Electrochemical synthesis of 2-arylimino-4,5-di(2-furyl)-1,3-dioxoles and (E)-1,2-di(2-furyl)vinylene bis(N-arylchloroformimidates). HF and B3LYP computational study of the topomerization mechanism of aryliminodioxoles

Article abstract of DOI:10.1016/j.tet.2009.02.082

Cathodic reductions of 2,2′-furils in the presence of N-arylcarbonimidoyl dichlorides lead to 2-arylimino-4,5-di(2-furyl)-1,3-dioxoles in high yields, along with minor amounts of (E)-1,2-di(2-furyl)vinylene bis(N-arylchloroformimidates). HF and B3LYP dens

Full text of DOI:10.1016/j.tet.2009.02.082

Tetrahedron 65 (2009) 3886–3892
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Electrochemical synthesis of 2-arylimino-4,5-di(2-furyl)-1,3-dioxoles and
(E)-1,2-di(2-furyl)vinylene bis(N-arylchloroformimidates). HF and B3LYP
computational study of the topomerization mechanism of aryliminodioxoles
,
a
a
b
Antonio Guirado a , Andres Zapata , Raquel Andreu , Carmen Ramırez de Arellano ,
*
´
´
´
Peter G. Jones c , Jesus Galvez
,
d,
*
*
´
a
´
´
´
´
Departamento de Quımica Organica, Facultad de Quımica, Universidad de Murcia, Campus de Espinardo, 30071 Murcia, Spain
b
Departamento de Qu´ımica Organica, Universidad de Valencia, 46100 Valencia, Spain
c Institut fu¨r Anorganische und Analytische Chemie, Technische Universita¨t Braunschweig, Postfach 3329, 38023 Braunschweig, Germany
d Departamento de Qu´ımica F´ısica, Universidad de Murcia, Spain
a r t i c l e i n f o
a b s t r a c t
Cathodic reductions of 2,20-furils in the presence of N-arylcarbonimidoyl dichlorides lead to 2-arylimino-
4,5-di(2-furyl)-1,3-dioxoles in high yields, along with minor amounts of (E)-1,2-di(2-furyl)vinylene bis(N-
arylchloroformimidates). HF and B3LYP density functional theory methods have been applied to the
determination of molecular geometries and to study the topomerization mechanism of aryliminodiox-
oles. The molecular structure of (E)-1,2-di(2-furyl)vinylene bis[N-(2-chloro-4-methylphenyl)chloro-
formimidate] has been determined by X-ray crystallography and compared with the calculated structure.
Ó 2009 Elsevier Ltd. All rights reserved.
Article history:
Received 30 October 2008
Received in revised form 24 February 2009
Accepted 26 February 2009
Available online 9 March 2009
Keywords:
Electrosynthesis
1,2-Diketones
Carbonimidoyl dichlorides
Dioxoles
Formimidates
1. Introduction
properties that can be exploited synthetically. Thus, they were
found to be reducible at relatively high cathodic potentials pro-
Electrochemical reductions of benzil and other diaryl-1,2-dike-
tones have been studied from various points of view. Reactions in
protic media lead to benzoins, whose formation corresponds to
a two-electron, two-proton process.1–3 The interest in these re-
actions is mainly mechanistic. Electrolyses in aprotic media carried
out in the presence of non-electroactive electrophilic reagents have
synthetic utility and are of great interest since under these condi-
tions electrogenerated intermediates can attack these reagents
instead of undergoing simple protonation. Alkylations4,5 in the
presence of alkyl halides or alkyl tosylates and acylations6–9 per-
formed in the presence either acyl halides or acid anhydrides are
standard reported reactions. Similar reductions were applied
viding isocyanides in near quantitative yields,14,15 but showed also
a high tendency to act exclusively as geminal dielectrophilic agents,
thereby capturing reactive intermediates generated by electro-
reduction of benzils or anils at relatively lower cathodic potentials,
yielding 2-arylimino-4,5-diaryl-1,3-dioxoles16,17 or 3,4,5-triaryl-2-
aryliminooxazolines,18 respectively. In order to expand this
preparative methodology, we attempted the synthesis of 2-aryli-
mino-4,5-diheteroaryl-1,3-dioxoles by electrochemical reduction
of commercially available starting materials such as 2,20-pyridil,
2,20-thenil, bis(pyrrol-2-yl)-1,2-ethanedione and 2,20-furils. In
a preliminary communication we reported that the only successful
experiments were those starting from furils,19 whereas the other
electrolyses led to isocyanides via indirect electroreduction of car-
bonimidoyl dichlorides present in the catholyte.20
to monothiobenzils leading to (Z)-a-benzoyloxy-b-benzoylthio-
stilbenes.10
In the course of this synthetic strategy we established that
carbonimidoyl dichlorides,11 which are inexpensive and easily
available reagents,12,13 show optimal chemical and electrochemical
In this paper we report full details of the electrosynthesis of
a new family of dioxole derivatives formed by electroreduction of
2,20-furils 1 in the presence of carbonimidoyl dichlorides.21 These
substances were generated along with minor amounts of com-
pounds that have been identified as a new class of formimidate
derivatives whose structure has been corroborated by X-ray crys-
tallography. As in the case of electrolysis products derived from
* Corresponding authors. Tel.: þ34 968367490; fax: þ34 968364148.
E-mail address: anguir@um.es (A. Guirado).
0040-4020/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2009.02.082

A. Guirado et al. / Tetrahedron 65 (2009) 3886–3892
3887
Table 1
benzils, the NMR spectra of the prepared aryliminodioxoles exhibit
a notable dependence upon temperature that is attributable to
a topomerization process whose mechanism has been now studied
by HF and B3LYP density functional theory methods.
Results of electrochemical reductions of furils 1 in the presence of carbonimidoyl
dichlorides 2
Ar
R
3 (yield %)
4 (yield %)
a
b
c
d
e
f
g
h
i
C6H5
4-ClC6H4
2,4-Cl2C6H3
4-NCC6H4
4-BrC6H4
2-Cl-4-CH3C6H3
C6H5
4-EtOOC-C6H4
2-Cl-4-CH3C6H3
2,4-Cl2C6H3
4-BrC6H4
H
H
H
H
H
H
CH3
CH3
CH3
CH3
CH3
CH3
74
76
73
73
74
76
75
75
73
74
67
70
8
12
11
11
13
10
Traces
Traces
Traces
Traces
Traces
Traces
2. Results and discussion
2,20-Furils 1 were reduced at constant cathodic potentials in the
presence of equimolar amounts of arylcarbonimidoyl dichlorides 2
(Scheme 1). After a short time the colour of the catholyte, initially
yellow, turned to purple. When the current was interrupted the
solutions became yellow again. This observation was repeated
throughout the electrolysis. The electricity consumption was 2 F/
mol of 1. After each preparative electrolysis the crude products
were precipitated by mixing the catholyte solutions with cold
water, after which they could easily be isolated and purified by
extraction and fractional crystallization. The main reaction prod-
ucts were obtained in good yields (Table 1) and were identified by
IR, MS, NMR spectroscopy and elemental analysis as the corre-
sponding 2-arylimino-4,5-di(2-furyl)-1,3-dioxoles 3. Electrolyses in
the presence of alkylcarbonimidoyl dichlorides (PhCH2CH2N]CCl2
and C6H11N]CCl2) were also carried out. However, these reactions
were unsuccessful, leading to a complex mixture of unidentified
products. The chemistry of various classes of 1,3-dioxoles has been
studied for a long time.17 However, with the exception of the
electrochemical method, only one preparative procedure for 2-
imino derivatives has been reported, with only two reaction ex-
amples and remarkably different yields, and requiring a complex
and expensive protocol that involves the prior synthesis of
bis(tributylstannyloxy)ethenes followed by reaction with
isothiocyanates.22
Ascorbic acid (E1/2¼0.18 V vs Ag/AgCl) and further free enediols
are substances having low oxidation potentials and a pronounced
antioxidant activity.23 However, enediol iminocarbonate 3a shows
a relatively high reluctance to be oxidized (E1/2¼1.03 V vs SCE) at
the same working electrode. Owing to the recent nature of the
development of our synthetic methodology, possible applications
of products of type 3 remain scarcely investigated. These have been
found to be hydrolyzable providing dioxolenones without need for
phosgene reactions.17 Nucleophilic attack, polymerization, photo-
chemical and electrochemical reactions seem to be interesting
fields to be explored.
j
k
l
4-Cl-2-CH3C6H4
formimidates) 4. The course of electrolyses varying the ratio of 2
(double or a half amount) was checked by TLC, showing no sig-
nificant differences. The molecule of 4f (Fig. 1) displays crystallo-
graphic inversion symmetry. Consistent with this, the geometry at
the central double bond is confirmed as trans. The interplanar angle
between the phenyl and furanyl rings is 60.4ꢀ. There are two no-
tably wide sp2 bond angles, namely C5#–C5–C1 129.7(4)ꢀ and C2–
C1–C5 131.5(5)ꢀ, but a search of the Cambridge Database24 revealed
that this is normal for the group C]C-(2-furanyl), with corre-
sponding average values of 127.8ꢀ and 132.3ꢀ, respectively, for 50
hits and 63 individual values.
Consistent with our proposal for the electrogeneration of 2-
arylimino-1,3-dioxoles derived from benzils,17 the formation of
products 3 can be explained on the basis of electrogeneration of
two nucleophilic centres that are geminally captured by the non-
electroactive dielectrophilic reagents present in the catholyte. The
formation of products 4 can be similarly explained, but with the
participation of two independent dielectrophilic molecules for
configurational reasons. It should be noted that the formation of
compounds similar to products 4 was not observed during elec-
troreductions of benzils.
NMR spectroscopy of products 3 showed remarkable tempera-
ture dependence. Assignments of spectra were made by DEPT; H,C-
COSY and selective decoupling techniques. As is reported in the
Experimental section, carbons pertaining to aryl groups attached to
nitrogen are labelled 100-400 or 1-600 depending on symmetry,
whereas the carbons of furyl groups supported by the dioxole ring
are denoted as 2-5 and 20-50. 13C NMR spectra recorded at ambient
temperature were inconsistent in the number of signals with re-
spect to configurationally stable compounds, but a moderate
Minor electrolysis products were also isolated or detected in
trace amounts; structures were determined by the usual spectro-
scopic techniques and confirmed by X-ray crystallography as a new
class of compounds: (E)-1,2-di(2-furyl)vinylene bis(N-arylchloro-
Ar
N
N
O
O
Ar
CCl2
2
+ 2 Cl
O
O
R
R
O O
2e
3
C
C
R
R
O
O
Cl
1
R
N
Ar
Ar
2
O
O
CCl2
N
2
+ 2 Cl
N
O
O
Ar
R
Cl
4
Scheme 1.

3888
A. Guirado et al. / Tetrahedron 65 (2009) 3886–3892
A
18
15
12
9
6
3
0
0
30
60
OCNC torsion angle (degrees)
90
120
150
180
Figure 1. The structure of the major disorder component of 4f in the solid state, with
thermal ellipsoids shown at 50% probability.
B
15
12
9
increase of temperature lowered this number to that expected for
non-configurationally stable substances. However, spectra at low
temperature provided almost the number of peaks predicted for
compounds with total configurational stability. 1H NMR spectra
were also highly temperature dependent.
In a previous paper17 NMR spectra of 2-arylimino-4,5-diaryl-1,3-
dioxoles at different temperatures demonstrated geometrical in-
terconversions involving a relatively low configurational stability
around the carbon–nitrogen double bond. In general, these facts
have been explained by two opposite models, called either ‘rotation’
or ‘inversion’ mechanisms.25 The rotation mechanism is conceived
as involving a polar transition state with loss of the carbon–nitrogen
double bond following an ‘out-of-plane’ fluctuation (Scheme 2, TS A,
torsion angle 90ꢀ). Conversely, the alternative inversion mechanism
implies rehybridization of the non-bonded electron pair at nitrogen
to a p orbital, with the carbon–nitrogen double bond character
remaining unaffected, in this way following an ‘in-plane’ molecular
fluctuation (Scheme 2, TS B).
To gain insight into the mechanism operating with compounds
3, a computational study on the predictions of both models was
performed at the B3LYP/6-311þþG(d,p)//B3LYP/6-31G(d) level of
theory.26 A summary of the results obtained for compound 3a is
displayed in Figure 2. Thus, panel A shows the energy profile for the
molecule structures related to the torsional motion about the
double bond C]N that occurs during the rotation mechanism.
Energy values are given relative to the most stable molecule (OCNC
dihedral angle z0ꢀ, CNC angle¼125.35ꢀ), and the profile was
generated by modifying the OCNC torsion angle with the initial CNC
angle constraint applied to all structures. Panel B shows the cor-
responding energy profile for the inversion mechanism, which was
generated by modifying the CNC angle without further constraints
(during this motion the OCNC dihedral angle remains z0ꢀ for all
molecule structures). From Figure 2 it follows that both profiles
show an energy maximum, which is attained at an OCNC torsion
angle¼90ꢀ (Panel A) and for a CNC angle¼180ꢀ (Panel B). Note,
6
3
0
120
150
180
CNC angle (degrees)
210
240
Figure 2. Panel A: Energy profile of the molecular interconversion according to the
rotational mechanism. This profile was generated by modifying the OCNC torsion angle
and with the constraint CNC angle¼125.35ꢀ applied to all structures. Panel B: Energy
profile for the inversion mechanism. The CNC angle was modified without further
constraints. Energy values are relative to the most stable molecule configuration.
Calculations were performed at the B3LYP/6-311þþG(d,p)//B3LYP/6-31G(d) level of
theory.
however, that the maximum for the inversion mechanism is
3.5 kcal/mol lower than for rotation. This implies that the mecha-
nism for the topomerization of these compounds mainly involves
an ‘in-plane’ inversion process. This was confirmed by obtaining the
transition state (TS) optimized structure, which was determined
without applying any constraints at the B3LYP/6-31G(d) level and
characterized by vibrational frequency calculations that gave a sole
imaginary frequency for the TS structure. The CNC angle in the TS
was 173.4ꢀ revealing that there is a small deviation from the in-
version mechanism in favour of the rotational one. In this context, if
we remove the constraints from the molecule structure for the
maximum energy in the rotation mechanism (Panel A, Fig. 3 CNC
angle¼125.35ꢀ), that configuration spontaneously reverts to the TS
structure for the inversion process in which the CNC angle¼173.35ꢀ.
Also, it is interesting to note that the aryl group, which is almost
coplanar with the dioxole ring during the inversion motion,
changes its configuration to orthogonal in the transition state. This
effect can be attributed to a gain of stabilization by orbital over-
lapping and also by lessening of steric hindrance (Scheme 3).
Figure 3 illustrates another key feature of the inversion mech-
anism, viz. the continuous shortening of the bond length C]N as
the transition state is reached (a similar shortening was also found
for the nitrogen–aryl bond, data not shown). Finally, the energy
barrier (¼Ea) for the inversion process was determined as the dif-
ference between the total molecular energy of the transition state
TS and that of the global minimum of the reactant. The value of Ea
including ZPE and thermal corrections obtained at the same level as
geometry optimizations was small, just 11.54 kcal/mol, whereas the
Ar
N
O
O
Ar
Ar
N
N
R
R
A
O
O
R
O
R
O
Ar
N
R
R
O
O
R
R
B
Scheme 2.
value of
D
Gs
is 13.05 kcal/mol.27
298

A. Guirado et al. / Tetrahedron 65 (2009) 3886–3892
3889
Table 2
Selected bond lengths and bond angles of crystal and calculated structures in crystal
structure of 4f and their differences
1.26
1.25
1.24
1.23
1.22
Bond
Crystal
Calculated
D
(Å)
Calculated
D
(Å)
structure (Å) structurea (Å)
structureb (Å)
N–C(6)
N–C(7)
O(2)–C(6)
O(2)–C(5)
C(5)–C(5)#1 1.316(8)
C(5)–C(1)
C(1)–C(2)
C(1)–O(1)
Cl(1)–C(6)
Cl(2)–C(8)
1.235(3)
1.425(3)
1.356(3)
1.431(3)
1.252
1.401
1.350
1.404
1.356
1.443
1.377
1.369
1.771
1.755
ꢁ0.017
1.232
1.404
0.003
0.021
0.027
0.051
ꢁ0.010
ꢁ0.002
ꢁ0.003
0.038
0.024
0.006 1.329
0.027
ꢁ0.030
0.012
ꢁ0.031
1.380
1.326
1.457
1.349
1.344
1.455(5)
1.346(7)
1.382(6)
1.725(2)
1.742(2)
0.013
ꢁ0.046 1.735
ꢁ0.010
ꢁ0.013 1.741
0.001
Bond angle
Crystal
Calculated
D
(ꢀ)
Calculated
D
(ꢀ)
structure (ꢀ) structurea (ꢀ)
structureb (ꢀ)
C(6)–O(2)–C(5)
116.88(18)
117.90
118.05
129.45
112.29
109.56
130.16
106.21
110.55
124.92
127.23
ꢁ1.02
119.02
ꢁ2.14
ꢁ4.01
1.19
C#(5)1–C(5)–O(2) 115.0(4)
C#(5)1–C(5)–C(1) 129.7(4)
ꢁ3.05 119.01
0.25 128.51
2.91 112.29
0.34 110.20
1.34 129.68
0.49 105.62
ꢁ0.05 110.77
ꢁ0.32 124.56
O(2)–C(5)–C(1)
O(2)–C(5)–O(1)
C(2)–C(1)–C(5)
C(4)–C(3)–C(2)
C(3)–C(4)–O(1)
N–C(6)–O(2)
115.2(3)
109.9(4)
131.5(5)
106.7(4)
110.5(4)
124.6(2)
127.40(18)
2.91
ꢁ0.30
1.82
120
140
160
CNC angle (degrees)
180
200
220
240
1.08
ꢁ0.27
0.04
Figure 3. Variation of the C]N bond length as a function of the CNC angle for the
N–C(6)–Cl(1)
0.17
126.57
0.83
inversion process. Other conditions as in Figure 1, Panel A.
a
Geometry optimized at the B3LYP/6-31G(d) level of theory.
Geometry optimized at the HF/6-31G(d) level of theory.
b
The accuracy of the computational methodology applied to
envisage molecular geometries was checked by comparing exper-
imental X-ray crystallography data and the calculated molecular
structure of 4f. The results obtained are shown in Table 2 for bond
lengths and bond angles and in Table 3 for selected dihedral angles.
A good agreement was found, with differences in bond lengths
z0.02Å and in bond angles z1ꢀ (Table 2). As expected, these dif-
ferences are a little larger for dihedral angles (Table 3). This is a well
known fact that has been ascribed to molecular distortion in the
crystal structure induced by packing effects. Also, and in accor-
dance with the previous theoretical analysis, data from Table 2
provide support for the view that a rotation mechanism is not in-
volved in the topomerization process. The C]N double bond
lengths found in the X-ray structure of 2-(2-chloro-4-methyl-
phenylimino)-4,5-diphenyl-1,3-dioxole17 (1.254(2) Å; cf. standard28
C(sp2) –C]N–C bond length of 1.279 Å) and also in the optimized
structure29 for 3a (1.257 Å) are unusually short. However, these
bonds might be expected to be longer if the molecular in-
terconversion process takes place through a polar mechanism since,
under these conditions, the double bond character of the C3–N bond
is lost.
arylimino-1,3-dioxoles show
a remarkable temperature de-
pendence, which is attributable to a configurational instability
according to an inversion process with a relatively low activation
barrier that has been calculated to be about 11 kcal/mol.
3. Experimental
3.1. General
NMR spectra were determined on Bruker AV-200, Bruker AV-
300 or Bruker AV-400 with tetramethylsilane as internal reference.
Electron-impact mass spectra were obtained on Thermoquest trace
MS spectrometer under an ionizing voltage of 70 eV. IR spectra
(Nujol emulsions) were recorded on a Nicolet Impact 400 Spec-
trometer. Microanalyses were performed on a Carlo Erba EA-1108
analyzer. Melting points were determined on a Bu¨chi Melting point
B-540, and are uncorrected. Electrochemical experiments were
Table 3
To conclude, it has been established that cathodic reduction of
difuryl-1,2-diketones carried out in the presence of carbonimidoyl
dichlorides has a specific use for preparing previously inaccessible
2-arylimino-4,5-di(2-furyl)-1,3-dioxoles 3 and (E)-1,2-di(2-furyl)-
vinylene bis(N-arylchloroformimidates) 4. NMR spectra of 2-
Selected dihedral angles of crystal and calculated structures of 4f and their
differences
Dihedral angle
Crystal
Calculated
D
(ꢀ) Calculated
structureb (ꢀ)
D
(ꢀ)
structure (ꢀ) structurea (ꢀ)
C(6)–O(2)–C(5)–C(5)#1 90.2(4)
C(6)–O(2)–C(5)–C(1)
ꢁ93.6(4)
C#(5)1–C(5)–C(1)–C(2) 177.4(6)
O(2)–C(5)–C(1)–C(2) 1.8(8)
92.62
ꢁ92.24
172.65
1.80
ꢁ7.52
178.03
ꢁ0.06
179.92
179.80
0.12
176.51
ꢁ4.05
ꢁ2.70
175.78
179.27
ꢁ2.42
94.22
ꢁ1.36 ꢁ90.29
ꢁ4.02
ꢁ3.31
9.31
4.75 168.09
0.00
6.86
ꢁ5.06
C(5)#1–C(5)–C(1)–O(1) ꢁ5.2(8)
2.32 ꢁ11.83
6.63
O(2)–C(5)–C(1)–O(1)
C(2)–C(1)–O(1)–C(4)
C(5)–C(1)–O(1)–C(4)
C(5)–C(1)–C(2)–C(3)
C(1)–C(2)–C(3)–C(4)
C(7)–N–C(6)–O(2)
C(7)–N–C(6)–Cl(1)
C(5)–O(2)–C(6)–N
N–C(7)–C(8)–C(9)
179.2(4)
ꢁ2.7(7)
179.3(5)
178.9(5)
0.6(8)
179.0(2)
ꢁ0.3(4)
ꢁ6.9(4)
178.4(2)
1.17 173.21
5.99
ꢁ2.64 ꢁ0.05
ꢁ0.62 179.89
ꢁ0.90 179.95
ꢁ2.65
ꢁ0.59
ꢁ1.05
0.51
1.63
1.77
N
0.48
0.09
O
O
2.49 177.37
3.75 ꢁ2.07
ꢁ4.20 ꢁ2.81
2.62 176.37
0.58 178.97
N
N
R
R
ꢁ4.09
O
O
O
O
2.03
C(12)–C(7)–C(8)–Cl(2) 179.85(17)
0.88
R
R
R
R
a
Geometry optimized at the B3LYP/6-31G(d) level of theory.
Geometry optimized at the HF/6-31G(d) level of theory.
b
Scheme 3.

3890
A. Guirado et al. / Tetrahedron 65 (2009) 3886–3892
performed with an Amel 552 potentiostat coupled to an Amel 721
integrator. Carbonimidoyl dichlorides 2 were prepared by standard
procedures.12
C d (CDCl3,
17H9Cl2NO4 requires: C, 56.38; H, 2.50; N, 3.87); 1H NMR
300 MHz): 6.55 (br s, 2H, H-4,40), 6.90 (d, 2H, J¼3.3, H-3,30), 7.25–7.33
(m, 2H, H-500,600), 7.43 (m, 1H, H-300), 7.57 (br s, 2H, H-5,50); 13C NMR
d
(CDCl3, 75.4 MHz): 111.44 (C-3,30), 111.99 (C-4,40), 124.43 (C-600),
All computations were performed with the Spartan’06 package
program.30 The most stable conformers were determined by using
the MMFF molecular mechanics method. Next, these conformers
were used as input for ab initio molecular orbital and density
functional theory calculations of geometry optimizations at the
Hartree–Fock and B3LYP levels of theory with the 6-31G(d) basis
set. Frequency calculations were performed at the same level of
theory as the geometry optimizations to characterize the stationary
points as local minima (equilibrium structures) and to evaluate the
zero-point energy (ZPE). No scaling procedures were used. Single-
point energies were calculated with the 6-311þþG(d,p) basis.
127.50 (C-500),128.60 (C-2,20), 129.11 (C-200), 129.36 (C-400),129.64 (C-
300), 140.10 (br, O–C]C–O), 140.24 (C-100), 144.25 (C-5,50), 149.83
(C]N–);MSm/z (%):363(Mþþ2, 34), 361 (Mþ, 66),187(24),146(39),
118 (100), 95 (50), 92 (31), 90 (31), 89 (43), 63 (22); IR (Nujol): 1827,
1729, 1682, 1651, 1593, 1516, 1383, 1217, 1102, 1019, 872, 760 cmꢁ1
.
3.2.4. 2-(4-Cyanophenylimino)-4,5-di(2-furyl)-1,3-dioxole (3d)
Yield 73%; crystallization from petroleum ether gave pale yellow
needles, mp 135–136 ꢀC. (Found: C, 67.99; H, 3.23; N, 8.75.
C18H10N2O4 requires: C, 67.92; H, 3.17; N, 8.80); 1H NMR
d (CDCl3,
300 MHz): 6.57 (m, 2H, H-4,40), 6.92 (d, 2H, J¼3.6, H-3,30), 7.34 (d,
3.2. Electrolysis procedure
2H, J¼8.4, H-200), 7.59–7.64 (m, 4H, J¼8.5, H-3,30,300); 13C NMR
d
(CDCl3, 50.3 MHz): 107.12 (C-400), 111.39 (C-3,30), 112.04 (C-4,40),
The electrochemical generation of products 3 and 4 was per-
119.16 (CN), 124.00 (C-200), 128.90 (C-2,20), 133.06 (C-300), 139.76 (O–
C]C–O), 144.26 (C-5,50), 147.88 (C-100), 149.82 (C]N–); MS m/z (%):
318 (Mþ, 8), 146 (19), 118 (100), 95 (52), 92 (29), 90 (30), 89 (43), 63
(20); IR (Nujol): 3155, 2223, 1746, 1723, 1675, 1601, 1502, 1273, 1221,
formed following the experimental procedure previously repor-
ted.10,31,32 Compounds
1 (5 mmol) were electrolyzed under
nitrogen atmosphere, in the presence of reagents 2 (5 mmol), at the
following cathodic potentials: ꢁ0.80 V versus SCE (1b,d); ꢁ0.90 V
(1c,h,f,i,j,l); ꢁ1.05 V (1a,e,g); ꢁ1.10 (1k). These potentials were
selected in order to provide operative current intensities. The du-
ration of the electrolyses ranged from 1.3 to 1.5 h. The average
current intensities were close to 12 mA/cm2 at the beginning and
0.9 mA/cm2 at the end. The cell voltage values remained below 5 V
in all cases. The electricity consumption was 2 F/mol for all cases.
All electrolysis products were isolated by dropping the catholyte
solution into cold brine (200 mL) and filtering or extracting the
mixture with diethyl ether. The ether layers were washed with cold
water and dried on anhydrous magnesium sulfate. A solid mixture
of reaction products was obtained by removing ether under re-
duced pressure. Then these were isolated in high purity by frac-
tional crystallization from acetonitrile. Products 4 crystallized at
room temperature, whereas crystallization of products 3 occurred
at ꢁ10 ꢀC from acetonitrile or petroleum ether.
1161, 1084, 1011, 954, 843, 739 cmꢁ1
.
3.2.5. 2-(4-Bromophenylimino)-4,5-di(2-furyl)-1,3-dioxole (3e)
Yield 75%; crystallization from acetonitrile gave pale brown
needles, mp 138–141 ꢀC. (Found: C, 54.88; H, 2.66; N, 3.83.
C17H10BrNO4 requires: C, 54.86; H, 2.71; N, 3.76); 1H NMR
d (CDCl3,
300 MHz, þ25 ꢀC): 6.55 (br s, 2H, H-4,40), 6.89 (d, 2H, J¼3.0, H-3,30),
7.16 (d, 2H, J¼8.7, H-200), 7.44 (d, 2H, J¼8.7, H-300), 7.56 (br s, 2H, H-
5,50); 1H NMR
d
(CDCl3, 300 MHz, þ60 ꢀC): 6.52 (dd, 2H, J¼3.4,1.8, H-
4,40), 6.86 (dd, 2H, J¼3.3, 0.6, H-3,30), 7.14 (d, 2H, J¼8.7, H-200), 7.42 (d,
2H, J¼8.7, H-300), 7.54 (dd, 2H, J¼1.7, 0.6, H-5,50); 1H NMR
d (CDCl3,
300 MHz, ꢁ60 ꢀC): 6.59 (m, 2H, H-4,40), [6.88 (d, 1H, J¼3.3), 7.02 (d,
1H, J¼3.3), H-3,30], 7.22 (d, 2H, J¼8.4, H-200), 7.47 (d, 2H, J¼8.4, H-300),
[7.60 (br s, 1H), 7.62 (br s, 1H), H-5,50]; 13C NMR
d (CDCl3, 75.4 MHz,
þ25 ꢀC): 111.09 (C-3,30), 111.83 (C-4,40), 116.94 (C-400), 124.96 (C-200),
128.76 (br, C-2-20), 131.85 (C-300), [139.94, 140.26 (O–C]C–O)],
142.43 (C-100), 144.03 (C-5,50), 148.95 (C]N–); 13C NMR
d (CDCl3,
3.2.1. 2-Phenylimino-4,5-di(2-furyl)-1,3-dioxole (3a)
75.4 MHz, þ60 ꢀC): 111.18 (C-3,30), 111.80 (C-4,40), 116.99 (C-400),
Yield 74%; crystallization from petroleum ether gave yellow
needles, mp 125–127 ꢀC. (Found: C, 69.53; H, 3.81; N, 4.80;
125.00 (C-200), 128.96 (C-2-20), 131.91 (C-300), 140.32 (O–C]C–O),
142.72 (C-100), 144.08 (C-5,50), 148.94 (C]N–); 13C NMR
d (CDCl3,
C17H11NO4 requires: C, 69.62; H, 3.78; N, 4.78); 1H NMR
d
(CDCl3,
75.4 MHz, ꢁ60 ꢀC): [110.78, 110.89 (C-3,30)], [111.85,111.90 (C-4,40)],
116.79 (C-400), 124.84 (C-200), [127.89, 128.18 (C-2,20)], 131.65 (C-300),
[139.26,139.83 (O–C]C–O)],141.62 (C-100), [143.83,143.98 (C-5,50)],
148.88 (C]N–); MS m/z (%): 373 (Mþþ2, 3), 371 (Mþ, 3),146 (18),118
(100), 95 (53), 92 (31), 90 (60), 63 (38); IR (Nujol): 1728, 1672, 1488,
200 MHz): 6.53 (br s, 2H, H-4,40), 6.88 (d, 2H, J¼3.5, H-3,30), 7.12 (t,
1H, J¼6.8, H-400), 7.24–7.37 (m, 4H, H-200,300), 7.54 (br s, 2H, H-5,50);
13C NMR (CDCl3, 50.3 MHz): 111.10 (C-3,30), 111.90 (C-4,40), 123.31
d
(C-200),124.17 (C-400),128.84 (br, C-2,20),128.99 (C-300),140.49 (br, O–
C]C–O), 143.41 (C-100), 144.06 (C-5,50), 148.78 (C]N–); MS m/z (%):
293 (Mþ, 5), 146 (22), 119 (55), 118 (100), 95 (55), 92 (30), 91(29), 90
(27), 64 (23), 63 (22); IR (Nujol): 3184, 1748, 1676, 1595, 1273, 1213,
1271, 1166, 1097, 1007, 953, 826, 742 cmꢁ1
.
3.2.6. 2-(2-Chloro-4-methylphenylimino)-4,5-di(2-furyl)-1,3-
dioxole (3f)
1164, 1083, 1005, 955, 820, 783, 750, 696, 691 cmꢁ1
.
Yield 75%; crystallization from acetonitrile gave orange needles,
mp 118–120 ꢀC. (Found: C, 63.14; H, 3.51; N, 4.03. C18H12ClNO4 re-
3.2.2. 2-(4-Chlorophenylimino)-4,5-di(2-furyl)-1,3-dioxole (3b)
Yield 76%; crystallization from acetonitrile gave brown flakes,
mp 138–140 ꢀC. (Found: C, 62.38; H, 3.11; N, 4.32. C17H10ClNO4 re-
quires: C, 63.26; H, 3.54; N, 4.10); 1H NMR
d (CDCl3, 200 MHz): 2.30
(s, 3H, CH3), 6.52 (br s, 2H, H-4,40), 6.86 (d, 2H, J¼3.3, H-3,30), 7.03
quires: C, 62.30; H, 3.08; N, 4.27); 1H NMR
d (CDCl3, 200 MHz): 6.55
(dd, 1H, J¼7.9, 1.6, H-500), 7.17 (d, 1H, J¼8.1, H-600), 7.23 (d, 1H, J¼1.4,
(br s, 2H, H-4,40), 6.89 (d, 2H, J¼3.1, H-3,30), 7.21 (d, 2H, J¼8.5, H-200),
H-300), 7.53 (br s, 2H, H-5,50); 13C NMR
d (CDCl3, 50.3 MHz): 20.60
7.28 (d, 2H, J¼8.5, H-300), 7.56 (br s, 2H, H-5,50); 13C NMR
d
(CDCl3,
(CH3), 111.18 (C-3,30), 111.85 (C-4,40), 123.26 (C-600), 127.32 (C-200),
127.95 (C-500), 128.93 (C-2,20), 130.21 (C-300), 134.71 (C-400), 138.62
(C-100), 140.23 (O–C]C–O), 144.05 (C-5,50), 149.33 (C]N–); MS m/z
(%): 341 (Mþ, 65), 218 (15), 167 (35), 146 (45), 132 (53), 118 (100), 95
(55); IR (Nujol): 3108, 1740, 1686, 1495, 1466, 1267, 1209, 1162, 1055,
50.3 MHz): 111.20 (C-3,30), 111.93 (C-4,40), 124.65 (C-200), 129.00 (C-
300), 129.30 (C-400), 140.15, 140.42 (O–C]C–Oþ), 142.05 (C-100), 144.14
(C-5,50), 149.07 (C]N–); MS m/z (%): 329 (M þ2, 17), 327 (Mþ, 35),
153 (37), 118 (100), 95 (77), 92 (37), 90 (57), 89 (41), 63 (36); IR
(Nujol): 3148,1729,1671,1489,1456,1165,1094, 954, 829, 742 cmꢁ1
.
958, 818, 752 cmꢁ1
.
3.2.3. 2-(2,4-Dichlorophenylimino)-4,5-di(2-furyl)-1,3-dioxole (3c)
Yield 73%; crystallization from acetonitrile gave pale yellow
needles, mp 132–134 ꢀC. (Found: C, 56.47; H, 2.52; N, 3.93.
3.2.7. 2-Phenylimino-4,5-bis(5-methyl-2-furyl)-1,3-dioxole (3g)
Yield 75%; crystallization from petroleum ether gave pale yellow
needles, mp 129–131 ꢀC. (Found: C, 69.97; H, 4.69; N, 4.32.

A. Guirado et al. / Tetrahedron 65 (2009) 3886–3892
3891
C19H15NO4 requires: C, 71.02; H, 4.71; 0N, 4.36); 1H NMR
(br s, 2H, H-3,30), 7.10–7.15 (m,1H, H-400), 7.25–7.38 (m, 4H, H-200,300);
d
(CDCl3,
2H, J¼3.2, H-3,30), 7.16 (d, 2H, J¼8.7, H-200), 7.43 (d, 2H, J¼8.7, H-300);
200 MHz, þ25 ꢀC): 2.37 (s, 6H, CH3, CH3 ), 6.13 (br s, 2H, H-4,40), 6.73
13CNMR
d
(CDCl3, 75.4 MHz):13.65(CH3, CH3 ),108.03 (C-4,40),111.77
0
(C-3,30), 116.73 (C-400), 125.03 (C-200), [128.10, 128.21 (C-2,20)], 131.81
(C-300), [138.40, 138.61 (O–C]C–O)], 142.68 (C-100þ), 149.31 (C]N–),
154.17 (C-5,50), 166.38 (C]O); MS m/z (%): 401 (M þ2, 11), 399 (Mþ,
11), 174 (93), 159 (100), 131 (32), 109 (32), 90 (17); IR (Nujol): 1729,
1H NMR
d
(CDCl3, 300 MHz, ꢁ60 ꢀC): [2.40 (s, 3H), 2.41 (s, 3H), CH3,
CH3 ], 6.18 (m, 2H, H-4,40), [6.75 (d, 1H, J¼3.6), 6.84 (d,1H, J¼3.3), H-
0
3,30], 7.20 (t, 1H, J¼7.2, H-400), 7.35–7.46 (m, 4H, H-200,300); 13C NMR
d
(CDCl3, 50.3 MHz, þ25 ꢀC): 13.63 (CH3), 107.98 (C-4,40), 111.65 (C-
1666, 1486, 1458, 1272, 1196, 1105, 961, 833, 805, 689 cmꢁ1
.
3,30), 123.27 (C-200), 123.88 (C-400), 128.09 (br, C-2,20), 128.84 (C-300),
138.78 (br, O–C]C–O), 143.53 (C-100), 149.02 (C]N–), 154.06 (C-
3.2.12. 2-(4-Chloro-2-methylphenylimino)-4,5-bis(5-methyl-2-
furyl)-1,3-dioxole (3l)
Yield 70%; crystallization from acetonitrile gave pale brown
granules, mp 116–118 ꢀC. (Found: C, 65.00; H, 4.41; N, 3.86.
5,50); 13C NMR
d
(CDCl3, 75.4 MHz, ꢁ60 ꢀC): [13.87, 13.90 (CH3,
CH3 )], [107.97, 107.99 (C-4,40)], [111.20, 111.34 (C-3,30)], 123.10 (C-
200), 123.87 (C-400), [127.25, 127.54 (C-2,20)], 128.84 (C-300), [137.93,
138.40 (O–C]C–O)], 142.76 (C-100), 148.99 (C]N–), [153.86, 153.94
(C-5,50)]; MS m/z (%): 321 (Mþ, 30), 184 (100), 109 (13), 77 (20); IR
0
C20H16ClNO4 requires: C, 64.96; H, 4.36; N, 3.79); 1H NMR
d
(CDCl3,
0
300 MHz): 2.27 (s, 3H, CH3), 2.37 (s, 6H, CH3, CH3 ), 6.12 (d, 2H, J¼2.4,
(Nujol): 1739,1669,1597,1464,1275,1208,1118,1019, 781, 698 cmꢁ1
.
H-4,40), 6.72 (br s, 2H, H-3,30), 7.12–7.17 (m, 3H, H-300,500,600); 13C NMR
0
(CDCl3, 75.4 MHz): 13.63 (CH3, CH3 ), 18.11 (CH3), 108.01 (C-4,40),
d
3.2.8. 2-(4-Ethoxycarbonylphenylimino)-4,5-bis(5-methyl-2-
furyl)-1,3-dioxole (3h)
111.73 (C-3,30), 123.04 (C-600), 126.14 (C-500), 128.20 (C-2,20)
, 128.52
*
(C-400) , 130.04 (C-300), 133.30 (C-200), 138.60 (O–C]C–O), 141.36 (C-
*
Yield 75%; crystallization from acetonitrile gave pale yellow
needles, mp 136–138 ꢀC. (Found: C, 67.30; H, 4.90; N, 3.61.
100), 148.68 (C]N–), 154.11 (C-5,50); MS m/z (%): 369 (Mþ, 4), 174
(90), 159 (100), 132 (28), 131 (39), 109 (68), 77 (45), 53 (52); IR
C22H19NO6 requires: C, 67.17; H, 4.87; N, 3.56); 1H NMR
d
(CDCl3,
(Nujol): 1723,1663,1485,1463,1274,1221,1111,1024, 965, 793 cmꢁ1
.
0
300 MHz): 1.39 (t, 3H, J¼7.2, CH3), 2.38 (s, 6H, CH3, CH3 ), 4.38 (q, 2H,
J¼7.2, CH2), 6.14 (br s, 2H, H-4,40), 6.74 (br s, 2H, H-3,30), 7.32 (d, 2H,
3.2.13. (E)-1,2-Di(2-furyl)vinylene bis(N-phenylchloroform-
imidate) (4a)
J¼8.4, H-200), 8.04 (d, 2H, J¼8.4, H-300); 13C NMR
d (CDCl3, 75.4 MHz):
13.57 (CH3, CH3 ),14.26 (CH3), 60.60 (CH2),108.02 (C-4,40),111.82 (C-
3,30), 123.06 (C-200), 125.77 (C-400), 128.19 (br, C-2,20), 130.50 (C-300),
138.40 (br, O–C]C–O), 148.10 (C-100), 149.70 (C]N–), 154.23 (C-
5,50), 166.38 (C]O); MS m/z (%): 393 (Mþ, 30), 174 (100), 159 (66),
146 (29), 131 (16), 109 (18); IR (Nujol): 1738, 1712, 1669, 1603, 1464,
Yield 8%; crystallization from acetonitrile gave yellow prisms,
mp 173–175 ꢀC. (Found: C, 61.52; H, 3.38; N, 6.00. C24H16Cl2N2O4
0
requires: C, 61.69; H, 3.45; N, 5.99); 1H NMR
d (CDCl3, 200 MHz):
6.57 (dd, 2H, J¼3.6, 1.9), 6.76 (dd, 4H, J¼8.4, 1.4), 6.85 (dd, 2H, J¼3.7,
0.6), 7.10 (tt, 2H, J¼7.4, 2.0), 7.22–7.31 (m, 4H), 7.58 (dd, 2H, J¼1.6,
1456, 1368, 1284, 1245, 1210, 1115, 1025, 968, 787, 702 cmꢁ1
.
0.7); 13C NMR
d (CDCl3, 50.3 MHz): 111.62 (CH), 112.33 (CH), 121.25
(CH), 124.93 (CH), 128.89 (CH), 133.74 (C), 138.25 (C), 143.58 (CH),
144.64 (C),145.60 (C); MS m/z (%): 467 (Mþþ1, 4), 431 (16), 313 (34),
312 (100); IR (Nujol): 1697, 1596, 1490, 1278, 1133, 1080, 1061, 1019,
3.2.9. 2-(2-Chloro-4-methylphenylimino)-4,5-bis(5-methyl-2-
furyl)-1,3-dioxole (3i)
Yield 73%; crystallization from petroleum ether gave orange
needles, mp 119–120 ꢀC. (Found: C, 65.00; H, 4.28; N, 3.83.
901, 751, 691 cmꢁ1
.
C20H16ClNO4 requires: C, 64.96; H, 4.36; N, 3.79); 1H NMR
d
(CDCl3,
3.2.14. (E)-1,2-Di(2-furyl)vinylene bis[N-(4-chlorophenyl)-
chloroformimidate] (4b)
Yield 12%; crystallization from acetonitrile gave pale brown
needles, mp 211–213 ꢀC. (Found: C, 53.71; H, 2.69; N, 5.17.
C24H14Cl4N2O4 requires: C, 53.76; H, 2.63; N, 5.22); 1H NMR
0
300 MHz): 2.31 (s, 3H, CH3), 2.37 (s, 6H, CH3, CH3 ), 6.12 (br s, 2H, H-
4,40), 6.73 (br s, 2H, H-3,30), 7.03 (dd, 1H, J¼8.1, 1.5, H-500), 7.18 (d, 1H,
J¼8.1, H-600), 7.203 (d, 1H, J¼1.5, H-300); 13C NMR
d (CDCl3, 75.4 MHz):
13.66 (CH3, CH3 ), 20.60 (CH3), 108.11 (C-4,40), 111.82 (C-3,30), 123.28
(C-600), 127.37 (C-200), 127.84 (C-500), 128.35 (C-2,20), 130.13 (C-300),
134.47 (C-400), 138.56 (br, O–C]C–O),þ138.75 (C-100), 149.63 (C]N–),
154.10 (C-5,50); MS m/z (%): 369 (M , 4), 174 (81), 159 (100), 132
(79),131 (44),109 (74), 77 (48), 53 (57); IR (Nujol): 1738, 1669, 1494,
d
(CDCl3, 300 MHz): 6.56 (dd, 2H, J¼3.3, 1.7), 6.68 (d, 4H, J¼8.7),
6.81 (d, 2H, J¼3.3), 7.22 (d, 4H, J¼8.7), 7.57 (d, 2H, J¼1.4); 13C NMR
d
(CDCl3, 75.4 MHz, þ45 ꢀC): 111.71 (CH), 112.35 (CH), 122.69 (CH),
129.08 (CH), 130.58 (C), 133.82 (C), 138.93 (C), 143.15 (C), 143.72
(CH), 145.56 (C); MS m/z (%): 534 (Mþ, 1), 174 (62), 172 (80), 111
(100), 95 (40), 75 (38); IR (Nujol): 1693,1486,1379,1285,1135,1087,
1466, 1270, 1214, 1118, 1103, 951, 790 cmꢁ1
.
3.2.10. 2-(2,4-Dichlorophenylimino)-4,5-bis(5-methyl-2-furyl)-1,3-
dioxole (3j)
903, 836, 751 cmꢁ1
.
Yield 74%; crystallization from petroleum ether gave pale yellow
needles, mp 140 ꢀC. (Found: C, 58.38; H, 3.43; N, 3.66. C19H13Cl2NO4
3.2.15. (E)-1,2-Di(2-furyl)vinylene bis[N-(2,4-dichlorophenyl)-
chloroformimidate] (4c)
requires: C, 58.48; H, 3.36; N, 3.59); 1H NMR
d
(CDCl3, 300 MHz):
Yield 11%; crystallization from acetonitrile gave pale green
needles, mp 193–195 ꢀC. (Found: C, 47.76; H, 1.95; N, 4.61.
0
2.37 (s, 6H, CH3, CH3 ), 6.12 (br s, 2H, H-4,40), 6.74 (br s, 2H, H-3,30),
7.18–7.24 (m, 2H, H-500,600), 7.41 (d, 01H, J¼2.1, H-300); 13C NMR
C24H12Cl6N2O4 requires: C, 47.64; H, 2.00; N, 4.63); 1H NMR
d (CDCl3,
d
(CDCl3, 75.4 MHz): 13.65 (CH3, CH3 ), 108.06 (C-4,40), 111.97 (C-
200 MHz): 6.58 (dd, 2H, J¼3.4, 1.3), 6.68 (d, 2H, J¼8.5), 6.86 (d, 2H,
3,30), 124.37 (C-600), 127.31 (C-500), 128.40 (br, C-2,20), 128.55 (C-200),
129.01 (C-400), 129.44 (C-300), 138.33 (br, O–C]C–O), 140.31 (C-100þ),
150.02 (C]N–),154.26 (C-5,50); MS m/z (%): 391 (Mþþ2, 2), 389 (M ,
11),174 (80),159 (100),131 (34),109 (44), 77 (23), 53 (42); IR (Nujol):
J¼3.5), 7.15 (dd, 2H, J¼8.5, 2.1), 7.33 (d, 2H, J¼2.1), 7.57–7.59 (m, 2H);
13C NMR
d (CDCl3, 50.3 MHz): 112.02 (CH), 112.32 (CH), 123.07 (CH),
126.86 (C),127.51 (CH),129.72 (CH),133.96 (C),141.20 (C),141.35 (C),
143.94 (CH), 145.36 (C); MS m/z (%): 602 (Mþ, 2), 380 (26), 208 (98),
206 (100), 193 (19), 171 (24), 147 (25), 145 (41), 95 (61); IR (Nujol):
1723, 1659, 1478, 1465, 1377, 1271, 1197, 1095, 1021, 966, 784 cmꢁ1
.
1691, 1474, 1377, 1288, 1166, 1149, 1099, 911, 736 cmꢁ1
.
3.2.11. 2-(4-Bromophenylimino)-4,5-bis(5-methyl-2-furyl)-1,3-
dioxole (3k)
3.2.16. (E)-1,2-Di(2-furyl)vinylene bis[N-(4-cyanophenyl)-
chloroformimidate] (4d)
Yield 67%; crystallization from acetonitrile gave pale yellow
needles, mp 124–126 ꢀC. (Found: C, 56.89; H, 3.48; N, 3.55.
Yield 11%; crystallization from acetonitrile gave yellow flakes,
mp 225–227 ꢀC. (Found: C, 60.49; H, 2.70; N, 10.78. C26H14Cl2N4O4
C19H14BrNO4 requires: C, 57.02;0H, 3.53; N, 3.50); 1H NMR
d (CDCl3,
300 MHz): 2.37 (s, 6H, CH3, CH3 ), 6.13 (d, 2H, J¼3.2, H-4,40), 6.73 (d,
requires: C, 60.36; H, 2.73; N, 10.83); 1H NMR
d (DMSO-d6,

3892
A. Guirado et al. / Tetrahedron 65 (2009) 3886–3892
200 MHz): 6.82 (br s, 2H), 6.94 (d, 4H, J¼8.2), 7.02 (d, 2H, J¼3.2),
Complete crystallographic data (excluding structure factors)
have been deposited at the Cambridge Crystallographic Data Centre
under the number CCDC 669292.
7.85 (d, 4H, J¼8.2), 8.06 (s, 2H); 13C NMR
d (DMSO-d6, 50.3 MHz):
107.80 (C), 112.45 (CH), 112.84 (CH), 118.57 (C), 121.84 (CH), 132.58
(CH), 133.73 (C), 139.97 (C), 144.05 (CH), 145.57 (C), 148.00 (C); MS
m/z (%): 516 (Mþ, 0.1), 165 (32), 163 (100), 147 (12), 144 (14), 102
(70), 95 (40), 75 (10); IR (Nujol): 3129, 2227, 1694, 1601, 1501, 1486,
Acknowledgements
1281, 1134, 1086, 1028, 912, 845, 759 cmꢁ1
.
We gratefully acknowledge the financial support of the Funda-
´
´
´
´
cion Seneca of the Comunidad Autonoma de la Region de Murcia
3.2.17. (E)-1,2-Di(2-furyl)vinylene bis[N-(4-bromophenyl)-
chloroformimidate] (4e)
(project 03035/PI/05).
Yield 13%; crystallization from acetonitrile gave pale brown
needles, mp 238–240 ꢀC. (Found: C, 46.14; H, 2.32; N, 4.50.
C24H14Br2Cl2N2O4 requires: C, 46.11; H, 2.26; N, 4.48); 1H NMR
Supplementary data
X-ray structural data of compound 4f; optimized geometries
and energies of the ground state and the TS of 3a are provided.
Supplementary data associated with this article can be found in the
online version, at doi:10.1016/j.tet.2009.02.082.
d
(CDCl3, 300 MHz, þ55 ꢀC): 6.55–6.61 (m, 2H), 6.62 (d, 4H, J¼8.2),
6.80 (d, 2H, J¼3.6), 7.37 (d, 4H, J¼8.4), 7.56 (br s, 2H); 13C NMR
d
(CDCl3, 75.4 MHz, þ55 ꢀC): 111.65 (CH), 112.33 (CH), 118.22 (C),
123.00 (CH), 131.98 (CH), 133.81 (C), 138.78 (C), 143.66 (CH), 143.77
(C), 145.54 (C); MS m/z (%): 622 (Mþ, 1), 218 (61), 216 (44), 157 (53),
155 (58), 118 (28), 102 (85), 95 (100), 90 (45), 76 (77), 75 (59); IR
References and notes
(Nujol): 1699, 1484, 1284, 1134, 1088, 1010, 905, 829, 750 cmꢁ1
.
1. Stapelfeldt, H. E.; Perone, S. P. Anal. Chem. 1968, 40, 815.
2. Stapelfeldt, H. E.; Perone, S. P. Anal. Chem. 1969, 41, 623.
3. Johnson, D. C.; Gaines, P. R. Anal. Chem. 1973, 45, 1670.
4. Simonet, J.; Lund, H. Bull. Soc. Chim. Fr. 1975, 2547.
5. Boujlel, K.; Simonet, J. Tetrahedron Lett. 1979, 1497.
3.2.18. (E)-1,2-Di(2-furyl)vinylene bis[N-(2-chloro-4-
methylphenyl)chloroformimidate] (4f)
Yield 10%; crystallization from acetonitrile gave yellow needles,
mp 174–176 ꢀC. (Found: C, 55.41; H, 3.19; N, 5.07. C26H18Cl4N2O4
6. Adams, C.; Kamkar, N. M.; Utley, J. H. P. J. Chem. Soc., Perkin Trans. 2 1979, 1767.
7. Guirado, A.; Barba, F.; Manzanera, C.; Velasco, M. D. J. Org. Chem. 1982, 47, 142.
8. Guirado, A.; Barba, F.; Tevar, A. Synth. Commun. 1984, 14, 333.
9. Guirado, A.; Barba, F.; Hursthouse, M. B.; Arcas, A. J. Org. Chem. 1989, 54, 3205.
10. Guirado, A.; LopezSanchez, E.; Andreu, R.; Zapata, A. Tetrahedron Lett. 2004, 45,
2075.
11. These compounds are sometimes also referred to as isocyanide dichlorides,
isonitrile dichlorides, carbylamine dichlorides, dichloromethyleneamines, or
carbonyl dichloride imides.
12. Kuehle, E.; Anders, B.; Zumach, G. Angew. Chem., Int. Ed. Engl. 1967, 6, 649.
13. Ulrich, H. The Chemistry of Imidoyl Halides; Plenum: New York, NY, 1968;
Chapter 2.
14. Guirado, A.; Zapata, A.; Fenor, M. Tetrahedron Lett. 1992, 33, 4779.
15. Guirado, A.; Zapata, A.; Gomez, J. L.; Trabalon, L.; Galvez, J. Tetrahedron 1999, 55,
9631.
requires: C, 55.34; H, 3.22; N, 4.96); 1H NMR
d (CDCl3, 200 MHz):
2.26 (s, 6H), 6.56 (dd, 2H, J¼3.5, 1.8), 6.63 (d, 2H, J¼7.9), 6.88 (d, 2H,
J¼3.5), 6.95 (dd, 2H, J¼8.1, 1.3), 7.13 (br s, 2H), 7.57 (d, 2H, J¼1.7); 13C
NMR
d (CDCl3, 50.3 MHz): 20.73 (CH3), 111.86 (CH), 112.27 (CH),
121.94 (CH), 125.43 (C), 127.88 (CH), 130.18 (CH), 133.78 (C), 135.78
(C), 139.81 (C), 140.53 (C), 143.76 (CH), 145.35 (C); MS m/z (%): 562
(Mþ, 1), 362 (27), 360 (41), 188 (64), 186 (100), 125 (37); IR (Nujol):
1687, 1494, 1462, 1379, 1162, 1136, 1087, 918, 855, 826, 744 cmꢁ1
.
16. Guirado, A.; Zapata, A.; Galvez, J. Tetrahedron Lett. 1994, 35, 2365.
17. Guirado, A.; Zapata, A.; Jones, P. G. Tetrahedron 1995, 51, 3641.
18. Guirado, A.; Zapata, A.; Jones, P. G. Tetrahedron 1995, 51, 10375.
19. Guirado, A.; Zapata, A.; Andreu, R.; Martiz, B. Tetrahedron Lett. 2002, 43, 1405.
20. This separate chemical behaviour cannot be explained by significant differ-
ences in the reduction potentials of these 1,2-diketones as evidenced by its Ep-
values (V vs SCE): 2,20-furil (ꢁ0.97); 2,20-thenil (ꢁ0.89); 2,20-pyridil (ꢁ0.88).
21. The reduction of parent compound 2a is a totally irreversible process (Ep¼
ꢁ1.83 V vs SCE), evidencing that these reagents have potential utility to react
with many other nucleophilic intermediates without interferences caused by
this electrochemical process.
22. Sakai, S.; Murata, M.; Wada, N.; Fujinami, T. Bull. Chem. Soc. Jpn. 1983, 56, 1873.
23. Hatanaka, M.; Takahashi, K.; Nakamura, S.; Mashino, T. Bioorg. Med. Chem.
2005, 13, 6763.
24. Allen, F. H. Acta Crystallogr. 2002, B58, 380.
25. Kessler, H. Angew. Chem., Int. Ed. Engl. 1970, 9, 219.
3.3. X-ray structure determination of compound 4f
Crystaldata:C26H18Cl4N2O4, Mr¼564.22, monoclinic, space group
C2/c, a¼12.443(3), b¼16.827(4), c¼12.381(3) Å,
b
¼99.966(18)ꢀ,
U¼2553.3(11) Å3 at ꢁ100 ꢀC; Z¼4, Dx¼1.468 g/cm3, F(000)¼1152,
m
¼0.5 mm. Data collection: A pale yellow tablet 0.7ꢂ0.3ꢂ0.1 mm
was mounted in inert oil on a glass fibre and transferred to the cold
gas stream of the diffractometer (Siemens P4). Measurements were
performed to 2qmax 50ꢀ with monochromated Mo K
a
radiation. Of
3469 measured reflections, 2262 were unique (Rint¼0.021) and were
used for all calculations. Structure refinement: The structures were
refined anisotropically against F2 (program SHELXL-97, G.M. Shel-
drick, University of Go¨ttingen). The methyl group was refined as
a rigid group, other H with a riding model. After initial refinement,
a significant peak of ca. 1.5 e/Å3 was identified as an alternative po-
sition for C5, and the second disorder component was extended
using an alternative position for the furyl group. The relative occu-
pations of the disorder components refinedto 3:1. Attempts torefine
the structure in the alternative space group Cc also led to a disor-
dered structure. Because of the inherent problems associated with
disordered structures, the molecular dimensions (especially of the
disordered groups) shouldbe interpretedwithcaution. Thefinal wR2
value was 0.0964 for all reflections, 189 parameters and 179 re-
straints (to the geometry of disordered groups), with R1 0.0391 for
26. An extensive study on this subject is in progress.
27. This value is in good agreement with that experimentally determined by Prof.
M. Galajov (Universidad de Alcala´ de Henares, Madrid, Spain; private com-
munication) for 2-(4-chlorophenylimino)-4,5-diphenyl-1,3-dioxole, a similar
compound obtained by our synthetic methodology. A NMR study by variable
temperature experiments gave
28. Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen, A. G.; Taylor, R.
J. Chem. Soc., Perkin Trans. 2 1987, S1.
D
Gs ¼15.0 kcal/mol.
298
29. Single crystals suitable for an X-ray diffraction analysis could not be obtained
for any of these compounds despite intensive effort.
30. Spartan’06; Wavefunction: Irvine, CA, 2006.
31. Caution must be exercised when handling perchlorates in order to exclude risk
of explosion. Evaporation of organic solutions containing perchlorates requires
to be carried out in vacuo and at moderate temperature. Contact with strong
acids must be avoided.
32. The electrolyses can also be carried out in acetonitrile–sodium
tetrafluoroborate.
reflections with I>2s
(I); max. Dr 0.22 e/Å3, S 1.05.