Erbium(III) triflate as an extremely active acylation catalyst

Article abstract of DOI:10.1002/adsc.200404132

Erbium(III) triflate is a powerful catalyst for the acylation of alcohols and phenols. The reaction works well for a large variety of simple and functionalized substrates by using different kinds of acidic anhydrides {Ac ₂O, (EtCO)₂O, [(CH₃)₃CO] ₂O, Bz₂O, and (CF₃CO)₂O} without isomerisation of chiral centres. Moreover, the catalyst can be easily recycled and reused without significant loss of activity.

Full text of DOI:10.1002/adsc.200404132

FULL PAPERS
Erbium(III) Triflate as an Extremely Active Acylation Catalyst
a,
b
b
b
Antonio Procopio, * Renato Dalpozzo, Antonio De Nino, Loredana Maiuolo,
a
b
Beatrice Russo, Giovanni Sindona
Dipartimento Farmaco-Biologico, Universit a` degli Studi della Magna Graecia, Complesso Ninì Barbieri,
8063 Roccelletta di Borgia (CZ), Italy
a
8
Fax: (þ39)-961-391-270, e-mail: procopio@unicz.it
b
Dipartimento di Chimica, Universit a` della Calabria, Ponte Bucci, 87030 Arcavacata di Rende (CS), Italy
Received: May 6, 2004; Accepted: August 23, 2004
Abstract: Erbium(III) triflate is a powerful catalyst Moreover, the catalyst can be easily recycled and
for the acylation of alcohols and phenols. The reaction reused without significant loss of activity.
works well for a large variety of simple and function-
alized substrates by usingdifferent kinds of acidic an-
hydrides {Ac O, (EtCO) O, [(CH ) CO] O, Bz O, and Keywords: acylation; erbium(III) triflate; homogene-
2
2
3
3
2
2
(
CF CO) O} without isomerisation of chiral centres. ous catalysis; lanthanides; Lewis acid catalysts
3 2
Introduction
rate constants (WERC) of these derivatives. In a screen-
ingtest it was found that the metals which exhibit go od
The principles of green chemistry can motivate the catalytic activity had pK values in the range from about
h
6
À1
chemists to accomplish their vital role in sustainable de- 4 to 10 and WERC values greater than 3.2Â10 M
À1 [6b]
velopment by inventing, designing, and applying new s .
chemical reagents and methods to reduce or eliminate
The lanthanoid family possesses the interestingfea-
[
1]
the use and generation of hazardous substances. In ture of a regular variation of these properties along
the last years we have directed much of our effort to- the series which can be used for tuningthrough a proper
wards lower environmental impact chemistry, by devel- choice of the cation. Therefore, many examples exist
opingnew catalytic reagents for the strategic protection/
deprotection steps of functional groups. Acylation is catalysts with efficacy varyingfrom one reaction to an-
one of the most important and widely used protection other. Recently, the relative Lewis acidities of lantha-
where rare-earth metal triflates are used as Lewis acid
[
2]
[
6c]
methods to preserve the hydroxy function duringthe
course of multistep syntheses.
Generally, acylation takes place by treatment of alco- be one of the most active cations. In fact its pK and
noid(III) triflates were evaluated by the use of tandem
mass spectrometry, in that study erbium(III) proved to
[
3]
[
7]
h
8
hols and phenols with acid anhydrides or acid chlorides WERC values are 7.9 and 1.4Â10 , respectively, which
in the presence of amines, but many other methods were are perfectly in accordance with the statements of Ko-
[
4]
proposed in the last decade. More recently, metal tri- bayashi et al. Nevertheless, Er(III) triflate has been in-
fluoromethanesulfonates were intensively developed explicably neglected although some examples of its suc-
[8]
as Lewis acid catalysts in the acylation protection of hy- cessful use in different reactions have been reported.
[2d,5]
droxy groups.
The strongelectron-withdrawingcapacity of the tri-
fluoromethanesulfonate anion enhances the Lewis Results and Discussion
[
6]
acid character of the catalyst and Kobayashi et al. not-
ed a correlation between the catalytic activity and the We have already introduced the use Er(OTf) as an effi-
3
hydrolysis constants (K ) as well as the water-exchange cient catalyst for the deprotection of acetals and ke-
h
[
2f]
tals, we now report a simple and efficient method for
the acylation of alcohols and phenols with different
acid anhydrides catalyzed by Er(III) triflate (Scheme 1).
First, we tested the catalytic activity of Er(OTf) in the
3
acetylation reaction of 1-octanol at room temperature
in different solvents and with different mol % of catalyst
using1.5 equivalents of acetic anhydride. On the basis of
our preliminary results, which are shown in Table 1,
Scheme 1.
Adv. Synth. Catal. 2004, 346, 1465–1470
DOI: 10.1002/adsc.200404132
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1465

FULL PAPERS
Antonio Procopio et al.
Yield [%]
Table 1. Attempted acetylation of 1-octanol in various solvents.
Entry
Solvent
Er(OTf) [mol %]
Time [min]
3
1
2
3
4
5
6
7
8
9
CH CN
0.1
0.05
0
20
40
90
45
90
–
–
–
–
–
>95
80
20
>95
30
35
40
45
85
35
3
CH CN
3
CH CN
3
CH NO
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
3
2
ethylic ether
THF
CH Cl
2
2
CHCl3
toluene
1
1
0
1
CH CN (not dry)
3
CH NO (not dry)
–
30
3
2
Er(OTf) acts more efficiently in dry polar aprotic sol-
The Ac O-Er(OTf) acetylatingsystem tolerates the
2 3
3
vents such as CH CN and CH NO (entries 1 and 4, presence of other functionalities on the substrates such
3
3
2
Table 1), while less satisfactory results were obtained as carbonyl and acetyl groups (entries 20 and 21, Ta-
in dry diethyl ether, THF, CH Cl , CHCl and toluene ble 2), no rearrangement took place with allylic and
2
2
3
(
entries 5–9, Table 1).
propargyl substrates (entries 12 and 16, Table 2), and
The absence of water seems to be essential and only also optically active substrates were efficiently acetylat-
low yields of acetylated product was obtained when ed without any loss of optical purity (entries 7 and 31,
not-dry CH CN and CH NO were used as solvents (en- Table 2) demonstratingthe mildness of this method.
3
3
2
tries 10 and 11, Table 1). Er(OTf) was still extremely No selective acetylation was observed when the present
3
active when only 0.05 mol % of catalyst was used in method was applied for the acetylation of a-d-glucose
the same conditions, but with less satisfactory results and only less than 20% of peracetylated sugar was ob-
(
entry 2, Table 1), meanwhile only 20% of acetylated tained; but an almost quantitative yield of this product
product was obtained in absence of catalyst (entry 3, (entry 33, Table 2) was collected in the presence of
Table 1). The catalyst can be reused several times with- 0.5 mol % of catalyst when acetic anhydride was used
out significant loss of activity. After work-up, the aque- as solvent. In spite of the fact that a 0.1 M solution of
ous phase can be evaporated under reduced pressure to Er(OTf) in water is only weakly acidic (pHꢀ5.9), and
3
[
9]
furnishthe Er(III) salt asa pale pink solid (85–90% re- the aqueous layer from the work-up in the present meth-
covered), which can be reused after dryingoverni gh t
od was also less acidic (pHꢀ6.6), the acid sensitive t-bu-
over P O . The recovered catalyst was used five times tyldimethylsilyl (TBDMS) and tetrahydropyranyl
2
5
in the acetylation reaction of the 1-octanol maintaining (THP) protective groups did not survive during the ace-
0.1 mol % of catalyst and the registered yields were al- tylation under these conditions and both the functions
ways higher than 90%. were replaced by the acetyl group to furnish the corre-
In order to explore the generality and the scope of er- spondingdiacetate (entries 48 and 49, Table 2). The
bium(III) triflate as a Lewis acid catalyst in acylation present protocol was tested also in the acetylation reac-
protections, the reaction was carried out on a variety tion of phenols (entries 34, 35, 39 and 44, Table 2). In all
of substrates usingdifferent acid anhydrides.
the cases nearly quantitative yields were obtained, even
Based on the results reported in Table 1, we generally for a phenol as highly crowded as the 2,6-di-t-butyl-p-
adopted a simple experimental procedure that involves cresol (BHT) which required simply in increase of the
stirringthe solution of substrate containingthe hydroxy
percentage of catalyst up to 0.5 mol % (entry 34, Ta-
function and acid anhydride in dry CH CN in the pres- ble 2), and no substantial differences in reactivity were
3
ence of only 0.1 mol % of Er(OTf)3.
registered on changing the electron requirements on
As shown in Table 2, not only primary (entries 1 and the aromatic moiety (entries 35, 39 and 44, Table 2). Fur-
2), but also secondary and tertiary alcohols and phenols thermore, no by-products arisingfrom Fries rearran ge -
2
underwent smooth acetylation with almost quantitative ment were obtained from any phenols submitted to
yields. No competitive dehydration was registered in the this acetylatingprocedure even after prolonged reaction
acetylation of secondary and tertiary substrates (en- times.
tries 7, 27, and 31, Table 2), and only in the case of the
In our previous work, we proposed the use of
heavy sterically hindered 2-phenylisopropanol, were a Ce(OTf) as a mild Lewis acid catalyst in acetylation re-
3
[
2d]
lower reaction temperature (À108C) and the use of actions, but we could not realize other kinds of acyla-
acetic anhydride as solvent necessary to suppress tion and also in the successfully reported acetylations
the competitive elimination reaction (entries 28–30, 1.0 mol % of catalyst was necessary, while only
Table 2).
0.1 mol % of Er(OTf) was sufficient to replicate these
3
1466
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asc.wiley-vch.de
Adv. Synth. Catal. 2004, 346, 1465–1470

Erbium(III) Triflate as Acylation Catalyst
FULL PAPERS
Table 2. Acylation of alcohols usingEr(OTf) 3 as catalyst.
[a, b]
Entry
Substrate
Acid anhydride (equivs.)
Er(OTf) [mol %]
T [8C]
Time [min]
Yield [%]
3
1
2
3
4
5
6
7
8
9
1-octanol
”
”
”
”
”
”
Ac O (1.5)
0.1
”
0.5
”
”
”
0.1
0.5
”
r.t
”
”
20
120
15
25
30
150
50
30
>95
”
2
(EtCO) O (1.5)
2
(EtCO) O (1.5)
”
”
”
”
”
”
”
2
(t-BuCO) O (1.5)
”
2
Bz O (3.0)
50
r.t.
”
r.t.
”
2
(CF CO) O (1.5)
3
2
Ac O (1.5)
2
”( þ)-menthol
(EtCO) O (1.5)
2
(t-BuCO) O (1.5)
35
2
10
11
12
”
”
Bz O (3.0)
”
”
0.1
50
r.t.
”
100
180
30
”
”
”
2
(CF CO) O (1.5)
3
2
Ac O (1.5)
2
13
14
15
16
”
”
”
(EtCO) O (1.5)
0.5
”
”
”
”
50
r.t
40
60
120
30
”
”
”
”
2
(t-BuCO) O (1.5)
2
Bz O (3.0)
2
Ac O (1.5)
0.1
2
17
18
19
20
”
”
”
(EtCO) O (1.5)
0.5
”
”
”
”
50
r.t.
25
35
”
”
”
”
”
2
(t-BuCO) O (1.5)
2
Bz O (3.0)
2
Ac O (1.5)
”
25
2
21
Ac O (1.5)
”
”
20
”
2
2
2
2
2
2
2
2
2
3
4
5
6
7
8
PhCH OH
”
”
”
Ac O (1.5)
0.1
0.5
”
”
”
”
”
”
50
r.t.
”
25
15
25
50
10
”
”
”
”
”
”
2
2
(EtCO) O (1.5)
2
(t-BuCO) O (1.5)
2
Bz O (3.0)
2
”
(CF CO) O (1.5)
3
2
t-BuOH
Ac O (1.5)
0.1
0.5
30
120
2
[
[
c]
c]
Ac O (1.5)
”
0
2
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
”
”
”
–
–
0.1
0.5
”
”À10
r.t
”
r.t
50
r.t
”
”
”
”
”
>95
”
Ac O as solvent
2
cholesterol
”
a-d-glucose
BHT
Ac O (1.5)
2
(CF CO) O (1.5)
240
100
60
20
15
20
30
25
20
25
30
480
25
10
15
”
”
”
”
”
”
”
”
”
”
”
”
”
”
”
”
”
3
2
[
d]
Ac O as solvent
2
Ac O (1.5)
”
2
4-MeO-C H -OH
”
0.1
0.5
”
6
4
”
”
”
(EtCO) O (1.5)
2
(t-BuCO) O (1.5)
”
2
Bz O (3.0)
”
50
r.t.
”
2
4-Me-C H -OH
Ac O (1.5)
0.1
0.5
”
”
”
0.1
0.5
”
”
0.1
”
6
4
2
”
”
”
”
(EtCO) O (1.5)
2
(t-BuCO) O (1.5)
”
2
Bz O (3.0)
50
r.t.
”
”
”
50
r.t.
”
2
(CF CO) O (1.5)
3
2
4-NO -C H -OH
Ac O (1.5)
2
6
4
2
”
”
”
(EtCO) O (1.5)
2
(t-BuCO) O (1.5)
2
Bz O (3.0)
2
[
[
d]
d]
HO(CH ) OTBDMS
Ac O (1.5)
20
30
”
”
2
4
2
HO(CH ) OTHP
”
2
4
[
a]
1
Unless otherwise specified, all products were identified by comparison of their EI-MS and H NMR data with those of au-
thentic compounds and data reported in the literature.
[10]
[
[
[
b]
Unless otherwise specified, isolated yield by flash column chromatography on silica gel is reported.
c]
1,4-Butandiol diacetate was the only product obtained.
d]
Only peracetate derivatives were obtained.
Adv. Synth. Catal. 2004, 346, 1465–1470
asc.wiley-vch.de
ꢀ 2004 WILEY-VCH VerlagGmbH & Co. KGaA, Weinheim
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FULL PAPERS
Antonio Procopio et al.
results. In view of this much higher activity, we decided and 32, Table 2) as well as p-cresol (entry 43, Table 2)
to explore the application of the Er(OTf) -acid anhy- were trifluoroacetylated in almost quantitative yields
3
dride protocol to other acylations. When 1-octanol in at room temperature in very short reaction times by us-
dry CH CN was treated with 1.5 equivs. of propionic an- ing1.5 equivalents of trifluoroacetic anhydride in dry
3
hydride in the presence of 0.1 mol % of erbium(III) tri- acetonitrile in the presence of 0.5 mol % of Er(OTf)3.
fluoromethanesulfonate the acylation proceeded
smoothly within 3 h with almost quantitative yield (en-
try 2, Table 2), but the reaction was completed in only
Conclusion
1
0
5 minutes when the amount of catalyst was raised to
.5 mol % (entry 3, Table 2).
The erbium(III) trifluoromethanesulfonate/acyl anhy-
drides protocol can be considered a tangible improve-
ment with respect to the other existingmethods which
involve the use of triflate derivatives as catalysts in the
preparation of acyl esters of alcohols and phenols, espe-
Surprisingly, the same result was reached when this
modified protocol was applied to introduce the pivalate
function, which is one of the most stubborn ester pro-
tecting gr oups due to its steric hindrance, and a quanti-
tative yield of 1-octyl pivalate was obtained in only 25
minutes (entry 4, Table 2).
To explore the generality of the method, structurally
different alcohols and phenols were submitted to the ac-
tion of the Er(III) triflate at 0.5 mol % in 1.5 equivalents
of propionic or pivaloyl anhydrides in dry acetonitrile.
No evident differences of reactivity were registered be-
tween primary (entries 3, 4, 21, and 22, Table 2) and sec-
ondary alcohols (entries 8, and 9, Table 2), or even be-
tween the two aliphatic anhydrides, and, again, no rear-
rangement took place for allylic and propargyl sub-
strates (entries 13, 14, 17 and 18, Table 2).
In order toextend the scope of this catalyst further, the
benzoylation of alcohols and phenols with the less reac-
tive benzoic anhydride was also investigated. The ben-
zoylation of 1-octanol was relatively slow in comparison
with the acylation usingother aliphatic carboxylic anhy-
drides, and only a 38% yield was obtained also after pro-
longed reaction time when the usual experimental pro-
tocol was applied. Better results were reached when
the reaction temperature was raised to 508C and
[2d]
cially with respect to our cerium(III) triflate method.
[10]
In fact, Sc(OTf) , which is much more expensive,
3
[
5c]
gave results quite similar to Er(OTf)3,
but by using
higher mol % of catalyst for acylations different from
acetylation and mixed anhydrides for propionic, pivalic
and trifluoroacetyl derivatives.
Er(OTf) is easy to handle and is one of the cheapest
3
commercially available lanthanoid triflate derivatives.
It is used in really catalytic amounts in the presence of
a very low excess of acyl anhydride. All acylation reac-
tions run smoothly at room temperature, except for
the most demandingbenzoylation, and almost under
neutral conditions. Moreover, it is possible to recover
the catalyst almost quantitatively and without a signifi-
cant loss of activity. Finally, to the best of our knowledge
Er(OTf) is the first triflate derivative proposed as a
3
Lewis acid catalyst in acylation reactions that shows
such a wide applicability.
3
.0 equivalents of benzoic anhydride were used in the
Experimental Section
presence of 0.5 mol % of Er(OTf) (entry 5, Table 2).
3
The present modified method permitted to easily obtain
benzoylated derivatives in almost quantitative yields,
not only from primary substrates (entries 5 and 25,
Table 2), but also from secondary ones (entry 10, Ta-
ble 2). Furthermore, also in the case of benzoylation,
no rearrangements were noted for allylic and propargyl
substrates (entries 15 and 19, Table 2).
Typical Procedures
In a model reaction 1-octanol (500 mg, 3.85 mmol) was added
to 1.0 mL of a solution of Ac O (0.590 g, 5.78 mmol) and
2
Er(OTf) (2.37 mg, 0.00385 mmol) in 5.0 mL of dry acetoni-
3
trile, the acetylation was complete in 20 min under these condi-
tions at room temperature affordinga 98% yield.
The Er(OTf) -benzoyl anhydride protocol was ap-
3
Acylations with propionic and pivalic anhydrides were still
plied with the same successful results in the benzoyla- conducted at room temperature but using0.5 mol %.
tion reaction of substituted phenols and the 4-me-
Acylationwith benzoic anhydride was carried out at 508C by
thoxy-, 4-methyl-, and 4-nitrophenol benzoylated deriv- using0.5 mol % of Er(OTf)
and 3.0 equivalents of Bz O.
3
2
Especially after pivalation and benzoylation the purification
of products requires a tedious work-up to separate the esters
from the remainingacyl anhydride. Therefore, methanol was
added at the end of the acylation reaction in order to convert
the remainingacyl anhydride to the correspondingmethyl es-
ter and after that, the product was obtained in sufficient purity
by simple filtration through a thin pad of silica gel with petro-
leum ether (60–808C).
atives were all obtained in excellent yields without evi-
dent differences in reactivity (entries 38, 42, and 47, Ta-
ble 2). Notably, the reported methods to form acyl esters
by usingLewis acid catalysts fail to mention the forma-
tion of trifluoroacetate derivatives and some of them ex-
[
4y]
plicitly declare failures in this attempt. Thus, we final-
ly extended the Er(OTf) -anhydride protocol to prepa-
3
ration of trifluoroacetate esters of alcohols and phenols.
All known products were identified by comparison of their
1
Both primary and secondary alcohols (entries 6, 11, 26 EI-MS and H NMR data with those of authentic compounds,
1468
ꢀ 2004 WILEY-VCH VerlagGmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
Adv. Synth. Catal. 2004, 346, 1465–1470

Erbium(III) Triflate as Acylation Catalyst
FULL PAPERS
when commercially available, and data reported in the litera-
[2] a) G. Bartoli, G. Cupone, R. Dalpozzo, A. De Nino, L.
Maiuolo, E. Marcantoni, A. Procopio, Synlett 2001, 189
7; b) G. Bartoli, G. Cupone, R. Dalpozzo, A. De Nino,
L. Maiuolo, A. Procopio, L. Sambri, A. Tagarelli, Tetra-
hedron Lett. 2002, 43, 5945; c) R. Dalpozzo, A. De Nino,
L. Maiuolo, A. Procopio, A. Tagarelli, G. Sindona, G.
Bartoli, J. Org. Chem. 2002, 67, 9093; d) R. Dalpozzo,
A. De Nino, L. Maiuolo, A. Procopio, M. Nardi, G. Bar-
toli, R. Romeo, Tetrahedron Lett. 2003, 44, 5621; e) G.
Bartoli, M. Bosco, R. Dalpozzo, E. Macantoni, M. Mas-
saccesi, S. Rivalsi, L. Sembri, Synlett 2003, 39; f) R. Dal-
pozzo, A. De Nino, L. Maiuolo, M. Nardi, A. Procopio,
A. Tagarelli, Synthesis 2004, 496.
[11]
ture.
EI-MS and H-NMR data of unknown compounds are listed
1
below.
1
Table 2, Entry 11: H NMR (300 MHz, CDCl ): d¼4.68 (m,
3
1
1
0
1
H, J¼10.86, 4.38 Hz), 1.94–2.03 (m, 1H), 1.80–1.93 (m, 1H),
.59–1.70 (m, 2H), 1.31–1.42 (m, 2H), 1.01–1.10 (m, 2H),
.88–0.97 (m, 6H), 0.76 (d, 3H, J¼6.96 Hz);GC-MS: m/z¼
þ
þ
83 [MÀCF ] (1), 138 [alcohol] (64), 95 [MÀ(CH ) CHÀ
3
3 2
þ
þ
CH ÀCF CO H] (100), 69 [CF3] (15); anal. calcd. for C
3
3
2
12
H F O : C 57.13, H 7.59, F 22.59, O 12,69; found: C 57.20, H
19
3
2
7
.60.
1
Table 2, Entry 18: H NMR (300 MHz, CDCl ): d¼4.63 (d,
3
2
H, J¼2.28 Hz), 2.40 (t, 1H), 1.18 (s, 9H); GC-MS: m/z¼85
þ
þ
[
3] a) W. Green, P. G. M. Wuts, Protective Groups in Organ-
[(CH ) CCO] (16), 57 [(CH ) C] (100), 55 [MÀ(CH )
3
3
þ
3
3
3 3
rd
CCO] (5); anal. calcd. for C H O : C 65.60, H 9.44, O
ic Synthesis, 3 edn., Wiley, New York, 1999, p. 150;
7
12
2
2
4.96; found: C 65.55, H 9.45.
b) A. L. Pearson, W. J. Roush, Handbook of Reagents
for Organic Synthesis: Activating Agents and Protecting
Groups, John Wiley and Sons, Chichester, 1999, p. 9;
c) P. J. Kocienski, Protecting Groups, George Thieme
Verlag, Stuttgart, 1994, p. 23.
1
Table 2, Entry 32: H NMR (300 MHz, CDCl ): d¼5.43 (m,
3
1
H), 4.823 (m, 1H), 2.36–2.50 (m, 2H, CH ), 2.01–2.05 (m, 2H,
2
CH ), 1.80–1.95 (m, 6H, 3CH ), 1.65–1.74 (m, 2H CH ), 1.40–
2
2
2
1
4
0
.60 (m, 8H, 3CH and 2CH), 1.06–1.25 (m, 8H, 2CH and
CH), 1.04 (s, 3H, CH ), 0.916 (d, 3H, J¼6.531 Hz, CH ),
2
2
3
3
[4] a) D. Horton, Organic Synthesis Collective Vol. V, Wiley:
New York, 1991, pp. 1–6; b) R. I. Zhdanov, S. M. Zheno-
darova, Synthesis 1975, 222; b) W. Steglich, G. Höfle, An-
gew. Chem. Int. Ed. Engl. 1969, 8, 981; G. Höfle, W. Steg-
lich, H. Vorbrüggen, Angew. Chem. Int. Ed. Engl. 1978,
17, 569; E. F. V. Scriven, Chem. Soc. Rev. 1983, 12, 129;
c) T. Sano, K. Ohaschi, T. Oriyama, Synthesis 1999,
1141; d) E. Vedejs, N. S. Bennett, L. M. Conn, S. T. Div-
er, M. Gingras, S. Lin, P. A. Oliver, M. J. Peterson, J. Org.
Chem. 1993, 58, 7286; E. Vedejs, S. T. Diver, J. Am.
Chem. Soc. 1993, 115, 3358; E. Vedejs, O. Daugulis,
S. T. Diver J. Org. Chem. 1996, 61, 430; e) H. Hagiwara,
K. Morohashi, H. Sakai, T. Suzuki, M. Ando, Tetrahe-
dron 1998, 54, 5845; f) A. C. Cope, E. Herrick, C. Org.
Synth. 1963, 4, 304; g) R. H. Baker, F. G. Bordwell,
Org. Synth. 1955, 3, 141; h) R. Borah, N. Deka, J, C. Sar-
ma, J. Chem. Res. Synopsis 1997, 110; K. P. R. Kartha,
R. A. Field, Tetrahedron 1997, 53, 11753; i) T. S. Jin,
J. R. Ma, Z. H. Zhang, T. S. Li, Synth. Commun. 1998,
.876 (d, 3H, J¼1.35 Hz, CH ), 0.854 (d, 3H, J¼1.357 Hz,
3
þ
CH ), 0.68 (s, 3H, CH ); GC-MS: m/z¼368 [MÀCF COO]
3
3
3
þ
(
6
100), 255 [MÀCF CO HÀ(CH ) CH(CH ) CHCH ] (43),
3
2
3
2
2
3
3
þ
9 [CF ] (41); anal. calcd. for C H F O : C 72.17, H 9.40, F
3 29 45 3 2
11.80, O 6.63; found: C 72.10, H 9.40.
1
Table 2, Entry 42: H NMR (300 MHz, CDCl ): d¼8.10–
3
8.40 (m, 2H, Ar), 7.45–7.65 (m, 3H, Ar), 7.05–7.25 (m, 3H,
þ
Ar), 2.37 (s, 3H, J¼0.21 Hz, CH ); GC-MS: m/z¼212 [M]
3
þ
þ
(
9), 105 [PhCO] (100), 77 [C H ] (40); anal. calcd. for
6 5
C H O : C 79.23, H 5.70, O 15.07; found: C 79.30, H 5.65.
1
4
12
2
1
Table 2, Entry 45: H NMR (300 MHz, CDCl ): d¼8.23–
3
8
7
1
.32 (m, 2H, Ar), 7.24–7.33 (m, 2H, Ar), 2.65 (q, 2H, J¼
.51 Hz, CH ), 1.29 (t, 3H, J¼7.51 Hz, CH ); GC-MS: m/z¼
2
3
þ
þ
þ
95 [M] (3), 139 [alcohol] (2), 57 [CH CH CO] (100);
3
2
anal. calcd. for C H NO : C 55.38, H 4.65, N 7.18, O 32.79;
found: C 55.30, H 4.65, N 7.20.
9
9
4
1
Table 2, Entry 46: H NMR (300 MHz, CDCl ): d¼8.22–
3
8.30 (m, 2H, Ar), 7.21–7.28 (m, 2H, Ar), 1.37 [s, 9H, (CH )
3
3
þ
þ
C], GC-MS: m/z¼223 [M] (1), 85 [(CH ) CCO] (24), 57
3
3
þ
[(CH ) C] (100); anal. calcd. for C H NO : C 59.19, H
3 3 11 13 4
2
8, 3173; j) E. Vedejs, O. Daugulis, J. Org. Chem. 1996,
5.83, N 6.28, O 28.70; found: C 59.12, H 5.80, N 6.24.
1
61, 5702; S. V. Pansare, M. G. Malusare, A. N. Rai, Synth.
Commun. 2000, 30, 2587; k) J. Iqbal, R. R. Srivastava, J.
Org. Chem. 1992, 57, 2001; l) S. Chandrasekhar, T. Ram-
achander, M. Takhi, Tetrahedron Lett. 1998, 39, 3263;
m) T. Okano, K. Miyamoto, K. Kiji, Chem. Lett. 1995,
Table 2, Entry 47: H-NMR (300 MHz, CDCl ): d¼8.34 (d,
3
2
H, J¼8.15 Hz, H þH ), 8.21 (d, 2H, J¼8.15 Hz, H þ
B1
B1’
A
H ), 7.69 (t, 2H, J¼7.52 Hz, H þH ), 7.55 (t, 2H, J¼
A’
A1
A1’
7
.52 Hz, H þH ) 7.43 (d, 2H, J¼7.52 Hz, H ); GC-MS:
B2
B2’
C2
þ
þ
m/z¼243 [M] (0.1), 105 [MÀPhCO] (100), 77 (31); anal.
2
45; n) G. W. Breton, J. Org. Chem. 1997, 62, 8952;
o) A. X. Li, T. S. Li, T. H. Ding, Chem. Commun. 1997,
389; p) S. S. Rana, J. J. Barlow, K. L. Matta, Tetrahedron
calcd. for C H NO : C 64.20, H 3.73, N 5.76, O 26.31; found:
13
9
4
C 64.15, H 3.70, N 5.80.
1
Lett. 1981, 22, 5007; G. W. Breton, M. J. Kurtz, S. L.
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207; r) S. Paul, P. Nanda, R. Gupta, A. Loupy, Tetrahe-
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M. Mittal, Tetrahedron 2001, 57, 7047; t) B. M. Choudary,
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8
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8, 3569.
[
9] The purity of recovered Er(OTf) was confirmed by com-
3
parison with the IR spectrum of commercial product.
[
10] Er(OTf) and Sc(OTf) can be purchased from Aldrich at
3
3
4
1.00 (5 g) and 206.4 (5 g) respectively.
[
11] Table 2, Entries 1, 7, 12, 16, 20–22, 27–31, 33–35, 39, 44,
[2d]
4
8, 49: see ref. Table 2, Entries 2, 3: Y. N. Min, L. H.
1470
ꢀ 2004 WILEY-VCH VerlagGmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
Adv. Synth. Catal. 2004, 346, 1465–1470