Photoinduced three-component reactions of tetracyanobenzene with alkenes in the presence of 1,3-dicarbonyl compounds as nucleophiles

Article abstract of DOI:10.1021/jo801448v

(Chemical Equation Presented) Photoinduced three-component reactions between tetracyanobenzene (TCNB), an aromatic olefin, and a β-dicarbonyl compound afford products composed of the three components via formal elimination of hydrogen cyanide, leading to the vicinal dialkylation of the olefin and the α-alkylation of the β-dicarbonyl compounds. It is shown that these reactions are initiated by photoinduced electron transfer (PET) from the olefin to the singlet excited TCNB and proceed by a nucleophile-olefin combination, aromatic substitution (NOCAS) reaction sequence with the enolized β-dicarbonyl compound as a nucleophile. Therefore, aromatic olefins are suitable substrates in photo-NOCAS reactions when TCNB is used as the electron acceptor. In addition, these results show that the enol of β-dicarbonyl compound serves as a carbon nucleophile to trap the alkene cation radical in PET reactions to lead to C-C bond formation.

Full text of DOI:10.1021/jo801448v

Photoinduced Three-Component Reactions of Tetracyanobenzene
with Alkenes in the Presence of 1,3-Dicarbonyl Compounds as
Nucleophiles
Zhi-Feng Lu, Yong-Miao Shen, Jia-Jun Yue, Hong-Wen Hu, and Jian-Hua Xu*
School of Chemistry and Chemical Engineering, Nanjing UniVersity,
Nanjing 210093, People’s Republic of China
xujh@nju.edu.cn
ReceiVed July 2, 2008
Photoinduced three-component reactions between tetracyanobenzene (TCNB), an aromatic olefin, and a
ꢀ-dicarbonyl compound afford products composed of the three components via formal elimination of
hydrogen cyanide, leading to the vicinal dialkylation of the olefin and the R-alkylation of the ꢀ-dicarbonyl
compounds. It is shown that these reactions are initiated by photoinduced electron transfer (PET) from
the olefin to the singlet excited TCNB and proceed by a nucleophile-olefin combination, aromatic
substitution (NOCAS) reaction sequence with the enolized ꢀ-dicarbonyl compound as a nucleophile.
Therefore, aromatic olefins are suitable substrates in photo-NOCAS reactions when TCNB is used as the
electron acceptor. In addition, these results show that the enol of ꢀ-dicarbonyl compound serves as a
carbon nucleophile to trap the alkene cation radical in PET reactions to lead to C-C bond formation.
Introduction
(which in the case of aromatic olefin is a better electron
acceptor than that derived from aliphatic olefin) followed by
protonation of the formed anion to give an anti-Markovnikov
addition product of the nucleophile to the olefin, with the
cyanoarene only playing the role of a sensitizer.2 On the other
hand, in the absence of a nucleophile, the neutral aromatic
olefin itself (which is more nucleophilic than aliphatic olefin)
would capture its cation radical to give a dimeric cation
radical, which upon BET from the cyanoarene anion radical
furnishes tetralin and cyclobutane products.3-5 The nucleo-
philes studied up to now are mainly limited to alcohol,6
cyanide7 and fluoride8 anion, and amines.9 Therefore, a
further extension of the type of reactants would not only serve
The photoinduced nucleophile-olefin combination, aro-
matic substitution (photo- NOCAS) reaction1 is a class of
novel three-component reactions between a cyanoarene (as
electron acceptor), an olefin (as electron donor), and a
nucleophile initiated by photoinduced electron transfer (PET)
between the cyanoarene (usually p-dicyanobenzene (DCNB)
or 1,2,4,5-tetracyanobenzene (TCNB)) and the olefin. The
olefin cation radical formed is captured by the nucleophile
to give nucleophile-olefin addition radical (nucleophile-olefin
combination), which takes part in radical pair combination
with the cyanoarene anion radical followed by extrusion of
a cyanide anion (aromatic substitution) to give the products.
While mechanistic issues of these reactions have been under
active research, the reaction scope in regard to the olefin
substrate and the nucleophile has so far been rather limited.
The olefins investigated are mainly aliphatic ones because it
is believed that for aromatic olefins, once the olefin cation
radical is trapped by the nucleophile, the subsequent reaction
pathway is back electron transfer (BET) from the cyanoarene
anion radical to the nucleophile-olefin addition radical
(2) (a) Neunteufel, R. A.; Arnold, D. R. J. Am. Chem. Soc. 1973, 95, 4080–
4081. (b) Arnold, D. R.; Snow, M. S. Can. J. Chem. 1988, 66, 3012–3026. (c)
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* Corresponding author. Phone: +86-25-83592709. Fax: +86-25-83317761.
(1) For a review, see: Mangion, D.; Arnold, D. R. Acc. Chem. Res. 2002,
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8010 J. Org. Chem. 2008, 73, 8010–8015
10.1021/jo801448v CCC: $40.75 2008 American Chemical Society
Published on Web 09/25/2008

Three-Component Reactions of Tetracyanobenzene
SCHEME 1
CHART 1
acetonitrile is determined to be in the range of 54.5-68.7%,
depending on the analytical methods (NMR,12 HPLC,13 or
UV-visible spectroscopy14). The alkene cation radical formed
in single electron transfer (SET) with the singlet excited TCNB
(1TCNB*)15 is trapped by the strongly nucleophilic acetylac-
etone enol to give the addition radical A, which on radical pair
combination with the TCNB anion radical (TCNB-•) and
extrusion of a cyanide anion gives product 1. An alternative
mechanism for the formation of 1 as shown in Scheme 3 can
also be envisaged. SET between the enol and 1TCNB* leads to
the enol cation radical, which gives the carbon centered radical
B by deprotonation. Radical addition of B to the alkene affords
the addition radical A, which combines with TCNB-• to give 1
after extrusion of a cyanide anion. In Scheme 3, the mechanism
for the formation of radical A is similar to that proposed in
thermal addition reactions of ꢀ-diketones to alkenes mediated
by the ground state one-electron oxidant ceric ammonium nitrate
(CAN).16,17 The formation of the carbon radical as B by CAN
induced oxidation of the diketone enol followed by deprotona-
tion of the enol cation radical to the solvent18 was proven by
ESR measurement,19 and these radicals tend to dimerize to give
the diketone dimers in the absence of added alkene.20 In the
presence of an alkene, the carbon radical (as B) adds to the
alkene to give an addition radical as A (Schemes 2 and 3).
Further SET from this radical to Ce(IV) leads to a carbocation
that on intramolecular cyclization gives dihydrofuran product.16,17
To examine the two possible mechanisms, we carried out a
control experiment, which showed that irradiation of TCNB with
acetylacetone in MeCN in the absence of an alkene resulted in
no net reactions and the two reactants are not consumed.
However, when the photolysis of TCNB with acetylacetone was
carried out with added biphenyl (BP) as a cosensitizer,21,22 both
TCNB and acetylacetone were found to be consumed steadily
to gave a complicated product mixture. These results suggest
to expand the scope of these reactions to increase their
synthetic value, but also shed new light on mechanistic details
for these photo-multicomponent reactions.
In our previous work on photoreactions of TCNB with a series
of aromatic olefins, we have shown that BET between the alkene
dimer cation radical and TCNB anion radical could not take
place because the latter is a too weak electron donor, and the
reaction takes a pathway of radical pair combination between
the alkene dimer radical and the TCNB anion radical to give a
product of (olefin dimerization-aromatic substitution) (Scheme
1).10 This result implies that aromatic alkenes would be even
better olefin substrates in the photo-NOCAS reactions than
aliphatic olefins whose reactions are often complicated by the
allylic deprotonation side reaction. As a part of our effort in
diversifying the reactant types in PET reactions to explore new
photo-multicomponent reactions, we report here photoreactions
of TCNB with aromatic alkenes in the presence of ꢀ-dicarbonyl
compound as added nucleophile.
Results and Discussion
Photoinduced reactions of TCNB with the alkenes and the
ꢀ-dicarbonyl compounds listed in Chart 1 were investigated.
I. Photoreactions of TCNB with r-Methylstyrene in
the Presence of ꢀ-Dicarbonyl Compounds. Irradiation of
TCNB (0.025 M) with R-methylstyrene (0.05 M) in the presence
of acetylacetone (0.2 M) in MeCN with light of λ > 300 nm
gave products 1 (78%), 2 (5%), and 3 (5%) (Chart 2 and Table
1). Products 2 and 3 are a pair of diastereomers derived from
the olefin dimerization-aromatic substitution reaction.10 Product
1 is a three-component reaction product and is proposed to be
formed by a reaction sequence as shown in Scheme 2.
ꢀ-Diketones have high enol contents in solutions of common
organic solvents.11 For acetylacetone, the enol content in
that, although SET between TCNB* and the diketone enol
1
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D. R.; Chan, M. S. W.; McManus, K. A. Can. J. Chem. 1996, 74, 2143–2166.
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Tetrahedron 2006, 62, 5663–5674.
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I. R.; Noukakis, D.; Gomes-Jahn, L.; Young, R. H.; Goodman, J. L.; Farid, S.
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(18) The mechanism of the oxidation of ꢀ-dicarbonyls by CAN has been
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R. A., II J. Org. Chem. 2007, 72, 5486–5492. (b) Zhang, Y.; Flowers, R. A., II
J. Org. Chem. 2003, 68, 4560–4562. The enol cation radical of mono-ketone is
moderately acidic. As an example, 4-methoxylphenylacetone enol cation radical
has a pKa ≈ 3.2. See: (c) Schepp, N. P. J. Org. Chem. 2004, 69, 4931–4935.
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J. Org. Chem. Vol. 73, No. 20, 2008 8011

Lu et al.
CHART 2
(which is a stronger electron donor than R-methylstyrene) is
thermodynamically feasible, the reactivity of the singlet ion
radical pair [TCNB-• enol+•] seems to be quite different from
that of the free enol cation radical formed in the thermal SET
reaction with the Ce4+ ions. For the singlet [TCNB-• enol+•]
pair, BET predominates to suppress any further reactions. This
is not a surprising fact taking into account the highly exothermic
nature of the PET process of the 1TCNB* with enol23a and the
relevant small energy gap for the BET process in the [TCNB-•
enol+•] pair.23e This means that the BET process would have
very high rate constant to result in inefficient ion radical pair
dissociation.23f,g Only with the use of the cosensitizer to mediate
the SET process to avert the formation of the geminal ion radical
pair could the fast BET be inhibited to allow ion radical pair
dissociation and the ensuing chemical reactions to take place.
Furthermore, singlet excited TCNB is a much stronger electron
(0.025 M) as a cosensitizer for 7 h resulted in a 68% TCNB
conversion to give 1 (80%), 2 (5%), and 3 (5%). Similarly,
adding anhydrous magnesium perchlorate (0.0125 M) to the
reaction mixture of TCNB, R-methylstyrene, and acetylacetone
raised the TCNB conversion to 79% and afforded 1 (79%), 2
(4%), and 3 (5%). Since BP has a similar oxidation potential
(1.90 V, SCE) as the alkene, the rate enhancement primarily
takes advantage of BP’s role as a relay in the electron transfer
1
between TCNB* and the alkene to circumvent the formation
of the singlet geminate ion radical pair [TCNB-• alkene+•],
leading to a suppression of the energy wasting BET process.
The longer lifetime of the BP cation radical than 1TCNB* also
helps to enhance the SET efficiency.21 These cosensitizer and
special salt effects lend further support to the mechanism
1
involving electron transfer between TCNB* and the styrene
as shown in Scheme 2.
Photoreaction of TCNB with R-methylstyrene in the presence
of benzoylacetone under the same conditions afforded products
acceptor (E ) 3.17 V, SCE)15 than the ground state CAN
red
1/2
red
(E ) 1.28 V, SCE). Since most alkenes without strong
1/2
electron-donating substituents have oxidation potential higher
than 1.28 V, in CAN-mediated addition reactions of ꢀ-diketones
with alkenes, CAN can only oxidize the diketone enol but not
the alkene. In contrast with this, in photoreactions of TCNB
with alkene in the presence of a ꢀ-diketone, electron transfer
from the alkenes to 1TCNB* is exothermic and therefore
thermodynamically favorable (see oxidation potentials of the
alkenes in Table 1). All these facts are in support of the
mechanism shown in Scheme 2 for the formation of product 1.
Significant cosensitizer effect21,22 and special salt effect24 in
accelerating the reaction were noticed in the photoreactions.
Therefore, while irradiation of TCNB (0.025 M), R-methylsty-
rene (0.05 M), and acetylacetone (0.2 M) in MeCN for 7 h led
to a 27% conversion of TCNB to give 1 (75%), 2 (3%), and 3
(4%), photolysis of the same reaction mixture with added BP
(22) (a) Schaap, A. P.; Siddiqui, S.; Prasad, G.; Palomino, E.; Lopez, L. J.
Photochem. 1984, 25, 167–181. (b) Schaap, A. P.; Siddiqui, S.; Gagnon, S. D.;
Lopez, L. J. Am. Chem. Soc. 1983, 105, 5149–5150. (c) Majima, J.; Pac, C.;
Sakurai, H. J. Am. Chem. Soc. 1981, 103, 4499–4508.
(23) (a) ∆GET for SET between 1TCNB* and the enol is estimated to be
<-2.17 eV by the Weller equation,23b assuming the oxidation potential of the
enols to be <1 V (SCE).18,23c,d (b) Rehm, D.; Weller, A. Isr. J. Chem. 1970, 8,
259–271. (c) Rock, M.; Schmittel, M. J. Chem. Soc., Chem. Commun. 1993,
1739–1741. (d) Lal, M.; Langels, A.; Deiseroth, H. J.; Schlirf, J.; Schmittel, M.
J. Phys. Org. Chem. 2003, 16, 373–379. (e) The BET process in the singlet ion
red
radical pair [TCNB-• enol+•] has a free energy change ∆GBET ) E (TCNB)-
1/2
ox
E
(enol) ≈-0.65-1 )-1.65 eV. This small energy gap for the BET process
1/2
implies that BET has a high rate constant. See:(f) Lewis, F. D.; Bedell, A. M.;
Dykstra, R. E.; Elbert, J. E.; Gould, I. R.; Farid, S. J. Am. Chem. Soc. 1990,
112, 8055–8064. (g) Gould, I. R.; Ege, D.; Moser, J. E.; Farid, S. J. Am. Chem.
Soc. 1990, 112, 4290–4301.
(24) (a) Gollnick, K.; Wellnhofer, G. J. Photochem. Photobiol. A: Chem.
1993, 74, 137–145. (b) Mizuno, K.; Ichinose, N.; Otsuji, Y. Chem. Lett. 1985,
14, 455–458.
8012 J. Org. Chem. Vol. 73, No. 20, 2008

Three-Component Reactions of Tetracyanobenzene
TABLE 1. Photoreactions of TCNB with Alkenes in the Presence of ꢀ-Dicarbonyl Compoundsa
a All the reactions were carried out in MeCN solution. [TCNB] ) 0.025 M, [alkene] ) 0.05 M, [ꢀ-dicarbonyl compound] ) 0.2 M. b Oxidation
potential vs SCE in MeCN. c Yield of isolated products.
SCHEME 2
SCHEME 3
4 (26%), 5 (21%), 6 (5%), and 7 (6%) and the untrapped
products 2 (2%) and 3 (2%) (Chart 2 and Table 1). The steric
configurations of products 4 and 5 can be assigned by
control experiment showed that when 4 was heated on silica
gel, it underwent decarbonylation to give 6 in 55% yield. Product
6 is proposed to be formed by an acid-catalyzed decomposition
mechanism shown in Scheme 4.
When dibenzoylmethane was used as nucleophile, products
8 (82%), 2 (2%), and 3 (2%) were formed. Also obtained is a
1,5-diketone product 9 derived from de Mayo reaction25 of
triplet excited dibenzoylmethane with the alkene. Dibenzoyl-
methane has rather strong absorption (λmax ) 339 nm, ꢀ )
1
comparison of their H NMR spectra with that of products 10
and 11 whose steric structures are based on an X-ray crystal-
lographic analysis of product 10 (vide infra). Products 4 and 5
are diastereomers. TLC monitoring of the reaction course
showed that compound 6 is not a primary product formed in
the photoreactions, but was formed during the silica gel
chromatographic separation of the reaction mixture. Indeed, a
J. Org. Chem. Vol. 73, No. 20, 2008 8013

Lu et al.
SCHEME 4
products (similar to 15 and 16) by acid-catalyzed decomposition
during the chromatographic separation by a mechanism shown
in Scheme 4.
In the photoreaction of TCNB with p-methylstyrene in the
presence of acetylacetone, product 19 (52%) was formed
together with 20 (8%) and 21 (19%). Considering the stronger
electron donor ability of p-methylstyrene as reflected by its lower
oxidation potential, the higher yields of 20 and 21 are the result
of the higher nucleophilicity of the neutral alkene.
For ethyl cinnamate, similar reactions with TCNB and
acetylacetone gave the three-component products 22 (24%) and
23 (58%) as diastereomers without the formation of the olefin
dimerization-aromatic substitution products. This result is
consistent with the high electrophilic reactivity of the cinnamate
cation radical and the low nucleophilicity of the neutral
cinnamates.
SCHEME 5
Photoreactions of TCNB, benzofuran, and acetylacetone led
to the formation of product 24 as the sole product in 86% yield.
The steric structure of 24 is also established by an X-ray
crystallographic analysis (see the Supporting Information).
It is seen that these three-component reactions with the
enolized 1,3-dicarbonyl compound as carbon nucleophiles result
in sequential formation of two C-C bonds at both carbon atoms
of the alkene, therefore contributing a new photochemical
scenario to the synthetically important strategy of tandem vicinal
dialkylation (dicarbocondensation) of alkenes.27-29 They also
provide a new method for selective R-alkylation of the ꢀ-dike-
tones30 without the complication of O-alkylation and R,R-
dialkylation in the conventional base-induced R-alkylation
reactions. Furthermore, these reactions lead to the addition of
1,3-dicarbonyls to a styrene derivative, which is an area of much
interest.31-33
26 900, in methanol) in the wavelength region used for the
photolysis and is excited in competition with TCNB.
With ethyl benzoylacetate as a nucleophile, the photoreaction
gave products 10 (21%) and 11 (17%) as diastereomers, together
with a significantly higher yield of 2 (15%) and 3 (10%) than
in the above-mentioned reactions with diketones as nucleophile.
The steric structure of 10 is established by an X-ray crystal-
lographic analysis (see the Supporting Information).
Conclusions
In this case, the much higher yield of the untrapped products
2 and 3 can be attributed to the lower enol concentration derived
from the benzoylacetate in the reaction mixture. It is known
that ꢀ-ketoesters have much lower enol contents than structurally
similar ꢀ-diketones. Therefore, while in pure liquid, acetylac-
etone has an enol content of 81%, only 22% of ethyl benzoy-
lacetate is in the enol form.1,26 This low concentration of the
enol in the reaction mixture enables the neutral R-methylstyrene
to compete more favorably with the enol to trap the alkene cation
radical to give products 2 and 3.
Photolysis of TCNB with R-methylstyrene in the presence
of dimedone (5,5-dimethylcyclohexa-1,3-dione) furnished prod-
ucts 12 (62%), 2 (5%), and 3 (6%), together with a dimeric
dimedone product 13. A control experiment showed that 13 can
be formed by either irradiation of dimedone alone or dimedone
in the presence of TCNB. We therefore propose that product
13 may derive from PET reaction of dimedone enol (as electron
donor) with its excited keto-form or singlet excited TCNB (as
electron acceptor) as shown in Scheme 5.
In summary, photoinduced three-component reactions of TC-
NB with alkene and ꢀ-dicarbonyl compound have been reported,
which provide new photochemical strategies for the tandem
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II. Photoreactions of TCNB with the Other Alkenes in
the Presence of 1,3-Diketone. Photoreactions of TCNB with
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(85%) as the sole product. Similar irradiation of TCNB with
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8014 J. Org. Chem. Vol. 73, No. 20, 2008

Three-Component Reactions of Tetracyanobenzene
and ꢀ-dicarbonyl compound in MeCN was purged with N2 for 30
min and then irradiated under continuous N2 purging. The reaction
course was monitored by TLC. At the end of the reaction, the
solvent was removed under reduced pressure and the residue was
separated by flash chromatography on a silica gel or neutral alumina
column with petroleum ether/ethyl acetate as eluents (gradient
elution).
Representative Procedure for the Preparative Photolysis of
TCNB with Alkenes in the Presence of ꢀ-Dicarbonyl Com-
pounds. A solution of TCNB (534 mg, 3 mmol), R-methylstyrene
(709 mg, 6 mmol), and acetylacetone (2.40 g, 24 mmol) in MeCN
(120 mL) was photolyzed for 14 h to reach a 85% conversion of
TCNB. The solvent was removed under reduced pressure and the
residue was separated by flash chromatography on a neutral alumina
column with petroleum ether/ethyl acetate as eluents to give 1 (735
mg, 78%), 2 (48 mg, 5%), and 3 (51 mg, 5%).
5-(4-Acetyl-5-oxo-2-phenylhexan-2-yl)benzene-1,2,4-tricarbo-
nitrile (1): colorless crystals from petroleum ether-acetone, mp
214-215 °C; 1H NMR (300 MHz, CDCl3) δ 8.19 (s, 1H), 7.96 (s,
1H), 7.37-7.34 (m, 3H), 7.08-7.05 (m, 2H), 3.53 (t, J ) 4.9 Hz,
1H), 2.92 (dd, J ) 13.6, 4.7 Hz, 1H), 2.81 (dd, J ) 13.6, 5.2 Hz,
1H), 2.14 (s, 3H), 1.74 (s, 6H) ppm; 13C NMR (100.6 MHz, CDCl3)
δ 202.5, 202.0, 158.1, 142.4, 139.4, 131.9, 129.1, 128.4, 128.2,
119.3, 118.4, 115.0, 114.4, 114.2, 113.4, 64.6, 47.3, 38.1, 29.1,
28.8, 25.5 ppm; IR (KBr) 3117, 2986, 2241, 2230, 1735, 1711,
1387, 1364, 1250, 1148, 914, 766, 699, 520 cm-1; MS (EI) m/z
(%) 351 (4), 326 (18), 284 (21), 268 (5), 257 (18), 256 (100), 242
(10), 229 (2), 215 (4), 178 (2), 113 (8), 77 (2), 71 (32), 43 (49).
Anal. Calcd for C23H19N3O2: C, 74.78; H, 5.18; N, 11.37. Found:
C, 74.61; H, 5.37; N, 11.22.
vicinal dialkylation of the alkene and for R-alkylation of the
ꢀ-dicarbonyl compounds. The reaction mechanisms have been
clarified. It is shown that these reactions proceed by a photo-
nucleophile-olefin combination, aromatic substitution (photo-
NOCAS) mechanism with the ꢀ-dicarbonyl compounds serving
as nucleophiles. We have shown that, aromatic alkenes such as
styrene derivatives are good alkene substrates in photo-NOCAS
reactions when TCNB is used as electron acceptor. The anti-
Markovnikov addition of the nucleophile to the alkene and the
alkene dimerization (leading to tetralin and cyclobutane prod-
ucts) are not competing with the three-component reactions
because back electron transfer from TCNB-• to the nucleophile-
alkene addition radical or the alkene dimeric radical is thermo-
dynamically unfavorable. The main side reactions to the three-
component reactions when using aromatic alkenes are the olefin
dimerization, aromatic substitution reactions (leading to products
2 and 3). We have also shown that there is a close correlation
between the nucleophilic reactivity of the diketones (in trapping
the alkene cation radicals) and the diketone enol content. With
an increase in the enol content of the diketone, the yield of the
three-component reactions is raised at the cost of products 2
and 3. To our knowledge, this is the first report on using
ꢀ-dicarbonyl compounds as nucleophilic trapping agent for
alkene cation radicals in photoinduced electron transfer reac-
tions. Since carbon nucleophiles have been rarely investigated
in PET reactions except for the cyanide anion,34 the introduction
of enolized ꢀ-dicarbonyl compounds as nucleophiles may serve
to expand the reaction scope of PET reactions and increase their
synthetic utility by enabling them for C-C bond formation.
Acknowledgement. This work was supported by the National
Natural Science Foundation of China (NSFC, 20572044) and
the International Scientific & Technological Exchange and Co-
operation Foundation from the Ministry of Science and Tech-
nology of China (2007DFA41590). Support from the Modern
Analytical Center at Nanjing University is also gratefully
acknowledged.
Experimental Section
General Procedures for the Preparative Photolysis of TCNB
with an Alkene in the Presence of a ꢀ-Dicarbonyl Compound.
The light source was a medium-pressure mercury lamp (500 W) in
a glass cooling water jacket to cut off light of wavelength shorter
than 300 nm. The solution of tetracyanobenzene (TCNB), alkene,
Supporting Information Available: Detailed experimental
section, 1H NMR and 13C NMR spectra of all new compounds,
and crystallographic information files of compounds 10 and 24.
This material is available free of charge via the Internet at
http://pubs.acs.org.
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Soc. Chim. Fr. 1995, 132, 843–849. (c) Vinogradov, M. G.; Dolinko, V. N.;
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(34) At the completion of the manuscript, a report by K. Mizuno and his
co-workers to use malononitrile as a carbon nucleophile to trap the alkene cation
radical had just been published. See: Ohashi, M.; Nakatani, K.; Maeda, H.;
Mizuno, K. Org. Lett. 2008, 10, 2741–2743.
JO801448V
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