References and Notes
-
1a
Grimsdale AC.
Müllen K.
Macromol. Rapid Commun.
2007,
28:
1676
-
1b
Chen P.
Yang G.
Liu T.
Li T.
Wang M.
Huang W.
Polym.
Int.
2006,
55:
473
-
1c
Scherf U.
List EJW.
Adv. Mater.
2002,
14:
477
- 2
Lyakhov SA.
Lyakhova EA.
Karpenko AS.
Mal’tsev GV.
Vel’cheva IV.
Litvinova LA.
Lebedyuk MN.
Khorokhorina GA.
Fedchuk VP.
Pharm. Chem. J.
2004,
38:
128
-
3a
Pan H.-L.
Fletcher TL.
J.
Med. Chem.
1965,
8:
491
-
3b
Morgan LR.
Thangaraj K.
LeBlanc B.
Rodgers A.
Wolford LT.
Hooper CL.
Fan D.
Jursic BS.
J.
Med. Chem.
2003,
46:
4552
- 4
Sulsky R.
Robl JA.
Biller SA.
Harrity TW.
Wetterau J.
Conolly F.
Jolibois K.
Kunselman L.
Bioorg. Med. Chem. Lett.
2004,
14:
5067
-
5a
Feringa BL.
J. Org. Chem.
2007,
72:
6635
-
5b
Eelkema R.
Pollard MM.
Katsonis N.
Vicario J.
Broer DJ.
Feringa BL.
J. Am. Chem. Soc.
2006,
128:
14397
-
5c
Pijper D.
Feringa BL.
Angew. Chem. Int.
Ed.
2007,
46:
3693
- 6
Heeney M.
Bailey C.
Giles M.
Shkunov M.
Sparrowe D.
Tierney S.
Zhang W.
McCulloch I.
Macromolecules
2004,
37:
5250
-
7a
Zheng G.
Wang Z.
Tang L.
Lu P.
Weber WP.
Sens. Actuators, B
2007,
122:
389
-
7b
Wang Z.
Xing Y.
Shao H.
Lu P.
Weber WP.
Org.
Lett.
2005,
7:
87
-
7c
Wang Z.
Zheng G.
Lu P.
Org.
Lett.
2005,
7:
3669
-
7d
Wang Z.
Li W.
Lu P.
Sens.
Actuators, B
2007,
122:
389
-
For selected examples, see:
-
8a
Dahl BJ.
Mills NS.
J.
Am. Chem. Soc.
2008,
130:
10179
-
8b
Johnson AW.
LaCount RB.
Tetrahedron
1960,
9:
130
-
9a
Ikeda Y.
Murai M.
Abo T.
Miki K.
Ohe K.
Tetrahedron
Lett.
2007,
48:
6651
-
9b
Miki K.
Fujita M.
Uemura S.
Ohe K.
Org. Lett.
2006,
8:
1741
- 10
Hennion GF.
Fleck BR.
J. Am. Chem. Soc.
1955,
77:
3253
-
14a
Yu J.
Gaunt MJ.
Spencer JB.
J. Org. Chem.
2002,
67:
4627
-
14b
Kim IS.
Dong GR.
Jung YH.
J. Org. Chem.
2007,
72:
5424 ; and references therein
11
General Procedure
of Ring-Opening Reaction of 2-Methylfuran
In
a flame-dried Schlenk tube, PtCl2 (6.5 mg, 0.025 mmol,
5 mol%) was dispersed in toluene (2.0 mL). To the solution were
added 1a (124 mg, 0.50 mmol) and 2-methylfuran
(90 µL, 1.0 mmol) at r.t. The mixture was stirred at 50 ˚C
for 7 h. The yellow suspension was cooled and the solvent was removed
under reduced pressure to give 2a. To remove
the platinum catalyst, the crude 2a was
dissolved in THF (30 mL) and the solution was passed through a short
Florisil column. The THF solution was evaporated under reduced pressure
to give 2a (99%, Z,Z/Z,E = 63:37).
In the case of [RuCl2(CO)3]2,
the THF solution obtained after a Florisil column was evaporated
in vacuo, and the residue was purified by centrifuge with hexane
and a small amount of THF to give a first crop of (E,E)-2a (ca. 65% yield).
The hexane and THF solution containing a small amount of (E,E)-2a was evaporated in vacuo, and the residue
was purified by column chromatography on SiO2 with hexane-EtOAc
(v/v = 4:1) to give a second
crop of (E,E)-2a (ca. 10% yield). The yield
in Scheme
[²]
was
obtained by combining first and second crops of (E,E)-2a.
12
Analytical Data
of (
E
,
E
)-2a, (
Z
,
Z
)-2a and (
Z
,
E
)-2a
Compound
(E,E)-2a: yield 74%; a yellow solid;
mp 203.7-204.1 ˚C. IR (KBr): 3054, 1752 (C=O),
1654, 1198, 1176, 728 cm-¹. ¹H
NMR (400 MHz, CDCl3): δ = 2.34 (s,
3 H), 2.51 (s, 3 H), 6.32 (d, J = 15.2
Hz, 1 H), 6.63 (dd, J = 11.2, 14.6
Hz, 1 H), 7.25-7.34 (m, 5 H), 7.63 (d, J = 14.6
Hz, 1 H), 7.68 (d, J = 8.0
Hz, 1 H), 7.70 (d, J = 8.0
Hz, 1 H), 7.77 (d, J = 8.0
Hz, 1 H), 7.79 (d, J = 8.0
Hz, 1 H). ¹³C NMR (100 MHz, CDCl3): δ = 21.1,
27.6, 119.9, 120.2, 125.2, 125.3, 127.3, 127.7, 128.8, 129.2, 130.8,
131.1, 132.3, 132.7, 135.6, 136.7, 140.3, 140.9, 141.6, 144.8, 168.2,
198.0. Anal. Calcd for C22H18O3:
C, 79.98, H, 5.49. Found: C, 79.87; H, 5.66.
Compounds
(Z,Z)-2a and (Z,E)-2a: yield
99%; a yellow solid. ¹H NMR (400 MHz,
CDCl3): δ [(Z,Z)-2a] = 2.27
(s, 3 H), 2.38 (s, 3 H), 6.14 (d, J = 11.7
Hz, 1 H), 7.04 (dd, J = 11.2,
11.7 Hz, 1 H), 7.04 (d, J = 11.7
Hz, 1 H), 7.22-7.37 (m, 4 H), 7.64-7.70 (m, 4
H), 7.77-7.80 (m, 1 H); δ [(Z,E)-2a] = 2.27
(s, 3 H), 2.56 (s, 3 H), 6.17 (d, J = 11.2
Hz, 1 H), 6.68 (dd, J = 11.2,
11.2 Hz, 1 H), 7.22-7.37 (m, 4 H), 7.49 (d, J = 15.1 Hz,
1 H), 7.64-7.70 (m, 2 H), 7.81 (d, J = 8.0 Hz,
2 H), 7.97 (dd, J = 11.7,
15.1 Hz, 1 H). ¹³C NMR (100 MHz, CDCl3): δ = 21.1,
21.2, 31.9, 31.9, 119.8, 119.8, 120.0, 125.0, 125.1, 125.1, 125.4,
126.6, 127.1, 127.1, 127.4, 127.6, 127.7, 128.4, 128.5, 128.7, 128.9,
129.0, 130.2, 130.5, 130.8, 132.9, 135.7, 135.7, 136.4, 136.5, 136.8,
140.0, 140.1, 140.3, 140.7, 140.8, 144.0, 145.6, 167.7, 168.4, 198.5,
198.6 (two carbon peaks could not be distinguished with other aromatic
carbons).
13 We reported that the Ru-catalyzed
reaction of 3-methylbut-1-yn-3-yl acetate with 2-methylfuran gave
the corresponding Z,E-isomer
regioselectively.
[9b]
Although we cannot
explain the difference at present, we presume that the reaction
of 1a using the ruthenium catalyst would
proceed via a completely different pathway.
15
General Procedure
of Isomerization Reaction
In a flame-dried Schlenk
tube, a mixture of (Z,Z)-2a and (Z,E)-2a (66 mg,
0.20 mmol, Z,Z/Z,E = 79:21)
and a transition-metal compound (0.010 mmol) were dispersed in toluene
(2.0 mL). The mixture was stirred at 50 ˚C for 7 h. The
yellow suspension was cooled, and the solvent was removed under
reduced pressure. The purification step using column chromatography
on SiO2 was necessary for Pd(PPh3)4-catalyzed
reaction. PdCl2 was purchased from Wako Pure Chemicals
Inc. (Japan) and used without further purification.
16 Without PtCl2, no (E,E)-2a was detected, and 1a was recovered
in 70% yield.
17 Although THF is one of the suitable
solvents for the isomerization reaction of 2a,
the reaction of 1a and
2-methylfuran
with PtCl2/PdCl2 in THF gave (E,E)-2a selectively but in a lower yield than
that in toluene because of unidentified byproduct formation.
18 Since the reaction using [RuCl2 (CO)3]2 gave
(E,E)-2a regioselectively, as shown in Scheme
[²]
, we also examined co-catalytic
system using [RuCl2 (CO)3]2 and
PtCl2. When the reaction of 1a with
2-methylfuran (2 equiv) in 5 mol% of PtCl2 and
5 mol% of [RuCl2(CO)3]2 was
carried out at 50 ˚C, we obtained 2a with
a mixture of three regioisomers (Z,Z/Z,E/E,E = 27:28:45)
in 93% yield. This indicates that the ruthenium complex
has comparatively lower catalytic activity for isomerization reaction
than palladium compounds shown in Table
[¹]
.
19
General Procedure
of Ring-Opening Reaction and Sequential Isomerization Reaction
In
a flame-dried Schlenk tube, PtCl2 (1.3 mg, 0.0050 mmol) and
PdCl2 (0.9 mg, 0.0050 mmol) were dispersed in toluene (4.0
mL). To this solution were added 1a (124
mg, 0.50 mmol) and 2-methylfuran (50 µL, 0.55 mmol) at
r.t. The mixture was stirred at 50 ˚C for 7 h. The yellow
suspension was cooled, and the solvent was removed under reduced pressure
to give 2a. To remove the transition-metal
catalysts, the crude 2a was dissolved in
THF (30 mL), and the solution was passed through a short Florisil
column. The THF solution was evaporated under reduced pressure to
give (E,E)-2a in 99% yield. For reactions
using other furans, the THF solution obtained after a Florisil column
was evaporated in vacuo, and the residue was purified by centrifuge
with hexane and a small amount of THF to give a first crop of (E,E)-2. The hexane and THF solution containing
a small amount of (E,E)-2 was evaporated in vacuo, and the residue
was purified by column chromatography on SiO2 with hexane-EtOAc
(v/v = 4:1) to give a second
crop of (E,E)-2. The yield in Table
[²]
was obtained by combining
first and second crops of (E,E)-2. The analytical
data of (E,E)-2 are summarized in the Supporting Information.
