Reduction of activated olefins by SmI2. Detouring the classical birch mechanism and a negative order in SmI2

Article abstract of DOI:10.1021/ja0686662

The reaction of an excess of 1,1-diaryl-2,2-dicyanoethylenes (1) with SmI₂ is biphasic for olefin with at least one available para position. The first phase is completed in less than 0.5 s with the second phase extending over a few hundred seco

Full text of DOI:10.1021/ja0686662

Published on Web 02/24/2007
Reduction of Activated Olefins by SmI2. Detouring the
Classical Birch Mechanism and a Negative Order in SmI2
Alexander Tarnopolsky and Shmaryahu Hoz*
Contribution from the Department of Chemistry, Bar-Ilan UniVersity, Ramat-Gan 52900, Israel
Received December 4, 2006; E-mail: shoz@mail.biu.ac.il
Abstract: The reaction of an excess of 1,1-diaryl-2,2-dicyanoethylenes (1) with SmI2 is biphasic for olefin
with at least one available para position. The first phase is completed in less than 0.5 s with the second
phase extending over a few hundred seconds. This phase is second order with respect to the radical anion,
which is formed in the dead-time of the mixing in the stopped flow spectrophotometer and is overall of -1
order in the initial concentration of SmI2. In this phase, a dimer is formed between two radical anions with
the formation of a C-C bond between a benzylic and a para position. The second phase is enhanced by
proton donors and shows an H/D kinetic isotope effect with MeOH. Minute amounts of ethylene glycol
accelerated the reaction to such an extent that the second phase is “absorbed” into the first, rendering it
rate determining. In this phase, the dianionic dimer disproportionates after protonation to furnish the neutral
species and the anion, which after second protonation provides the reduced product. When the two para
positions are occupied by substituents, the reaction takes place by the traditional Birch reduction sequence
of electron-proton-electron-proton-transfer steps. It is shown that the detour mechanism, coupling followed
by disproportionation, should be typical of olefin but not of carbonyl reduction. This difference stems from
the dissimilarity in protonation rate on carbon and oxygen.
Introduction
transfer steps. Moreover, this study suggests that, in many cases,
the reduction mechanism of CdC bonds will differ from the
Since its introduction by Kagan1 in 1977, SmI2 has become
one of the most popular reagents in single electron-transfer-
based synthetic chemistry. Research efforts in recent years
focused on additives that facilitate the reaction as well as on
the study of the intimate details of the reaction of SmI2 with
various substrates and functional groups.2 Surprisingly, very little
has been done to advance our understanding of the reduction
of carbon-carbon double bonds.3 This paper reports that the
reduction of CdC bonds by SmI2 to produce the hydrogenated
compound takes a route entirely different from the traditional
Birch reduction sequence4 of electron-proton-electron-proton-
reduction of the corresponding CdO bonds by SmI2.
Specifically, we have studied the reaction shown in eq 1 and
discovered that when mono- or unsubstituted 1,1-diaryl-2,2-
dicyanoethylenes (1) react with SmI2, they display a mechanism
entirely different from that of the disubstituted substrates,
although affording the same type of final product (2) in a
quantitative yield.
(1) Namy, J. L.; Girard, P.; Kagan, H. B. New J. Chem. 1977, 1, 5-7. For
some recent reviews, see: (a) Edmonds, D. J.; Johnston, D.; Procter, D. J.
Chem. ReV. 2004, 104, 3371-3403. (b) Kagan, H. B. Tetrahedron 2003,
59, 10351-10372. (c) Steel, P. G. J. Chem. Soc., Perkin Trans. 1 2001,
2727-2751. (d) Krief, A.; Laval, A.-M. Chem. ReV. 1999, 99, 745-777.
(e) Molander, G. A.; Harris, C. R. Tetrahedron 1998, 54, 3321-3354. (f)
Molander, G. A.; Harris, C. R. Chem. ReV. 1996, 96, 307-338.
(2) (a) Enemaerke, R. J.; Hertz, T.; Skrydstrup, T.; Daasbjerg, K. Chem.-Eur.
J. 2000, 6, 3747-3754. (b) Prasad, E.; Knettle, B. W.; Flowers, R. A., II.
J. Am. Chem. Soc. 2004, 126, 6891-6894. (c) Molander, G. A.; McKie, J.
A. J. Org. Chem. 1992, 57, 3132-3139. (d) Pedersen, H. L.; Christensen,
T. B.; Enemærke, R. J.; Daasbjerg, K.; Skrydstrup, T. Eur. J. Org. Chem.
1999, 565-572. (e) Hutton, T. K.; Muir, K. W.; Procter, D. J. Org. Lett.
2003, 5, 4811-4814. (f) Imamoto, T.; Takeyama, T.; Yokoyama, M.
Tetrahedron Lett. 1984, 25, 3225-3226. (g) Imamoto, T.; Hatajima, T.;
Takiyama, N.; Takeyama, T.; Kamiya, Y.; Yoshizawa, T. J. Chem. Soc.,
Perkin Trans. 1 1991, 3127-3135. (h) Chopade, P. R.; Prasad, E.; Flowers,
R. A. J. Am. Chem. Soc. 2004, 126, 44-45. (i) Dahlen, A.; Hilmersson,
G.; Knettle, B. W.; Flowers, R. A., II. J. Org. Chem. 2003, 68, 4870-
4875. (j) Dahlen, A.; Nilsson, A.; Hilmersson, G. J. Org. Chem. 2006, 71,
1576-1580. (k) Hasegawa, E.; Curran, D. P. J. Org. Chem. 1993, 58,
5008-5010. (l) Prasad, E.; Flowers, R. A., II. J. Am. Chem. Soc. 2005,
127, 18093-18099.
Results and Discussion
To simplify the kinetics of the reaction, the reduction of 1
was performed with substrates in a large excess over SmI2. The
(4) Allinger, N. L.; Cava, M. p.; DeJonj, D.; Johnson, C. R.; Lebel, N. A.;
Stevens, C. L. Organic Chemistry; Worth Publishing: New York, 1973; p
382.
(3) (a) Yacovan, A.; Bilkis, I.; Hoz, S. J. Am. Chem. Soc. 1996, 118, 261-
262. (b) Yacovan, A.; Hoz, S. J. Org. Chem. 1997, 62, 771-772.
9
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J. AM. CHEM. SOC. 2007, 129, 3402-3407
10.1021/ja0686662 CCC: $37.00 © 2007 American Chemical Society

Reduction of Activated Olefins by SmI2
A R T I C L E S
Scheme 1
Table 1. Effect of Variable Concentrations of [SmI2]0 on the
Second-Order Rate Constant of DP (25 mM)
[SmI2]
(mM)
kobs
(M-1 s-
1
)
1.5
3
4.4
6
10 000
6700
4700
2700
Figure 1. Spectra of the radical anion of MA (1.5 mM) and SmI2 (9 mM)
in THF.
rates of reaction were monitored using stopped flow spectro-
scopy. Upon mixing the THF solutions of the SmI2 and the
substrate, the spectrum of SmI2 vanishes completely and the
radical anion of the substrate is quantitatively and immediately
obtained (within the “dead-time” of the mixing). This species
is characterized by two distinct absorptions around 430 and 550
nm. Figure 1 shows the spectrum of the radical anion of MA.5
DP and MA display the following unexpected features: (a)
The reaction is biphasic with the first phase completed in less
than 0.5 s and the second phase extending over a few hundred
seconds. (b) The first phase is second order in the initially
formed radical anion. (c) A plot of log k of the first phase versus
the log of the initial concentration of SmI2 shows a negative
order (-1). (d) The first phase is insensitive to the presence of
proton donors. Yet, they greatly enhance the second phase. At
a high proton donor concentration, the reaction is accelerated
to such an extent that the second phase is “absorbed” in the
first phase, rendering it rate determining. (e) The H/D kinetic
isotope effect for the second phase with MeOH reaches the value
of 2.7, and the kinetic order in MeOH varies from 0.3 to 1 as
MeOH concentration increases. The reaction of DP and MA
(substrates having at least one unsubstituted phenyl group) is
biphasic (see Figure S1). The two phases will be discussed
separately below.
the mono- or unsubstituted substrates. Dimerization seems,
therefore, to be the preferred option. Ab initio calculations
(computations were performed at the B3LYP/6-31+G* level
using the Gaussian 03 code6) show that, in the unsubstituted
radical anion, high spin density (0.41) is concentrated on the
benzylic carbon (Scheme 1).
Thus, on the basis of spin density, a pinacol-type coupling is
expected with bonding between the two benzylic positions.
However, this mode of dimerization is unlikely because of the
large steric hindrance. The difference in the reactivity pattern
between the disubstituted and the mono- or unsubstituted
substrates suggests that the para position is involved in the
dimerization. Indeed, the spin density at the para position is
also relatively high (0.16), suggesting dimerization through this
position. Coupling between two para positions, which encom-
passes a loss of aromaticity of two rings, is less likely than a
benzylic-para position bond formation (3).
Substrates substituted at both para positions display an entirely
different behavior, and their reaction times are in the range of
hundreds of seconds.
We assume, therefore, that the dimer has the structure 3,
which finds precedent in other systems.7
Nature of the First Phase. The disappearance of the
absorptions of the radical anion showed a perfect fit to a second-
order reaction in the radical anion. Quenching the reaction
mixture after the first phase showed this not to be the product-
forming step. Even after 60 s, only 34% of the reduced product
was formed. The bimolecular nature of this phase may cor-
respond either to a disproportionation forming a dianion or to
a dimer formation. The first possibility could be safely ruled
out on the basis that the reaction of substrates that are
disubstituted by electron-donating (DA ) para di-MeO, DM
) para di-Me) or by electron-attracting (DCl ) para di-Cl)
substituents is slower by ca. 3 orders of magnitude than that of
The rate constant for the dimerization of the radical anion of
DP ([DP] ) 5-12.5 mM; [SmI2] ) 1.25 mM) is 10 750 (
450 M-1 s-1, and for the dimerization of the radical anion of
MA ([MA] ) 6.5-25 mM; [SmI2] ) 1.5 mM) it is 5670 (
290 M-1 s-1. The lower rate constant for MA probably reflects
the statistical factor for coupling at the para position.
One of the most interesting results obtained in this study is
the negative order (-1) found in the initial concentration of
the SmI2. As can be seen from Table 1 and Figure 2 (for MA,
see Table S1), the second-order rate constant decreases as the
initial concentration of SmI2 increases.
(5) A similar spectrum was obtained upon mixing a solution of the substrate
with a solution of Na/benzophenone in THF. The absorptions in this case
were slightly shifted to longer wavelengths, 460 and 580 nm.
(6) Frisch, M. J.; et al. (for complete reference, see Supporting Information).
(7) Shiue, J.-S.; Lin, C.-C.; Fang, J.-M. Tetrahedron Lett. 1993, 34, 335-
338.
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J. AM. CHEM. SOC. VOL. 129, NO. 11, 2007 3403

A R T I C L E S
Tarnopolsky and Hoz
Scheme 2
Figure 2. A plot of the effect of different initial SmI2 concentrations on
the second order of the first phase for the reaction of DP (25 mM).
Figure 3. A plot of the effect of the total Sm+3 concentration on the second-
order rate constants of the first phase for the reaction of DP (12.5 mM)
and SmI2 (1.25 mM).
Table 2. Effect of the Added Sm+3 on the Second-Order Rate
Constants of the First Phase for the Reaction of DP (12.5 mM)
and SmI2 (1.25 mM)
clear that the reduction process is highly endothermic.9 The
change from an endothermic to an exothermic process is due
to the Coulombic interaction energy gained by the ion pairing
of the Sm+3 and the radical anion.
3
[Sm+
]
kobs
1
(mM)
(M-1 s-
)
0
14 000
13 000
7100
0.83
1.25
3.75
However, the large samarium cation with its solvation sphere
and possibly also with one or two iodide ions in its vicinity
may sterically inhibit the dimerization. Dimerization can
therefore take place mainly with the “free” radical anion. If the
ion pairing equilibrium is significantly tilted toward the paired
ions, and dimerization takes place from the minute amount of
the free radical anion, then the inhibition will be linearly
proportional to the concentration of the inhibitor (Sm+3) as we
have observed.10 A possible additional cause for the inhibition
could be that the counterion changes the spin distribution in
the radical anion (Scheme 1) in such a way that largely reduces
the likelihood of dimerization (reducing the product of the spin
densities on the bond forming carbon atoms).
Thus, the suggested reaction mechanism (Scheme 2) seems
to adequately accommodate all of the observed phenomena of
the first phase. We go next to the second phase.
Nature of the Second Phase. The kinetics of this phase is
insensitive (zero order) to variations in the initial concentrations
of the substrate and the SmI2. It is first order in the dimer and
of varying order in the added MeOH. While the dimer
absorption vanishes only after several hundred seconds in the
absence of a proton donor, in the presence of 1.25 M MeOH,
35% of the product was already obtained after 1 s. The rate
3200
It should be emphasized that the rate of the reaction increases
with the increase in the initial concentration of the SmI2.
However, doubling the initial concentration of SmI2 doubles
the concentration of the radical anion, and, due to the bimo-
lecular nature of the reaction, the rate should increase by 4-fold.
Thus, a 2-fold increase in the rate corresponds to the observed
negative order.
This behavior is typical for the presence of an inhibitor
introduced to the reaction mixture at its beginning. Because the
reactions show a very good fit, within a run, to a second-order
reaction, it implies that the concentration of the inhibitor is
constant during the reaction time. Upon mixing of the reactants,
two new species are produced, the radical anion and Sm+3
.
However, only the concentration of Sm+3 remains constant, and,
therefore, Sm+3 is likely to be the inhibitor. To confirm this
conclusion, we have generated in situ variable amounts of Sm+3
by titrating with I2 an excess of SmI2 initially introduced into
the reaction mixture. Results shown in Table 2 and Figure 3
(for MA, see Table S2) clearly demonstrate the inhibitive nature
of Sm+3 8
.
A conceivable inhibition mechanism follows. Comparing the
reduction potential of DP and oxidation potential of SmI2, it is
(9) The reduction potential of DP in THF vs SCE is -1.08 V (ref 3a), whereas
that of SmI2 is -0.9 V (Enemærke, R. J.; Daasbjerg, K.; Skrydstrup, T.
Chem. Commun. 1999, 343. Shabangi, M.; Flowers, R. A., II. Tetrahedron
Lett. 1997, 38, 1137-1140).
(8) In this case, the rate constants decrease because the increase in the Sm+3
concentration is not accompanied by an increase in the radical anion
concentration.
(10) One has to assume that the average association constant of Sm+3 to the
dimer is similar to that of the radical anion, thereby maintaining a nearly
constant concentration of Sm+3
.
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Reduction of Activated Olefins by SmI2
A R T I C L E S
Figure 5. A plot of the log of the second-order reaction of DA (12.5 mM)
with SmI2 (2.5) versus the log of MeOH concentration.
Figure 4. The dependence of the first-order rate constants of the second
phase of the reaction of DP (12.5 mM) and SmI2 (2.5 mM) on the
concentration of MeOH.
Table 4. Second-Order Rate Constant for the Reaction of DA
(12.5 mM) with SmI2 (2.5 mM) in the Presence of Varying
Concentrations of MeOH
[MeOH]
(M)
kobs
Table 3. First-Order Rate Constant for the Reaction of DP (12.5
mM) with SmI2 (2.5 mM) in the Presence of Varying
Concentrations of MeOH
1
(M-1 s-
)
1.25
1900
1100
560
300
150
0.625
0.313
0.156
0.078
[MeOH]
(M)
kobs
1
(s-
)
0.156
0.313
0.625
1.25
0.38
0.47
0.62
1.1
Ethylene glycol is known to enhance reductions by SmI2
much more than the other alcohols.12 Using ethylene glycol
concentrations much smaller than MeOH (0.01-0.05 M)
enhanced the second phase to such an extent that only the first
phase was observed.
2.5
2.31
law for the disappearance of the dimer absorption (followed at
430 nm) is given in eq 2.
Disubstituted Substrates. The disubstituted substrates (DA,
DM, and DCl, kinetic data were gathered for DA, while DM
and DCl were only qualitatively examined) reacting with SmI2
show the same absorption bands around 430 and 550 nm as
DP and MA. Yet, only one phase is observed, the duration of
which is in the order of several hundred seconds (see Figures
S2, S3). The absorption of the radical anion decreases mono-
tonically, retaining its shape all along. The reactions are second
order in the radical anion, and their rates are largely enhanced
by added MeOH. The reactions are first order in MeOH (Table
4, Figure 5) with no kinetic H/D isotope effect (kH/kD ) 1.13
( 0.15) for concentrations of MeOH between 0.125 and 2.0
M.
d[dimer]
2 dt
-
) k2nd[dimer][ROH]n, n ≈ 0.3-1 (2)
Shown in Figure 4 and Table 3 (for MA, see Table S3) is the
gradual change in the reaction order of MeOH from ca. 0.3 at
low concentration to ca. 1 at higher concentration in the reaction
of DP.
This may indicate the existence of two competing mecha-
nisms: at low concentrations of MeOH, a mechanism where
proton transfer takes place only after the rate-determining step
()zero order in MeOH), and at higher MeOH concentration, a
mechanism where proton transfer takes place at the rate-
determining step. A possible mechanism for the proton-donor-
independent process is the cleavage of the dimer to the neutral
reactant and its dianion (eq 3).
The most plausible mechanism for the reaction of the
disubstituted substrates is a reversible protonation of the radical
anion forming an internal return complex with a rate-determining
electron transfer from another radical anion (eq 4).
This indeed is a very slow step, and, therefore, in the absence
of an appreciable amount of a proton donor, the reaction
stretches over several hundred seconds. As the concentration
of the proton donor increases, the protonation becomes the
dominant path (see SPECFIT11 simulation in the Supporting
Information). As a result, the order in MeOH increases toward
1 and a kinetic H/D isotope effect is obtained (kH/kD ) 2.7;
[SmI2] ) 2.5 mM; [DP] ) 12.5 mM and [MeOH] ) 1.25 M).
The absence of a kinetic H/D isotope effect is due to the
reversible proton transfer within the internal return complex.13
Thus, when the two para positions are taken by substituents
that block the dimerization path, the traditional Birch sequence
(11) SPECFIT Global Analysis System (v. 2.11, Spectrum Software Associates).
(12) Dahlen, A.; Hilmersson, G. Tetrahedron Lett. 2001, 42, 5565-5569.
9
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A R T I C L E S
Tarnopolsky and Hoz
of electron-proton-electron-proton transfer takes place. How-
ever, this process is much slower than the detour mechanism.
How frequently would a detour mechanism, similar to the
one above, be encountered? Our analysis suggests that it may
be encountered in many cases of olefin reduction by SmI2,
although not in carbonyl reductions. The major reason for the
detour mechanism is the sluggishness of the protonation of the
radical anion relative to the coupling (dimerization) route. Let
us first compare protonation of a negatively charged carbon with
that of a negatively charge oxygen. The alcohol derived from
the carbonyl compound will, in most cases, be of acidity similar
to that of the protonating alcohol. According to the Eigen
mechanism,14 proton transfer between two heteroatoms has a
negligible intrinsic barrier, and the protonation rate of the
alkoxide will be nearly diffusion-controlled. The situation is
entirely different with olefins. For an olefin to accept an electron
from SmI2, its corresponding anion has to be relatively stable.
We have found, for example, that activation by a phenyl and a
cyano group, as in R-cyanostilbene, is insufficient to promote
a reaction. Thus, the olefin should be activated by strong
electron-attracting groups such as two cyano groups as in the
present case. This will lead to anions more resistant to
protonation. In the absence of pKa values in THF, we will use
the DMSO values determined by Bordwell et al.15 In DMSO,
the pKa of malononitrile (the model activating group in the
present study) is 11, and that of MeOH is 29. Thus, there is a
huge thermodynamic barrier for protonation on the correspond-
ing carbanion. In addition, it is well known that protonation on
carbon has a significant intrinsic barrier that is absent in proton
transfer between heteroatoms.16 As a consequence of the kinetic
and the thermodynamic barriers, at the closed shell level,
protonation on carbanions will be many orders of magnitude
slower than that on alkoxide. Turning now to the open shell
species, the radical anions, a number of effects must be
considered. We note that a radical at the R position to oxygen
increases its acidity by about 5 pKa units.17 A similar effect is
expected for the double bond system. Therefore, the reactivity
gap between the protonation on the carbonyl and the olefin-
based radical anions will be retained. Finally, we must also
consider the effect of the interaction of the Sm+3 cation with
the various negatively charged species. The trivalent samarium
is known to be very hard, while the delocalized radical anions
are relatively soft. Therefore, they will be somewhat stabilized
by Sm+3 as a gegenion slowing down the protonation rate. On
the other hand, the interaction with the Sm+3 cation may increase
the acidity of the proton donor. Brown18 has shown that
complexation to Eu+3 increases the acidity of MeOH by ca. 10
pKa units. Assuming a similar effect with Sm+3, this will reduce
the pKa of MeOH to 19. This will bring again the protonation
on the radical anion of the carbonyl compound to the vicinity
of the diffusion-controlled rate. However, the protonation rate
on the olefinic radical anion will be many orders of magnitude
below that value.
In conclusion, it is reasonable to assume that the effect of
placing an odd electron at a position R to the negative charge,
on the one hand, and the interaction of the Sm+3 with the radical
anions, on the other, are similar although not necessarily
identical in both cases. Therefore, the aforementioned thermo-
dynamic and kinetic barriers are the origin of the vast reactivity
gap, which greatly favors protonation on the radical anion of
carbonyl over that of an olefin. This sluggishness in protonation
on olefinic radical anions diverts them from reacting in the
normal Birch mechanism to the alternative detour mechanism.
It should be pointed out that the reduction of olefins of lower
activity (such as the R-cyanostilbene mentioned above) could
be achieved by using additives such as HMPA19 that enhance
the electron-transfer rate. In this case, the radical anion formed
may be basic enough to undergo rapid protonation. In addition,
using different solvents may decrease the acidity gap mentioned
above. SmI2 was recently shown to be stable in water.2l Using
water as an example is, therefore, very instructive in this case.
In water, the pKa of malononitrile (which serves as a model for
the activating group in the present system) remains 11.20 Yet,
that of MeOH is reduced from 29 in DMSO to 16, and that of
water itself is 15.5. It is thus possible that a large enough
concentration of additives such as water or alcohol, which were
found to increase the reaction rates, may provide,2k,j in addition
to their other enhancing effects, the micro environment needed
for such proton transfer.
Experimental Section
THF was refluxed over Na wire with benzophenone and distilled
under argon. Water content was determined (K.F. Coulometer 652) to
be 20 ppm. SmI2 was diluted as needed from a 0.1 M commercial THF
solution. The concentration of the SmI2 solution was spectroscopically
determined (λ ) 615 nm; ꢀ ) 635). All of the 1,1-diaryl-2,2-
dicyanoethylenes used in the kinetic studies are known compounds.3a,21,22
The kinetics of the reactions was followed using a stopped flow
spectrophotometer (Hi-Tech SF-61DX2) in a glove box under nitrogen
atmosphere. The reactions were monitored at 430 and/or 550 nm. In
cases where a proton donor was used, the proton donor was mixed
with the substrate solution. The water content in the THF solutions
was determined (ca. 20 ppm) using a K.F. Coulometer-652. Because
of the variable water content, all rate constants reported here were
determined within a series of measurements performed on the same
day using the same stock solutions. At the end of each series, the first
measurement was repeated to ensure reproducibility within a set. The
deviation did not usually exceed 8%. The kinetics were analyzed using
KinetAsyst (v. 2.2 Hi-Tech Ltd.) and the SPECFIT Global Analysis
System (v. 2.11, Spectrum Software Associates).11
Supporting Information Available: Figure S1: Diode array
spectra for the reaction of DP with SmI2. Short phase, 0.4 s
and long phase, 200 s. Figure S2: Reaction of DA (25 mM)
with SmI2 (1.25 mM). Figure S3: Reaction of DA (25 mM)
with SmI2 (6 mM); ethylene glycol (25 nm). Table S1: Effect
of variable concentrations of [SmI2]0 on the second-order rate
constant of MA (25 mM). Table S2: Effect of the added Sm+3
on the second-order rate constants of the first phase for the
(13) (a) Cram, D. J.; Kingsbury, C. A.; Rickborn, B. J. Am. Chem. Soc. 1961,
83, 3688-3696. (b) Hine, J.; Philips, C.; Maxwell, J. I. J. Org. Chem.
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G.; Smith, W. K.; Ziegler, G. R.; Niemeyer, H. M.; Kruger, T. L. J. Am.
Chem. Soc. 1973, 95, 4254-4257. (d) Macciantelli, D.; Seconi, G.; Eaborn,
C. J. Chem. Soc., Perkin Trans. 2 1978, 834-838. (e) Thibblin, A.; Jencks,
W. P. J. Am. Chem. Soc. 1979, 101, 4963-4973. (f) Fishbein, J. C.; Jencks,
W. P. J. Am. Chem. Soc. 1988, 110, 5087-5095.
(14) Eigen, M. Angew. Chem., Int. Ed. Engl. 1964, 3, 1.
(15) Bordwell, F. G. Acc. Chem. Res. 1988, 21, 456-463.
(16) Bell, R. P. The Proton in Chemistry; Chapman and Hall: London, 1973;
p 131.
(19) Inanaga, J.; Ishikawa, M.; Yamaguchi, M. Chem. Lett. 1987, 1485-1486.
(20) Pearson, R. G.; Dillon, R. L. J. Am. Chem. Soc. 1953, 75, 2439-2443.
(21) Bruice, T. C.; Bradbury, W. C. J. Org. Chem. 1966, 28, 3403.
(22) Charles, G. Bull. Soc. Chim. Fr. 1963, 1559.
(17) Hayon, E.; Simic, M. Acc. Chem. Res. 1974, 7, 114.
(18) Neverov, A. A.; Gibson, G.; Brown, R. S. Inorg. Chem. 2003, 42, 228-
234.
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Reduction of Activated Olefins by SmI2
A R T I C L E S
reaction of MA. Table S3: First-order rate constant for the
reaction of MA in the presence of varying concentrations of
MeOH. A SPECFIT simulation was run fro the second phase
of DP. Complete ref 6. Archive file of the B3LYP/6-31+G*
calculation of the radical anion of DP. This material is available
free of charge via the Internet at http://pubs.acs.org.
JA0686662
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