Table 1. GaCl3-Mediated Formylation of Adamantane (1)
yields (%)a
entry
reaction conditions
2
1
1
2
3
4
5
6
7
8
9b
10
11
12
GaCl3 1 mmol, 1,2-DCE 1 mL, CO 10 atm, 80 °C, 12 h
GaCl3 1 mmol, 1,2-DCE 1 mL, CO 1 atm, 80 °C, 12 h
GaCl3 1 mmol, 1,2-DCE 1 mL, CO 10 atm, rt, 12 h
GaCl3 1 mmol, 1,2-DCE 1 mL, CO 1 atm, rt, 1 h
GaCl3 1 mmol, 1,2-DCE 0.5 mL, CO 1 atm, rt, 40 min
GaCl3 1.5 mmol, 1,2-DCE 0.5 mL, CO 1 atm, rt, 40 min
GaCl3 1 mmol, CH2Cl2 0.5 mL, CO 1 atm, rt, 40 min
GaCl3 1 mmol, cyclohexane 0.5 mL, CO 1 atm, rt, 40 min
GaCl3 1 mmol, 1,2-DCE 0.5 mL, CO 1 atm, rt, 40 min
AlCl3 1 mmol, 1,2-DCE 0.5 mL, CO 1 atm, rt, 40 min
GaBr3 1 mmol, 1,2-DCE 0.5 mL, CO 1 atm, rt, 40 min
AlBr3 1 mmol, 1,2-DCE 0.5 mL, CO 1 atm, rt, 40 min
47
0
1
0
20
40
15
1
15
55
68
25
6
63
55
77
84
76
34
19
75
58
60
22
a GC yield. b Methylcyclopentane (2 mmol) was added.
addition to the usual main product, 1-adamantanecarboxylic
acid (60-75%). Olah subsequently reported that AlCl3 can
also be used to mediate the formylation of 1 in CH2Cl2 but
that the carboxylic acid was still the major product and the
yield of the aldehyde was low (maximum of 21%).5 More
recently, Akhrem reported that 2 is formed in nearly
quantitative yield when CH2Br2/2AlBr3 is used as an elec-
trophile precursor (E+) to abstract a hydride from 1 with
methylcyclopentane as the hydride source.6 In many of the
cases reported so far, more than equimolar amounts of acids
compared to the substrates are necessary for the reaction to
proceed effectively.
Meanwhile, GaCl3,7,8 a mild Lewis acid compared to
AlCl3, is also known to generate carbocations from tertiary
alkanes, similar to AlCl3. Yamaguchi reported on GaCl3-
catalyzed reactions of alkanes with aromatics and proposed
that the reaction is initiated by hydride abstraction from the
alkane by GaCl3.8 Accordingly, it would be expected that
GaCl3 would effectively promote the carbonylation of
adamantane. Herein, we report on the GaCl3-mediated
reaction of adamantane with CO leading to 1-adamantane-
carboxaldehyde. The reaction does not require excess GaCl3,
and a hydride source is not required for the reaction to
proceed.
It was interesting to discover that GaCl3 functions as a
promoter of the formylation of adamantane. Thus, the
reaction of adamantane (1, 1 mmol) and GaCl3 (1 mmol) in
1,2-dichloroethane (1 mL) under 10 atm of CO at 80 °C for
12 h gave 1-adamantanecarboxaldehyde (2) in 47% GC yield
with the nearly complete consumption of adamantane (entry
1, Table 1 ). The report by Akhrem6 that the formylation of
adamantane could be achieved, even at room temperature
under 1 atm of CO, inspired us to carry out the reaction under
milder reaction conditions. However, when the CO pressure
was lowered to 1 atm at 80 °C, 1 was completely consumed
with none of the desired aldehyde 2 being detected (entry
2). On the other hand, a reaction at room temperature at 10
atm of CO resulted in the formation of the aldehyde in
moderate yield with 20% of unreacted 1 being recovered
(entry 3). Moreover, we could successfully lower the CO
pressure to 1 atm when the reaction was conducted at room
temperature, although the conversion was not as high (entry
4). After a series of experiments, we found that the yield
could be improved by decreasing the amount of solvent used
to 0.5 mL and by shortening the reaction time to 40 min.
Thus, the conversion was increased by 85%, giving 2 in 77%
(entry 5). Furthermore, when 1.5 mmol of GaCl3 was used,
1 was fully consumed and 2 was produced in a yield of 84%
(entry 6).
(3) Takeuchi, K.; Akiyama, F..; Miyazaki, T.; Kitagawa, I.; Okamoto,
K. Tetrahedron 1987, 43, 701. Olah, G. A.; Prakash, G. K. S.; Marinez, E.
R. Angew. Chem., Int. Ed. 2000, 39, 2547 and references therein.
(4) Farooq, O.; Marcelli, M.; Prakash, G. K. S.; Olah, G. A. J. Am. Chem.
Soc. 1988, 110, 864.
(5) Olah, G. A.; Wang, Q. Synthesis 1992, 1090.
(6) Akhrem, I.; Churilova, I.; Bernadyuk, S.; Vol’pin, M. Tetrahedron
Lett. 1996, 37, 5775. Akhrem, I. S.; Churilova, I. M.; Bernadyuk, S. Z.;
Vol’pin, M. E. Russ. Chem. Bull. 1997, 46, 491. Akhrem, I. S. Russ. Chem.
Bull. 2003, 52, 2606.
(7) Recently, GaCl3 has been found to show a unique catalytic activity.
Chatani, N.; Inoue, H.; Kotsuma, T.; Murai, S. J. Am. Chem. Soc. 2002,
124, 10294. Viswanathan, G. S.; Li, C.-J. Synlett 2002, 1553. Amemiya,
R.; Fujii, A.; Arisawa, M.; Yamaguchi, M. J. Organomet. Chem. 2003,
686, 94. Bez, G.; Zhao, C.-G. Org. Lett. 2003, 5, 4991. Chatani, N.; Oshita,
M.; Tobisu, M.; Ishii, Y.; Murai, S. J. Am. Chem. Soc. 2003, 125, 7812.
Usugi, S.; Yorimitsu, H.; Shinokubo, H.; Oshima, K. Org. Lett. 2004, 6,
601. Amemiya, R.; Nishimura, Y.; Yamaguchi, M. Synthesis 2004, 1307.
Amemiya, R.; Fujii, A.; Yamaguchi, M. Tetrahedron Lett. 2004, 45, 4333.
(8) Yonehara, F.; Kido, Y.; Morita, S.; Yamaguchi, M. J. Am. Chem.
Soc. 2001, 123, 11310. Yonehara, F.; Kido, Y.; Sugimoto, H.; Morita, S.;
Yamaguchi, M. J. Org. Chem. 2003, 68, 6752.
A systematic examination of the solvents used revealed
that dichloromethane is also appropriate for the reaction,
while the use of cyclohexane gave a lower yield (entries 7
4324
Org. Lett., Vol. 6, No. 23, 2004