Methyl methacrylate. Unusual two-electron transfer reaction and carbanion generation

Full text of DOI:10.1021/jo990070s

4956
J . Org. Chem. 1999, 64, 4956-4958
Meth yl Meth a cr yla te. Un u su a l
Tw o-Electr on Tr a n sfer Rea ction a n d
Ca r ba n ion Gen er a tion
Zbigniew J edlin˜ski,* Henryk J aneczek, and
Izabela Bosek
Centre of Polymer Chemistry, Polish Academy of Sciences,
41-800 Zabrze, Poland
Received J anuary 14, 1999
A single electron transfer (SET) mechanism is very
common in many organic reactions. Such reactions are
usually induced by organometallic complexes of transition
metals or alkali metal complexes with arenes, radical
anions being formed as reactive intermediates.1-3 The
competition between electron transfer (SET) and SN2
mechanisms has been observed in some organic synthe-
ses, e.g., in the reaction of aromatic radical anions with
alkyl halides and methane sulfonates.4 The theoretical
aspects of single electron transfer in liquid solutions and
in solids have recently been discussed.5
We have recently reported on the unusual two-electron
transfer to â-lactones and styrene resulting in carbanions
formation.6 Since carbanions are intermediates in many
organic reactions, the novel route to carbanions via two-
electron transfer and its utility in organic synthesis is of
importance. Thus the question arises if two-electron
transfer is a general mechanism operating also in the
reactions of other compounds.
In this communication we present recent results on the
unusual two-electron transfer to methyl methacrylate.
Methyl methacrylate (MMA) is very versatile, reacting
with alkyllithium,7 Grignard reagents,7,8 aluminum,9
titanium,10 and lanthanide11 metaloorganics. Since one-
electron transfer (SET) to methyl methacrylate resulting
in formation of a radical anion intermediate has been
reported,2,3,11 the novel two-electron transfer reaction to
MMA is discussed.
F igu r e 1. The 39K NMR spectrum of the potassium complex
with 18C6 (a) before the reaction with methyl methacrylate
(b) after the reaction.
cations provided the possibility of alkali metal solubili-
zation in aprotic solvents.14,15 The resulting alkali metal
solutions contain complexed metal cations, solvated
electrons, and metal anions. If the process of metal
solubilization is performed according to the results of
kinetic studies performed by us previously,16 the amount
of electrons in the solution is negligible and metal
complexes M+/crown,M- (where M ) K or Na, crown )
18C6) are the main products of alkali metal dissolution
in an aprotic solvent.17,18 The alkali metal supramolecular
complexes were found to induce two electrons toward
electrophiles.6
The reaction of alkali metal supramolecular complex
(K+,crown,K-) with MMA was performed in an aprotic
solvent.19 It turned out that in the model reaction (methyl
methacrylate:metal complex ) 1:1) two electrons were
transferred to the MMA forming dianion 2, which un-
derwent protonation instantly by the solvent and yielded
a respective carbanion 3 (Scheme 1).
The discovery of macrocyclic ligands as crown ethers
and cryptands12,13 which are able to complex alkali metal
(1) Kochi, I. K. Angew. Chem., Int. Ed. Engl. 1988, 27, 1227-1388.
(2) Garst, I. F. Acc. Chem. Res. 1971, 4, 400-406.
(3) (a) Scott, N. D.; Walker, J . F. U.S. Patent 2,150,39, 1939. Chem.
Abstr. 1939, 33, 4602.6 (b) Szwarc, M.; Rembaum, A. J . Polym. Sci.
1956, 100, 189-191.
(4) (a) Sorenson, H. S.; Daasbjerg, K. Acta Chem. Scand. 1998, 52,
51-61. (b) Eberson, L.; Hartshorn, M. P.; Persson, O.; Rander, F. Chem.
Commun. 1996, 215.
Thus the main products in the model reaction of MMA
with the complex of potassium molar ratio 1:1, after
(5) Mikkelsen, K. V.; Ratner, M. A. Chem. Rev. 1987, 87, 113-153.
(6) (a) J edlin˜ski, Z.; Misiołek, A.; Kurcok, P. J . Org. Chem. 1989,
54, 1500-1501. (b) J edlin˜ski, Z.; Czech, A.; J aneczek, H.; Kowalczuk,
M. J . Am. Chem. Soc. 1995, 117, 8678-8679. (c) Szwarc, M.; J aneczek,
H.; J edlin˜ski, Z. Macromolecules 1997, 30, 4498. (d) J edlin˜ski, Z. Acc.
Chem. Res. 1998, 31, 55-61.
(14) Dye, J . L. Prog. Inorg. Chem. 1984, 32, 327-441.
(15) Edwards, P. P.; Ellaboudy, A. S.; Holton, D. M. Nature 1985,
317, 242-243.
(16) J edlin˜ski, Z.; Stolarzewicz, A.; Grobelny, Z.; Szwarc, M. J . Phys.
Chem. 1984, 88, 6094-6095.
(17) (a) J edlin˜ski, Z.; Soko´ł, M.; Grobelny, J . J . Phys. 1991, C5, 291-
296. (b) J edlin˜ski, Z.; Soko´ł, M. Pure Appl. Chem. 1995, 67, 587-592.
(18) J edlin˜ski, Z. Pure. Appl. Chem. 1993, 65, 483-488.
(19) Reaction of methyl methacrylate with supramolecular com-
plexes of potassium: The THF solution of 18C6 (0.2 mol/dm3) was kept
in contact with potassium mirror for 15 min at temp 0 °C under inert
gas atmosphere. Then, to the blue metal solution, filtered through glass
frit, the equivalent amount of methyl methacrylate in THF solution
was added till the blue color of the solution disappeared. After 5 min
of stirring, protonation, methylation, or deuteration of the reaction
mixture was performed by addition of methanol, iodomethane, or
deuterated methanol (methyl-d3 alcohol-d1) in THF, respectively. The
reaction products present in the discolorized solution after protona-
tion, deuteration, or methylation were analyzed by GC-MS spectro-
metry.
(7) Hsieh, H. L.; Quirk, M. P. Anionic Polymerization; Marcel
Dekker: New York, 1996; p 644.
(8) (a) J oh, Y.; Kotabe, Y. Macromolecules 1976, 3, 337-340. (b)
Hatada, K.; Nakanishi, H.; Ute, K.; Kitayama, T. Polym. J . 1986, 18,
581-591.
(9) Adachi, T.; Sugimoto, H.; Aida, T.; Inoue, S. Macromolecules
1993, 26, 1238-1243.
(10) Abe, H.; Imai, K.; Matsumoto, M. J . Polym. Sci. 1968, C23, 469.
(11) (a) Yasuda, H.; Yamamoto, H.; Yamashita, M.; Yokota, K.;
Nakamura, A.; Miyake, S.; Kai, Y.; Kanehisa, N. Macromolecules 1993,
26, 7134-7143. (b) Boffa, L. S.; Novak, B. M. Tetrahedron 1997, 53,
15367-15396.
(12) Pedersen, C. J . J . Am. Chem. Soc. 1970, 92, 386-391.
(13) Lehn, J . M. Struct. Bonding (Berlin) 1973, 16, 1-69.
10.1021/jo990070s CCC: $18.00 © 1999 American Chemical Society
Published on Web 06/09/1999

Notes
J . Org. Chem., Vol. 64, No. 13, 1999 4957
F igu r e 2. The 13C NMR (a) and the 13C DEPT (b) spectrum of MMA oligomers obtained in the presence of K-/K+,18C6 complex
in THF, at 20 °C (MMA:K- ) 2:1).
Sch em e 1

4958 J . Org. Chem., Vol. 64, No. 13, 1999
Notes
protonation by CH3OH or deuteration by CD3OD, are
2-methylpropanoic acid methyl ester 4 or respective
deuterated compound 5 as evidenced by GC-MS analysis.
The methylation of 1:1 reaction products by CH3I, yields
2,2-dimethylpropanoic acid methyl ester 6 (Scheme 1a).
The yield of these products is up to 80%.
Evidence on the transfer of two electrons was also
provided by 39K NMR. It was found that the signal of
the potassium anion in the 39K NMR spectrum of the
metal complex disappeared after the reaction with methyl
methacrylate, the resonance signal of cation becoming
more intensive. It means that in this reaction the
potassium anion, after the transfer of two electrons to
the methyl methacrylate molecule, is converted into
potassium cation (Figure 1).
In summary, results on the two-electron reduction of
MMA by potassium supramolecular complex are pre-
sented. The molar ratio of MMA to the complex is 1:1.
Due to the transfer of two electrons by potassium anion
to methyl methacrylate molecule carbanion of methyl
methacrylate is formed. The latter being a strong nu-
cleophile is able to react with electrophiles yielding
respective functionalized methyl methacrylate. The MMA
“living” polymers and block polymers can be also pro-
duced if the MMA monomer is present in excess.
Ack n ow led gm en t. The financial support of this
work by the State Committee of Scientific Research:
Grant KBN (no. 3T09A11513) is acknowledged.
The 13C NMR and the 13C DEPT spectra of oligomers,
obtained in the reaction of MMA with K-/K+,18C6
complex in THF, molar ratio 2:1 or 3:1 (Scheme 1b),
indicate the presence of a terminal methine proton, which
can be formed as the end group due to two-electron
transfer to the monomer MMA (Figure 2).
If MMA is present in excess in the reaction with alkali
metal supramolecular complex the “living” MMA poly-
mers are formed.
Su p p or tin g In for m a tion Ava ila ble: Characteristic data
of protonated, deuterated, and methylated products of the
reaction of methyl methacrylate with 18-Crown-6 potassium
complex. This material is available free of charge via the
Internet at http://pubs.acs.org.
J O990070S