160 J. CHEM. RESEARCH (S), 1999
J. Chem. Research (S),
1999, 160±161$
Lanthanide Bis[bis(1,1,1,3,3,3-hexafluoro-2-
propoxy)sulfonyl]amide as a Novel Effective
Acylation Catalyst$
Jin Nie,* Zhongming Zhao, Jun Xu and Dafan Liu
Department of Chemistry, Huazhong University of Science and Technology, Wuhan 430074,
Hubei, P.R. China
Lanthanide complexes Ln(BHFPSA)3 fBHFPSA N[SO2OCH(CF3)2]2g catalyse the acylation of alcohols or phenols
under very mild conditions to afford esters in high yields.
Table 2 Effect of solvents on acetylation catalysed by
Although 4-(dimethylamino)pyridine, 4-pyrrolidinopyridine
and tributylphosphine (Bu3P) etc. are known to be eec-
a
Sm(BHFPSA)3
tive basic catalysts in the acylation of alcohols with acid
anhydrides, there is great demand for acid catalysts to
generate esters under mild conditions.1±4 Since metal tri¯ates
have been employed as versatile Lewis acid catalysts,5 we
are interested in preparing some metal bis[bis(per¯uoro-
alkyl)sulfonyl]amides or bis[bis(poly¯uoroalkoxy)sulfonyl]-
amides to investigate their utility as Lewis acid catalysts.6±8
We report here on the acylation of alcohols or phenols
with acid anhydrides by using a catalytic amount of the
lanthanide bis[bis(1,1,1,3,3,3-hexa¯uoro-2-propoxy)sulfonyl]-
amide [Ln{N[SO2OCH(CF3)2]2}3 or Ln(BHFPSA)3].
Entry
Solvent
t/min
1 (35c)
4
6
Conversion (%)b
1
2
3
4
5
6
7
8
CH3NO2
CH2Cl2
PhCH3
THF
99
99
99
99
99
99
99
99
6
Et2O
10
56
611
620
CHCl3
DMF
CH3CN
aA solution of benzyl alcohol (0.25 M) was used. bThe conversion
was determined by gas chromatographic analysis of the crude
product. c0.1 mol% catalyst was used at 0 8C.
Results and discussion
Initially, the model reaction of benzyl alcohol (1 equiv.)
with acetic anhydride (1.5 equiv.) in dichloromethane at
30 8C was carried out to screen the catalytic activities of
lanthanide bis[bis(1,1,1,3,3,3-hexa¯uoro-2-propoxy)sulfonyl]-
amides as the Lewis acids (Table 1). Compared with the
samarium tri¯ate [Sm(OTf)3], the catalytic amount of
Ln(BHFPSA)3 (0.25 mol%) showed very strong Lewis acid
catalytic activities in the model reaction and Yb(BHFPSA)3
was found to be the most eective. Ishihara et al.'s results4
indicated that the lanthanide tri¯ates, Ln(OTf )3, were not
good catalysts for the acylation of alcohols. Thus, the
enhanced Lewis acidity of the lanthanide metal ions might
be attributed to the bulky and weakly coordinating proper-
ties of their counter anion, [N{SO2OCH(CF3)2}2] .9,10 As
Sm(BHFPSA)3 was more easily prepared and its catalytic
activity was similar to that of Yb(BHFPSA)3 we used it as
the catalyst in most cases.
The eect of solvents on the model reaction under the
in¯uence of 1 mol% of Sm(BHFPSA)3 is shown in Table 2.
Under these conditions, the solvent eect on the catalytic
reaction might depend on the polarity and coordinating
property of these solvents. The reaction proceeded faster in
nitromethane than in other organc solvents and it was much
slower in dimethylformamide and acetonitrile.
Several examples of the acylation of dierent alcohols
with acid anhydrides catalysed by Sm(BHFPSA)3 are
shown in Table 3. In most cases the reactions took place
smoothly in the presence of 0.1±0.25 mol% of catalyst to
aord the esters in good yields under very mild conditions.
The acylation of sec-phenethyl alcohol with acetic anhydride
in nitromethane proceeded more than ten times faster
than that in dichloromethane (entries 2 and 3 in Table 3)
and the acylation of sec-phenethyl alcohol (1 equiv.) with
benzoic anhydride (1 equiv.) also gave a satisfactory result
after the reaction had proceeded for only two hours (entry 5
in Table 3). In the case of acylation of phenols with acetic
anhydride, that of 2,6-di-tert-butyl-4-methylphenol was rela-
tively slow even in nitromethane in comparison with the
acylation of other phenols (entries 6±12 in Table 3). For
acid-sensitive substrates such as tertiary alcohols, the reac-
tion successfully proceeded using acid anhydride as a solvent
under very mild conditions and the amount of esters
increased when the reactions were carried out at as low
a temperature as possible (entries 13±17 in Table 3). In
most cases of DMAP or PPY-catalysed acetylation of
tertiary alcohols, it is necessary to use more than 10 mol%
of DMAP or PPY and an excess of amine at conditions of
high concentration.1,2 It is noted that when 1 mol% of
Sm(BHFPSA)3 was used to catalyse the acylation of 1-ethyl-
cyclohexanol with acetic anhydride at 0 8C, a yield of more
than 95% for the ole®n was detected after just 3 min. This
indicated that the acylation would proceed more smoothly
when less catalyst is used.
Table 1 Ln(BHFPSA)3 catalysed acetylation of benzyl alcohol
in CH2Cl2 at 30 8Ca
Entry
Catalyst
t/min
Conversion (%)b
1
2
3
4
5
6
No cat.
Sm(OTf)3
La(BHFPSA)3
Sm(BHFPSA)3
Ga(BHFPSA)3
Yb(BHFPSA)3
1440
640
60
17
13
<10
<40
99
99
99
c
9
99
aA solution of benzyl alcohol (0.25 M) was used. bThe conversion
was determined by gas chromatographic analysis of the crude
product. c1 mol% catalyst was used.
com).
$This is a Short Paper as de®ned in the Instructions for Authors,
Section 5.0 [see J. Chem. Research (S), 1999, Issue 1]; there is there-
fore no corresponding material in J. Chem. Research (M).