Simple Synthesis of a Weak Nucleophilic Base (4-Ethyl-2,6-diisopropyl-3,5-dimethylpyridine) Evidencing a Double Janus Group Effect

Article abstract of DOI:10.1021/jo035416k

By analogy with 2,6-di-tert-butylpyridine and its 4-methyl-substituted derivatives, which are nonnucleophilic bases, 4-ethyl-2,6-diisopropyl-3,5-dimethylpyridine (4) is also such a base. The isopropyl groups (Janus-like groups) are forced by the neighboring methyl groups to turn their tert-butyl-analogue face toward the heteroatom, thereby protecting it sterically against electrophilic attack. The synthesis proceeds in two stages via the corresponding pyrylium salt 3 that is obtained by alkene diacylation. X-ray data for 4, its picrate, and the hexafluorophosphate of 3 confirm that the ground-state conformation agrees with the Janus effect prediction. The chemical behavior of 4 indicates that it is indeed a weak nucleophilic base, which is able to substitute the nonnucleophilic bases in organic syntheses. The compound 3 reacts at normal pressure with methylamine or ethylamine, forming N-alkylpyridinium salts. The cationic polymerization of isobutene in the presence of 4 was also investigated.

Full text of DOI:10.1021/jo035416k

Sim p le Syn th esis of a Wea k Nu cleop h ilic Ba se
(4-Eth yl-2,6-d iisop r op yl-3,5-d im eth ylp yr id in e) Evid en cin g a Dou ble
J a n u s Gr ou p Effect
Alexandru T. Balaban,*,† Ion Ghiviriga,‡ Edmund W. Czerwinski,§ Priyadarsi De,| and
Rudolf Faust|
Texas A&M University at Galveston, 5007 Avenue U, Galveston, Texas 77551, Department of Chemistry,
University of Florida, Gainesville, Florida 32611, Department of Human Biological Chemistry and
Genetics, University of Texas Medical Branch, Galveston, Texas 77555, and Chemistry Department,
University of Massachusetts, Lowell, 1 University Avenue, Lowell, Massachusetts 01854
balabana@tamug.edu
Received September 27, 2003
By analogy with 2,6-di-tert-butylpyridine and its 4-methyl-substituted derivatives, which are
nonnucleophilic bases, 4-ethyl-2,6-diisopropyl-3,5-dimethylpyridine (4) is also such a base. The
isopropyl groups (J anus-like groups) are forced by the neighboring methyl groups to turn their
“tert-butyl-analogue face” toward the heteroatom, thereby protecting it sterically against electrophilic
attack. The synthesis proceeds in two stages via the corresponding pyrylium salt 3 that is obtained
by alkene diacylation. X-ray data for 4, its picrate, and the hexafluorophosphate of 3 confirm that
the ground-state conformation agrees with the J anus effect prediction. The chemical behavior of 4
indicates that it is indeed a weak nucleophilic base, which is able to substitute the nonnucleophilic
bases in organic syntheses. The compound 3 reacts at normal pressure with methylamine or
ethylamine, forming N-alkylpyridinium salts. The cationic polymerization of isobutene in the
presence of 4 was also investigated.
In tr od u ction
complexed normally with pyridines substituted in the R
positions (2 and 6) with one methyl group and one
isopropyl group but not with those having one methyl
group and one tert-butyl group. It was found that there
was a normal complexation of such LRSs with pyridine
2, where the isopropyl group could rotate freely, but
practically none with the isomeric pyridine 1, where the
isopropyl was constrained by the neighboring methyl
group to turn its tert-butyl-like face toward the site of
the complexation with the LSR.4
Starting from this observation, we now report the
simple synthesis of a new nonnucleophilic base, 4-ethyl-
2,6-diisopropyl-3,5-dimethylpyridine (4), starting from
inexpensive reagents in only two reaction steps. In
addition to the J anus effect, a gear effect2,6 may also take
place in a pentasubstituted pyridine such as 4.
Freely rotating isopropyl groups offer two kinds of
faces, like the mythological god J anus who looked toward
both the past and the future (bridging the months of two
consecutive years), hence the name J anus group effect.1-4
One face of an isopropyl group is tert-butyl-like, associ-
ated with a considerable steric effect, and the other two
faces are ethyl-like. Previously, we had tested this effect
in two isomeric-substituted pyridines, 2-isopropyl-3,6-
dimethylpyridine (1) and 6-isopropyl-2,3-dimethylpyri-
dine (2).4
Earlier, one of us had reported a synthesis of 2,6-di-
tert-butyl-4-methylpyridine from its pyrylium analogue
obtained by the diacylation of isobutene (IB) (actually,
tert-butyl chloride, which is easier to handle) with piv-
aloyl chloride in the presence of tin tetrachloride.7 Other
It was shown earlier5 that lanthanide shift reagents
(LSRs) such as Eu(dpm)3, Eu(fod)3, Pr(dpm)3, or Pr(fod)3
† Texas A&M University at Galveston.
(5) Balaban, T. S.; Uncuta, C.; Gheorghiu, M. D.; Balaban, A. T.
Tetrahedron Lett. 1985, 26, 4669-4672.
‡ University of Florida.
§ University of Texas Medical Branch.
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Klatte, G.; Memiaghe, J . A.; Metzger, J .; Oniciu, D.; Pierrot-Sanders,
J . Tetrahedron 1983, 39, 4209-4219.
| University of Massachusetts, Lowell.
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10.1021/jo035416k CCC: $27.50 © 2004 American Chemical Society
Published on Web 12/18/2003
536
J . Org. Chem. 2004, 69, 536-542

Simple Synthesis of a Weak Nucleophilic Base
Lewis acids cause the decarbonylation of pivaloyl chlo-
ride, but an expensive Brønsted acid (triflic acid) can also
be employed.8 The workup is tedious, and the yields are
not high. The synthesis of pyrylium salts via alkene
diacylation has been called the Balaban-Nenitzescu-
Praill reaction.9
pyridines.29 Enolizable aldehydes and ketones afford
enolic triflates with triflic anhydride and these nonnu-
cleophilic bases;30 such enolic esters are important in
carbohydrate research;31 other similar esters can be used
for palladium-catalyzed couplings.32 Radical cations of
thianthrene33 or anthracene34 act as one-electron oxidants
in the presence of these nonnucleophilic bases. An in-
teresting biological application of the two nonnucleophilic
pyridines mentioned above is to use them as hypoli-
paemic agents for lowering cholesterol levels.35
Syn th esis of 4-Eth yl-2,6-d iisop r op yl-3,5-d im eth -
ylp yr yliu m Sa lts a n d 4. Upon dropwise addition of
concentrated hexafluorophosphoric acid into a mixture
of isobutyric anhydride and 3-ethyl-3-pentanol (triethyl-
carbinol), a rapid exothermal diacylation takes place. On
cooling, 4-ethyl-2,6-diisopropyl-3,5-dimethylpyrylium hexa-
fluorophosphate (3) crystallizes (admixed with a small
amount of the hexafluorophosphate of the monoacylation
product, 5-ethyl-2,4-dimethylhept-4-en-3-one) and can be
separated by filtration and washing with diethyl ether.
Recrystallization from ethanol or acetic acid and washing
with ethyl ether give 3, mp 235 °C. In the reaction, a
sufficient amount of isobutyric anhydride needs to be
present both for the diacylation and for binding of the
water that comes with the 60% hexafluorophosphoric acid
(5.4 mol of water for each mole of HPF6).
It has long been known that 2,6-di-tert-butylpyridine
(DTBP)10 or 2,6-di-tert-butyl-4-methylpyridine,7,8 which
are commercially available at the present time at a fairly
high cost, are nonnucleophilic bases. This fact makes
them useful for many applications, e.g., as proton traps
for living cationic polymerizations, inhibiting chain branch-
ing, and lowering the polydispersity.11-21 Such pyridines
distinguish between Brønsted acids, which are able to
protonate them, and Lewis acids such as BF3 or SO3,
which do not interact with them.8,22-24 From NMR data,
one can infer how protonated pyridines interact with
anions or how the bases are chemisorbed on solid
surfaces.25 Benzylic triflates can be prepared with triflic
anhydride in the presence of DTBP and are used in situ
for the living polymerization of tetrahydrofuran.26 Highly
isotactic poly(isobutyl vinyl ether) was obtained with
titanium-based Lewis acids and 2,6-di-tert-butyl-4-
methylpyridine.27 On the other hand, the electrochemical
polymerization of pyrrole is inhibited by DTBP, owing
to proton scavenging.28 Rate constants between the
vinylic cations and DTBP are the lowest among all
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4446. (c) Kwon, Y.; Cao, X. Y.; Faust, R. Macromolecules 1999, 32,
6963-6968.
Triethylcarbinol was selected in this synthesis because
its dehydration affords a single alkene, namely, 3-ethyl-
2-pentene. In theory, other tertiary or secondary alcohols,
e.g., tri-n-propylcarbinol, may also be employed, leading
to the pentasubstituted compounds related to 3 or 4, but
triethylcarbinol is the simplest one.
The crystal and molecular structure of 3 was deter-
mined by X-ray crystallography and showed (Figure 1a)
that the two isopropyl groups are in a conformation that
(16) (a) Faust, R.; Iva´n, B.; Kennedy, J . P. J . Macromol. Sci., Chem.
1991, A28, 1. (b) Fodor, Z.; Gyor, M.; Wang, H. C.; Faust, R. J .
Macromol. Sci., Chem. 1993, A30, 349-363.
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Crich, D.; Li, H. J . Org. Chem. 2000, 65, 801-805. (c) Crich, D.; Smoth,
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1999, 18, 464-473.
J . Org. Chem, Vol. 69, No. 2, 2004 537

Balaban et al.
F IGURE 1. From top to bottom: the molecular structures
of (a) the pyrylium salt 3, (b) the pyridine 4, and (c) its
picrate 5.
has the pairs of methyl groups mirroring each other and
being oriented toward the heteroatom but not bisecting
exactly the heterocyclic ring, with the anion probably
being responsible for the incomplete alignment of the
isopropyl hydrogens with the 3- and 5-methyl groups.
Subsequent treatment with aqueous ammonia con-
verted 3 into the title product 4 in high yield. After ex-
F IGURE 2. From top to bottom: the molecular structures of
(a) the pyrylium salt 3, (b) the pyridine 4, and (c) its picrate 5
(side views).
traction with diethyl ether, 4 can be purified by distil-
lation at reduced pressure, and being a little soluble in
n-pentane, it can be recrystallized for attaining high
538 J . Org. Chem., Vol. 69, No. 2, 2004

Simple Synthesis of a Weak Nucleophilic Base
F IGURE 3. Stereoviews (side oriented for the heterocycle) of the structure of pyridine 4 (top) and its picrate 5 (bottom) calculated
by MM2.
purity. Its X-ray structure is shown in Figure 1b, reveal-
ing that the two isopropyl groups are also shielding the
heteroatom but in intercalated conformations. A crystal-
line picrate 5 of this pyridine was prepared; its crystal
and molecular structures were determined by X-ray
crystallography and showed (Figure 1c) that the two
isopropyl groups are in an “eclipsed conformation”, which
has their two methyl groups oriented toward the het-
eroatom, bisecting exactly the planar pyridinium ring,
i.e., in a conformation in which the isopropyl groups exert
the same steric shielding as the tert-butyl groups. The
only difference is that in 4 the isopropyl groups may turn
(provided that the molecule has sufficient energy), al-
leviating the shielding, as shown by the quaternization
that can proceed at normal pressure. Side views of the
three molecular structures along the plane of the het-
erocycle illustrate the notable differences between the
conformations of the pair of isopropyl groups (Figures
2a-c).
Interestingly, the molecular mechanics (MM2) calcula-
tions reproduce not only the J anus-like orientation of
isopropyl groups but also their “staggered” conformation
in the pyridine 4, as well as their “eclipsed” conformation
in the corresponding pyridinium picrate 5 (Figure 3).
Neither Eu(fod)3 nor Pr(fod)3 showed any complexation
with 4, which behaved with LSR just like DTBP and its
4-methyl derivative.
the respective pyrylium salts, which had been described
earlier.7a,39,4039-40
Analogously, hexasubstituted N-methyl- or N-ethylpy-
ridinium salts (as hexafluorophosphates, 6 and 7, re-
spectively) can be obtained in high yield from 3 and
methylamine or ethylamine at normal pressure, indicat-
ing that the steric shielding caused by the J anus effect
can be overcome provided that the reaction has a high
driving force.
Ca tion ic P olym er iza tion of IB in th e P r esen ce of
P yr id in e 4. The cationic polymerization of IB was car-
ried out with the 2-chloro-2,4,4-trimethylpentane (TMPCl)/
titanium tetrachloride (TiCl4) initiating system in a
hexanes (Hex)/methyl chloride (MeCl) (60:40, v/v) solvent
mixture at -80 °C without (denoted as “no DTBP”) and
with the following proton traps: DTBP, 2,6-diisopropyl-
4-methylpyridine (H-1), and compound 4 (H-2). The first-
order plot of ln([M]0/[M]) versus time for the cationic
polymerization of IB is presented in Figure 4. According
to the first-order plot, termination cannot be detected
during the polymerization of up to ∼80% monomer
conversions. The slope of the ln([M]0/[M]) versus time plot
gives the apparent rate constants of polymerization (kapp).
The kapp values are similar in the [proton trap] ) 0.004-
0.008 mol/L concentration range, while in the absence of
DTBP, the polymerization rate is significantly higher
because of the initiation from protic impurities.
The Mn and Mw/Mn versus conversion plots are shown
in Figures 5 and 6, respectively. The molecular weights
follow the theoretical Mn-conversion line, indicating the
absence of the chain transfer during the polymerization.
The polydispersity index (PDI) decreases for all three
proton traps with increasing conversion because of the
DTBP or its 4-methyl-derivative can be quaternized by
reacting with methyl fluorosulfate only at high pres-
sure;36 other N-alkyldi-tert-butyl derivatives are not
formed from the corresponding pyrylium salts with
alkylamines. However, it should be mentioned that DTBP
and its 4-methyl-derivative can readily afford N-amino
derivatives37 and that the corresponding N-oxides can
also be prepared38 via the reaction of hydroxylamine with
(39) Schmitz, E. Chem. Ber. 1958, 91, 1488-1494.
(40) Balaban, A. T.; Dinculescu, A.; Dorofeenko, G. N.; Fischer, G.
W.; Koblik, A. V.; Mezheritskii, V. V.; Schroth, W. In Pyrylium Salts:
Syntheses, Reactions and Physical Properties; Katritzky, A. R., Ed.;
Advances in Heterocyclic Chemistry, Supplement; Academic Press:
New York, 1982; Vol. 2, p 129.
(36) Hou, C. J .; Okamoto, Y. J . Org. Chem. 1982, 47, 1977-1979.
(37) Gawinecki, R.; Karner, B. Monatsh. Chem. 1994, 125, 35-41.
(38) Weber, H.; Rohn, T. Z. Naturforsch. 1990, 45B, 701-706.
J . Org. Chem, Vol. 69, No. 2, 2004 539

Balaban et al.
F IGURE 4. First-order plot of ln([M]0/[M]) versus time for
the cationic polymerization of IB initiated by TMPCl/TiCl4 in
Hex/MeCl (60:40, v/v) at -80 °C. [TMPCl] ) 0.002 M, [IB] )
2.0 M, and [TiCl4] ) 0.036 M with (a) DTBP, (b) H-1 and (c)
H-2.
F IGURE 5. Variation of Mn with the conversion for (a) DTBP,
(b) H-1, and (c) H-2. Reaction conditions are the same as those
in Figure 4.
dynamic exchange between the dormant and living
centers during polymerization. In conclusion, all three
proton traps efficiently trap adventitious protons. This
was a rather expected finding, because even the nonsub-
stituted pyridine can be used as a proton scavenger. In
this case, however, the pyridine/TiCl4 complex is the
active proton scavenging species. Because of this complex
formation, polymerization is absent when the concentra-
tion of the unhindered pyridines is equal to or higher
than that of TiCl4.
To elucidate the complex formation, polymerizations
were also carried out at [TiCl4] ) [proton trap] ) 0.036
mol/L, and in 12 min, 62.3, 9.1, and 26% of the monomer
conversion was found for DTBP, H-1, and H-2, respec-
tively. The conversion for DTBP is virtually identical with
540 J . Org. Chem., Vol. 69, No. 2, 2004

Simple Synthesis of a Weak Nucleophilic Base
lization from 120 mL of ethanol or a smaller volume of acetic
acid followed by washing of the product on the filter with ethyl
ether afforded white crystals with mp 235 °C. The yield was
around 50%. HRMS: calcd for C15H25O+PF6-, 221.1905; found,
221.1903. Fragments at m/z ) 220, 205 (base peak), 197, 192,
1
177, 155, 135, 107, 91, 77, 65, 55, and 43. H NMR in DMSO
(δ, ppm; J , Hz): 1.16 (3H, t, J ) 7.6, 4-Me), 1.35 (12 H, d, J )
7.0, 2,6-Me4), 2.44 (6H, s, 3,5-Me2), 2.95 (2H, q, J ) 7.6, 4-CH2),
3.71 (2H, septet, J ) 7.0, 2,6-CH). 13C NMR in DMSO (δ,
ppm): 11.6 (4-Me), 13.0 (3,5-Me2), 19.8 (2,6-Me4), 25.3 (4-CH2),
31.8 (2,6-CH), 129.9 (C-3,5), 175.1 (C-4), 178.9 (C-2,6). The
corresponding perchlorate (from 70% perchloric acid, which
contains 2.4 mol of water per mole of HClO4) was obtained in
55% yield and had mp 142-143 °C. Anal. Calcd for C15H25
ClO5: C, 56.16; H, 7.85. Found: C, 56.25; H, 7.81.
-
Syn th esis of 4. The above pyrylium salt 3 was heated to
boiling with 30 mL of ethanol and an excess of concentrated
aqueous ammonia. The conversion into 4 was complete in a
few minutes. The cooled solution was diluted with an equal
volume of water and extracted three times with ethyl ether.
The base from the combined extracts was extracted with an
excess of 10% hydrochloric acid, and the aqueous acid layer
was treated with an excess of aqueous sodium hydroxide for
regenerating the base. After three extractions with ethyl ether,
the combined organic layer was dried over powdered potassium
hydroxide, and the solvent was evaporated under reduced
pressure. The liquid product 4 was distilled in a vacuum, bp
104 °C/4 Torr, mp 37-38 °C. The yield of the reaction was
85-90%. Anal. Calcd for C15H25N: C, 82.13; H, 11.49; N, 6.39.
Found: C, 81.79; H, 11.13; N, 6.41. HRMS: calcd for C15H25N,
219.1987; found, 219.1983. Fragments at m/z ) 218, 204 (base
peak), 191, 188, 176, 171, 163, 143, 131, 97, 83, 71, 69, 55,
F IGURE 6. Variation of PDI with the conversion for the
cationic polymerization of IB in Hex/MeCl (60:40, v/v) at -80
°C. [TMPCl] ) 0.002 M, [IB] ) 2.0 M, [TiCl4] ) 0.036 M, and
[DTBP] ) [H-1] ) [H-2] ) 0.004 M.
that obtained in the presence of [DTBP] ) 0.004 and
0.008 M, indicating the absence of the complex formation
between TiCl4 and DTBP. For H-1 and H-2, the lowered
conversions do suggest the complex formation for which
the equilibrium constant is much higher for H-1 com-
pared to H-2.
1
and 43. H NMR in DMSO (δ, ppm; J , Hz): 1.02 (3H, t, J )
Con clu sion
6.8, 4-Me), 1.14 (12 H, d, J ) 7.7, 2,6-Me4), 2.18 (6H, s, 3,5-
Me2), 2.59 (2H, q, J ) 6.8, 4-CH2), 3.19 (2H, h, J ) 7.7, 2,6-
CH). 13C NMR in DMSO (δ, ppm): 19.8 (4-Me), 13.5 (3,5-Me2),
22.5 (4-CH2 and 2,6-Me4), 31.4 (2,6-CH), 124.5 (C-3,5), 149.2
(C-4), 159.9 (C-2,6). For preparing enol esters, in particular
cholesta-3,5-dien-3-yl trifluoromethanesulfonate41 when a non-
nucleophilic base is needed,32,41 this pyridine served exactly
as well as 2,6-di-tert-butylpyridine. Picrate 5 of 4, mp from
ethanol 150 °C. Anal. Calcd for C21H28N4O7: C, 56.24; H, 6.29;
N, 12.49. Found: C, 56.41; H, 6.33; N, 12.69.
Triethylcarbinol reacts with isobutyric anhydride and
Brønsted acids yielding a 4-ethyl-2,6-diisopropyl-3,5-
dimethylpyrylium salt, which can be converted by am-
monia into 4. Owing to a double J anus effect, the
isopropyl groups are shielding the heteroatom like tert-
butyl groups, as shown by X-ray crystallography. Thus,
pyridine 4 is a weakly nucleophilic base and can substi-
tute 2,6-di-tert-butylpyridine or its 4-methyl derivative
in its uses as a nonnucleophilic base.
Rea ction of th e P yr yliu m Sa lt 3 w ith Meth yla m in e.
4-Ethyl-2,6-diisopropyl-1,3,5-trimethylpyridinium hexafluoro-
phosphate (6) was prepared in 88% yield from 3 by refluxing
for 3 h in ethanol with a small excess of methylamine and with
a small amount of acetic acid. Mp from ethanol: 248 °C. Anal.
Calcd for C16H28F6NP: C, 50.66; H, 7.44; N, 3.39. Found: C,
50.73; H, 7.15; N, 3.74. 1H NMR in DMSO (δ, ppm, J , Hz):
1.12 (3H, t, J ) 7.7, 4-Me), 1.44 (12H, d, J ) 7.2, 2,6-Me2),
2.83 (2H, q, J ) 7.7, 4-CH2), 2.46 (6H, s, 3,5-Me2), 3.88 (2H,
septet, J ) 7.2, 2,6-CH), 4.11 (3H, s, 1-Me). 13C NMR in DMSO
(δ, ppm): 12.2 (4-Me), 16.2 (3,5-Me2), 19.7 (2,6-Me4), 24.3
(4-CH2), 30.8 (2,6-CH), 43.5 (1-Me), 133.5 (C-3,5), 159.1 (C-
2,6), 161.2 (C-4).
Exp er im en ta l Section
NMR spectra were recorded on a Varian Inova spectrometer
equipped with a 5 mm indirect detection probe, operating at
1
500 MHz for H and at 125 MHz for 13C NMR. Chemical shifts
1
are reported in parts per million relative to TMS. The H and
13C NMR chemical-shift assignments are based on the one-
bond and long-range 1H-13C correlations seen in the ghmbc
(gradient heteronuclear multiple-bond correlation) spectra.
Syn th esis of th e P yr yliu m Sa lt 3. A mixture of 11.6 g
(12.1 mL, 0.1 mol) of triethylcarbinol and 101 g (106 mL, 0.64
mol) of isobutyric anhydride was placed in a three-necked flask
equipped with an efficient stirrer (at the end of the reaction,
the crystal slurry is quite thick), immersed thermometer,
dropping funnel, and reflux condenser. Then about one-third
from 25 g (15 mL, 0.1 mol) of 60% hexafluorophosphoric acid
(which contains 5.4 mol of water per mole of HPF6) was added
dropwise, allowing the temperature to rise fairly rapidly to
about 90 °C (otherwise the product crystallizes, and the mixing
becomes difficult), and the remaining acid was added at such
a rate as to allow the temperature to stay in the range of 90-
100 °C. When the addition was complete, the mixture was
cooled to room temperature. A total of 100 mL of ethyl ether
was added to the mixture, and the crystallized off-white
product was filtered off and washed thoroughly with ether on
the filter. It contained as an impurity the hexafluorophosphate
of the unsaturated ketonic monoacylation product. Recrystal-
Rea ction of 3 w ith Eth yla m in e. In a similar manner, the
pyrylium salt 3 afforded 1,4-diethyl-2,6-diisopropyl-3,5-dim-
ethylpyridinium hexafluorophosphate (7) with ethylamine with
mp from ethanol 228 °C. Anal. Calcd for C17H30F6NP: C, 51.90;
1
H, 7.69; N, 3.56. Found: C, 52.11; H, 7.38; N, 3.57. H NMR
in DMSO (δ, ppm, J , Hz): 1.13 (3H, t, J ) 7.6, 4-Me), 1.47
(12H, d, J ) 7.2, 2,6-Me2), 1.50 (3H, t, J ) 6.7, 1-Me), 2.82
(2H, q, J ) 7.6, 4-CH2), 2.48 (6H, s, 3,5-Me2), 4.52 (2H, q, J )
6.7, 1-CH2), 3.85 (2H, septet, J ) 7.2, 2,6-CH). 13C NMR in
DMSO (δ, ppm): 11.8 (4-Me), 16.3 (3,5-Me2), 16.7 (1-Me), 20.3
(2,6-Me4), 23.6 (4-CH2), 30.6 (2,6-CH), 49.8 (1-CH2), 134.1
(C-3,5), 158.4 (C-2,6), 162.1 (C-4).
Ca tion ic P olym er iza tion s of IB. Ma ter ia ls. MeCl and
IB were dried in the gaseous state by passing them through
(41) Cacchi, S.; Morera, E.; Ortar, G. Org. Synth. 1990, 68, 138-
147.
J . Org. Chem, Vol. 69, No. 2, 2004 541

Balaban et al.
inline gas-purifier columns packed with BaO/Drierite. They
were condensed in the cold bath of a glovebox prior to
polymerization. TiCl4 (Aldrich, 99.9%) and DTBP (Aldrich,
97%) were used as received. The synthesis of TMPCl and
purification of Hex and methanol have been published else-
where.15
P olym er iza tion s. All polymerizations were carried out
under a dry nitrogen atmosphere in an MBraun 150-M glove-
box (Innovative Technology Inc., Newburyport, MA). Large (75
mL) culture tubes were used as the polymerization reactors.
The total volume of the reaction mixture was 10 mL. The
polymerization was quenched with excess prechilled methanol.
The polymer was recovered and purified by reprecipitation
from Hex/methanol. Monomer conversions were determined
by gravimetric analysis.
Barbara, CA), model 712 sample processor, and five Ul-
trastyragel GPC columns connected in the following series:
500, 103, 104, 105, and 100 Å. THF was used as a carrier solvent
with a flow rate of 1 mL/min.
Ack n ow led gm en t. The support of the Sigma-Ald-
rich Company is acknowledged. Thanks are expressed
to Dr. M. A. Ilies (Texas A&M University at Galveston)
for experimental assistance with elemental analyses and
to Dr. T. Marriott (Rice University) for the HRMS. R.
Faust thanks the National Science Foundation (CHE-
0131106) for financial support.
Ch a r a cter iza tion of P olym er s. Molecular weights were
measured with a Waters HPLC system equipped with a model
510 HPLC pump, model 410 differential refractometer, model
441 absorbance detector, online multiangle laser light scat-
tering detector (MiniDawn, Wyatt Technology Inc. Santa
Su p p or tin g In for m a tion Ava ila ble: Crystal data for 3-5
and ghmbc NMR spectra for 3, 4, 6, and 7. This material is
available free of charge via the Internet at http://pubs.acs.org.
J O035416K
542 J . Org. Chem., Vol. 69, No. 2, 2004