Synthesis of cyclohexadienylstannanes - Novel example of vinylic SRN1 mechanism: A theoretical and experimental study

Article abstract of DOI:10.1016/j.jorganchem.2008.04.018

The reaction of trimethyltinsodium (1) with 1-(diethoxyphosphoryl)oxy-1,3-cyclohexadienes in liquid ammonia under irradiation affords the corresponding 1-trimethylstannylcyclohexadienes. We suggest that these reactions occur by an S_RN1 mechanism. On the other hand, 2-(diethoxyphosphoryl)oxy-1,3-cyclohexadiene reacts very slowly towards 1 and the substitution product decomposes under the reaction conditions employed. Thus, structurally similar compounds do not behave in the same way under ET conditions. We suggest that this behavior is mainly due to differences in spin density of their radical anions, which affect their fragmentation rates. Our results are supported by computational calculations.

Full text of DOI:10.1016/j.jorganchem.2008.04.018

Journal of Organometallic Chemistry 693 (2008) 2458–2462
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Note
Synthesis of cyclohexadienylstannanes – Novel example of vinylic SRN1
mechanism: A theoretical and experimental study
a
a
a
Viviana B. Dorn , Mercedes A. Badajoz , Marıa T. Lockhart , Alicia B. Chopa a, ,1, Adriana B. Pierini b,1
*
´
a Departamento de Química, Universidad Nacional del Sur, Avenida Alem 1253, 8000 Bahía Blanca, Argentina
b INFIQC, Departamento de Química Orgánica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Ciudad Universitaria, X5000HUA Córdoba, Argentina
a r t i c l e i n f o
a b s t r a c t
Article history:
The reaction of trimethyltinsodium (1) with 1-(diethoxyphosphoryl)oxy-1,3-cyclohexadienes in liquid
ammonia under irradiation affords the corresponding 1-trimethylstannylcyclohexadienes. We suggest
that these reactions occur by an SRN1 mechanism. On the other hand, 2-(diethoxyphosphoryl)oxy-1,3-
cyclohexadiene reacts very slowly towards 1 and the substitution product decomposes under the reac-
tion conditions employed. Thus, structurally similar compounds do not behave in the same way under
ET conditions. We suggest that this behavior is mainly due to differences in spin density of their radical
anions, which affect their fragmentation rates. Our results are supported by computational calculations.
Ó 2008 Elsevier B.V. All rights reserved.
Received 27 December 2007
Received in revised form 7 April 2008
Accepted 14 April 2008
Available online 27 May 2008
Keywords:
Cyclohexadienyltin
Vinylic SRN1
Trimethyltinsodium
DFT
1. Introduction
[8] the SRN1 mechanism prevails over ionic routes even with sub-
strates containing vinylic and allylic hydrogen(s).
Although vinyl substrates are very unreactive toward nucleo-
philic substitution [1], multiple mechanisms for nucleophilic sub-
stitution reactions with vinylic systems (SNV) are known [1,2].
Mainly, the mechanistic route depends on structural features.
In contrast with the various examples reported in the literature
related with ionic nucleophilic vinylic substitutions, there have
been reported only few examples associated with vinylic radical
nucleophilic substitutions (SRN1). It should be mentioned that not
only the substrate structure but also the nature of the anion are
essential factors for the prevalence of an SRN1 vinylic route over io-
nic pathways and it is necessary an appropriate combination of
both [3–6]. Thus, only vinyl systems supporting, at least, a phenyl
group afforded the substitution product by SRN1. Moreover, when
the anion basicity prevails over its reducing character the presence
of both vinylic and allylic hydrogen(s) should be avoided. Recently,
we have demonstrated that the diethoxyphosphoryloxy group can
act as an excellent nucleofuge in the reaction of aryl phosphate es-
ters [7] as well as vinyl diethyl phosphate esters (vinylDEP) [4],
with trimethyl- and triphenyltin anions in liquid ammonia under
irradiation, and that these reactions take place through an SRN1
mechanism. Because of the reducing character of organotin anions
The synthesis of vinylstannanes from vinylDEP is of interest not
only from a mechanistic point of view but also as an alternative
route [9] for the synthesis of vinylstannanes starting from carbony-
lic substrates.
We now report the experimental results and a theoretical study
of the reaction of cyclohexadienylDEPs with 1 in liquid ammonia.
As far as we know this reaction represents the first example of a
vinylic SRN1 route without the presence of aryl groups attached
to the vinylic system.
The proposed mechanism is a chain process in which radicals
and radical anions are involved as intermediates, as it is illustrated
in Scheme 1 [10].
In few systems this chain process is initiated by spontaneous ET
from the nucleophile to the substrate forming the vinylic radical
anion (Eq. (1)) [10]. Stimulation by UV light or by Fe2+ has been re-
cently applied in vinylic SRN1 reactions [3–5]. It should be noted
that the coupling with the nucleophile (Eq. (3)) is not the only reac-
tion that vinyl radicals can undergo: hydrogen atom transfer from
the solvent is one of the most important side reactions (Eq. (5)).
This competitive reaction is diminished by using liquid ammonia
as solvent [10].
A phenyl group attached to a vinylic carbon increases the stabil-
ity of the p-system and, particularly, lowers its LUMO, being this
beneficial to the SRN1 substitution since this increases the electron
affinity of the substrate [11]. Taking into account the energy of the
LUMO MO in cyclohexadienyl systems [12] and the excellent
* Corresponding author. Tel./fax: +54 291 4595187.
E-mail addresses: abchopa@uns.edu.ar (A.B. Chopa), adriana@fcq.unc.edu.ar (A.B.
Pierini).
1
nucleofuge character of
a diethoxyphosphoryloxy group, we
Member of CIC.
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.04.018

V.B. Dorn et al. / Journal of Organometallic Chemistry 693 (2008) 2458–2462
2459
Table 1
VyX
+
Nu
(VyX)
Vy
+
Nu
(1)
(2)
(3)
(4)
(5)
Photostimulated reactions of (diethoxyphosphoryl)oxy-1,3-cyclohexadienes with
Me3SnNa (1) in liquid ammoniaa
(VyX)
+
X
Entry
Substrate
Time (h)
Product
Yield (%)b
Vy
+
+
Nu
(VyNu)
VyNu
DEP
SnMe3
(VyNu)
Vy
+ VyX
SH
+
(VyX)
1
6
27
VyH
+
S
3a
2a
Scheme 1. Vinylic SRN1 mechanism.
DEP
SnMe3
2
3
8
6
0c
considered that cyclohexadienylDEPs may possibly be adequate
substrates for the predominance of an SRN1 mechanism. Thus, we
started the study of the reaction of 1- (2a) and 2-(diethoxyphos-
phoryl)oxy-1,3-cyclohexadiene (2e) with 1 in liquid ammonia.
The results obtained are summarized in Table 1. The results pre-
sented are average yields of three to four runs.
3e
2e
SnMe3
DEP
44d
Significant differences were found in both reactions. Thus, 2a
reacted with 1, by a photostimulated reaction, rendering 1-tri-
methylstannyl-1,3-cyclohexadiene (3a, 27%) together with starting
material, not quantified (entry 1). We found that no substitution
product was formed when the reaction was carried out in the dark,
recovering almost quantitatively the starting substrate. These
results indicate the occurrence of a photo electron-induced sub-
stitution route. In order to improve the yield of 3a, we carried
out a reaction using an excess of 1. An increase in the 1/2a ratio
(5/1) produced a complex reaction mixture from which neither
3a nor 2a could be detected.
Otherwise, in the reaction of isomer 2e and 1 (1/1.2 ratio), even
after 8 h under irradiation, no substitution product, i.e., 2-tri-
methylstannyl-1,3-cyclohexadiene (3e) was detected and the
starting substrate was recovered in 85% (entry 2). It should be
mentioned that some unidentified stannylated products were
detected (CG/MS). When the reaction was carried out in the
presence of an excess of 1 (1/2e, 5/1 ratio), once more a complex
mixture of unidentified products was obtained without the
presence of 2e.
2b
3b
2be
4
5
6
7
6
6
6
6
12
3b
SnMe3
DEP
46d
15
2c
3c
2ce
DEP
3c
SnMe3
49d,f
3d
2d
SnMe3
DEP
8
8
0g
We also found that there is no reaction between either 1-(dieth-
oxyphosphoryl)oxy-4-methyl-1,3-cyclohexadiene (2b) or 1-(dieth-
oxyphosphoryl)oxy-6-methyl-1,3-cyclohexadiene (2c) and 1 in the
dark (6 h) and the unreacted precursors were recovered in each
case. Nevertheless, under irradiation in the same time period, the
substitution products 1-trimethylstannyl-4-methyl-1,3-cyclohexa-
diene (3b) and 1-trimethylstannyl-6-methyl-1,3-cyclohexadiene
(3c) were obtained in 44% and 46% yields, respectively (entries 3
and 5). It should be mentioned that both photostimulated reac-
tions were largely inhibited by addition of p-dinitrobenzene (p-
DNB) (10%), a well-known radical anion trap and inhibitor of the
2f
3f
a
Substrate/1 molar ratio 1/1.2; [Substrate] = 5.45 mM. No substitution products
were detected without irradiation.
b
Isolated yield unless otherwise stated.
85% of substrate recovered.
c
d
2–4% of the reduced cyclohexadiene parent compound.
e 10% p-DNB added.
f
GC/MS, relative percentage in the crude product.
88% of substrate recovered.
g
SRN1 propagation cycle (entries 4 and 6) [3,10]. These results
clearly indicate that these substrates also react with 1 by the
It should be mentioned that in experiments 3, 5 and 7, together
with the corresponding substitution products 3b, 3c and 3d there
were detected the related reduction products, i.e., 1-methyl-1,3-
cyclohexadiene (4b), 5-methyl-1,3-cyclohexadiene (4c) and 2-
methyl-1,3-cyclohexadiene (4d) in ca. 2–4%. When these reactions
were carried out in the dark no reduction products were detected.
We inferred that their presence may be due to the competitive
hydrogen abstraction reaction by the radical intermediate from
ammonia (Scheme 1, Eq. (5)).
Taking into account the possibility that the 2-trimethylstannyl-
cyclohexadienes are being formed but are not isolable under the
reaction conditions employed, as suggested but one referee, we
carried out a series of reactions, at shorter times, employing 2e
as starting material. The products mixtures were analyzed by CG/
MS and we informed the relative percentages obtained. When
the photostimulated reaction between 2e and 1 was quenched at
SRN1 mechanism.
In addition, we have carried out the synthesis of 1-(diethoxy-
phosphoryl)oxy-3-methyl-1,3-cyclohexadiene (2d). Unfortunately,
2d was difficult to purify because it decomposed either on column
chromatography or by distillation. Anyway, we carried out the
reaction of 2d, without previous purification, with 1. Meanwhile,
the reaction carried out in the dark (6 h) was negative recovering
the starting material, under irradiation the corresponding 1-tri-
methylstannyl-3-methyl-1,3-cyclohexadiene (3d) was detected as
principal product, as characterized by GC/MS (entry 7). When we
carried out the reaction of 2-(diethoxyphosphoryl)oxy-5-methyl-
1,3-cyclohexadiene (2f) with 1, no substitution product was de-
tected even after 8 h under irradiation and the starting substrate
was almost completely recovered (88%) together with small
amounts of unidentified stannylated compounds (entry 8).

2460
V.B. Dorn et al. / Journal of Organometallic Chemistry 693 (2008) 2458–2462
30 min, compound 3e was detected in 6% yield, together with
starting material (92%) and traces of unidentified stannylated
compounds (2%). The mixtures obtained under similar conditions
but at longer reaction times (1 h and 2 h, respectively) showed that
meanwhile the yield of compound 3e decreased (1.5% and none,
respectively) the yield of the unidentified stannylated compounds
increased (11.5% and 13%, respectively); in both cases the starting
material was recovered in about 87%. It should be mentioned that
the reaction of 2e and 1 in the dark, after 1 h, showed the absence
of 3e as well as of the unidentified stannylated compounds, recov-
ering the starting substrate. These results indicate that there is a
photostimulated electron transfer (PET) between 2e and 1 render-
ing product 3e, which decomposed under the reaction conditions
employed. Moreover, the results point out that this PET reaction
is inhibited with time (perhaps due to the presence of the decom-
position products?) and similar mixtures were obtained after
either 2h or 8 h of reaction.
In order to compare the reactivity of both 2a and 2e towards 1
we carried out the photostimulated reaction (30 min) of a mixture
of 2a (1 mmol) and 2 e (1 mmol) with 1 (1.2 mmol). This competi-
tion reaction showed, as expected, that the relative reactivity of 2a
is higher than 2e towards 1. Thus, by CG/MS we detected 3a and 3e
in a ratio of 5/1, together with large amounts of both starting sub-
strates and traces of unidentified stannylated compounds.
These results were unexpected since as the p* MO energy is not
likely to be affected by the position of the DEP group in the ring, all
the substrates would have similar electron affinities making
feasible their single-electron reduction (Scheme 1, Eq. 1)). Thus,
we inferred that the dissimilar reactivity observed would be
probably due to differences in the fragmentation rates of the radi-
cal anions formed (Scheme 1, Eq. (2). Moreover, we considered that
the fact that no reduction products (coming from the abstraction of
hydrogen from ammonia by the vinyl radical) were found in the
reaction of either 2e or 2f with 1, was a signal that step 2 did
not take place.
In order to obtain information on this matter we theoretically
study the neutrals and the radical anions of compounds 2a0 and
2e0, the dimethoxyphosphoryloxy (DMP) analogs of 2a and 2e.
The calculations were performed with the B3LYP [13] DFT [14]
functional and the 6-31+G* basis set known to be an appropriate
methodology for the theoretical study of the electronic and geo-
metric properties of radical anions [15]. Some of the relevant
parameters calculated for the system are presented in Table 2.
The LUMO MOs of the neutrals have p symmetry and they are, as
expected, similar in energy (ꢀ1.049 eV and ꢀ1.081 eV for 2a0 and
2e0, respectively) [16]. The unpaired electron of both radical anions
locates in the butadienyl p system. In going from the neutrals to
the radical anions elongation of both C@C double bonds and short-
ening of the Csp2–Csp2 single bond are the main geometric modifi-
cations of the p system (Table 2). Also C–O elongation and O–
P(O) shortening occur along the electron capture.
From the above mentioned results it is evident that, in the sys-
tems studied, the substitution products were formed through an
SRN1 mechanism: the reactions did not take place in the dark and
their rates were significantly reduced when p-DNB was added. It
is also evident that the incidence of the SRN1 mechanism appears
to be dependent on some structural features of the starting sub-
strate. Meanwhile compounds supporting the DEP group on car-
bon-2 react very slowly towards 1 and the substitution product
decomposes under the reaction conditions employed, substrates
supporting the nucleofuge on carbon-1, did afford the substitution
products in rather low to good yields.
The C–C bond distances of the butadienyl systems of these
intermediates correlate with the localization of the unpaired elec-
tron mainly at the terminal carbons of the butadienyl p system of
both radical anions with a considerably low density at the Cipso to
the DMP group in 2e0Åꢀ. The unpaired spin distribution of both
intermediates is shown in Fig. 1. This spin density does not modi-
fied when methanol is included in the calculation of both species to
model a polar protic solvent within a continuum model.
Table 2
B3LYP/6-31+G* main geometric and electronic properties of 2a0, 2e0 and their radical anions
Compound
Bond distances (Å)
LUMO (eV)
AEAa (eV)
Spin densityb
C4–C3
C3–C2
C2–C1
C–O
O–P(O)
P@O
2a0
1.345
1.388
1.345
1.405
1.466
1.419
1.465
1.410
1.341
1.409
1.341
1.385
1.399
1.489
1.402
1.450
1.612
1.572
1.617
1.596
1.478
1.491
1.478
1.484
ꢀ1.0495
ꢀ1.0816
ꢀ0.135
ꢀ0.082
2a0 ꢁꢀ
2e0
0.46 (0.40)
0.04 (0.09)
2e0 ꢁꢀ
a
Adiabatic electron affinity [AEA = ERDMP ꢀ ERDMP-ꢁ (zero-point energy corrected)].
b
Mulliken spin density at Cipso to the DMP leaving group. NBO spin density within parentheses.
Fig. 1. Gas phase B3LYP/6-31 + G* spin density of 2a0 and 2e0
.
Åꢀ
Åꢀ

V.B. Dorn et al. / Journal of Organometallic Chemistry 693 (2008) 2458–2462
2461
for 119Sn) using CDCl3 as solvent. Chemical shifts (d) are reported
in ppm from TMS with solvent resonance as the internal standard
(1H: d 7.27 ppm and 13C: d 77.0 ppm), or Me4Sn (119Sn). Coupling
constants (J) are given in Hz. NMR spectra were recorded at
25 °C. Mass spectra were obtained with a GC/MS instrument
(HP5-MS capillary column, 30 m, 0.25 mm i.d. ꢂ 0.25 lm)
equipped with 5972 mass selective detector operating at 70 eV
(EI). GC analyses were carried out on a Shimadzu GC-9A chromato-
graph, equipped with a flame-ionization detector and a 2 m packed
column (1.5% OV17 9A SUS Chrom 103 80/1000). Heating program:
initial temperature: 50 °C, initial time: 5 min, speed of heating:
5 °C/min and final temperature: 250 °C. Retention times (tR) are gi-
ven in minutes.
Table 3
B3LYP/6-31+G* energetic and main geometric properties of transition states for
ꢁꢀ
ꢁꢀ
dissociation of 2a0 and 2e0
Åꢀ
Åꢀ
2a0
2e0
DE (RDMPꢁꢀ ? Rꢁ + DMPꢀ)a
ꢀ3.22
ꢀ1.88
a
Ea
3.9
7.2
Transition state
Bond distances (Å)
C–O
O–P(O)
P(O)
C1–C2
C2–C3
C3–C4
1.807
1.545
1.500
1.383
1.441
1.367
1.768
1.560
1.492
1.369
1.433
1.365
Chargesb
at oxygen: Colefinic–OP
Me–OP
(O)P
ꢀ0.69
(ꢀ0.98)
ꢀ0.62
(ꢀ0.86)
ꢀ0.85
(ꢀ1.15)
2.13
(2.60)
0.57
(0.54)
ꢀ0.68
(ꢀ0.97)
ꢀ0.63
(ꢀ0.86)
ꢀ0.81
(ꢀ1.11)
2.18
(2.61)
0.41
(0.41)
2.2. Photostimulated reaction in liquid ammonia
Irradiation was conducted in a reactor equipped with four
250 W UV lamps emitting maximally at 350 nm water-cooled.
The following procedure of the reaction of 1-(diethoxyphospho-
ryl)oxy-1,3-cyclohexadiene (2a) with 1 is representative of all.
90 mL of sodium-dried ammonia were condensed into a three-
necked, round-bottomed Pyrex flask equipped with a cold finger
condenser, a nitrogen inlet and a magnetic stirrer. Me3SnCl
(0.120 g, 0.6 mmol) and sodium metal (0.033 g, 1.44 mg atom)
were added. When the blue color disappeared, 2a (0.116 g,
0.50 mmol) was added and then the mixture irradiated with stir-
ring for 6 h. The reaction was quenched by adding ammonium
chloride, and ammonia was allowed to evaporate. The residue
was treated with water and then extracted three times with ether
(25 mL). Ether extracts were washed with brine and dried over
anhydrous MgSO4. Ether removal under reduced pressure followed
by column chromatography over silica gel 60-120 employing n-
hexane as eluent, afforded cyclohexadienylstannane 3a as a colour-
less oil (0.033 g, 27%).
At phosphorous
Spin densityb
at C (C–OP)
a
kcal/mol.
b
Mulliken analysis. NBO analysis within parentheses.
The spin distribution calculated can a priori be taken as an indi-
Åꢀ
cation of a more facile dissociation for type 2a0 intermediates. It
has been shown that the nodal properties of the MO that hosts
the unpaired electron and the unpaired spin density distribution
are relevant factors for the cleavage of radical anions [17]. This
reaction is possible through an intramolecular dissociative ET (in-
tra-DET) from the p system to the r* C–O bond. The potential en-
ergy surfaces (PES) evaluated for the dissociation show this intra-
DET taking place adiabatically for both intermediates. The ener-
getic and main geometric properties of the transition states (TS)
evaluated are presented in Table 3. As shown in Table 3, and as ex-
pected from the low spin density at the Cipso to its leaving group,
radical anion 2e0Åꢀ is the one that dissociates with higher activation
energy (7.2 kcal/mol vs 3.9 kcal/mol for 2a0ꢀ). Moreover, similar
activation energy is obtained by evaluation of the intra-DET under
a continuum model solvent (It has to be kept in mind that the reac-
tions occur in liquid NH3 at ꢀ33 °C). Also, despite both radical an-
ions dissociate exothermically, the cleavage of 2e0ꢁꢀ occurs with
lower exothermicity (see Table 3). A schematic profile of both
PES is presented in Fig. 9 of the Supplementary Information.
We thought that these theoretical results support, without
doubts, the experimental results. This system is an interesting
example of isomers whose radical anions dissociate with similar
thermochemistry but different activation energy due to differences
in their SOMOs composition despite they have similar energy dif-
ference between the p and r* MOs involved in the intra-DET [17].
In general, the scope for a vinylic SRN1 route is rather limited
due to severe competitions by ionic routes. We informed now
the first example of vinylic SRN1 mechanism without the incidence
of an aryl moiety attached to the vinylic system. We also informed
another example that shows that structurally similar compounds
do not behave in the same way under ET conditions and that this
behavior is mainly due to differences in spin density of their radical
anions.
Cyclohexadienylstannanes were difficult to isolate due to pro-
tonolysis and can be isolated by chromatography only if the silica-
gel is pretreated with triethylamine and/or the eluent contains
triethylamine (1%).
3. Identification of the products
3.1. 1-Trimethylstannyl-1,3-cyclohexadiene (3a)
Colourless oil; tR: 10.9 min; 1H NMR: d (ppm) 0.15 (9H, s,
2JHSn = 52.0/54.4 Hz), 2.90–2.18 (4H, m), 5.77–5.64 (2H, m), 5.96
3
1
(1H, m, JHSn = 67.4 Hz); 13C NMR d (ppm) ꢀ9.9 (CH3Sn, JCSn
=
=
3
2
328.6/343.9 Hz), 22.7 (CH2, JCSn = 27.6 Hz), 28.4 (CH2, JCSn
2
4
38.2 Hz), 125.0 (CH, JCSn = 61.0 Hz), 127.1 (CH, JCSn = 14.3 Hz),
3
1
134.2 (CH, JCSn = 29.9 Hz), 142.5 (C, JCSn = 452.5/473.0 Hz); 119Sn
NMR d (ppm) ꢀ33.6; MS: m/z = 244 (M+, 6%), 229 (47), 199 (4), 165
(36), 151 (18), 135 (34), 120 (17), 79 (100), 51 (8). Anal. Calc. for
C9H16Sn: C, 44.52; H, 6.64. Found: C, 44.61; H, 6.53%.
3.2. 1-Trimethylstannyl-4-methyl-1,3-cyclohexadiene (3b)
Colourless oil; tR: 13.5 min; 1H NMR: d (ppm) 0.12 (9H, s,
2JHSn = 51.8/54.6 Hz), 1.79 (3H, s), 2.04 (2H, t, J = 9.5 Hz), 2.29
(2H, t, J = 9.5 Hz), 5.67 (1H, m), 6.04 (1H, m, JHSn = 66.4 Hz); 13C
3
1
NMR: d (ppm) ꢀ9.9 (CH3Sn, JCSn = 328.1/343.3 Hz), 23.7 (CH3),
3
2
28.5 (CH2, JCSn = 28.8 Hz), 29.1 (CH2, JCSn = 43.3 Hz), 119.9 (CH,
2. Experimental
2JCSn = 61.6 Hz),
134.7
(CH,
3JCSn = 31.2 Hz),
136.9
(C,
4JCSn = 12.4 Hz), 138.2 (C); 119Sn NMR: d (ppm) ꢀ32.7; MS: m/
z = 258 (M+, 4%), 243 (3), 213 (5), 165 (4), 151 (27), 135 (38), 120
(26), 93 (100), 77 (41), 65 (9), 51 (18); Anal. Calc. for C10H18Sn:
C, 46.76; H, 7.06. Found: C, 46.63; H, 6.98%.
2.1. General
1H, 13C and 119Sn NMR spectra were recorded on a Bruker ARX
300 spectrometer (300 MHz for 1H, 75.5 MHz for 13C, 112 MHz

2462
V.B. Dorn et al. / Journal of Organometallic Chemistry 693 (2008) 2458–2462
3.3. 1-Trimethylstannyl-6-methyl-1,3-cyclohexadiene (3c)
Acknowledgements
Colourless oil; tR: 12.4 min; 1H NMR d (ppm) 0.16 (9H, s,
2JHSn = 51.9/54.0 Hz), 1.02 (3H, d, J = 7.1 Hz), 1.98 (1H, m), 2.29
(1H, m), 2.41 (1H, m), 5.74 (1H, m), 5.85 (1H, m), 6.03 (1H, m,
The authors acknowledge financial support from the Consejo
´
Nacional de Investigaciones Cientıficas y Técnicas (CONICET), the
´
Comisión de Investigaciones Cientıficas (CIC), the Universidad Nac-
1
3JHSn = 66.1/69.2 Hz); 13C NMR d (ppm) ꢀ8.8 (CH3Sn, JCSn = 325.3/
ional del Sur, the Universidad Nacional de Córdoba and the AN-
PCyT. CONICET is also thanked for a research fellowship to V.B.D.
3
3
341.9 Hz), 20.4 (CH3, JCSn = 16.0 Hz), 30.9 (CH2, JCSn = 24.6 Hz),
2
2
33.1 (CH, JCSn = 35.8 Hz), 124.2 (CH, JCSn = 59.2/62.4 Hz), 126.2
4
3
(CH, JCSn = 14.1 Hz), 133.1 (CH, JCSn = 29.9 Hz), 149.1 (C); 119Sn
NMR d (ppm) ꢀ32.1; MS: m/z = 258 (M+, 2%), 243 (42), 213 (6),
165 (100), 151 (30), 135 (51), 120 (24), 93 (79), 77 (40), 65 (11),
51 (7); Anal. Calc. for C10H18Sn: C, 46.76; H, 7.06. Found: C,
46.69; H, 6.99%.
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.jorganchem.2008.04.018.
References
3.4. 1-Trimethylstannyl-3-methyl-1,3-cyclohexadiene (3d)
[1] M.B. Smith, J. March, March’s Advanced Organic Chemistry, John Wiley, New
York, 2001. p. 428.
[2] (a) Z. Rappoport, Acc. Chem. Res. 14 (1981) 7;
tR: 14.0 min; MS: m/z = 258 (M+, 9%), 243 (48), 213 (4), 165 (45),
151 (23), 135 (30), 120 (16), 93 (100), 77 (37), 65 (9), 51 (7).
(b) Z. Rappoport, Recl. Trav. Chim. Pays-Bas 104 (1985) 309;
(c) Z. Rappoport, Acc. Chem. Res. 25 (1992) 474.
[3] C. Galli, Z. Rappoport, Acc. Chem. Res. 36 (2003) 580. and references cited
therein.
[4] A.B. Chopa, V.B. Dorn, M.A. Badajoz, M.T. Lockhart, J. Org. Chem. 69 (2004)
3801.
3.5. General procedure for the synthesis of (diethoxyphosphoryloxy)-
1,3-cyclohexadienes
The method used was essentially that described by Rubottom
et al [18], trapping the enolate with diethylchlorophosphate.
[5] (a) A.N. Santiago, G. Lassaga, Z. Rappoport, R.A. Rossi, J. Org. Chem. 61 (1996)
1125;
(b) E. Córsico, R.A. Rossi, J. Org. Chem. 69 (2004) 6425.
[6] D.-Y. Zhou, H.-Y. Dou, Ch.-X. Zhao, Q.-Y. Chen, J. Fluorine Chem. 127 (2006)
740.
3.6. Computational procedure
[7] (a) A.B. Chopa, M.T. Lockhart, G. Silbestri, Organometallics 21 (2002) 5874;
(b) A.B. Chopa, M.T. Lockhart, V.B. Dorn, Organometallics 21 (2002) 1425;
(c) A.B. Chopa, M.T. Lockhart, G. Silbestri, Organometallics 19 (2000) 2249.
[8] R.E. Dessy, R.L. Pohl, R.E. King, J. Am. Chem. Soc. 88 (1966) 5117.
[9] (a) E. Piers, L.A. Tse, Tetrahedron Lett. 25 (1984) 3155;
(b) S. Matsubara, J.-I. Hibino, Y. Morizawa, K. Oshima, H. Nozaki, J. Organomet.
Chem. 285 (1985) 163;
(c) W.D. Wulff, G.A. Peterson, W.E. Bauta, K.-S. Clan, K.L. Faron, S.R. Gilbertson,
R.W. Kaesler, D.C. Yang, C.K. Murray, J. Org. Chem. 51 (1986) 277;
(d) A. Darwish, M. Chong, J. Org. Chem. 72 (2007) 1507.
[10] R.A. Rossi, A.B. Pierini, A.B. Peñéñory, Chem. Rev. 103 (2003) 71.
[11] C. Galli, P. Gentili, Z. Rappoport, J. Org. Chem. 59 (1994) 6786.
[12] I. Fleming (Ed.), Frontier Orbitals and Organic Chemical Reactions, John Wiley
& Sons, Chichester, 1994.
[13] (a) C. Lee, W. Yang, R.G. Parr, Phys. Rev. B 37 (1988) 785;
(b) A.D. Becke, Phys. Rev. A 38 (1988) 3098;
(c) E. Miehlich, A. Savin, H. Stoll, H. Preuss, Chem. Phys. Lett. 157 (1989) 200.
[14] W. Kohn, I. Sham, J. Phys. Rev. 140 (1965) A1133.
[15] (a) D.M.A. Vera, A.B. Pierini, Phys. Chem. Chem. Phys. 6 (2004) 2899;
(b) J.G. Uranga, D.M.A. Vera, A.N. Santiago, A.B. Pierini, J. Org. Chem. 71 (2006)
6596.
[16] We have previously shown the good correlation within the Koopman theorem
between LUMOs energy and vertical electron affinities. See Ref. [15a].
[17] The rate constant for fragmentation of substituted haloaromatic radical anions
(RA) usually follows the order ortho > para > meta. For example, the cleavage of
m-chloroacetophenone RA has been determined to be >20 times slower than
that of its para isomer (D.D. Tanner, J.J. Chen, L. Chen, C. Luelo, J. Am. Chem.
Soc. 113 (1991) 8074). The lower reactivity of the meta-derivatives was
ascribed to differences in the adiabaticity of the intra-DET due to the nodal
properties of the p SOMOs. See: A.B. Pierini, D.M.A. Vera, J. Org. Chem. 68
(2003) 9191.
[18] G.M. Rubottom, J.M. Gruber, J. Org. Chem. 42 (1977) 1051.
[19] <http://www.gaussian.com>.
[20] Jaguar, version 6.0, Schrödinger L.L.C., New York, NY, 2005. See, <http://
www.schrodinger.com>.
[21] (a) S. Miertus, E. Scrocco, J. Tomasi, Chem. Phys. 55 (1981) 117;
(b) S. Miertus, J. Tomasi, Chem. Phys. 65 (1982) 239;
The calculations were performed with GAUSSIAN 03 [19] and the
Jaguar programs [20]. The initial conformational analysis of com-
pounds 2a0 and 2e0 was performed with the semiempirical AM1
method. The geometry of the most stable conformers thus ob-
tained was used as starting point for the B3LYP studies of their rad-
ical anions. The exploration of the potential surface for the
dissociation of the radical anions was carried out varying the se-
lected coordinate (Colefinic–OP bond distance) with full optimiza-
tion for the remainder degrees of freedom. The characterization
of all stationary points was done by Hessian matrix calculations
of geometries obtained with full optimization for a minimum
and by using the TS methodology for a transition state. The Berny
analytical gradient optimization routines were used. The requested
convergence on the density matrix was 10ꢀ9 atomic units, the
threshold value for maximum displacement was 0.0018 Å, and that
for the maximum fore was 0.00045 Hartree/Bohr. In all the cases,
the spin contamination along the whole fragmentation paths was
negligible. The zero point energy corrections were made at the 6-
31+G* level for the thermodynamic quantities. The energies in
solution were obtained with full geometry optimization within
the Tomasi’s polarized continuum model (PCM) [21] as imple-
mented in GAUSSIAN 03. Compounds 2a0 and 2e0 have negative elec-
tron affinities (EA); for these species the conventional valence
anion state has been characterized as the radical anion. The basis
sets and methodologies have been already tested and expected to
yield the right anion state, reproducing EAs within few tenths of eV
[15]. The natural bond orbital (NBO) analyses were performed
using the NBO program as implemented in GAUSSIAN 03 [22]. The
figures were built with the GAUSSVIEW program using a spin density
isosurface of 0.02. The potential surfaces evaluated in the presence
of methanol (dielectric constant = 33.62, probe radius (rp) =
2.00196 Å) to model a protic solvent were performed with the Jag-
uar program [20] and the continuum solvent model [23] therein
implemented. The stationary points on this potential surface were
located by following the procedure outlined for similar studies in
the gas-phase.
(c) M. Cossi, V. Barone, R. Cammi, J. Tomasi, Chem. Phys. Lett. 255 (1996) 327.
[22] (a) J.E. Carpenter, Ph.D. Thesis, University of Wisconsin (Madison, WI), 1987;
(b) J.E. Carpenter, F. Weinhold, J. Mol. Struct. (Theochem) 169 (1988) 41.
Program NBO 3.2: E.D. Glendering, A.E. Reed, J.E. Carpenter, F. Weinhold,
University of Wisconsin found.
[23] (a) D.J. Tannor, B. Marten, R. Murphy, R.A. Friesner, D. Sitkoff, A. Nicholls, M.
Ringnalda, W.A. Goddard, B. Honig, J. Am. Chem. Soc. 116 (1994) 11875;
(b) B. Marten, Kim, C. Cortis, R.A. Friesner, R.B. Murphy, M. Ringnalda, D.
Sitkoff, B. Honig, J. Phys. Chem. 100 (1996) 11775.