ¼ 446 [M þ K]þ (100).
REFERENCES
1. (a) Bartholomew, D. 1,3,5-Triazines. In Comprehensive Heterocyclic Chemistry II; A. J.
Boulton (Ed.); Pergamon: Oxford, 1996; vol. 6, pp. 575; (b) Giacomelli, G.; Porcheddu,
A.; De Luca, L. Curr. Org. Chem. 2004, 8, 1497–1519.
2. (a) Forbes, D. C.; Barrett, E. J.; Lewis, D. L.; Smith, M. C. Tetrahedron Lett. 2000, 41,
9943–9947; (b) Bandgar, B. P.; Pandit, S. S. Tetrahedron Lett. 2002, 43, 413–3414;
(c) Giacomelli, G.; Porcheddu, A.; Salaris, M. Org. Lett. 2003, 5, 2715–2717.
3. (a) Blotny, G. Tetrahedron Lett. 2003, 44, 1499–1501; (b) De Luca, L.; Giacomelli, G.;
Porcheddu, A. Org. Lett. 2002, 4, 553–555; (c) Sun, L.; Pei, G.; Niu, H.; Wang, Q.; Li,
C. Synthesis 2008, 3919–3924.
4. De Luca, L.; Giacomelli, G.; Porcheddu, A. J. Org. Chem. 2002, 67, 5152–5155.
5. (a) De Luca, L.; Giacomelli, G.; Porcheddu, A. J. Org. Chem. 2002, 67, 6272–6274; (b)
Furuya, Y.; Ishihara, K.; Yamamoto, H. J. Am. Chem. Soc. 2005, 127, 11240–11241.
6. Karimi, B.; Hazarkhani, H. Synthesis 2003, 2547–2551.
7. De Luca, L.; Giacomelli, G.; Porcheddu, A. J. Org. Chem. 2001, 66, 7907–7909.
8. Porcheddu, A.; Giacomelli, G.; Salaris, M. J. Org. Chem. 2005, 70, 2361–2363.
9. Kangani, C. O.; Day, B. W. Org. Lett. 2008, 10, 2645–2648.
10. Chu, G.; Zhang, Y.; Li, C.; Zhang, Y. Synthesis 2009, 3828–3832.
11. Wang, Q.; Sun, L.; Jiang, Y.; Li, C. Beilstein J. Org. Chem. 2008, 4, No. 51.
12. (a) Olah, G. A.; Ohannesian, L.; Arvanaghi, M. Chem. Rev. 1987, 87, 671–686; (b) Schall,
A.; Reiser, O. Sci. Synth. 2007, 25, 605–653.
13. Perrotin, P.; Sinnema, P. J.; Shapiro, P. J. Organometallics 2006, 25, 2104–2107.
14. Kushner, D. J.; Baker, A.; Dunstall, T. G. Can. J. Physiol. Pharm. 1999, 77, 79–88.
15. Carlsen, L.; Egsgaard, H.; Harpp, D. N. J. Chem. Soc., Perkin Trans. 2 1981, 1166–1170.