Dual behavior of alcohols in iodine-catalyzed esterification under solvent-free reaction conditions

Article abstract of DOI:10.1016/j.tetlet.2009.02.224

The dual behavior phenomenon of alcohols in iodine-catalyzed esterification under solvent-free reaction conditions (SFRCs) is described; the governing factor is the stability of the carbonium ion generated from the alcohol; high concentration reaction conditions (HCRCs) or dilute solutions are much less suitable. In the case of benzylic alcohols, loss of optical activity was noted, whereas alkyl alcohols furnished a product with retention of stereochemistry.

Full text of DOI:10.1016/j.tetlet.2009.02.224

Tetrahedron Letters 50 (2009) 2347–2352
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Dual behavior of alcohols in iodine-catalyzed esterification under
solvent-free reaction conditions
*
ˇ ˇ
Marjan Jereb , Dejan Vrazic , Marko Zupan
ˇ
Faculty of Chemistry and Chemical Technology, University of Ljubljana, Aškerceva 5, PO Box 537, 1001 Ljubljana, Slovenia
a r t i c l e i n f o
a b s t r a c t
Article history:
The dual behavior phenomenon of alcohols in iodine-catalyzed esterification under solvent-free reaction
conditions (SFRCs) is described; the governing factor is the stability of the carbonium ion generated from
the alcohol; high concentration reaction conditions (HCRCs) or dilute solutions are much less suitable. In
the case of benzylic alcohols, loss of optical activity was noted, whereas alkyl alcohols furnished a product
with retention of stereochemistry.
Received 10 November 2008
Revised 3 February 2009
Accepted 27 February 2009
Available online 5 March 2009
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
Iodine
Catalyst
Esterification
Solvent-free
1. Introduction
kenes and further into indane derivatives in the presence of iodine
under SFRC.10 We have also demonstrated that iodine is able to dis-
Important tasks of modern chemistry are preservation of the
environment and the development of new methods and technolo-
gies.1 One of the important strategies is performing reactions with-
out the use of a solvent.2 However, transformations under solvent-
free reaction conditions (SFRCs) can undergo a different scenario,
while heat exchange is very important particularly in exothermic
reactions.3 Recently, the important role of a small amount of sol-
vent in solid-state reactions and reactions under highly concen-
trated conditions was established.4 Esterification is an important
transformation in organic chemistry,5 and several different ap-
proaches for this reaction have been developed.6 More reactive
precursors can be employed for esterification, but acids and alco-
hols in conjunction with a Lewis catalyst are still primarily used.7
A Lewis catalyst could activate either the alcohol or acid depending
on its structure, which is finally reflected in the stereochemistry of
the reaction product. However, the principal drawbacks of the
majority of Lewis catalysts are moisture-sensitivity, high cost,
and toxicity. Many esterification methods require azeotropic re-
moval of water, or at least the presence of a drying agent. Iodine
is a versatile and mild Lewis catalyst for the activation of alcohols
and acids.8 Recently, research was published describing iodine-cat-
alyzed esterification with a large excess of alcohol at an elevated
temperature and this method appears to be highly water tolerant.9
We have already shown that alcohols can be transformed into al-
criminate between H2O, MeOH, and H2O2 and, on the other hand,
between OH, OMe, and OOH groups.11 In order to clarify the role
of iodine in the transformation of alcohols in the presence of acids
under SFRC, the dual behavior of alcohols in esterification reactions
is described in this Letter.
Initially, the esterification of cyclohexanol with acetic acid at
85 °C in a 1:1 molar ratio with and without I2 was studied. After
2.5 h, only trace amounts of ester were detected without I2; in
the presence of iodine (3 mol %) a conversion of 61% was achieved.
The reaction could be further accelerated (85% conversion) using a
twofold molar excess of acid, indicating that a much lower excess
was necessary than that mentioned in studies already published.9
Encouraged with this finding, we studied the effect of the structure
of the alcohol on the course of the esterification (Table 1). It is evi-
dent that pentanol 1a and hexadecanol 1b could be readily esteri-
fied in high yields (entries 1 and 2). It is known that the ring size of
cycloalkanols plays an important role when the formation of carb-
ocationic intermediates is the main reaction route. Cyclopentanol
was the most reactive and the reactivity of the cycloalkanols de-
creased slightly with increased ring size (entries 3, 5, 7, and 9);
alcohols 1c–f were converted efficiently to the corresponding es-
ters (entries 4, 6, 8, and 10).
Interestingly, HCOOH (3 equiv) reacted efficiently (85–96%)
with alcohols 1a–f without I2, while in the presence of I2 up to
5% higher conversion was achieved. Next, we evaluated the role
of water in the iodine-catalyzed esterification of cyclooctanol
and, as seen in Figure 1, the conversion decreased from 86% to
44% as the water content increased (up to 9 mmol).
* Corresponding author. Tel.: +386 1 241 92 48; fax: +386 241 92 20.
E-mail address: marjan.jereb@fkkt.uni-lj.si (M. Jereb).
ˇ
Present address: Jozef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia.
0040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2009.02.224

2348
M. Jereb et al. / Tetrahedron Letters 50 (2009) 2347–2352
Table 1
The role of alcohol 1 in the iodine-induced esterification with acetic acid 2b
O
R1
I2
R1-OH
+
CH3COOH
O
CH3
3
1
2b
Entry
Alcohol
1
Reaction conditionsa
3
Conversionb (%)
1
2
3
4
5
6
7
8
9
CH3(CH2)3CH2OH
CH3(CH2)14CH2OH
a
b
c
c
d
d
e
e
f
A / 2.5 h
A / 2.5 h
B / 0.5 h
A / 2.5 h
B / 0.5 h
A / 2.5 h
B / 0.5 h
A / 2.5 h
B / 0.5 h
A / 2.5 h
ab
bb
cb
cb
db
db
eb
eb
fb
88 (74)
93 (85)
61
89 (68)
50
85 (70)
44
86 (71)
45
n = 1
n = 1
n = 2
n = 2
n = 3
n = 3
n = 4
n = 4
OH
CH2
n
10
f
fb
85 (71)
a
1 mmol of 1, (A) 3 mmol of 2b; (B) 1 mmol of 2b and 0.03 mmol of I2, 85 °C.
b
Conversion determined by 1H NMR, values in parentheses refer to isolated yields.
100
CH3COOH. The sole product in each case was the acetate ester with
complete retention of configuration.
86
90
80
70
60
50
40
30
20
10
0
All these examples favor activation of the acid or both reactants
and are against the formation of carbocationic intermediates. Nor-
bornenol is known to undergo esterification with HCOOH when
used in large excess,12 however, 4c and 4d furnished the expected
formate esters in 93–94% yields with 3 equiv of HCOOH. Alcohols
4a and 4e gave formate analogues in 67% and 69% conversion with-
out I2, and in 89% and 95% conversion in the presence of I2. In addi-
tion, we investigated the effect of the amount of acid on the
conversion of (À)-menthol (Fig. 2). After 7 h, using 1 equiv of
CH3COOH, we achieved 65% conversion, however, the conversion
rose to 83% when using 3 equiv of CH3COOH.
68
57
44
Introduction of a phenyl ring to a saturated carbon atom en-
hances the stability of carbonium ions when formed.
0
3
6
9
H2O (mmol)
Consequently, we investigated both the electronic and steric
stabilizing effects on benzyl alcohol 6a and 1-phenylethanol 6b
(Scheme 1 and Table 3). Both alcohols reacted readily (85% and
74% conversion) with HCOOH without I2, but conversion in the
presence of I2 was higher (entries 1 and 5). Acetic acid is less reac-
tive than formic acid, whilst octanoic and benzoic acids are far less
reactive (entries 2–4). A careful analysis of the crude reaction mix-
ture revealed the presence of another type of product, namely
dibenzyl ether 7a (entry 3), which was a major product in the case
of benzoic acid (entry 4). Alcohol 6b is less reactive than 6a, and
85% conversion into 8ba was achieved after 6 h, with only a small
amount of ether 7b being formed; its amount increased with long-
er reaction times (entries 6 and 7). Propionic acid is a little less
reactive than acetic acid, as reflected in the higher dimer propor-
tion, similar to octanoic acid (entries 7–12). The reactivity of
branched and sterically hindered and solid acids is still lower
and the amount of 7b is increased (entries 13–18). Finally, the ste-
reochemical outcome was tested utilizing (S)-Mosher’s acid and
the same result was obtained regardless of the absolute configura-
tion of 1-phenylethanol. An equimolar mixture of diastereoiso-
meric esters was formed accompanied by small amounts of 7b
(entries 19–21). This result strongly suggests that iodine activates
the alcohol, thus forming a cationic intermediate which conse-
quently leads to a loss of the stereochemical integrity.
Figure 1. The effect of the amount of water on the iodine (0.03 mmol) induced
esterification of cyclooctanol (1f, 1 mmol) with CH3COOH (3 mmol) (T = 85 °C,
2.5 h).
The transformation is suppressed to a significant extent, but
somewhat less than might be expected for a reversible reaction.
The role of water was examined further in the reaction of 1d/2b,
(1:1) where the drying agent Na2SO4 was added (40, 60, and
80 mol %). This brought no advantage, which however, means that
the water formed did not shift the equilibrium toward the
reactants.
From the above experiments it is evident that the acid is more
likely to be activated than the alcohol. Thus, the esterification of
alcohols where a stereochemical outcome and a potential rear-
rangement would be indicators of carbocationic intermediates
were examined (Table 2). Firstly, a mixture of trans/cis (66:34) 4-
tert-butylcyclohexanol 4a was reacted with CH3COOH and a mix-
ture of esters 5a was formed in almost the same ratio (67:33). This
indicates that activation of 4a did not take place and the involve-
ment of carbocations is less likely. Additionally, it was discovered
that the trans alcohol was more reactive than the cis stereoisomer.
Conversion of 4a after 14 h at 85 °C was 68%, while the trans/cis ra-
tio of acetate 5a was altered to 71:29 in favor of the trans isomer.
2-Adamantanol 4b was esterified to 5b without any rearrange-
ment. Norbornene derivatives are very sensitive to the Meerw-
ein–Wagner rearrangement and hydride shifts when cationic
species are intermediates. However, no rearrangement took place
and 5c and 5d were the exclusive products. Finally, the optically
pure menthol enantiomers 4e and 4f were esterified with
Introduction of a methoxy group to the phenyl ring can influ-
ence substantially the reaction course, particularly if cationic inter-
mediates are implicated. The reaction pathways are depicted in
Scheme 1. Indeed, 4-methoxybenzyl alcohol 6e exhibited the most
complex behavior in this study; it is much more reactive than 6a,
yet dimerization of 6e is more pronounced, and in addition ipso-
substitution also occurred without I2 (Table 4, entry 1).

M. Jereb et al. / Tetrahedron Letters 50 (2009) 2347–2352
2349
Table 2
The effect of the structure of alcohol 4 on the stereochemistry of esterifications with acetic acid 2b induced by iodine
Alcohol
Ester
Reaction timea (h)
24
Conversionb (%)
78 (70)
OH
OAc
Trans/cis = 1.9
Trans/cis = 2.0
t-Bu
t-Bu
5a
4a
OAc
OH
5
92 (75)
87 (72)
86 (69)
83 (78)
85 (81)
4b
5b
2.5
2.5
7
4c
5c
5d
OH
OAc
OH
OAc
4d
OAc
OH
Me
Me
Me
Me
Me
Me
Me
4e
5e
5f
OAc
OH
Me
Me
Me
Me
7
Me
4f
a
Reaction conditions: 1 mmol of 4, 3 mmol of 2b, and 0.03 mmol of I2, 85 °C.
b
Conversion determined by 1H NMR, values in parentheses refer to isolated yields.
90
decreased with the diminishing reactivity of the acid; concomi-
tantly, the latter two processes became more pronounced (entries
2 and 3). In the case of benzoic acid, the dimer 7c was the major
product along with 9, however, no ester was formed (entry 4). In
a separate experiment it was established that 9 was not formed
from 7c and benzoic acid in the presence of I2. 1-(4-Methoxy-
phenyl)ethanol 6f possesses a higher reactivity than 6e; high con-
versions were readily achieved at rt with all the acids tested
(entries 5–8). The highest proportion of dimer 7d was obtained
with benzoic acid (entry 8), while no ipso-substitution took place.
In an independent experiment, dimer 7d was reacted with HCOOH
in the absence of I2 and 77% conversion to the formate ester was
noted, 4% of 1-(4-methoxyphenyl)ethanol was also formed. In
addition, the role of the amount of acid and its structure on the
esterification of cyclohexanol 1d was investigated (Table 5). It is
evident that the molar ratio is an essential factor in terms of the
reaction progress. The reactivity of the acids decreases with length-
ening of the alkyl chain and with branching.
83
77
80
70
60
50
40
30
20
10
0
73
65
1
1.5
2
3
CH3COOH (mmol)
Figure 2. The effect of amount of acetic acid 2b on the iodine (0.03 mmol) induced
esterification of (À)-menthol (4e, 1 mmol, 85 °C, 7 h).
The role of the reaction conditions (SFRCs vs high concentration
reaction conditions HCRCs) and the role of iodine on esterification
reactions were examined (Table 6). It is evident that formic acid, in
contrast to acetic acid, reacts to a significant extent with all three
alcohols without iodine, confirming the important role of pKa (en-
tries 3, 9, and 15). The concentration of reactants was found to be
of paramount importance; the highest conversions were achieved
Both alcohols 6a and 6e reacted well (85% and 89%) with
HCOOH without I2, whereas the distribution of the products varied
only slightly from the catalyzed reaction. The proportion of ester

2350
M. Jereb et al. / Tetrahedron Letters 50 (2009) 2347–2352
6a: R1 = R2 = H
2a: R3 = H
2b: R3 = Me
2c: R3 = Et
6b: R1 = H, R2 = Me
6c: R1 = H, R2 = Me( R)
6d: R1 = H, R2 = Me( S)
6e: R1 = OMe, R2 = H
6f: R1 = OMe, R2 = Me
R2
R1
R3
2d: R3 = i-Pr
6
OH
3
2e
: R = t-Bu
2f: R3 = Heptyl
2g: R3 = Ph
2
HO
I2
2h: R3 = (S)-PhC(OMe)CF3
O
8aa: R1 = R2 = R3 = H
1
2
3
8ab
: R = R = H, R = Me
8af: R1 = R2 = H, R3 = Heptyl
8ag: R1 = R2 = H, R3 = Ph
8ba: R1 = R3 = H, R2 = Me
DIMERIZATION
R1
SUBSTITUTION
R1
1
2
3
8bb
: R = H, R = R = Me
7a: R1 = R2 = H
8bc: R1 = H, R2 = Me, R3 = Et
8
7b: R1 = H, R2 = Me
7c: R1 = OMe, R2 = H
7d: R1 = OMe, R2 = Me
7
8bd: R1 = H, R2 = Me, R3 = i-Pr
8be: R1 = H, R2 = Me, R3 = t-Bu
8bf: R1 = H, R2 = Me, R3 = Heptyl
8bg: R1 = H, R2 = Me, R3 = Ph
O
R2
O
R2
O
R3
R2
8bh: R1 = H, R2 = Me, R3 = (S)-PhC(OMe)CF3
8ea: R1 = OMe, R2 = R3 = H
R1
8eb: R1 = OMe, R2 = H, R3 = Me
8ef: R1 = OMe, R2 = H, R3 = Heptyl
8fa: R1 = OMe, R2 = Me, R3 = H
MeO
OMe
1
2
3
8fb
: R = OMe, R = R = Me
9
8ff: R1 = OMe, R2 = Me, R3 = Heptyl
8fg: R1 = OMe, R2 = Me, R3 = Ph
IPSO SUBSTITUTION
Scheme 1. Reaction pathways of benzylic alcohols in I2-catalyzed esterification under SFRC.
Table 3
tion conditions. Water has a surprisingly modest deteriorating
influence on the reaction. Formic acid exhibited the highest reac-
tivity among the tested acids since it reacted without iodine; long-
er chain aliphatic and branched chain acids were less reactive,
signifying the influence of pKa. The aliphatic alcohols, utilized as
stereochemical probe yielded esters with retention of stereochem-
istry, indicating that activation of the acid or both reactants takes
place. Loss of stereochemical integrity was observed in the case
of both chiral 1-phenylethanols suggesting carbocationic interme-
diates. Three types of transformation were established: esterifica-
tion, dimerization of the starting alcohol and ipso-substitution in
the case of 4-methoxybenzyl alcohol. Primary and secondary ben-
zylic alcohols are more reactive than aliphatic alcohols, whilst the
introduction of a methoxy group enhanced their reactivity.
Typical experimental procedure: To a stirred mixture of alcohol
(1 mmol) and acid (3 mmol), I2 (0.03 mmol) was added. The reac-
tion mixture was stirred at an appropriate temperature (reaction
temperature, 55 °C or 85 °C) until TLC showed complete or at least
high conversion of the starting material. The mixture was cooled to
room temperature, diluted with tert-butyl methyl ether, washed
with aqueous Na2S2O3, NaHCO3, and water and dried over anhy-
drous Na2SO4. The solution was filtered and the solvent removed
under reduced pressure. The crude reaction mixture was subjected
to column chromatography using hexane or petroleum ether/tert-
butyl methyl ether mixtures and pure product(s) were obtained.
The effect of carboxylic acid 2 and phenyl substituted alcohol 6 on iodine-induced
transformations
Entry
Alcohol
Acid
R3
Reaction conditionsa
Conv. (%)
Subst./Dim.
8:7
6
R2
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
a
a
a
a
b
b
b
b
b
b
b
b
b
b
b
b
b
b
b
c
H
H
H
H
H
Me
Heptyl
Ph
H
H
Me
Me
Me
3 h / 25 °C
92
87
88
86
85
89
46
84
82
43
81
81
31
75
15
72
77
84
88
88
90
100
100
91:9
44:56
98:2
24 h / 55 °C
74 h / 85 °C
192 h / 55 °C
6 h / 25 °C
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
144 h / 25 °C
20 h / 25 °C
144 h / 25 °C
17 h / 55 °C
20 h / 25 °C
144 h / 25 °C
72 h / 55 °C
20 h / 25 °C
144 h / 25 °C
20 h / 25 °C
144 h / 25 °C
72 h / 55 °C
22 h / 55 °C
166 h / 25 °C
166 h / 25 °C
166 h / 25 °C
89:11
74:26
81:19
80:20
50:50
69:31
68:32
32:68
50:50
17:83
26:74
48:52
43:57
94:6
Et
Et
Heptyl
i-Pr
i-Pr
t-Bu
t-Bu
t-Bu
Ph
M. A.b
M. A.b
M. A.b
97c:3
97c:3
d
Subst. = substitution; Dim. = dimerization.
a
1 mmol of 6, 3 mmol of 2, and 0.03 mmol of I2.
b
M. A. = Mosher‘s acid: (S)-(À)-
a
-methoxy-a-trifluoromethylphenylacetic acid.
c
Equimolar mixture of diastereoisomeric esters.
2. Spectral data of selected compounds
2.1. 4-Methoxybenzyl octanoate 8ef
under SFRC, reactions in CH2Cl2 under HCRCs were considerably
retarded (entries 1, 2, 7, and 8), while only a minor suppression
was noted in the case of 6f (entries 13 and 14). Reactivity under
SFRC is still unpredictable, HCOOH in many cases reacts without
a catalyst, exhibiting acidity that is a crucial parameter in combina-
tion with SFRC.
In conclusion, we have demonstrated that iodine is an efficient
dual role catalyst for esterification under solvent-free reaction con-
ditions, which are superior to dilute and high concentration reac-
Column chromatography (SiO2, petroleum ether/tert-butyl
methyl ether (15:1) and preparative TLC [SiO2, (petroleum ether/
tert-butyl methyl ether (97:3)], yield 42%, colorless oil, 1H NMR
(CDCl3, 300 MHz,): d 0.87 (t, J = 6.7 Hz, 3H), 1.14–1.38 (m, 8H),
1.49–1.70 (m, 2H), 2.32 (t, J = 7.5 Hz, 2H), 3.81 (s, 3H), 5.04 (s,
2H), 6.88 (d, J = 8.7 Hz, 2H), 7.29 (d, J = 8.7 Hz, 2H). 13C NMR (CDCl3,
75.5 MHz): d 14.0, 22.6, 25.0, 28.9, 29.1, 31.6, 34.4, 55.3, 65.9,

M. Jereb et al. / Tetrahedron Letters 50 (2009) 2347–2352
2351
Table 4
The role of a methoxy substituent on the phenyl ring of alcohol 6 and carboxylic acid structure 2 on iodine-induced transformations
Entry
6
R3
Reaction conditionsa
Conversion (%)
Subst./Dim./Ipso
8:7:9
1
2
3
4
5
6
7
8
6e
6e
6e
6e
6f
6f
6f
6f
H
Me
Heptyl
Ph
H
Me
Heptyl
Ph
0.67 h / 25 °C
3 h / 55 °C
5 h / 55 °C
1 h / 25 °C
0.5 h / 25 °C
6 h / 25 °C
6 h / 25 °C
6 h / 25 °C
100
98
92
61
100
96
74:13:13
75:2:23
63:11:26
68:32
90:10
67:33
85
92
79:21
37:63
a
1 mmol of 6, 3 mmol of 2, and 0.03 mmol of I2.
Table 5
The role of the structure of acid 2 on the iodine-induced esterification of cyclohexanol
1d
J = 8.7 Hz, 2H), 7.36 (d, J = 8.7 Hz, 2H), 7.40–7.46 (m, 2H), 7.48–
7.56 (m, 1H), 8.01–8.07 (m, 2H). 13C NMR (CDCl3, 75.5 MHz): d
22.1, 55.2, 72.6, 113.9, 127.5, 128.3, 129.6, 130.6, 132.8, 133.8,
159.3, 165.8. m/z (EI): 256 (M+, 30%), 135 (100), 105 (49), 77
(32). HRMS calcd for C16H16O3 256.1099, found 256.1103. IR (neat):
2978, 2934, 2836, 1715, 1611, 1515, 1451, 1269, 1248, 1176, 1111,
Acid R3COOH
Ratio
Reaction timea (h)
3
Conversionb (%)
R3
2
1d:2
Me
Me
Me
Et
i-Pr
t-Bu
b
b
b
c
d
e
1:1
1:2
1:3
1:3
1:3
1:3
2.5
2.5
2.5
2.5
6
db
db
db
dc
dd
de
61
78
85 (70)
86 (75)
84 (77)
83 (60)
1062, 1032, 831, 712 cmÀ1
.
2.3. Bis(1-phenylethyl) ether 7b
120
a
1 mmol of 1d, 1–3 mmol of 2, and 0.03 mmol of I2, 85 °C.
Column chromatography (SiO2, hexane), yield 81%, colorless oil
(a mixture of diastereoisomers), 1H NMR (CDCl3, 300 MHz): d 1.35
(J = 6.5 Hz, 6H) (major isomer), 1.44 (d, J = 6.4 Hz, 6H), 4.19 (q,
J = 6.5 Hz, 2H) (major isomer), 4.49 (q, J = 6.4 Hz, 2H), 7.02–7.37
(m, 20H). m/z (EI): 211 (M+ÀMe, 4%), 121 (15), 105 (100). IR (neat):
3061, 3029, 2974, 2928, 2880, 1491, 1449, 1368, 1205, 1091, 1029,
b
Conversion determined by 1H NMR, values in parentheses refer to isolated yields.
113.9, 128.3, 130.0, 159.6, 173.8. IR (neat): 2929, 2856, 1736, 1614,
1514, 1462, 1249, 1162, 1109, 1036, 822 cmÀ1. Anal. Calcd for
C16H24O3: C, 72.69; H, 9.15. Found: C, 72.83; H, 9.41.
948, 760, 700 cmÀ1
Acknowledgements
We are grateful to Dr. B. Kralj and Dr. D. Zigon at the Mass Spec-
.
2.2. ( )-(4-Methoxyphenyl)ethyl benzoate 8fg
Column chromatography (SiO2, tert-butyl methyl ether), yield
20%, viscous colorless oil, 1H NMR (CDCl3, 300 MHz): d 1.66 (d,
J = 6.6 Hz, 3H), 3.79 (s, 3H), 6.09 (q, J = 6.6 Hz, 1H), 6.87 (d,
ˇ
ˇ
troscopy Centre at the ‘Jozef Stefan’ Institute in Ljubljana, to Profes-
Table 6
The effect of reaction conditions, alcohol and acid structure on transformations: SFRC vs solution
Alcohol
OH
Entry
Acid
I2 (%)
Reaction conditionsa
Reaction time (h)
Conversion. (%)
1
2
3
4
5
6
2a
2a
2a
0
0
0
3
0
3
A
B
SFRC
SFRC
SFRC
SFRC
6
6
6
6
2.5
2.5
27
13
88
94
9
2a
2bb
2bb
86
OH
7
8
9
10
11
12
2a
2a
2a
0
0
0
3
0
3
A
B
SFRC
SFRC
SFRC
SFRC
3
3
3
3
24
24
13
7
85
92
15
87
2a
2bc
2bc
13
14
15
16
17
18
2a
2a
2a
2a
2b
2b
0
0
0
3
0
3
A
B
SFRC
SFRC
SFRC
SFRC
0.5
0.5
0.5
0.5
6
80
60
89
100
8
Me
OH
6
96
OMe
a
b
c
1 mmol of alcohol, 3 mmol of acid with or without 0.03 mmol of iodine: SFRC or addition of CH2Cl2: A—1 mL, B—2 mL at 25 °C.
85 °C.
55 °C.

2352
M. Jereb et al. / Tetrahedron Letters 50 (2009) 2347–2352
Locatelli, M.; Massaccesi, M.; Melchiorre, P.; Sambri, L. Adv. Synth. Catal. 2005,
ˇ
ˇ
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