1744
K. K. Chauhan et al.
LETTER
References and Notes
Table 3 The In(OTf)3 catalysed acylation of amines
(1) Scriven, E. F. V. Chem Soc. Rev. 1983, 12, 129.
(2) Chandrasekhar, S.; Ramachander, T.; Takhi, M. Tetrahedron
Lett. 1998, 39, 3263.
Entry
Amine
Yield
(%)
Product
NH2
NHAc
(3) Procopiou, P. A.; Baugh, S. P. D.; Flack, S. S.; Ingliss, G. G.
A. J. Org Chem. 1998, 63, 2342.
1
99
(4) Saravanan, P.; Singh, V. K. Tetrahedron Lett. 1999, 40, 2611.
(5) (a) Ishihara, K.; Kubota, M.; Kurihara, H.; Yamamoto, H. J.
Am. Chem. Soc. 1995, 117, 4413. (b) Ishihara, K.; Kubota, M.;
Kurihara, H.; Yamamoto, H. J. Org. Chem. 1996, 61, 4560.
(6) For previous work on the use of indium complexes as Lewis
acids see Ali, T.; Chauhan, K. K.; Frost C. G. Tetrahedron
Lett. 1999, 40, 5621 and references therein.
NH2
NHAc
Me
Me
Me
Me
2
94
H2N
AcHN
(7) Strem catalogue No. 17, 1997-99; Scandium triflate (min.
97%) £25.00/g; Indium triflate (99%) £8.00/g.
3
4
92
98
91
(8) All compounds have been adequately characterised.
Acetoxymethylbenzene: 1H NMR (CDCl3, 270 MHz) d 2.07
(3H, s), 5.09 (2H, s), 7.32-7.35 (5H, m). 1-acetoxy-1-
phenylethane: 1H NMR (CDCl3, 270 MHz) d 1.53 (3H, d,
J=6.6 Hz), 2.06 (3H, s), 5.85 (1H, q, J= 6.6 Hz), 7.24-7.35
(5H, m). (1R)-(-)-menthylacetate: 1H NMR (CDCl3, 270
MHz) d 0.76 (3H, d, J= 7.0 Hz), 0.89 (3H, d, J= 7.0 Hz), 0.90
(3H, d, J= 6.6 Hz), 0.84-1.14 (3H, m), 1.30-1.60 (2H, m),
1.79-1.93 (2H, m), 1.93-2.04 (2H, m), 2.03 (3H, s), 4.67 (1H,
dt, J= 4.4, 10.8 Hz). Trans-(±)-1-acetoxy-2-
NH2
NHAc
H
H
H
NH2
NHAc
5
NH2
NHAc
H
phenylcyclohexane: 1H NMR (CDCl3, 270 MHz) d 1.20-1.60
(4H, m), 1.70-1.90 (4H, m), 1.96 (3H, s), 2.6 (1H, dt, J= 3.8,
10.8 Hz), 4.90 (1H, m), 7.17-7.40 (5H, m). Acetoxybenzene:
1H NMR (CDCl3, 270 MHz) d 2.23 (3H, s), 7.04-7.36 (5H, m).
(9) All compounds have been adequately characterised. 1,2-
diacetoxy-1-phenylethane: 1H NMR (CDCl3, 270 MHz) d
2.04 (3H, s), 2.11 (3H, s), 4.24-4.35 (2H, m), 6.00 (1H, q, J=
4.2 Hz) 7.26-7.37 (5H, m). bis-2-acetoxyethylether: 1H NMR
(CDCl3, 270 MHz) d 2.09 (6H, d, J= 1.1 Hz), 3.69-3.73 (4H,
m), 4.22-4.25 (4H, m). (±)-2,2'-diacetoxy-1,1'-binaphthyl: 1H
NMR (CDCl3, 270 MHz) d 1.86 (6H, s), 7.16-7.49 (8H, m),
7.92-8.01 (4H, m). 1,1,1-tris-(acetoxymethyl)ethane: 1H
NMR (CDCl3, 270 MHz) d 1.02 (3H, s), 2.07 (9H, s), 4.00
(6H, s). hexa-O-acetyl-D-mannitol: 1H NMR (CDCl3, 270
MHz) d 2.06 (6H, s), 2.08 (6H, s), 2.10 (6H, s), 4.10 (4H, m),
5.05 (2H, m), 5.44 (2H, m).
zyl alcohol. Of these, the only effective alternative proved
to be 1-cyclohexenyl acetate which prompted an extreme-
ly rapid acetylation reaction (Scheme). This is no doubt
due to the unstable enol liberated tautomerising instanta-
neously to the ketone and the reaction becoming com-
pletely irreversible.
OAc
OH
OAc
(10) All compounds have been adequately characterised. N-
phenylacetamide: 1H NMR (CDCl3, 270 MHz) d 2.16 (3H, s),
7.07-7.48 (5H, m), 7.65 (1H, br s). N-(2,6-
In(OTf)3 (0.1 mol%)
MeCN
dimethylphenyl)acetamide: 1H NMR (CDCl3, 270 MHz) d
1.73 (1H, s), 2.15 (3H, s), 2.19 (6H, s), 7.03-7.17 (3H, m). N-
(2-biphenyl)acetamide: 1H NMR (CDCl3, 270 MHz) d 2.02
(3H, s), 7.15-7.51 (9H, m), 8.24 (1H, d, J= 8.0 Hz). N-
benzylacetamide: 1H NMR (CDCl3, 270 MHz) d 2.03 (3H, s),
4.43 (2H, d, J= 5.7 Hz), 6.17 (1H, br s), 7.27-7.34 (5H, m).
trans-diacetamido-(1R, 2R)-(–)-1,2-cyclohexane: 1H NMR
(CDCl3, 270 MHz) d 1.27 (4H, m), 1.75 (2H, m), 1.94 (6H, s),
2.03 (2H, m), 3.65 (2H, m), 6.15 (2H, br s).
>95% 5 minutes
Scheme
In summary, we have demonstrated that the inexpensive,
commercially available complex indium triflate is a pow-
erful catalyst for the acylation of alcohols. Although the
optimum system employs enol esters as acyl donors, the
relative cost of 1-cyclohexenyl acetate compared with
acetic anhydride suggests that for practical purposes ace-
tic anhydride is the donor of choice.
Article Identifier:
1437-2096,E;1999,0,11,1743,1744,ftx,en;L12699ST.pdf
Acknowledgement
We are grateful to Pfizer Limited. (Sandwich) for funding a CASE
award to KKC and to the University of Bath for further funding.
Synlett 1999, No. 11, 1743–1744 ISSN 0936-5214 © Thieme Stuttgart · New York