Exploring the reaction of iodine with α-diazo esters

Article abstract of DOI:10.1002/poc.1420

In this paper we describe the unprecedented reaction between a-diazo esters 1 and iodine. The reaction, carried out in the presence of aqueous NaHCO ₃, afforded the Z-isomer of the corresponding unsaturated-2-iodo ester 8, The configuration of

Full text of DOI:10.1002/poc.1420

Research Article
Received: 25 February 2008,
Revised: 9 June 2008,
Accepted: 12 June 2008,
Published online in Wiley InterScience: 11 July 2008
(www.interscience.wiley.com) DOI 10.1002/poc.1420
Exploring the reaction of iodine with
a-diazo esters
a
a
a
*
Giancarlo Verardo , Paola Geatti and Alberto Gambi
In this paper we describe the unprecedented reaction between a-diazo esters 1 and iodine. The reaction, carried out in
the presence of aqueous NaHCO3, afforded the Z-isomer of the corresponding unsaturated-2-iodo ester 8. The
configuration of compounds 8 was determined using the 3JC—H coupling between carbonyl carbon atom and alkene
proton. Mechanistic considerations accounting for the observed phenomena and including quantum chemical
calculations are proposed. Copyright ß 2008 John Wiley & Sons, Ltd.
Keywords: amino acid esters; a-diazo esters; alkyl nitrites; iodine; unsaturated iodo esters; ab initio calculations
the reaction mixture was treated with a saturated sodium
INTRODUCTION
metabisulphite solution and analysed by GC–MS. The GC–MS
profile showed the presence of eight reaction products, identified
as methyl (Z)-4-methyl-2-pentenoate (2a), methyl (E)-4-methyl-
2-pentenoate (3a), methyl 4-methyl-2-oxopentanoate (4a),
methyl 2-hydroxy-4-methylpentanoate (5a), methyl 2-iodo-
A few years ago, we have studied the reaction of some diazo
compounds[1,2] in the presence of a ruthenium(II) organometallic
catalyst. As an extension of our interest in this field, we have now
investigated in detail the reaction of iodine with a-diazo
esters[3–5] yielding the Z-isomer of the corresponding 2-iodo-
2-unsaturated esters. These derivatives, usually prepared via the
condensation reaction of aldehydes with arsonium salts[6] or
(ethoxycarboxyiodomethyl)triphenylphosphonium iodide,[7–9]
are useful building blocks in the Sonogashira coupling
reaction.[10]
It is well documented that the reaction of halogens with
diazoalkanes or a-diazo ketones produces gem-dihalides.[11–21] In
the particular case of phenylselenyl halides, subsequent
oxidation of the selenium atom allowed the formation of
2-halo-2-unsubstituted carbonyl compounds.[22–24]
In contrast, the reaction of halogens, and in particular iodine,
with a-diazo esters has no precedent so far. In fact, only two
reports described the use of a-diazo esters in the formation of the
corresponding (Z)-2-fluoro-, (E)- and/or (Z)-2-bromo- and (Z)-2-
iodo-2-unsaturated esters, but these reactions were carried out in
the presence of phenylselenyl fluoride[23] and the hexafluoropho-
sphate of bis(sym-collidine)bromine(I) or iodine(I),[25] respectively.
In particular, the reaction leading to the iodo esters was tested
only with a substrate and the main reaction product was the
(Z)-2-unsubstituted ester due to the decomposition by collidine
of the diazo group.
The aim of this contribution is to describe and rationalize,
including quantum chemical calculations, the experimental
results observed exploring the reaction of iodine with some
a-diazo esters prepared according to Takamura[4] but using
tert-butyl nitrite as diazotizing agent and CH2Cl2 as solvent.
4-methylpentanoate
(6a), methyl (E)-2-iodo-4-methyl-2-
pentenoate (7a), methyl (Z)-2-iodo-4-methyl-2-pentenoate (8a)
and methyl 2,2-diiodo-4-methylpentanoate (9a). It is interesting
to notice that compounds 4a, 5a and 8a made up some 94% of
the total amount (Scheme 1), as determined from the integrated
gas chromatographic peaks, and the main product was the
unsaturated iodo ester 8a (68%, GC yield) and not the saturated
geminal diiodo derivative 9a (1%, GC yield) as described for
a-diazo ketones.
We proposed the mechanistic pathway depicted in Scheme 3
for the formation of compounds 2a–9a taking into consideration
that (i) the CH2Cl2 solution of a-diazo ester 1a,[4] was utilized in
the subsequent reaction with iodine without purification and
therefore excess tert-butyl nitrite, acetic acid and water were
present (Scheme 2), and (ii) the tert-butyl nitrite-iodine system
was found to oxidize secondary alcohols to ketones.[26]
The reaction of iodine with the a-diazo ester 1a yields the
a-iodo-a-diazonium ion 10 (Scheme 3, path a) which, in the
presence of iodide ion or water, losses a proton and N2 to
give the unsaturated iodo ester 8a, the main reaction product,
and its isomer 7a (Scheme 3, path b). The reaction of 10 leading
to the saturated diiodo ester 9a is disfavoured probably because
of steric hindrance. The a-diazo ester 1a may also react with
a proton (acetic acid and HI present) to give the diazonium ion 11
(Scheme 3, path c) which produces the methyl 2-hydroxy-
4-methylpentanoate (5a) and the methyl 2-iodo-4-
methylpentanoate (6a) by the reaction with water or iodide
*
Correspondence to: G. Verardo, Department of Chemical Sciences and Tech-
nology, University of Udine, via del Cotonificio 108, I-33100, Udine, Italy.
E-mail: giancarlo.verardo@uniud.it
RESULTS AND DISCUSSION
Our first approach to this reaction was the slow addition of a
mixture of iodine in CH2Cl2 to a vigorously stirred solution of
methyl 2-diazo-4-methylpentanoate (1a) in CH2Cl2 at 0 8C under
argon and in the dark. After stirring at room temperature for 4 h,
a
G. Verardo, P. Geatti, A. Gambi
Department of Chemical Sciences and Technology, University of Udine, via
del Cotonificio 108, I-33100, Udine, Italy
J. Phys. Org. Chem. 2009, 22 24–30
Copyright ß 2008 John Wiley & Sons, Ltd.

REACTION OF IODINE WITH ꢀ-DIAZO ESTERS
Scheme 1. Reaction of methyl 2-diazo-4-methylpentanoate (1a) and iodine. The numbers in parentheses represent the percentages calculated from the
integrated gas chromatographic peaks
ion, respectively. Finally, compound 5a may be oxidized[26] to
methyl 4-methyl-2-oxopentanoate (4a) and, in the presence of HI,
it forms 6a by a substitution reaction or the two isomeric
unsaturated esters 2a and 3a by dehydration.
When the reaction was carried out with the a-diazo ester 1a
obtained after purification (refer to Experimental Section) from
acetic acid and excess tert-butyl nitrite (Scheme 2), the GC–MS
profile showed that, also in this case, the main reaction product
was 8a (66%, GC yield) but the second most abundant one was
the saturated iodo ester 6a (20%, GC yield). Furthermore, as
expected under these reaction conditions, we did not observe
the presence of methyl 4-methyl-2-oxopentanoate (4a) because
excess tert-butyl nitrite was previously eliminated under reduced
pressure.
At this point, as the precursor of the main side products was
the diazonium ion 11 (Scheme 3, path c), the neutralization of the
acidity produced in path b (Scheme 3) should favour path a and
then the formation of 8a (Scheme 3, path b).
Indeed, when iodine was slowly added to a vigorously stirred
mixture of 1a in CH2Cl2 and saturated aqueous NaHCO3 at 0 8C in
the dark, the GC–MS analysis of the reaction mixture, obtained
after stirring for 4 h at room temperature, showed that the yield of
8a was increased to 89%. Column chromatography (silica gel;
hexane/Et2O, 97:3) of the residue obtained after work-up gave 8a
in 66% yield. The same result was obtained when the reaction
was carried out with 1a obtained from the racemic mixture of
leucine methyl ester.
calculations to characterize the relevant regions of the ground
state potential energy surface (PES) associated with the proposed
reactions.
Density functional theory (DFT) calculations were carried out to
model the ground state PES for the reactions starting from
Scheme 2, where the a-amino ester (leucine methyl ester,
LeuMe), gives 1a, and all the other pathways described in
Scheme 3.
These DFT calculations were run using the Gaussian
03 program package[27] and performed with the B3LYP method
which combines Becke’s three-parameter nonlocal hybrid
exchange potential[28,29] with the nonlocal correlation functional
of Lee et al.,[30] and the 6–31þG(d,p) standard basis set. The MidiX
basis set,[31] as implemented in the Gaussian package, was used
for the iodine atom.
For all the molecules involved in the reactions described in
Schemes 2 and 3, the structures were optimized to determine the
nature of any stationary points. PES has therefore been generated
for molecules with the overall stoichiometry C11H24O4N2I2. For
the intermediate compounds 10 and 11, the iodide salts labelled
as 10a and 11a, respectively, were taken into account during the
calculations.
Additional self-consistent reaction field (SCRF) calculations
were performed to take into account the solvent effect for all the
molecules in CH2Cl2 (e ¼ 8.93) at 0 8C. Analytic frequency
calculations were performed using the same SCRF method
and model chemistry. From the output of these computations the
zero-point energy (ZPE) corrections to the total electronic energy
are available together with the thermal enthalpies and Gibbs free
Following our efforts to investigate theoretically the reactions
of iodine with a-diazo esters, we performed electronic structure
Scheme 2.
J. Phys. Org. Chem. 2009, 22 24–30
Copyright ß 2008 John Wiley & Sons, Ltd.
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G. VERARDO, P. GEATTI AND A. GAMBI
Scheme 3. Proposed mechanism pathway for the formation of compounds 2a–9a
energies. For all surfaces, the molecules must fulfil the
stoichiometric requirements of that surface. The total energy
of the chosen initial step, labelled with START and corresponding
to the preparation of the a-diazo ester 1a (Scheme 2), was taken
as the global zero, that is the reference point for all the other
species formed. These energy data are collected in Table 1
whereas in Fig. 1 are depicted the reaction pathways leading to
the formation of the observed species.
Table 1. Relative energies, enthalpies and Gibbs free energies (in unit of kJ/mol) of the stationary points, all having the overall
stoichiometry C11H24O4N2I2, located in this study
Gas, 0 K
CH2Cl2, 273.15 K
DE
DE
0.0
DH
DG
0.0
START
LeuMe þ t-BuONO þ I2
1a þ t-BuOH þ I2 þ H2O
10a þ t-BuOH þ H2O
0.00
ꢀ91.43
ꢀ55.59
ꢀ208.85
ꢀ220.69
ꢀ271.69
24.67
0.0
ꢀ123.17
A
B
C
D
E
AA
F
G
H
I
ꢀ107.55
ꢀ154.33
ꢀ65.41
ꢀ73.97
ꢀ71.95
7a þ N2 þ H2O þ HI þ t-BuOH
8a þ N2 þ H2O þ HI þ t-BuOH
9a þ N2 þ H2O þ t-BuOH
1a þ t-BuOI þ HI þ H2O
11a þ H2O þ t-BuOI
ꢀ222.66
ꢀ235.54
ꢀ276.69
16.26
ꢀ252.78
ꢀ266.21
ꢀ291.40
ꢀ12.25
ꢀ330.91
ꢀ346.41
ꢀ324.94
ꢀ37.28
ꢀ5.93
ꢀ13.67
ꢀ21.94
ꢀ18.48
6a þ N2 þ H2O þ t-BuOI
5a þ N2 þ HI þ t-BuOI
ꢀ214.88
ꢀ172.47
ꢀ150.20
ꢀ147.04
ꢀ219.82
ꢀ219.75
ꢀ174.19
ꢀ167.65
ꢀ164.76
ꢀ222.83
ꢀ231.86
ꢀ195.58
ꢀ197.79
ꢀ198.20
ꢀ256.77
ꢀ266.59
ꢀ224.99
ꢀ272.38
ꢀ269.11
ꢀ343.93
2a þ N2 þ HI þ H2O þ t-BuOI
3a þ N2 þ HI þ H2O þ t-BuOI
4a þ N2 þ 2HI þ t-BuOH
J
K
In the first column total energies for the gas phase at 0 K are reported. The last three columns report, respectively, the total energies,
enthalpies and Gibbs free energies for the molecules in CH2Cl2 solvent at 273.15 K.
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Copyright ß 2008 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2009, 22 24–30

REACTION OF IODINE WITH ꢀ-DIAZO ESTERS
Figure 1. Schematic potential energy diagram for the reactions described in Schemes 2 and 3.The values are the relative Gibbs free energies (in kJ/mol)
reported in Table 1
The first column of Table 1 reports the total energies for the
molecules taken in the gas phase at 0 K and in the last three
columns are reported the total energies, the enthalpies and Gibbs
free energies for the solution in CH2Cl2 at 0 8C, respectively.
The comparison of the energies involved in the reactants and
products is based on the Gibbs free energies in order to take into
account the entropic factor which becomes significant when the
number of molecular species change. In Fig. 1 ‘path c’, which is
related to the release of Hþ during the formation of 8a (refer to
text above), is also reported.
As can be seen from Table 1 and Fig. 1, the most energetically
favourable pathways direct to the production of 8a and 4a. The
differences in energies among the several stable compounds are
consistent with the relative yields assessed experimentally.
The focus of this study was on the thermodynamics of the
reactions investigated. The transition states and kinetics were not
considered because of their complexity for this kind of reactions
and therefore, there can be large energy barriers between
reactants and products. However, the thermodynamics of the
reactions enable the identification of the energetically most
favourable reaction paths.
Barton et al.[32] reported that 3b-hydroxy-5a-pregnan-20-one
hydrazone in the presence of iodine and Et3N gave, under the
influence of the base, 20-iodo-5a-pregn-20-en-3b-ol according to
the mechanism reported in Scheme 4.
In our case, we have proposed (Scheme 3) that compound 8a
arises from the diazonium ion 10 and not from the geminal
diiodo derivative 9a because (i) the reaction proceeds also in the
absence of a base, (ii) the reaction of iodide with 10 leading to 9a
is affected by steric hindrance and, finally, (iii) when the reaction
was carried out in the presence of NaHCO3, the GC–MS analysis of
the reaction mixture showed that 8a and 9a were present in the
Scheme 4.
J. Phys. Org. Chem. 2009, 22 24–30
Copyright ß 2008 John Wiley & Sons, Ltd.
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G. VERARDO, P. GEATTI AND A. GAMBI
Chart 1.
ratio 89:1 which remained the same after 4 days with a pH of the
final reaction mixture of ca. 9. This is a clear indication that the
unsaturated halo ester 8a did not come from the saturated dihalo
ester 9a.
carrier gas). After preliminary compound identification with the
help of the available mass spectral libraries (Wiley and NIST mass
spectral database), each recorded spectrum was carefully
examined to securely establish the nature of the eluted
component. IR spectra were obtained with a Nicolet FT-IR Magna
550 spectrophotometer from a thin film supported on KBr disks
We extended the reaction to the a-diazo derivatives of leucine
benzyl ester (1b), phenylalanine methyl ester (1c),
4-chlorophenylalanine (1d) and 4-methylphenylalanine (1e)
ethyl ester. The GC–MS analysis evidenced that also in these
cases the main reaction product was the Z-isomer of the
unsaturated iodo ester 8. After silica gel chromatography benzyl
(Z)-2-iodo-4-methyl-2-pentenoate (8b), methyl (Z)-2-iodo-3-
phenyl-2-propenoate (8c), ethyl (Z)-3-(4-chlorophenyl)-2-iodo-2-
propenoate (8d)[9] and ethyl (Z)-2-iodo-3-(4-methylphenyl)-2-
propenoate (8e)[9] could be isolated in 75, 66, 70 and 71% yields,
respectively (Chart 1). The reaction of the a-diazo derivatives of
alanine benzyl ester (1f), valine methyl (1g) and benzyl (1h) ester
with iodine gave the corresponding 2-iodo-2-unsaturated esters
8f–8h in 52, 58 and 55% yields, respectively (Chart 1).
and recorded in the range 4000–400 cmꢀ1 1H and 13C NMR
.
spectra were recorded on a Bruker AC-F 200 spectrometer at 200
and 50 MHz, respectively, using CDCl3 at room temperature as
solvent. NMR peak locations are reported as d-values from TMS.
Some 1H multiplets are characterized by the term app (apparent):
this refers only to their appearance and may be an over-
simplification. Routine monitoring of reactions was performed
using Merck silica gel 60 F254 coated on aluminium-supported
TLC plates. Column chromatography was performed with silica
gel 60 (230–400 mesh) and hexane/Et2O (97:3, v/v) as eluent.
Elemental analyses were performed with a Carlo Erba Mod.
1106 elemental analyser.
The configuration of the unsaturated iodo esters 8a–8e was
3
unambiguously determined using the JC—H coupling between
carbonyl carbon atom and alkene proton. The selective
General procedure for the synthesis of a-diazo esters
1a–1h[4]
decoupling of the a-protons of the alcoholic-ester moiety
3
revealed a JC—H coupling constant value ranging from 5.6
A mixture of a-amino ester (6.0 mmol), acetic acid (0.10 ml,
1.8 mmol) and tert-butyl nitrite (0.86 ml, 7.2 mmol) in CH2Cl2
(30 ml) was gently refluxed for 2 h under argon. The reaction
mixture was allowed to cool to room temperature and used in the
subsequent reaction with iodine.
and 6.5 Hz in agreement with the Z configuration.[33,34]
Compounds 8 are thermally and photochemically unstable.
CONCLUSIONS
In this report we have described the reaction of a-diazo esters 1
with iodine. This unprecedented reaction afforded the Z-isomer
of the corresponding unsaturated-2-iodo ester 8 as the main
product contrary to what is reported with a-diazo ketones.
Reaction of methyl 2-diazo-4-methylpentanoate (1a) with
iodine
A mixture of iodine (0.28 g, 1.1 mmol) in CH2Cl2 (5 ml) was slowly
added to the CH2Cl2 (5 ml) solution of 1a prepared as described
above using leucine methyl ester (0.145 g, 1.0 mmol) at 0 8C under
argon and in the dark. After stirring at room temperature for 4 h,
the reaction mixture was treated with a saturated sodium
metabisulphite solution to eliminate excess iodine and analysed
by GC–MS. The GC–MS[36] profile showed the presence of methyl
(Z)-4-methyl-2-pentenoate (2a), methyl (E)-4-methyl-2-pentenoate
(3a), methyl 4-methyl-2-oxopentanoate (4a), methyl 2-hydroxy-4-
methylpentanoate (5a), methyl 2-iodo-4-methylpentanoate (6a),
methyl (E)-2-iodo-4-methyl-2-pentenoate (7a), methyl (Z)-2-iodo-
4-methylpentenoate (8a) and methyl 2,2-diiodo-4-methyl-
pentanoate (9a) in 1, 1, 20, 6, 2, 1, 68 and 1% yields, respectively,
calculated from the integrated gas chromatographic peaks.
EXPERIMENTAL
General remarks
All reagents and solvents were used as purchased from
commercial suppliers (Aldrich, Fluka, CSPS Pharmaceuticals)
without further purification. tert-Butyl nitrite was prepared
according to described method.[35] GC–MS analyses were
performed with a Fisons TRIO 2000 gas chromatograph–
quadrupole mass spectrometer, working in the positive ion
70 eV electron impact mode, equipped with a MDN-5S capillary
column (Supelco, 30 m ꢁ 0.25 mm i.d.; flow rate, 0.8 ml/min; He as
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Copyright ß 2008 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2009, 22 24–30

REACTION OF IODINE WITH ꢀ-DIAZO ESTERS
Purification of a-diazo esters 1a–1h prepared
Methyl (Z)-2-iodo-3-phenyl-2-propenoate (8c)
The CH2Cl2 solution of the a-diazo ester 1 (30 ml), obtained as
described above, was successively washed with a saturated
NaHCO3 solution (2 ꢁ 15 ml) to eliminate acetic acid and
saturated brine (15 ml), and dried over Na2SO4. After
filtration, CH2Cl2 and excess tert-butyl nitrite were distilled off
under reduced pressure affording the a-diazo ester 1 in pure
form.
1.1 g, (66% yield). IR (film): n ¼ 2951, 1718, 1637, 1598, 1493, 1446,
1443, 1254, 1237, 1201, 1076, 1032, 765, 692 cmꢀ1 1H NMR
.
(CDCl3): d ¼ 3.87 (s, 3 H, CH3), 7.35–7.45 (m, 3 H, Harom), 7.70–7.79
(m, 2 H, Harom), 8.25 (s, 1 H, CH) ppm. 13C NMR (CDCl3): d ¼ 53.7,
—
—
89.9, 128.2, 129.4, 130.0, 135.3, 148.2, 164.2 ppm. EI-MS (70 eV):
m/z (%) ¼ 288 [Mþ] (26), 257 (9), 161 (100), 129 (34), 121 (18), 115
(13), 102 (27). Anal. calcd. for C10H9IO2 (288.08): C 41.69, H 3.15;
found: C 41.58, H 3.22.
Reaction of purified methyl 2-diazo-4-methylpentanoate
(1a) with iodine
Ethyl (Z)-3-(4-chlorophenyl)-2-iodo-2-propenoate (8d)[9]
1.41 g (70% yield). IR (film): n ¼ 2980, 1715, 1595, 1491, 1260,
The reaction was carried out as described above but using a
solution of the purified a-diazo ester 1a (0.156 g, 1.0 mmol)
in CH2Cl2 (5 ml). After treatment, the GC–MS[36] profile showed
the presence of methyl (Z)-4-methyl-2-pentenoate (2a),
methyl (E)-4-methyl-2-pentenoate (3a), methyl 2-hydroxy-4-
methylpentanoate (5a), methyl 2-iodo-4-methylpentanoate
(6a), methyl (E)-2-iodo-4-methyl-2-pentenoate (7a), methyl
(Z)-2-iodo-4-methylpentenoate (8a) and methyl 2,2-diiodo-4-
methylpentanoate (9a) in 2, 2, 8, 20, 1, 66 and 1% yields,
respectively, calculated from the integrated gas chromatographic
peaks.
1071, 780, 636 cmꢀ1
.
1H NMR (CDCl3): d ¼ 1.35 (t, 3 H, J ¼
7.0 Hz, CH3), 4.28 (q, 2 H, J ¼ 7.0 Hz, CH2), 7.45 (app d, 2 H,
J ¼ 8.1 Hz, Harom), 7.68 (app d, 2 H, J ¼ 8.1 Hz, Harom), 8.43 (s, 1 H,
CH) ppm. 13C NMR (CDCl3): d ¼ 14.6, 59.3, 91.1, 128.7, 129.3,
—
—
132.3, 134.1, 149.0, 165.0 ppm. EI-MS (70 eV): m/z (%) ¼ 338 [Mþ,
37Cl] (18), 336 [Mþ, 35Cl] (55), 211 (16), 209 (50), 183 (32), 181 (100),
138 (25), 136 (80). Anal. calcd. for C11H10ClIO2 (336.56): C 39.26,
H 2.99; found: C 39.33, H 2.82.
Ethyl (Z)-2-iodo-3-(4-methylphenyl)-2-propenoate (8e)[9]
1.33 g (71% yield). IR (film): n ¼ 2980, 1715, 1596, 1503, 1443,
1
1240, 1183, 765, 635 cmꢀ1. H NMR (CDCl3): d ¼ 1.28 (t, 3 H, J ¼
General procedure for the synthesis of Z-unsaturated-2-iodo
esters 8a–8h
7.0 Hz, CH2CH3), 2.35 (s, 3 H, CH3), 4.25 (q, 2 H, J ¼ 7.0, OCH2), 7.20
(app d, 2 H, J ¼ 7.7 Hz, Harom), 7.65 (app d, 2 H, J ¼ 7.7 Hz, Harom),
8.25 (s, 1 H, CH) ppm. 13C NMR (CDCl3): d ¼ 14.8, 20.5, 60.0, 89.8,
—
—
A mixture of iodine (1.67 g, 6.6 mmol) in CH2Cl2 (30 ml) was slowly
added to a mixture of the appropriate purified a-diazo ester 1
(6.0 mmol) in CH2Cl2 (30 ml) and 5% aqueous NaHCO3 (35 ml) at
0 8C under argon and in the dark. After stirring at room
temperature for 4 h, the organic phase was separated and
successively washed with a saturated aqueous sodium metabi-
sulphite solution (2 ꢁ 15 ml) to eliminate excess iodine and
saturated brine (15 ml), and dried over anhydrous Na2SO4. After
filtration, CH2Cl2 was distilled off under reduced pressure and the
residue was purified by silica gel column chromatography using
hexane/Et2O (97:3, v/v) to furnish the unsaturated-2-iodo esters
8a–8h as pale yellow oils (purity >95% by 1H NMR spectroscopy).
128.0, 128.9, 134.7, 138.1, 149.5, 165.1 ppm. EI-MS (70 eV): m/z
(%) ¼ 316 [Mþ] (60), 189 (50), 161 (100), 115 (83). Anal. calcd.
for C12H13IO2 (316.14): C 45.59, H 4.14; found: C 45.43, H 4.22.
Benzyl 2-iodoacrylate (8f)
0.90 g (52% yield). IR (film): n ¼ 3042, 2955, 1720, 1592, 1461,
1372, 1253, 1157, 1092, 1030, 1002, 945, 795, 753, 738, 702,
1
639 cmꢀ1. H NMR (CDCl3): d ¼ 5.24 (s, 2 H, PhCH2), 6.59 (d, 1 H,
J ¼ 1.4 Hz, CHH), 7.30–7.43 (m, 5 H, Harom), 7.46 (d, 1 H, J ¼
1.4 Hz, CHH) ppm. 13C NMR (CDCl3): d ¼ 68.5, 96.3, 128.1, 128.5,
128.6, 135.2, 140.0, 162.2 ppm. EI-MS (70 eV): m/z (%) ¼ 288 [Mþ]
(10), 217 (15), 181 (38), 153 (15), 143 (10), 133 (30), 127 (10), 117
(21), 91 (100). Anal. calcd. for C10H9IO2 (254.07): C 41.69, H 3.15;
found: C 41.77, H 3.20.
Methyl (Z)-2-iodo-4-methyl-2-pentenoate (8a)
1.0 g, (66% yield). IR (film): n ¼ 2963, 2930, 2871, 1724, 1648, 1612,
1466, 1435, 1328, 1248, 1142, 1030, 892, 751 cmꢀ1 1H NMR
.
Methyl 2-iodo-3-methyl-2-butenoate (8g)
(CDCl3): d ¼ 1.09 [d, 6 H, J ¼ 6.6 Hz, CH(CH3)2], 2.60–2.85 (m, 1 H,
—
CH), 3.81 (s, 3 H, OCH3), 6.99 (d, 1 H, J ¼ 9.2 Hz,
CH) ppm.
—
0.84 g (58% yield). IR (film): n ¼ 2982, 2956, 1718, 1628, 1438,
13C NMR (CDCl3): d ¼ 20.6, 36.4, 53.4, 91.5, 158.9, 163.5 ppm. EI-MS
(70 eV): m/z (%) ¼ 254 [Mþ] (75), 222 (8), 181 (15), 179 (26), 127
(21), 112 (33), 95 (100), 73 (41), 67 (31), 41 (31), 39 (31). Anal. calcd.
for C7H11IO2 (254.07): C 33.09, H 4.36; found: C 33.14, H 4.30.
1245, 1216, 1014, 857 cmꢀ1
.
1H NMR (CDCl3): d ¼ 1.94 (s,
3 H, CH3CCH3), 2.00 (s, 3 H, CH3CCH3), 3.77 (s, 3 H, OCH3) ppm.
13C NMR (CDCl3): d ¼ 20.5, 28.6, 52.0, 89.3, 154.6, 163.5 ppm. EI-MS
(70 eV): m/z (%) ¼ 240 [Mþ] (100), 209 (46), 208 (67), 181 (24), 127
(10), 73 (27), 59 (24), 54 (33), 53 (58), 41 (51). Anal. calcd.
for C6H9IO2 (240.09): C 30.02, H 3.78; found: C 30.15, H 3.60.
Benzyl (Z)-2-iodo-4-methyl-2-pentenoate (8b)
1.48 g (75% yield). IR (film): n ¼ 2963, 2931, 2870, 1718, 1652,
Benzyl 2-iodo-3-methyl-2-butenoate (8h)
1
1610, 1458, 1235, 1142, 1010, 748, 697 cmꢀ1. H NMR (CDCl3):
d ¼ 1.07 (d, 6 H, J ¼ 6.6 Hz, CH(CH3)2], 2.60–2.85 (m, 1 H, CH), 5.24
1.04 g (55% yield). IR (film): n ¼ 3030, 2978, 2934, 1720, 1630,
1440, 1263, 1120, 1035, 760, 685 cmꢀ1. 1H NMR (CDCl3): d ¼ 2.08
(s, 3 H, CH3CCH3), 2.10 (s, 3 H, CH3CCH3), 5.27 (s, 2 H, PhCH2),
7.23–7.48 (m, 5 H, Harom) ppm. 13C NMR (CDCl3): d ¼ 22.8, 31.8,
67.5, 84.0, 127.9, 128.2, 128.5, 135.4, 152.4, 165.1 ppm. EI-MS
(70 eV): m/z (%) ¼ 316 [Mþ] (3), 189 (15), 171 (58), 91 (100). Anal.
—
(s, 2 H, PhCH2), 7.01 (d, 1 H, J ¼ 9.2 Hz,
CH), 7.28–7.47 (m,
—
5 H, Harom) ppm. 13C NMR (CDCl3): d ¼ 20.6, 36.6, 68.2, 91.0, 128.2,
128.3, 128.6, 135.5, 159.2, 162.8 ppm. EI-MS (70 eV): m/z (%) ¼ 330
[Mþ] (4), 288 (7), 203 (28), 185 (8), 157 (8), 91 (100). Anal. calcd.
for C13H15IO2 (330.17): C 47.29, H 4.58; found: C 47.36, H 4.63.
J. Phys. Org. Chem. 2009, 22 24–30
Copyright ß 2008 John Wiley & Sons, Ltd.
www.interscience.wiley.com/journal/poc

G. VERARDO, P. GEATTI AND A. GAMBI
calcd. for C12H13IO2 (316.14): C 45.59, H 4.14; found: C 45.48,
H 4.23.
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Acknowledgements
Financial support was obtained from MIUR (FURD 2006–2007).
The authors are grateful to Dr P. Martinuzzi for recording 1H and
13C NMR spectra and Mr P. Padovani for expert instrumental
maintenance.
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Copyright ß 2008 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2009, 22 24–30