Chem. Pap.
oxidative coupling of styrene with 2-phenylpyridine
derivatives via C–H activation (Brasse et al. 2013). Their
mechanistic study found that the turnover-limiting step is
the migratory insertion of the alkene into the Rh-C(aryl)
bond. Later, Yuki Fukui and co-workers reported that two
tunable arylative cyclizations of 1,6-enynes were catalyzed
by [Cp*RhCl]2 via C–H activation of O-substituted N-hy-
droxybenzamides (Fukui et al. 2014), and the mechanistic
investigations of these two reactions clearly indicated that
the C–H bond cleavage process was also involved in the
turnover-limiting step.
0.06 mmol) in methanol (2.00 mL). The obtained was
stirred for 1 h at room temperature. The mixture was
cooled, and then the precipitate was separated by cen-
trifugation. The final product was a yellow powder, which
was recrystallized from dichloromethane (Jia et al. 2016).
1
Yield 52.7%. H-NMR (600 MHz, CDCl3, TMS, d): 4.46,
3.75 and 3.58 (3b, 4H, CH=CH); 3.86 (m, 1H, CH2CH2-
CHCOO); 2.96 (m, 2H, NCH2CH2); 2.55, 2.48 2.36 and
2.15 (4 m, 8H, HC=CHCH2CH2); 1.95 (m, 2H, CH2CH2-
CH2CHCOO); 1.89 (b, 1H, NH); 1.73 (b, 1H, COOH); 1.65
(m, 2H, NCH2CH2CH2CH). 13C-NMR (150 MHz, CDCl3,
TMS, d): 206.96, 132.11, 63.89, 55.43, 49.94, 30.94, 29.90,
25.58. IR (KBr): 3427.87, 2930.79, 1719.43, 1619.13,
1375.66, 1282.79, 1194.70, 1085.57, 934.80, 802.01,
728.21 cm-1. Elemental analysis for C13H19NO2Rh: calcd.
C 34.57, H 5.15, N 1.55; found C 34.65, H 5.24, N 1.50
(See Figs. S4–S6 in the Supporting Information).
However, the use of Rh-diene complexes, i.e., Rh(-
cod)(L-amino acid), has not been explored in oxidative
coupling reactions. In this study, a chiral catalyst, Rh(-
cod)(L-Pro) (cod is 1,5-cyclooctadiene; L-pro is L-proline),
was synthesized and purified by recrystallization, and the
oxidative coupling reaction between salicylaldehyde and
phenylacetylene was catalyzed by the rhodium and Cu(II)
catalysts (See Scheme 1). The catalytic efficiencies and
mechanisms of these catalysts are discussed.
Rh(cod)(L-Phe): This compound was prepared and
purified by a method similar to that for Rh(cod)(L-Pro) (Jia
1
et al. 2016). The H-NMR, 13C-NMR and IR spectra of
Rh(cod)(L-Phe) see Figs. S7–S9 in the Supporting
Information).
Experimental
Rh(cod)(L-Val): This compound was prepared and
Synthesis of Rh(cod)(L-Pro), Rh(cod)(L-Val), and Rh(-
cod)(L-Phe) : The chiral Rh catalysts, Rh(cod)(L-Pro),
Rh(cod)(L-Val) and Rh(cod)(L-Phe), were synthesized
according to Scheme 2. The all reaction procedures were
conducted under dry nitrogen.
purified by a method similar to that for Rh(cod)(L-pro) (Jia
1
et al. 2016). The H-NMR, 13C-NMR and IR spectra of
Rh(cod)(L-Pro) See Figs. S10–S12 in the Supporting
Information).
Synthesis of 2-phenyl-4H-chromen-4-one (3): Rh(-
cod)(L-phenylalanine) (2.2 mg, 0.01 mmol), C5H2Ph4
(7.2 mg, 0.02 mmol) and Cu(OAc)2ÁH2O (200.0 mg,
1.00 mmol) were placed in a two-necked flask. Then, sal-
icylaldehyde (0.50 mL, 0.50 mmol), phenylacetylene
(0.50 mL, 0.50 mmol) and o-xylene (2.80 mL, 0.04 mmol)
were added, and the resulting mixture was stirred under N2
at 120 °C for 5.5 h. The raw product was extracted with
ether, and the final product was isolated by column chro-
matography on silica gel with hexane. The solid products
were recrystallized from hexane to give a yield of 88%
(white crystals). GC spectrum appeared one peak at
11.196 min. 1H-NMR (600 MHz, DMSO-d6, TMS, d):
7.62 (d, 2H, HC–C–C=O in Ph and C=CH–O), 7.61 (d, 2H,
HC–C–C=C–O in o-Ph to alkenyl), 7.51 (m, 1H, HC=C–
C–O in m-Ph to oxygen), 7.50 and 7.49 (2t, 2H, HC–C–C–
C=C–O in m-Ph to alkenyl), 7.46 (s, 1H, HC–C–C–C–
C=C–O in p-Ph to alkenyl), 7.45 (s, 1H, HC=C–C–C=O in
m-PhH to carbonyl), 7.44 (t, 1H, HC–C–O in Ph). 13C-
NMR (150 MHz, DMSO-d6, TMS, d): 73.91, 76.81, 77.02,
77.23, 81.56, 121.82, 128.45, 129.22, 132.52 ppm. IR
(KBr): 3049, 2952, 2925, 2854, 2190, 1740, 1484,
1251 cm-1 (see Figs. S13–S15). Anal Calcd for C15H10O2:
calcd. C 91.43, H 7.20, O 1.37; found C 91.08, H 6.50, O
2.42. Additional data for the products of catalysis by the
rhodium catalysts are listed in Table 1.
[Rh(cod)Cl]2: This compound was synthesized and
purified according to the literature procedure (Staubitz
et al. 2015). Yield 55%. 1H-NMR (600 MHz, CDCl3,
TMS, d): 4.42 (s, 8H, CH=CH), 2.50 (s, 8H, CHCH2CH2),
1.76 (s, 8H, CHCH2CH2). 13C-NMR (150 MHz, CDCl3,
TMS, d): 78.63, 30.85. IR (KBr): 3433, 2988, 2936, 2873,
2828, 1640, 1468, 1299, 1151, 994, 960, 867, 816, 775,
486 cm-1 (See Figs. S1–S3 in the Supporting Information).
Rh(cod)(L-Pro): A solution of L-proline (14.10 mg,
0.13 mmol) and NaOH (4.88 mg, 0.12 mmol) in H2O
(0.60 mL) was added with [Rh(cod)Cl]2 (30.00 mg,
Cu oxidant,
N
H
*
O
O
Rh
O
O
H
Rh(cod)(L-Pro)
+
H2
O
OH
N
R
*
Rh
3
1
2
O
O
-R=
:
:
-CH2C6H5
-CH(CH3)2
Rh(cod)(L-Phe)
Rh(cod)(L-Val)
Scheme 1 Oxidative coupling reaction of salicylaldehyde and
phenylacetylene using Rh(cod)(L-Pro), Rh(cod)(L-Phe) and Rh(-
cod)(L-Val) and Cu(II) as catalysts
123