September 2006
1305
The Reaction of Isopropyl Diphenylmethyl Ether (4a) Using 2- methane (2g) 4957-14-6, fluorene (2h) 86-73-7, indan (2i) 496-11-7, 4-
Propanol at 350 °C In a tubular steel bomb reactor (10 ml) were placed 4a
(453 mg, 2.0 mmol) and 2-propanol (5.0 ml) under an argon atmosphere, and
methylbiphenyl (2j) 644-08-6, 2-methylfluorene (2k) 1430-97-3, N,N-di-
methyl-2-aminofluorene (2l) 13261-62-6, benzophenone (3a) 119-61-9, (4-
the reactor was sealed with an steel cap. The reactor was kept at 350 °C for methylphenyl) phenyl ketone (3b) 643-65-2, (2-naphthyl) phenyl ketone (3c)
5 h in a sand bath. After the reactor was cooled to room temperature in a 644-13-3, phenyl (4-pyridyl) ketone (3d) 14548-46-0, (2-methylphenyl)
water bath, AcOEt (30 ml) and H2O (20 ml) were added to the resulting mix- phenyl ketone (3e) 131-58-8, (3-methylphenyl) phenyl ketone (3f) 643-65-2,
ture, and the two liquid layers were then separated. The organic layer was di(4-methylphenyl) ketone (3g) 611-97-2, fluorenone (3h) 486-25-9, in-
washed with brine (20 ml), dried over Na2SO4, and concentrated under re-
duced pressure. The residue was purified by column chromatography on sil- diphenylmethyl ether (4a) 5670-79-1, 9-methylfluorene (5a) 2523-37-7, 2,9-
ica gel (hexane–AcOEt as the eluent) to afford 2a (334 mg, 99%). dimethylfluorene (5b) 1430-97-3, 2-amino-N,N,9-trimethylfluorene (5c)
The transformation of Fluorenes (2h, 2k, and 2l) to 9-Methylfluorenes 727415-21-6, 9-benzylfluorene (7a) 1572-46-9, 9-(4-methylbenzyl)fluorene
danone (3i) 83-33-0, 4-biphenylcarboxaldehyde (3j) 3218-36-8, isopropyl
(5) Using Methanol at 450 °C In a tubular steel bomb reactor (10 ml)
were placed 2 (2.0 mmol), sodium methoxide (270 mg, 5.0 mmol) and
methanol (3.0 ml) under an argon atmosphere, and the reactor was sealed
with a steel cap. The reactor was kept at 450 °C for 5 h in a sand bath. After
the reactor was cooled to room temperature in a water bath, AcOEt (30 ml)
and H2O (20 ml) were added to the resulting mixture, and the two liquid lay-
ers were then separated. The organic layer was washed with saturated
NaHCO3 (20 ml) and brine (20 ml), dried over Na2SO4, and concentrated
under reduced pressure. The residue was purified by column chromatogra-
phy on silica gel, giving the 9-methylfluorene (5) in the yield shown in Table
(7b) 745809-62-5.
Results and Discussion
Reaction of Diarylmethanols in Alcohol Medium under
Supercritical Conditions We first examined the reactivity
of diarylmethanols (1) in several alcohols under supercritical
conditions (Eq. 2, Table 1). When 1a was treated with
methanol at 400 °C for 5 h, the direct reduction was smoothly
performed to give the corresponding alkane 2a as a single
product in 79% yield (entry 1). It was interesting to note that
ketone 3a was not observed at all, as compared with the reac-
tion of 1a in supercritical water.12) In ethanol, the reduction
of 1a also proceeded to give 2a in 83% yield (entry 2). The
best result was obtained when the reaction was carried out
1
3. 5a: H-NMR (CDCl3, 500 MHz) d: 7.79—7.74 (m, 2H), 7.55—7.49 (m,
2H), 7.38—7.28 (m, 4H), 3.94 (q, 1H, Jꢀ7.6 Hz), 1.52 (d, 3H, Jꢀ7.6 Hz);
13C-NMR (CDCl3, 125 MHz) d: 149.1, 140.6, 127.0, 126.7, 124.0, 119.8,
42.4, 18.2. 5b: 1H-NMR (CDCl3, 500 MHz) d: 7.69 (d, 1H, Jꢀ7.5 Hz), 7.64
(d, 1H, Jꢀ7.5 Hz), 7.46 (d, 1H, Jꢀ8.0 Hz), 7.37—7.27 (m, 3H), 7.15 (d, 1H,
Jꢀ8.0 Hz), 3.83 (q, 1H, Jꢀ7.5 Hz), 2.42 (s, 3H), 1.49 (d, 3H , Jꢀ7.5 Hz);
13C-NMR (CDCl3, 125 MHz) d: 149.2, 148.8, 140.5, 137.8, 136.7, 127.7,
126.8, 126.6, 126.4, 124.7, 123.9, 119.5, 42.2, 21.6, 18.2. 5c: 1H-NMR using 2-propanol (entry 3). On the other hand, the reduction
(CDCl3, 500 MHz) d: 7.62—7.58 (m, 2H), 7.45—7.40 (m, 1H), 7.33—7.14
(m, 2H), 6.86 (s, 1H), 6.77—6.61 (m, 1H), 3.87 (q, 1H, Jꢀ7.4 Hz), 3.00 (s,
6H), 1.50 (d, 3H, Jꢀ7.4 Hz); 13C-NMR (CDCl3, 125 MHz) d: 150.6, 150.3,
148.1, 141.1, 129.7, 125.7, 124.9, 123.6, 120.4, 118.4, 111.6, 108.1, 42.4,
41.0, 18.5.
of 1a in tert-butanol proceeded with great difficulty; ketone
(3a) was obtained as the main product (35%) along with 2a
(27%) (entry 4). These facts suggested that the hydrogen at
the a-position of the alcohol medium plays an important role
in the reduction of 1. This reduction also smoothly proceeded
in the case of the substrate bearing 4-methyl (1b), 2-naphtyl
(1c), and 4-pyridyl (1d) groups (entries 5, 6, and 7, respec-
tively).
The Reaction of Fluorenes (2h) with Formaldehyde at High Tempera-
ture In a tubular steel bomb reactor (10 ml) were placed 2h (332 mg,
2.0 mmol), sodium methoxide (270 mg, 5.0 mmol) and an aqueous solution
of formaldehyde (37w%, 3.0 ml) under an argon atmosphere. The reactor
was sealed with a steel cap. The reactor was kept at 450 °C for 5 h in a sand
bath. After the reactor was cooled to room temperature in a water bath,
AcOEt (30 ml) and H2O (20 ml) were added to the resulting mixture, and the
two liquid layers were then separated. The organic layer was washed with
saturated NaHCO3 (20 ml) and brine (20 ml), dried over Na2SO4, and con-
centrated under reduced pressure. The residue was purified by column chro-
matography on silica gel (30 g, petroleum ether : chloroformꢀ50 : 0, 48 : 2,
46 : 4, 44 : 6, 42 : 8, 40 : 10, 35 : 15, 30 : 20, 25 : 25, and 0 : 50 eachꢁ50 ml),
giving the 9-methylfluorene (5a) in the yield shown in Table 4, entry 1.
The Reaction of Fluorenes (2h) with Benzaldehyde Derivatives at
High Temperature In a tubular steel bomb reactor (10 ml) were placed 2h
(332 mg, 2.0 mmol), sodium methoxide (270 mg, 5.0 mmol) and the benz-
aldehyde derivative (3 ml) under an argon atmosphere. The reactor was
(2)
Reaction of Diaryl Ketones in 2-Propanol under Super-
critical Conditions As the reduction of diarylmethanol (1)
to diarylalkane (2) quite smoothly proceeded without the for-
mation of diaryl ketone (3) in 2-propanol under supercritical
conditions, we next studied the reactivity of diaryl ketone (3)
in 2-propanol at high temperatures.14) When ketone 3a was
sealed with a steel cap. The reactor was kept at 350 °C for 5 h in a sand bath. reacted with 2-propanol at 350 °C for 5 h, alkane 2a was ob-
After the reactor was cooled to room temperature in a water bath, toluene
(30 ml) and H2O (20 ml) were added to the resulting mixture, and the two
liquid layers were then separated. The organic layer was washed with satu-
rated NaHCO3 (20 ml) and brine (20 ml), dried over Na2SO4, and concen-
tained as a single product in good yield (Eq. 3 and Table 2,
entry 1). The influence of temperature on this reduction was
then investigated. The reduction of 1a did not proceed at
250 °C, and the unchanged 3a was recovered in quantitative
yield (entry 2). Although the reduction of 1a proceeded at
300 °C, the product selectivity was not observed; alcohol 1a
trated under reduced pressure. After removal of the excess benzaldehyde by
bulb-to-bulb distillation, the residue was purified by column chromatogra-
phy on silica gel (30 g, petroleum ether : chloroformꢀ50 : 0, 48 : 2, 46 : 4,
44 : 6, 42 : 8, 40 : 10, 35 : 15, 30 : 20, 25 : 25, and 0 : 50 eachꢁ50 ml), giving
9-benzylfluorenes (7a, 7b) in the yield shown in Table 4, entries 2 and 3. 7a:
1H-NMR (CDCl3, 500 MHz) d: 7.69—7.15 (m, 13H), 4.23 (t, 1H, Jꢀ7.7 Hz),
3.10 (d, 2H, Jꢀ7.7 Hz); 13C-NMR (CDCl3, 125 MHz) d: 146.8, 140.8, 139.8,
Table 1. Reduction of 1 to 2 in Several Alcohols at 400 °C
1
Ar1
Ar2
Alcohol
Yield of 2 (%)a)
129.5, 128.3, 127.0, 126.6, 124.6, 119.8, 49.7, 40.1. 7b: H-NMR (CDCl3,
Entry
1
500 MHz) d: 7.29—7.07 (m, 12H), 4.20 (t, 1H, Jꢀ7.4 Hz), 3.06 (d, 2H,
Jꢀ7.4 Hz), 2.44 (s, 3H); 13C-NMR (CDCl3, 125 MHz) d: 146.9, 140.8,
129.3, 129.1, 128.9, 128.7, 127.0, 126.6, 124.8, 119.7, 48.7, 39.6, 21.1.
The registry numbers are as follows: diphenylmethanol (1a) 91-01-0,
(4-methylphenyl)(phenyl)methanol (1b) 1517-63-1, (2-naphtyl)(phenyl)-
methanol (1c) 35060-38-9, (phenyl)(4-pyridyl)methanol (1d) 33974-27-5,
diphenylmethane (2a) 101-81-5, (4-methylphenyl)(phenyl)methane (2b)
620-83-7, (2-naphtyl)(phenyl)methane (2c) 613-59-2, (phenyl)(4-pyridyl)-
methane (2d) 2116-65-6, (2-methylphenyl)(phenyl)methane (2e) 713-36-0,
(3-methylphenyl)(phenyl)methane (2f) 620-47-3, di(4-methylphenyl)-
1
2
3
4
5
6
7
1a
1a
1a
1a
1b
1c
1d
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
4-MeC6H4
2-naphtyl
4-pyridyl
MeOH
EtOH
79
83
95
27b)
91
87
90
i-PrOH
t-BuOH
i-PrOH
i-PrOH
i-PrOH
a) Isolated yield. b) Ketone 3a was obtained in 35% yield.