3
090
R. Umeda et al.
LETTER
1
2
donating and electron-withdrawing groups on aromatic sponding alkyl aryl ketones. In the manuscript, they sug-
ring proceeded to give the corresponding esters 3ba,ca,da gested that coordinatively unsaturated complex,
in good yields (entries 9–11). For the reaction, there is no ReBr(CO) , which was generated in situ the decarbonyla-
4
significant reactivity difference between the aroyl and tion of CO coordinated with ReBr(CO) , acts as a Lewis
5
acyl chlorides. The reaction of 2a with octanoyl chloride acid catalyst. Thus, we proposed that the decarbonylation
(
1e) and 2-ethylhexanoyl chloride (1f) proceeded to give of CO coordinated with ReBr(CO) to form the Re-
5
the esters 3ea and 3fa in 95% and 88% yields, respective- Br(CO) , is the first step at the catalytic reaction. Acyl and
4
ly (entries 12 and 13). When the 2,2-diethylheptanoyl aroyl chlorides is coordinated to the ReBr(CO) generated
4
chloride (1g), which have a sterically hindered group, was in situ. The activated species reacts with the oxygen of
used as an acyl chloride, no acylative cleavage product ether 2 and the elimination of chloride anion produces the
3
ga was formed (entry 14).
oxonium salt. The cleavage of the carbon–oxygen bond of
oxonium salt gave the ester 3. On the other hand, the reac-
tion pathway including the generation of acyl cation
Table 2 Rhenium-Catalyzed Reaction of Ether 2 with Aroyl or
Acyl Chloride 1a
+
+
(
RCO ) and aroyl cation (ArCO ), which are generated by
O
O
the reaction of acyl and aroyl chlorides and ReBr(CO)4,
cannot be ruled out. Thus, we suggested that the nature of
the eliminated groups played the important rule on the
yields and the selectivity of the products 3.
cat. ReBr(CO)5
O
+
R3
R2
R1
OR2
R1
Cl
1
2
3
Entry 1
R1
2
R2
R3
3
Yield
b
In summary, we developed a new catalytic method for the
acylative and aroylative cleavage of the carbon–oxygen
bond of ethers with acyl and aroyl chlorides giving the
esters in moderate to good yields.
(
%)
1
1a
Ph
2a
2b
2c
2d
2e
2f
i-Pr
i-Pr
3aa
3ab
3ac
3ad
3ae
3af
90
43
83
trace
0
2c,d 1a
C H
C H
8
17
8
17
3c
4
1a
1a
1a
1a
1a
1a
All
Bn
Ph
Me
Et
All
Bn
Ph
Acknowledgment
This research was supported by a Grant-in-Aid for Science Re-
search, and Strategic Project to Support the Formation of Research
Bases at Private Universities from the Ministry of Education, Cul-
ture Sports, Science and Technology of Japan.
5
6
t-Bu
t-Bu
s-Bu
72
76
83
82
88
94
95
88
0
7
2g
2h
2a
2a
2a
2a
2a
2a
3ag
3ah
3ba
3ca
3da
3ea
3fa
References and Notes
8
Et
(
1) (a) Larock, R. C. Ether Cleavage, In Comprehensive
Organic Transformations, 2nd ed.; Wiley-VCH: Weinheim,
9e
1b 4-MeC H
6 4
1
999. (b) Bhatt, M. V.; Kulkarni, S. U. Synthesis 1983, 249.
1
1
1
1
0e
1c
4-MeOC H
6
4
(
c) Burwell, R. L. Jr. Chem. Rev. 1954, 54, 615.
3
4
1e
(2) It was found that Lewis acids, group 5 or 6 metal complexs,
1d 4-ClC H
6
4
5
6
7
metals such as Al and Zn, and iodine can be used as a
useful catalyst for the transformation. However, many of
these methods involve some disadvantages (i) the use of
toxic, expensive, and unstable agents, (ii) the formation of
2
1e
1f
C H
7 15
3f
4
BuCHEt
C H CEt
2
mixtures of products, (iii) low yields, and (iv) limitation of
the substrates.
1
1g
3ga
5
11
a
(3) (a) Ganem, B.; Small, V. R. Jr. J. Org. Chem. 1974, 39,
Reaction conditions: 1 (0.6 mmol), 2 (0.5 mmol), ReBr(CO) (2.5
5
3728. (b) Ahmad, S.; Iqbal, J. Chem. Lett. 1987, 953.
mol%), and DCE (3.0 mL) at 80 °C for 2 h.
b
(c) Iqbal, J.; Khan, M. A.; Srivastava, R. R. Tetrahedron
Lett. 1988, 29, 4985. (d) Iqbal, J.; Srivastava, R. R.
Tetrahedron 1991, 47, 3155. (e) Oriyama, T.; Kimura, M.;
Oda, M.; Koga, G. Synlett 1993, 437. (f) Mimero, P.;
Saluzzo, C.; Amouroux, R. Tetrahedron Lett. 1994, 35,
GC yield based on 2.
For 5 h.
c
d
ReBr(CO) (12.5 mol%) was used.
5
e
For 12 h.
For 9 h.
f
1553. (g) Green, L.; Hemeon, I.; Singer, R. D. Tetrahedron
Lett. 2000, 41, 1343. (h) Coles, S. J.; Costello, J. F.; Draffin,
W. N.; Hursthouse, M. B.; Paver, S. P. Tetrahedron 2005,
For the reaction of dioctyl ether with 1a, the formation of
6
1, 4447. (i) Yadav, J. S.; Reddy, B. V. S.; Reddy, P. M. K.;
Dash, U.; Gupta, M. K. J. Mol. Catal. A: Chem. 2007, 271,
66. (j) Suresh, V.; Suryakiran, N.; Rajesh, K.; Selvam,
J. J. P.; Srinivasulu, M.; Venkateswarlu, Y. Synth. Commun.
008, 38, 92.
1
- and 2-chlorooctane and octenes were identified with
GC analysis. In order to clarify the reaction pathway,
a stoichiometric reaction of dioctyl ether (2b) with
2
ReBr(CO) was carried out at 80 °C; however, 2b was re-
5
2
covered. Narasaka has already reported the rhenium com-
plex catalyzed the Friedel–Crafts acylation of aromatic
compounds having electron-donating groups such as
methoxy and methyl with acyl chlorides giving the corre-
(
4) (a) Guo, Q.; Miyaji, T.; Gao, G.; Hara, R.; Takahashi, T.
Chem. Commun. 2001, 1018. (b) Guo, Q.; Miyaji, T.; Hara,
R.; Shen, B.; Takahashi, T. Tetrahedron 2002, 58, 7327.
5) Luzzio, F. A.; Bobb, R. A. Tetrahedron 1999, 55, 1851.
(
Synlett 2010, No. 20, 3089–3091 © Thieme Stuttgart · New York