Metal-free oxidative C-C bond formation of active methylenic sp3 C-H bonds with benzylic sp3 C-H and allylic sp3 C-H bonds mediated by DDQ

Article abstract of DOI:10.1016/j.tetlet.2010.07.080

An efficient and simple method for the oxidative coupling of benzylic and allylic sp³ C-H bonds with active methylenic sp³ C-H bonds under metal-free conditions was developed by employing 2,3-dichloro-5,6- dicyanobenzoquinone (DDQ) as an oxidant. The reaction was shown to proceed smoothly for various 1,3-dicarbonyl compounds with a range of benzylic and allylic substrates in good to excellent yields.

Full text of DOI:10.1016/j.tetlet.2010.07.080

Tetrahedron Letters 51 (2010) 4898–4903
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Metal-free oxidative C–C bond formation of active methylenic sp3 C–H
bonds with benzylic sp3 C–H and allylic sp3 C–H bonds mediated by DDQ
*
D. Ramesh, U. Ramulu, S. Rajaram, P. Prabhakar, Y. Venkateswarlu
Natural Products Laboratory, Organic Division-I, Indian Institute of Chemical Technology, Hyderabad 500 007, India
a r t i c l e i n f o
a b s t r a c t
An efficient and simple method for the oxidative coupling of benzylic and allylic sp3 C–H bonds with
active methylenic sp3 C–H bonds under metal-free conditions was developed by employing 2,3-
dichloro-5,6-dicyanobenzoquinone (DDQ) as an oxidant. The reaction was shown to proceed smoothly
for various 1,3-dicarbonyl compounds with a range of benzylic and allylic substrates in good to excellent
yields.
Article history:
Received 4 June 2010
Revised 8 July 2010
Accepted 13 July 2010
Available online 16 July 2010
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Metal-free
Oxidative coupling
C–C bond formation
DDQ
1,3-Dicarbonyl
Carbon–carbon bond construction1 is a very important step in
organic synthesis and is the foundation for the formation of com-
plex structures from simple precursors. Transition-metal-catalyzed
coupling reactions of various reactive functional groups are among
the most useful protocol for the C–C bond formation,2 the reaction
may be further enhanced from the view point of atom-efficiency3
and green chemistry.4 The development of direct C–C bond-form-
ing reactions of prior unmodified C–H substrates is an important
task and attracted more interest in recent years.5 Such transforma-
tions will avoid the pre-functionalization of C–H bonds and make
the synthetic scheme shorter and atom-economical. In this con-
text, important progress has been made toward direct utilization
of allylic and benzylic sp3 C–H bond rather than pre-functionaliza-
tion. Most of the strategies based on cross-coupling reactions of sp3
C–H bonds limited to a
-hetero aromatic compounds6,7 or require
carbene precursors,8 directing groups9, and stoichiometric metal
reagents.10 However, only a few methods are available for forming
new C–C bonds by utilizing two different C–H bonds, among them
Trost’s group reported C–C bond formation directly from an allylic
sp3 C–H bond in two steps in the late 1970s.11 Recently, some
methods have been reported for the direct coupling of active
methylenic sp3 C–H bonds with simple allylic sp3 C–H bonds in
the presence of CuBr/CoCl2/tBuOOH (Scheme 1) catalyst system,12
similarly with simple benzylic sp3 C–H bonds using FeCl2/tBuOOtBu
catalyst system13 and Cu(ClO4)2/tBuOOBz/bathophenanthroline
ligand system.14 Despite great advantage of these reactions, there
are still certain limitations such as the use of one or two transition
metals in these transformations and use of peroxide as an oxidizing
O
O
R3
O
O
Ar
O
O
n
R1
R2
R1
R2
R1
R2
DDQ, CH3NO2
CH NO
DDQ,
3
2
Ar
R3
R1=
R2= CH3, C6H5;
CH3, C6H5, 4-CH3OC6H4, 4-BrC6H4, 2 - thienyl, 1- naphthyl;
n
n= 1,2
CH3
,
R3
,
,
C6H5
,
=
CH3
Ar
C6H5
C6H5
Cl
Scheme 1. Oxidative C–C bond formation of active methylenic sp3 C–H bonds with benzylic sp3 C–H and allylic sp3 C–H bonds.
* Corresponding author. Tel.: +91 40 27193167; fax: +91 40 27160512.
E-mail addresses: luchem@iict.res.in, luchem@yahoo.com (Y. Venkateswarlu).
0040-4039/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2010.07.080

D. Ramesh et al. / Tetrahedron Letters 51 (2010) 4898–4903
4899
Table 1
Optimization of reaction conditionsa
O
O
O
O
DDQ
Ph
Ph
Ph
Ph
CH3NO2, 80oC
1a
2a
MeO
MeO
Ph
Ph
3a
Entry
Solvent
Temp (°C)
Time (h)
Yieldb (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
THF
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
80
rt
50
80
80
8
8
8
8
8
8
6
6
6
6
6
6
6
6
10
25
20
75
62
65
78
NRc
51
10
71
84
77d
60e
CH3CN
Dioxane
CH2Cl2
CHCl3
CCl4
DCE
Hexane
Neat
CH3NO2
CH3NO2
CH3NO2
CH3NO2
CH3NO2
80
a
Conditions: 1a (0.2 mmol), 2a (1 mmol), and DDQ (0.24 mmol) in neat or the presence of indicated solvent and
temperature.
b
Isolated yield.
No reaction based on TLC analysis.
Compound 2a (0.5 mmol).
c
d
e
Compound 2a (0.2 mmol).
Table 2
Oxidative coupling between diaryl benzylic C–H bond and various 1,3-dicarbonyl compoundsa
Entry
Substrate 1
Substrate 2
Product 3
Time (h)
Yieldb (%)
O
O
O
O
Ph
Ph
Ph
Ph
Ph
1
6
84
79
2a
2a
MeO
MeO
1a
Ph
3a
O
O
O
O
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Br
Ph
2
3
6
8
Ph
1b
3b
O
O
O
O
Ph
Ph
Ph
78
72
80
2a
2a
1c
Br
Ph
O
3c
O
O
O
Ph
Ph
Ph
4
5
8
8
1d
Ph
3d
O
O
O
O
Ph
Ph
Ph
S
Ph
Ph
2a
Ph
S
1e
3e
a
Conditions: 0.2 mmol of 1, 1 mmol of 2, and 0.24 mmol of DDQ in nitromethane at 80 °C.
Isolated yield.
b

4900
D. Ramesh et al. / Tetrahedron Letters 51 (2010) 4898–4903
Table 3
Oxidative coupling between cyclic benzylic C–H bonds and various 1,3-dicarbonyl compoundsa
Entry
Substrate 1
Substrate 2
Product 3
Time (h)
Yieldb (%)
O
O
O
O
Ph
Ph
Ph
Ph
1b
1
6
60
2b
3f
O
O
O
O
Ph
Ph
2
MeO
6
62
MeO
1a
2b
2b
3g
O
O
O
O
Ph
Ph
S
S
1e
3
8
58
3h
O
O
O
O
Ph
Ph
Ph
Ph
4
5
8
8
64
61
2c
2c
1b
3i
O
O
O
O
Ph
Ph
MeO
MeO
1a
3j
a
Conditions: 0.2 mmol of 1, 1 mmol of 2, and 0.24 mmol of DDQ in nitromethane at 80 °C.
Isolated yield.
b
reagent under heating conditions. There are some general prob-
lems with metal-catalyzed reactions, such as cost of transition-me-
tal catalyst and difficulty in the preparation of ligand or catalyst.
Some metals are toxic in nature and heavy metal residues may
present in the preparation of the compounds. Additionally, in view
of the increased attention to environmental problems, transition-
metal-free methods are preferable for the coupling reactions.15
Although excellent results are available for C–C bond-forming
reactions involving an oxidative coupling between sp3 C–H and
sp3 C–H bonds, reactions under metal-free conditions are rare. Fur-
thermore, there is no protocol for the direct coupling of the two
types of sp3 C–H bonds (allylic and benzylic) with active methylen-
ic sp3 C–H bonds by using single oxidizing reagent or catalyst sys-
tem. Herein, we report a simple and highly efficient oxidative
coupling of active methylenic sp3 C–H bonds with two types of
sp3 C–H bonds such as simple allylic sp3 C–H and benzylic sp3 C–
dehydrogenating reagent to bring about this transformation and
the results are summarized in Table 1. The reaction was examined
by using various solvents to facilitate this transformation. When
the reaction was performed in tetrahydrofuran, acetonitrile, and
dioxane it afforded the desired product in low yields (Table 1, en-
tries 1–3). However, the corresponding product was obtained in
high yield in dichloromethane, chloroform, carbon tetrachloride,
and dichloroethane (Table 1, entries 4–7). No product was ob-
served when the reaction was performed in hexane (Table 1, entry
8). However, in the absence of solvent the reaction afforded the
corresponding product in moderate yield (Table 1, entry 9). When
the reaction was carried out in nitromethane at room temperature,
the yield of the product was 10% (Table 1, entry 10). Perceptibly in-
creased yields were observed at elevated reaction temperatures in
nitromethane (Table 1, entries 11 and 12). Decreasing the equiva-
lents of 2a resulted in reduced yield (Table 1, entries 12–14). When
the reaction was carried out between 1a (0.2 mmol) and 2a
(1 mmol) using DDQ (0.24 mmol) in nitromethane at 80 °C, the
reaction proceeded smoothly and afforded the desired product in
excellent yield (Table 1, entry 12). To define the scope of the reac-
tion mediated by DDQ under metal-free conditions, we have
carried out various benzylic and allylic sp3 C–H bonds with 1,3-
dicarbonyl compounds.
H
bonds promoted by 2,3-dichloro-5,6-dicyanobenzoquinone
(DDQ) without using any metal catalyst. DDQ is a commercially
available and important oxidation reagent in organic chemistry.16
Earlier, we17 and others18 have reported some oxidative coupling
reactions using DDQ.
The initial studies were carried out by reacting 1a with 2a as a
prototype reaction under various reaction conditions using DDQ as

D. Ramesh et al. / Tetrahedron Letters 51 (2010) 4898–4903
4901
Table 4
Oxidative coupling between acyclic benzylic C–H bonds and various 1,3-dicarbonyl compoundsa
Entry
Substrate 1
Substrate 2
Product 3
Time (h)
Yieldb (%)
O
O
O
O
Ph
CH3
2d
Ph
Ph
Ph
Ph
Ph
Ph
Ph
CH3
3k
1
8
68
57
1b
O
O
O
O
CH3
Ph
Ph
CH3
Cl
2
8
2e
1b
Cl
O
3l
O
O
O
Ph
CH3
2d
2d
H3C
CH3
H3C
Ph
CH3
3
4
8
8
51
56
CH3
O
1f
3m
O
O
O
Ph
CH3
Ph
Ph
CH3
S
S
1e
Ph
3n
a
Conditions: 0.2 mmol of 1, 1 mmol of 2, and 0.24 mmol of DDQ in nitromethane at 80 °C.
Isolated yield.
b
Table 5
Oxidative coupling between allylic C–H bonds and various 1,3-dicarbonyl compoundsa
Entry
Substrate 1
Substrate 2
Product 3
Time (h)
Yieldb(%)
O
O
O
O
Ph
Ph
1
6
68
64
58
60
2f
MeO
MeO
1a
3o
O
O
O
O
Ph
Ph
Ph
Ph
2
3
6
8
2f
2f
1b
3p
O
O
O
O
Ph
Ph
3q
1c
O
Br
Br
O
O
O
Ph
Ph
3r
4
5
8
6
S
S
2f
1e
O
O
O
O
Ph
Ph
3s
65c
2g
MeO
MeO
1a
(continued on next page)

4902
D. Ramesh et al. / Tetrahedron Letters 51 (2010) 4898–4903
Table 5 (continued)
Entry
Substrate 1
Substrate 2
Product 3
Time (h)
Yieldb(%)
63c
O
O
O
O
Ph
Ph
O
Ph
Ph
6
6
2g
1b
3t
O
O
O
Ph
Ph
3u
7
6
59c
S
S
2g
1e
a
Conditions: 0.2 mmol of 1, 1 mmol of 2, and 0.24 mmol of DDQ in nitromethane at 80 °C.
Isolated yield.
At 50 °C.
b
c
The benzylic C–H bond of diphenylmethane was reacted effi-
article can be found, in the online version, at doi:10.1016/j.tet-
let.2010. 07.080.
ciently with a range of 1,3-dicarbonyl compounds and the corre-
sponding products were obtained in excellent yields (Table 2,
entries 1–5). 1,3-Dicarbonyl compounds bearing aromatic ring with
both electron-donating and electron-withdrawing groups in para
position afforded excellent yields (Table 2, entries 1 and 3). Compar-
atively a low yield was obtained with 1,3-dicarbonyl substrates
bearing a naphthalene group (1d) (Table 2, entry 4), probably be-
cause of the steric effect of the naphthalene group. Hetero aryl such
as thienyl substrate (1e) was also found to react with diphenylme-
thane to give the desired product in good yield (Table 2, entry 5).
Substrates with less activated cyclic benzylic sp3 C–H bond such
as 1,2,3,4-tetrahydronaphthalene and acenaphthene were reacted
with various 1,3-dicarbonyl compounds and the desired products
were obtained in good yields (Table 3, entries 1–5). To explore the
generality of the reaction, we also examined the reactions of less
activated acyclic benzylic sp3 C–H bond substrates such as ethylben-
zene and para-ethylchlorobenzene with various 1,3-dicarbonyl
compounds and found that the reactions proceeded well and gave
the respective products in good yields (Table 4, entries 1–4).
Substrates with allylic sp3 C–H bond such as cyclohexene (2f)
and cyclopentene (2g) were subjected to alkylation with various
1,3-dicarbonyl compounds and afforded the desired products in
good yields (Table 5, entries 1–7). 1,3-Dicarbonyl compounds bear-
ing aromatic ring with both electron-donating and electron-with-
drawing groups in para position afforded good yields (Table 5,
entries 1, 3, and 5). Furthermore, hetero aryl dicarbonyl compound
(1e) also gave the desired products in good yields (Table 5, entries
4 and 7).
References and notes
1. (a)Beccalli, E. M.;Broggini, G.; Martinelli, M.;Sottocornola, S. Chem. Rev. 2007, 107,
5318–5365; (b) Fagnoni, M.; Dondi, D.; Ravelli, D.; Albini, A. Chem. Rev. 2007, 107,
2725–2756; (c) Li, C. Chem. Rev. 2005, 105, 3095–3165; (d) Dilman, A. D.; Ioffe, S. L.
Chem. Rev. 2003, 103, 733–772; (e) Fagnou, K.; Lautens, M. Chem. Rev. 2003, 103,
169–196; (f) Ritleng, V.; Sirlin, C.; Pfeffer, M. Chem. Rev. 2002, 102, 1731–1769; (g)
Trost, B. M.; Toste, F. D.; Pinkerton, A. B. Chem. Rev. 2001, 101, 137–202.
2. Metal-Catalyzed Cross-Coupling Reactions; Diederich, F., Stang, P. J., Eds.; Wiley-
VCH: New York, 1998.
3. (a) Trost, B. M. Science 1991, 254, 1471–1477; (b) Trost, B. M. Angew. Chem., Int.
Ed. Engl. 1995, 34, 259–281; (c) Trost, B. M. Acc. Chem. Res. 2002, 35, 695–705.
4. (a) Winterton, N. Green Chem. 2001, 3, G73–G75; (b) Anastas, P. T.; Warner, J. C.
Green Chemistry Theory and Practice; Oxford University Press: New York, 1998.
5. (a) Dyker, G. Angew. Chem., Int. Ed. 1999, 38, 1698–1712; (b) Naota, T.; Takaya,
H.; Murahashi, S. I. Chem. Rev. 1998, 98, 2599–2660; (c) Chatani, N.; Asaumi, T.;
Yorimitsu, S.; Ikeda, T.; Kakiuchi, F.; Murai, S. J. Am. Chem. Soc. 2001, 123,
10935–10941; (d) Goossen, L. J. Angew. Chem., Int. Ed. 2002, 41, 3775–3778; (e)
Arndtsen, B. A.; Bergman, R. G.; Mobley, T. A.; Peterson, T. H. Acc. Chem. Res.
1995, 28, 154–162; (f) Chen, H.; Schlecht, S.; Semple, T. C.; Hartwig, J. F. Science
2000, 287, 1995–1997; (g) Goldman, A. S. Nature 1993, 366, 514; (h) Crabtree,
R. H. J. Organomet. Chem. 2004, 689, 4083–4091; (i) Jia, C.; Kitamura, T.;
Fujiwara, Y. Acc. Chem. Res. 2001, 34, 633–639.
6. (a) Basle, O.; Li, C.-J. Green Chem. 2007, 9, 1047–1050; (b) Li, C.-J.; Li, Z. Pure
Appl. Chem. 2006, 78, 935–945; (c) Li, Z.; Li, C.-J. J. Am. Chem. Soc. 2005, 127,
6968–6969; (d) Pastine, S. J.; Gribkov, D. V.; Sames, D. J. Am. Chem. Soc. 2006,
128, 14220–14221; (e) Li, Z.; Li, C.-J. J. Am. Chem. Soc. 2005, 127, 3672–3673; (f)
Li, Z.; Li, C.-J. Eur. J. Org. Chem. 2005, 3173–3176; (g) DeBoef, B.; Pastine, S. J.;
Sames, D. J. Am. Chem. Soc. 2004, 126, 6556–6557.
7. (a) Wantanabe, T.; Oishi, S.; Fujii, N.; Ohno, H. Org. Lett. 2008, 10, 1759–1762;
(b) Hitce, J.; Retailleau, P.; Baudoin, O. Chem. Eur. J. 2007, 13, 792–799; (c)
Lafrance, M.; Gorelsky, S. I.; Fagnou, K. J. Am. Chem. Soc. 2007, 129, 14570–
14571; (d) Dong, C.-G.; Hu, Q.-S. Angew. Chem., Int. Ed. 2006, 45, 2289–2292; (e)
Ren, H.; Knochel, P. Angew. Chem., Int. Ed. 2006, 45, 3462–3465.
In summary, we have developed an efficient method for the di-
rect oxidative coupling of active methylenic sp3 C–H bonds with
benzylic sp3 C–H and allylic sp3 C–H bonds by using DDQ as a
dehydrogenating reagent.19 This method has several advantages:
(1) no metal is required for the reaction. (2) It proceeds without
additional reagent. (3) Simple benzylic and allylic substrates can
be used directly without pre-functionalization. (4) It gives the de-
sired products in good to excellent yields.
8. (a) Davies, H. M. L. Angew. Chem., Int. Ed. 2006, 45, 6422–6425; (b) Davies, H. M.
L.; Beckwith, R. E. J. Chem. Rev. 2003, 103, 2861–2903; (c) Davies, H. M. L.; Loe,
Ø. Synthesis 2004, 2595–2608; (d) Müller, P.; Tohill, S. Tetrahedron 2000, 56,
1725–1731.
9. (a) Mousseau, J. J.; Larivée, A.; Charette, A. B. Org. Lett. 2008, 10, 1641–1643; (b)
Campeau, L.-C.; Schipper, D. J.; Fagnou, K. J. Am. Chem. Soc. 2008, 130, 3266–
3267; (c) Giri, R.; Maugel, N.; Li, J.-J.; Wang, D.-H.; Breazzano, S. P.; Saunders, L.
B.; Yu, j.-Q. J. Am. Chem. Soc. 2007, 129, 3510–3511; (d) Chen, X.; Goodhue, C. E.;
Yu, J.-Q. J. Am. Chem. Soc. 2006, 128, 12634–12635; (e) Kalyani, D.; Deprez, N.
R.; Desai, L. V.; Sanford, M. S. J. Am. Chem. Soc. 2005, 127, 7330–7331; (f)
Zaitsev, V. G.; Shabashov, D.; Dagulis, O. J. Am. Chem. Soc. 2005, 127, 13154–
13155; (g) Shabashov, D.; Dagulis, O. Org. Lett. 2005, 7, 3657–3659; (h) Desai, L.
V.; Hull, K. L.; Sanford, M. S. J. Am. Chem. Soc. 2004, 126, 9542–9543.
10. (a) Richter, J. M.; Whitefield, B. W.; Maimone, T. J.; Lin, D. W.; Castroviejo, M. P.;
Baran, P. S. J. Am. Chem. Soc. 2007, 129, 12857–12869; (b) Baran, P. S.;
DeMartino, M. P. Angew. Chem., Int. Ed. 2006, 45, 7083–7086; (c) Nishino, H.;
Kamachi, H.; Baba, H.; Kurosawa, K. J. Org. Chem. 1992, 57, 3551–3557; (d)
Trost, B. M.; Dietsche, T. J. J. Am. Chem. Soc. 1973, 95, 8200–8201.
Acknowledgments
The authors are thankful to CSIR, New Delhi, India, for financial
assistance and to the Director of Indian Institute of Chemical Tech-
nology for his encouragement.
11. Trost, B. M.; Strege, P. E.; Webber, L.; Fullerton, T. J.; Dietche, T. J. J. Am. Chem.
Soc. 1978, 100, 3407–3408.
Supplementary data
12. Li, Z.; Li, C.-J. J. Am. Chem. Soc. 2006, 128, 56–57.
13. Li, Z.; Cao, L.; Li, C.-J. Angew. Chem., Int. Ed. 2007, 46, 6505–6507.
14. Borduas, N.; Powell, D. A. J. Org. Chem. 2008, 73, 7822–7825.
15. (a) List, B. Tetrahedron 2002, 58, 5573–5590; (b) List, B. Synlett 2001, 1675–
1686; (c). Acc. Chem. Res. 2004, 37.
Supplementary data (typical detailed experimental procedure
and analytical data for all the compounds) associated with this

D. Ramesh et al. / Tetrahedron Letters 51 (2010) 4898–4903
4903
16. (a) Ying, B.-P.; Trogden, B. G.; Kohlman, D. T.; Liang, S. X.; Xu, Y.-C. Org. Lett.
2004, 6, 1523–1526; (b) Fu, P. P.; Harvey, R. G. Chem. Rev. 1978, 78, 317–361;
(c) Walker, D.; Heibert, J. D. Chem. Rev. 1967, 67, 153–195.
17. Damu, G. L. V.; Selvam, J. J. P.; Venkata Rao, C.; Venkateswarlu, Y. Tetrahedron
Lett. 2009, 50, 6154–6158.
6.84–6.77 (2H, m), 6.27 (1H, d, J = 11.5 Hz), 5.33 (1H, d, J = 11.5 Hz), 3.81 (3H, s);
13C NMR (75 MHz, CDCl3): d 194.3, 192.2, 163.6, 141.88, 141.83, 137.0, 133.1,
131.0, 128.55, 128.51, 128.4, 128.2, 126.5, 113.7, 62.2, 55.4, 52.3; MS (ESI) m/z:
443 [M+Na]+; HRMS (ESI) m/z calcd for C29H24O3Na: 443.1623, found: 443.1627.
2-Benzhydryl-1-(naphthalen-1-yl)-3-phenylpropane-1,3-dione (3d):
18. (a) Cheng, D.; Bao, W. J. Org. Chem. 2008, 73, 6881–6883; (b) Zhang, Y.; Li, C.-J.
Angew. Chem., Int. Ed. 2006, 45, 1949–1952; (c) Zhang, Y.; Li, C.-J. J. Am. Chem.
Soc. 2006, 128, 4242–4243.
19. A typical experimental procedure and spectral data of some representative
compounds.
IR (KBr):
m
3055, 2922, 2853, 1689, 1591, 1495, 1448, 1359, 1249, 1200, 1074,
1026, 969, 779, 744, 699 cmÀ1
;
1H NMR (300 MHz, CDCl3): d 7.88–7.86 (2H, m),
7.80–7.73 (3H, m), 7.62 (1H, d, J = 7.5 Hz), 7.45–6.99 (16H, m), 6.42 (1H, d,
J = 12.0 Hz), 5.39 (1H, d, J = 12.0 Hz); 13C NMR (75 MHz, CDCl3): d 196.3, 194.0,
141.9, 141.4, 137.1, 136.5, 133.6, 133.1, 132.6, 130.0, 128.6, 128.52, 128.50,
128.3, 128.2, 127.9, 127.8, 126.6, 126.5, 126.4, 125.4, 123.9, 65.9, 52.6; MS (ESI)
m/z: 463 [M+Na]+; HRMS (ESI) m/z calcd for C32H24O2Na: 463.1673, found:
463.1667.
Typical experimental procedure: To a solution of 1,3-dicarbonyl compound 1
(0.2 mmol), allylic, or benzylic sp3 C–H compound 2 (1 mmol) in CH3NO2 was
added DDQ (0.24 mmol) and the resulting mixture was stirred at 80 °C for the
indicated time. After completion of the reaction as noticed by TLC, the reaction
mixture was cooled to room temperature and filtered. The filtrate was diluted
with water (10 mL) and extracted into ethyl acetate (3 Â 10 mL). The combined
organic layer was dried over anhydrous Na2SO4 and concentrated under reduced
pressure to give crude residue, which was purified on silica gel column
chromatography using hexane and ethyl acetate as the eluent to give the pure
product.
2-(Cyclohex-2-enyl)-1,3-diphenylpropane-1,3-dione (3p):
IR (Neat):
m
3062, 3025, 2926, 2856, 1696, 1665, 1596, 1448, 1270, 1192, 1075,
1001, 802, 760, 690 cmÀ1
;
1H NMR (300 MHz, CDCl3): d 8.02–7.96 (4H, m), 7.58–
7.39(6H, m), 5.77–5.69 (1H, m), 5.55–5.47 (1H, m), 5.28 (1H, d, J = 10.0 Hz), 3.55–
3.43 (1H, m), 2.05–1.97 (2H, m), 1.83–1.34 (4H, m); 13C NMR (75 MHz, CDCl3): d
194.9, 194.5, 137.2, 137.0, 133.4, 133.3, 132.3, 129.2, 129.15, 128.7, 128.66, 62.8,
37.1, 27.4, 25.1, 21.1; MS (ESI) m/z: 327 [M+Na]+; HRMS (ESI) m/z calcd for
2-Benzhydryl-1-(4-methoxyphenyl)-3-phenylpropane-1,3-dione (3a):
C21H20O2Na: 327.1360, found: 327.1348.
IR (KBr):
m
;
3058, 2928, 2855, 1685, 1598, 1507, 1451, 1266, 1173, 1028, 975, 837,
700 cmÀ1
1H NMR (300 MHz, CDCl3): d 7.89–7.81 (4H, m), 7.50–7.01 (13H, m),