Polymerization of t-butyl vinyl ether mediated by an aluminum Lewis acid-TrF system and its complex structure-tacticity correlation

Article abstract of DOI:10.1246/bcsj.74.1445

A variety of aluminum (aryloxide)s were used with triphenylmethyl fluoride (TrF) initiator for the isoselective cationic polymerization of t-butyl vinyl ether. This contribution discusses the relationship between polymer tacticity and counteranion structure, which changed according to the bulkiness, strength and chirality of the Lewis acid combined with TrF so as to make the ionic pair more interactive in the polymerization process. Newly developed organoaluminum activators, 15 and 22, showed mm = 55-57%, which is a more than 10% increase in mm compared with achiral aluminum compounds.

Full text of DOI:10.1246/bcsj.74.1445

c. Jpn.
© 2001 The Chemical Society of Japan
Bull. Chem. Soc. Jpn., 74, 1–10 (2001) 1445
e Chemical
ciety of Ja-
n
e Chemical
ciety of Ja-
n
Polymerization of t-Butyl Vinyl Ether Mediated by an Aluminum Lewis
Acid–TrF System and Its Complex Structure–Tacticity Correlation
Cationic Polymerization
M. Oishi et al.
Masataka Oishi and Hisashi Yamamoto*
01
Graduate School of Engineering, Nagoya University, CREST, Japan Science and Technology Corporation (JST),
Chikusa, Nagoya 464-8603
SJA8
09-2673
025
(Received January 26, 2001)
A variety of aluminum (aryloxide)s were used with triphenylmethyl fluoride (TrF) initiator for the isoselective cat-
ionic polymerization of t-butyl vinyl ether. This contribution discusses the relationship between polymer tacticity and
counteranion structure, which changed according to the bulkiness, strength and chirality of the Lewis acid combined
with TrF so as to make the ionic pair more interactive in the polymerization process. Newly developed organoaluminum
activators, 15 and 22, showed mm = 55–57%, which is a more than 10% increase in mm compared with achiral alumi-
num compounds.
01
01
.1
Sequential 1,3-polyol fragments are often encountered in
naturally occurring complex molecules.1 In both biological
systems and material science, stereocontrol of the fundamental
structure represented by poly(vinyl alcohol) (PVA) and its be-
havior in polar media have attracted a great deal of attention in
the field of advanced materials.2 Over the past four decades,
methods for synthesizing PVA have focused on radical poly-
merization of vinyl acetates and have provided efficient routes
to syndiotact-rich PVA due to the generally inexpensive mono-
mers, easy conversion of precursors into PVA by saponifica-
tion, and industrial feasibility.3 On the other hand, among a
myriad of reports on cationic polymerization of alkyl vinyl
ethers, we are intrigued about why Et2O•BF3 can best polymer-
ize t-butyl vinyl ether in an isoselective manner under optimal
Lewis Acid Activators. First, we investigated the cationic
polymerization of t-butyl vinyl ether catalyzed by well-estab-
lished boron and aluminum Lewis acids in the presence of a
relatively stable triphenylmethyl halide (TrX) initiator. In the
absence of any cation sources, trace contaminants in the reac-
tion vessel and some decomposed fragments originating from
the monomer, activators, or their ligand molecules can initiate
polymerization. In contrast, a trityl cation can unambiguously
function as an efficient initiator for the formation of the first
carbon–carbon bond with a monomer.5 We primarily focused
on quite fundamental information such as the appropriate size
for a halogen atom to link an oxonium cation and Lewis acid
and how bulky Lewis acid activators can relieve complete dis-
sociation of an ionic pair or provide a similar trend of poor ste-
reoregularity, as has been observed in halogenated or polar me-
dia.4b Polymerization data are shown in Table 1; these results
clearly demonstrate that a non-trivial fluorine-stabilizing effect
enhances or preserves isotact stereoregularity under the given
polymerization conditions (particularly entry 3 vs 4). In the
area of homogeneous Ziegler catalysis, Marks and co-workers
reported that tris(perfluoroaryl)borane and aluminum activa-
tors had a significant counter anion effect on the predominant
formation of monomeric or dimeric zirconocenium ions.8 The
strong steric encumbrance for cation–anion interaction exem-
plified by B(C12F9)3, ATPH, and ATPH-Br activators decreases
mm ratios from those seen with B(C6F5)3, MAD, and MABR,
respectively. Simple organoaluminums such as AlMe3 and
Et2AlF have completely different tendencies with regard to
tacticity. The solid-state structures of AlR3 (R = Me, Et) and
fluoride ion were studied by Natta and Atwood on the basis of
diffraction analysis. They reported an anionic dinuclear com-
plex structure with colinearity among Al–F–Al atoms (Chart
1).9 This irregular but interesting counter anion structure can
be considered in the case of TrF/AlMe3 and would allow a dis-
crete ionic pair, resulting in active and atactic polymerization.
Unlike AlMe3, Et2AlF is known to exist as a tetrameric com-
plex in solution: due to intrinsic viscosity, the structure is esti-
conditions.2,4,5
Early studies by two research groups,
Higashimura et al. and Kunitake et al. , concluded that a small
ionic radius for the counter anion and use of non-polar solvent
enhanced the isotactic index. This trend is somewhat different
from that followed by other vinyl ether monomers such as
isobutyl vinyl ether.5 To gain an insight into selective chain-
growth and to further improve stereoregularity, we hypothe-
sized that a tightly coordinated ionic pair or reactive dormant
species could be achieved by the proper choice of a bridging
atom and a Lewis acid, and that the course of carbon–carbon
bond propagation would be substantially reflected by the coor-
dination sphere of the Lewis acid component linked with the
termini. Very recently, a similar approach has been presented
by Sawamoto and co-workers in the polymerization of isobutyl
vinyl ether effected by chloride initiator/(ArO)2TiCl2/2,6-di-t-
butyl-4-methylpyridine (DTBMP) systems.6 Herein we dis-
cuss the relationship between polymerization activity/tacticity
and counter anion structure created by a range of chiral as well
as achiral aluminum-based Lewis acids.7
Results and Discussion
I. Cationic Polymerization by Achiral Fluorinated Initia-
tor. A. Comparison of Boron- and Aluminum-Based

1446 Bull. Chem. Soc. Jpn., 74, No. 8 (2001)
Table 1. Polymerization of t-Butyl Vinyl Ether by Boron or Aluminum-Based Initiator a)
Cationic Polymerization
Conditions
°C, h
Yieldb)
%
Entry
Initiator
mm/mr/rrc)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Et2O•BF3
TrBF4
TrCl-B(C6F5)3
TrF-B(C6F5)3
TrCl-B(C12F9)3
MAD
−78, 4
−78, 1
−78, 2
−78, 0.5
−78, 0.5
−78, 1
90
82
92
87
95
15
75
85
93
29
90
74
77
81
63:30:7
65:28:7
atactic
44:39:17
atactic
atactic
atactic
MABR
−78, 1
TrF-MAD
TrF-MABR
TrF-ATPH
TrF-ATPH-Br
TrF-AlMe3
TrF-AlEt2F
TrF-Al(C6F5)3
−78, 0.5
−78, 0.5
−78–25, 10
−78, 0.5
−78, 1
43:42:15
42:42:16
38:41:21
25:46:29
33:44:23
49:37:14
42:44:14
−78, 0.5
−78, 0.5
a) All polymerizations were carried out in toluene under an argon atomosphere as
follows: solvent 10 mL; initiator = 0.10 mmol; monomer = 10.0 mmol.
b) MeOH-insoluble fraction. c) Estimated by 13C NMR measurement.
Chart 1.
Chart 2.
Table 2. 1H NMR Data of iBuAl(OAr)2
a)
mated to be polymeric or more crowded than anticipated from
the formula.10 Furthermore, the additional fluorine and possi-
ble formation of highly fluorinated aluminums Tr-F-AlFnEt3–n
by disproportionation, in spite of insoluble and almost inactive
AlF3, can play a crucial role in increasing activity and isotac-
ticity, as seen in entries 1 and 2. The fact that a small fluorine
atom emerged as the best choice from the high affinity of B-F
and Al-F, based on bond-strength data in diatomic molecules,
suggests the formation of an active and rather compact ionic
pair even with the use of bulkier Lewis acids.11
B. Reaction between Bis(aryloxy)aluminum Hydride or
Isobutyl and Trityl Fluoride: Cationic Polymerization Me-
diated by the Resulting Complexes. Next, we examined
the modification of an aluminum Lewis acid–TrF system.
Olah and co-workers recently reported that some carbocations
can be stabilized by apically bound fluoride ions within a dis-
torted trigonal bipyramidal structure.12,13 The above proposed
model of tight coordination between a boron or aluminum met-
al center and a fluorine atom, and stabilization of the carboca-
tion/oxonium ion by fluorine throughout the polymerization
reaction, can be further extended to the generation of difluoro-
aluminate counter anions, which would hopefully enable diva-
lent equilibration–stabilization toward the counter cation and
possibly rotation of the ligand on aluminum (Chart 2).
iBu group
R3Al
iBu3Al
12b)
CH2
0.25
0.47(d)
0.42(d)
−1.40(d)
CH
1.91
1.83(m)
1.77(m)
0.62(m)
CH3
0.98
0.77(d)
0.70(d)
0.34(d)
13
14
a) Measured in C6D6 at r.t.; b) Identical with literature
data.16
(ArO)2AlH and (ArO)2AlBui, were synthesized according to
the methods of Barron, Ittel, and Lehmkuhl15, 16 and their H
1
NMR data are described in Table 2.
NMR-scale reactions of (BHT)2AlH•OEt2 or (BHT)2AlBui
with 1 or 2 molar amounts of TrF were performed in C6D6 at
room temperature. In each case, a colorless solution of alumi-
num bis(aryloxide) turned to a dark brownish suspension upon
In light of the slight carbonyl alkylating ability of (ArO)2Al-
R,14 reductive cleavage of the carbon–fluorine bond of TrF
should be considered for the formation of (ArO)2Al-F; ideally,
2 molar amounts of TrF could complete the direct production
of difluoroaluminates, with a general formula of Tr+[µ-
F2Al(OAr)2]−. Two types of reducing aluminum precursors,
the addition of TrF.
In a stoichiometric reaction of
1
(BHT)2AlH•OEt2 and TrF, the H NMR spectrum obtained
clearly indicated not only resonance peaks reminiscent of
(BHT)2AlH•OEt2, and aromatic proton peaks based on a triph-
enylmethyl group, but also new three peaks at 5.41, 3.26, and

M. Oishi et al.
Bull. Chem. Soc. Jpn., 74, No. 8 (2001) 1447
Table 3. Polymerization of t-Butyl Vinyl Ether Initiated by TrF-(ArO)2AIR (2:1) Systema)
c)
Conditions
Yieldb)
Mnc) × 10−4
Mw/Mn
Entry
(ArO)2AIR
(BHT)2AIH•OEt2
°C, h
−78, 12
−48, 1
−78, 0.5
−78, 0.5
−78, 0.5
%
64
99
89
84
65
mm/mr/rrd)
41:41:18
44:38:18
47:40:13
40:42:18
46:40:14
1
2
3
4
5
7.97
6.87
4.15
3.29
3.24
18.3
3.94
3.56
3.78
4.17
12
13
14
a) The polymerization was conducted in dry toluene under Ar. TrF:Al:monomer = 2:1:100. b) MeOH insol-
uble fraction. c) Estimated by GPC using polystyrene standards. d) Determined by 13C NMR analysis.
1.11 ppm, which we assigned to a CH proton of triphenyl-
methane, CH2, and CH3 protons of free ether, respectively, and
which were taken as evidence of the expected conversion of
TrF to TrH. On the other hand, a 1:2 mixture of aluminum/
TrF showed, in addition to the aforementioned resonance sig-
for entries 1 and 2, the resulting dark solutions of Al/TrF (1:2)
display high activity, with mm uniformly > 40%. The sup-
pression of decreasing isotacticity can be explained by more
efficient cation-stabilization with additional fluorine. These
results encouraged us to the use of chiral (aryloxy)aluminums
as chiral counter anion components in combination with TrF.
II. Design and Synthesis of New Aluminum Lewis Acids.
Binaphthyl-based ligation for the formation of chiral bidentate
aluminum Lewis acids is well-documented in organic synthe-
sis.17 Recent advances in the design of new types of monoden-
tate chiral phenolic ligands have been made with regard to axi-
al chirality of m-terphenyl-2ꢀ-ols in our laboratory.18 In this
study, we sought to replace t-Bu groups with chiral terpenes,
represented by menthyl groups. With regard to our synthetic
strategy, there are only limited examples of Pd- or Cu-cata-
lyzed cross-coupling between bromopyridine and menthyl
Grignard reagent, and these give lower yields.19 Additionally,
as a preliminary experiment, methanesulfonic acid (−)-men-
thol and (+)-neomenthol esters were exposed to 2-(meth-
oxymethoxy)phenyllithium ether in THF, but no coupling
1
nals, some unassignable peaks in the H NMR spectrum.
However, regardless of the stoichiometry, the existence of TrF
was suggested by 19F NMR measurements; i.e., the original
peak (−127.18 ppm) was completely displaced upfield at
−163.27 ppm. Similarly, ether-free (BHT)2AlBui was treated
with TrF in C6D6. Again, the insoluble species was not charac-
terized, but the relatively clean formation of TrH with collapse
of the iBu group was observed from the 1H NMR spectra with
Al/TrF ratios of both 1:1 and 1:2. As a result of the above
spectroscopic data, we predict that the insoluble material in ar-
omatic hydrocarbon solvent includes highly fluorinated alumi-
nate species. In this context, we next examined the polymer-
ization of t-butyl vinyl ether using 1:2 mixtures of
(BHT)2AlH•OEt2 or various (ArO)2AlBui and TrF. The results
of polymerization summarized in Table 3 indicated that, except
Scheme 1. a) (1) n-BuLi/THF-hexane, 0 °C, (2) B(OMe)3, (3) NH4Cl aq; b) cat. [Pd(PPh3)4], methenyl triflate, Cs2CO3/DME–H2O,
80 °C; c) 3 M HCl aq-THF, reflux; d) (1) n-BuLi/THF–hexane, 0 °C, (2) (−)-menthone, −78 °C, (3) 3 M HCl aq-THF, reflux; e)
(1) cat. Raney® nickel, H2 (1 atm)/EtOH, r.t., (2) 3 M HCl aq-THF, reflux; f) 1,1ꢀ-thiocarbonyldimidazole/THF, reflux; g) n-Bu-
SnH/xylenes, reflux; h) Br2/CH2Cl2, 0 °C–r.t.

1448 Bull. Chem. Soc. Jpn., 74, No. 8 (2001)
Cationic Polymerization
products were obtained due to steric hindrance and the lower
nucleophilicity relative to anions of cyclopentadiene deriva-
tives.20 Thus, we began our synthesis of chiral phenols with a
menthenyl group at ortho positions via repeated Suzuki cou-
pling, as shown in Scheme 1.
menthyl-major mixture was subjected to recycling preparative
HPLC and essentially pure 7 was obtained as a colorless oil.
The relatively broad multiple resonance of a benzylic proton at
2.83–2.97 ppm in 1H NMR would be characteristic of a menth-
yl configuration, while the benzylic proton of 6 would be ob-
served at 3.52–3.60 ppm. To offset any suspicion regarding
the stereochemistry, we obtained a crystal of the p-nitroben-
zoate ester of stereoisomer 6 and carried out an X-ray diffrac-
tion analysis, whereas the ester from 7 is no longer crystalline.
Figure 1 shows the ORTEP diagram of dimer molecules of the
ester from 6, which clarifies the absolute configuration and the
location of the phenolate moiety axial to the cyclohexane ring.
The reaction of AlMe3 and 3a was performed in dry hexane
or toluene at r.t. under Ar (Scheme 2). The desired air- and
Menthenyl triflate, which we chose as a coupling partner
due to its physical stability, can be indirectly prepared from
(−)-menthone via regioselective formation of the silyl enol
ether in an acceptable yield.21 The triflate was reacted with
arylboronic acid at 80 °C in the presence of Cs2CO3 base under
the influence of catalytic Pd(PPh3)4 to furnish the desired cou-
pling product 2a. Furthermore, a boronic acid group was in-
troduced at the 6 position of 2a, and a second Suzuki coupling
was then conducted under the same conditions. Final removal
of methoxymethyl (MOM) protection by means of HCl/THF/
H2O gave rise to 2,6-dimenthenylphenol 3a in an overall yield
of 68%. Similarly, the p-chloro derivative 3b was synthesized
to be used as a ligand for the chiral counterpart of MABR.
Moreover, to obtain new chiral and Lewis acidic aluminum
tris(aryloxide)s, dibromophenols 9 and 10 were synthesized
via 6 and 7, respectively. Hydrogenation of 2a or 8 was carried
out using a variety of transition metal catalysts. For 2a,
Pd(OH)2 was the most active, but gave a mixture of neomenth-
yl and menthyl configurations (86:14). Fortunately, stereose-
lectivity of > 99% for the neomenthyl configuration was es-
tablished using a Raney® nickel catalyst, though with lower
activity (50% yield; r.t., 96 h). On the other hand, an attempted
hydrogenation of 8 was unsuccessful even with promising cat-
alysts: Pd(OH)2, Raney® nickel, PtO2 and Crabtree’s Ir+. To
identify a synthetic route for menthyl stereoselection, we stud-
ied the reductive cleavage of 5, which is simply accessible by
anionic coupling of 1a with (−)-menthone, removal of MOM
ether and successive thiocarbonate formation from 4 and 1,1ꢀ-
thiocarbonyldiimidazole. Dissolving metal-mediated reduc-
tion of 5 was highly susceptible to the reaction conditions. For
example, Li-naphthalenide was used in THF at −100 °C to
give a mixture of 6 and 7 in a yield of 71% (77:23), whereas
Li/NH3, Li/NH3/t-BuOH, and Ba in THF are too active even
below at −78 °C and give 4 or 8 as a major product. Our opti-
mization experiments gave moderate menthyl selectivity
(62%) attained by n-Bu3SnH reduction in o-xylene reflux. The
Fig. 1. ORTEP drawing of o-neomenthylphenyl p-nitro-
benzoate derived from 6.
Scheme 2. New aluminum Lewis acids with chiral aryloxides.

M. Oishi et al.
Bull. Chem. Soc. Jpn., 74, No. 8 (2001) 1449
Table 4. Selected Bond Lengths, Bond Angels, and Torsional Angles of 15
Bond Lengths
Al(l)–O(2)
1.716(1)
Al(l)–O(0)
O(2)–C(19)
C(4)–C(7)
C(9)–C(13)
C(4)–C(17)
C(8)–C(27)
1.708(1)
1.360(2)
1.487(2)
1.488(2)
1.349(2)
1.342(2)
Al(l)–O(26)
O(3)–C(20)
C(8)–C(16)
C(10)–C(11)
C(6)–C(13)
C(10)–C(22)
1.947(2)
1.365(2)
1.495(2)
1.493(2)
1.339(2)
1.338(2)
Bond Angels
O(2)–Al(1)–O(3)
O(3)–Al(1)–C(26)
Al(1)–O(3)–C(20)
C(16)–C(8)–C(27)
C(6)–C(13)–C(9)
C(23)–C(8)–C(27)
C(6)–C(13)–C(35)
113.6(1)
121.3(1)
132.0(1)
120.0(2)
119.1(1)
123.0(2)
122.0(1)
O(2)–Al(1)–C(26)
Al(1)–O(2)–C(19)
C(7)–C(4)–C(17)
C(11)–C(10)–C(22)
C(5)–C(4)–C(17)
C(22)–C(10)–C(42)
123.7(1)
131.0(1)
120.2(1)
120.0(2)
122.6(1)
122.5(2)
Torsional Angles
O(3)–Al(1)–O(2)–C(19)
C(26)–Al(1)–O(2)–C(19)
Al(1)–O(2)–C(19)–C(7)
Al(1)–O(3)–C(20)–C(9)
C(17)–C(4)–C(7)–C(19)
C(20)–C(9)–C(13)–C(6)
73.9(1)
−119.3(2)
37.5(1)
53.0(1)
−70.2(2)
−74.3(2)
O(2)–Al(1)–O(3)–C(20)
C(26)–Al(1)–O(3)–C(20)
Al(1)–O(2)–C(19)–C(11)
Al(1)–O(3)–C(20)–C(16)
C(27)–C(8)–C(16)–C(20)
C(22)–C(10)–C(11)–C(19)
50.7(1)
−116.4(2)
−144.5(2)
−128.1(2)
114.2(2)
122.6(2)
a) Bond lengths are given in Å, and angles in °. See Fig. 2 for the numbering.
moisture-sensitive methylaluminum bis(aryloxide) 15 was iso-
lated by recrystallization from saturated hexane solution, and
the solid-state structure was characterized by a diffraction
study at −80 °C. Selected bond lengths, bond angles, and tor-
tional angles are shown in Table 4. As can be seen in Fig. 2,
the characteristic features are as follows: (1) the structure has
almost C2 symmetry in terms of the Al–Me bond, (2) summa-
tion of the aluminum bonds indicates coordinative unsaturation
of the aluminum center; i.e., aluminum has sp2 geometry, and
(3) all of the menthenyl isopropyl groups are located in the
same orientation to each phenolate face, excluding the forma-
tion of other isomeric conformers. In comparison with the
MAD structure, the steric environment around the aluminum
coordination site is fairly sophisticated, with two menthenyl
groups in the proximity of the Al–Me bond. Other new alumi-
num compounds, 16, 17, and 18, were prepared from 3b, 9,
and 10 in toluene solution, respectively, and used for a poly-
merization study without any characterization (Scheme 2).
III. Polymerization Using Chiral Aluminum Lewis Ac-
ids. A. Polymerization Catalyzed by a Chiral Methylalu-
minum Bis(aryloxide)–TrF System. As discussed above,
we examined chiral aluminum Lewis acids 15–18 modified
from MAD, MABR, and ATPH-Br with regard to the cationic
polymerization. Our preliminary results with methylalumi-
num binaphtholate derivatives–TrF (1:1) showed that Lewis
acids with substantial steric bulk are needed for successful ini-
tiation upon activation of C–F bond of the TrF initiator. As
shown in Table 1, chiral Lewis acids 15–18 were exposed to
TrF in dry toluene at −78 °C and the resulting complex was
reacted with excess monomer at −78 °C. The results are
shown in Table 5. The best mm ratio was reproducibly ob-
tained with Entry 1, although the molecular weight distribution
was very broad. Other chiral and halogenated Lewis acids 16–
18 can act as strong activators, to provide atactic polymers.
The poly(vinyl ether) obtained in Entry 1 was treated with dry
HBr gas in CHCl3 at 0 °C. NMR analysis of the precipitated
PVA after neutralization gave similar isotacticity. 13C NMR
measurement indicated a high intensity of mmmm, as observed
Fig. 2. ORTEP drawing of 15. All hydrogen atoms are omit-
ted for clarity.

1450 Bull. Chem. Soc. Jpn., 74, No. 8 (2001)
Table 5. Polymerization of t-Butyl Vinyl Ether Catalyzed by a Chiral Lewis Acid-TrFa)
Cationic Polymerization
c)
Entry
Lewis acid
Yieldb)/%
Mnc) × 10−4
Mw/Mn
mm/mr/rrd)
1
2
3
4
15
16
17
18
76
99
97
75
9.06
17.40
8.85
7.56
6.22
2.11
1.79
57:36:7
32:46:22
32:44:24
22:47:31
9.46
a) Polymerization was performed at −78 °C for 0.5 h under Ar; b) MeOH insoluble solid; c) Estimated
by GPC (polystyrene standards, THF); d) Determined by 13C NMR assay.
two singlet methyl peaks in its 1H NMR spectrum. Treatment
of Lewis acid solutions with 2 molar amounts of TrF at room
temperature followed by the addition of t-butyl vinyl ether at
−78 °C, resulted in the immediate formation of viscous solu-
tions. After the usual work-up, the desired polymers were iso-
lated and characterized by GPC and 13C NMR analyses. As
can be seen in Table 6, Lewis acids 20–22 have moderate to
good activities, and give isotact-rich polymers with fairly
broad Mw/Mn values. It is still unclear why 19 gave only oligo-
meric material. The higher isotacticity in Entry 4 approaches
the result with 15. The π-electrons of the triarylsilyl groups
may play a crucial role in the formation of a sterically more in-
teractive ionic pair within the chain-end (Entry 20 vs 21 and
22).
Scheme 3. Binaphtholate-based isobutylaluminums.
with Et2O•BF3. At present, no valuable information was ob-
tained from the NMR spectra to elucidate the detailed mecha-
nism of isoselective monomer insertion in the chain-end transi-
tion state, but we should consider that the observations in Ta-
ble 5 are due to the results of chirality matching or mismatch-
ing.
B. Active Cationic Polymerization Mediated by a Bi-
naphthol-Based Isobutylaluminum–TrF (1:2) System.
We encountered difficulty in the synthesis and reaction of a
chiral isobutyl derivative of 15. Thus, we attempted to use of
isobutylaluminum binaphtholates, which are thought to have
more vacant space around aluminum. As for (BHT)2AlBui, a
variety of 3,3ꢀ-disilylated binaphthols were treated with an
equimolar amount of iBu3Al at 60 °C in toluene to produce 19–
22 (Scheme 3).
Conclusion
We have demonstrated that, upon combination with TrF,
highly modified/sterically bulky aluminum Lewis acids can en-
hance isotact-selectivity in the cationic polymerization of t-bu-
tyl vinyl ether. These results are highly informative for under-
standing the important roles of fluorine and group 13 Lewis ac-
ids, although they somewhat conflict with an earlier finding
that larger counteranions tended to decrease the mm ratio. Our
results indicated that the structure of the whole counteranion as
well as the use of a fluoride-based initiator, the number of fluo-
rines and other conditions that are appropriate for minimizing
the cation–anion distance, are essential factors in designing
highly isoselective activators. Notably, the present results indi-
cated that chiral aluminum Lewis acids, 15 and 22, are effec-
Unlike achiral isobutylaluminums, Lewis acid 20, for in-
stance, has two unequivalent iBu doublet methylene peaks and
Table 6. Polymerization of t-Butyl Vinyl Ether Mediated by Binaphthol-Based Chiral Alminum Lewis Acid–TrF Systema)
c)
Entry
Lewis acid
Yieldb)/%
Mnc) × 10−4
Mw/Mn
mm/mr/rrd)
1
2
3
4
19
20
21
22
no polym
—
—
—
72
74
51
2.84
3.25
4.62
8.22
11.4
7.40
44:43:13
52:37:11
55:34:11
a) Polymerization was performed at −78 °C for 0.5 h under Ar; b) MeOH insoluble solid; c) Estimated by GPC
(polystyrene standards, THF); d) Determined by 13C NMR measurement.

M. Oishi et al.
Bull. Chem. Soc. Jpn., 74, No. 8 (2001) 1451
purification of TrF. Therefore, dimethylaminosulfer trifluoride
(DAST) was used as a fluorinating agent to complete the conver-
sion. To a solution of TrOH (5.0 mmol, 1.3 g) in CH2Cl2 (15 mL)
was added DAST (5 mmol, 0.66 mL) via a plastic disposable sy-
ringe at −78 °C, and the mixture was stirred overnight while be-
ing allowed to warm to room temperature. The resulting mixture
was poured into a separatory funnel containing water. Extraction
with ether and concentration of the organic extract gave a yellow-
ish solid, which was washed with ice water and then dissolved in
hot hexane. Analytically pure TrF was obtained by crystallization
from decanted hexane solution (1.18 g, 90%). 282 MHz 19F NMR
(CDCl3) δ − 127.21 (s).
tive activators.
Experimental
All manipulations of oxygen- and moisture-sensitive materials
were performed in an argon-filled glovebox or by standard
Schlenk techniques unless otherwise specified. Hydrocarbons
(pentane, hexane, and toluene), ether solvents, and the monomer
(ether, tetrahydrofuran, and t-butyl vinyl ether, Aldrich, 98%)
were distilled from Na/benzophenone ketyl in the presence or ab-
sence of 18-crown-6 before use.
NMR spectra were recorded on either Varian INOVA 500 (FT
1
1
500 MHz, H; 125 MHz, 13C) or Gemini-300 (FT 300 MHz, H;
75 MHz, 13C; 282 MHz, 19F) instruments. Chemical shifts for H
1
Preparation of Menthenyl Triflate. Synthesis of the title
compound has been reported in the literature, but we could not re-
produce the reported good yield.32 We mainly used the following
amine-free procedure.33 To a THF solution (20 mL) of trimethyls-
ilyl enol ether (17 mmol, 3.9 g) derived from (−)-methone in 87%
yield was added a solution of n-BuLi (1.6 M in hexane, 12.5 mL)
at −78 °C under an argon atmosphere. After this mixture was
stirred at −78 °C for 0.5 h and at 0 °C for 1.5 h, a THF solution
(15 mL) of N-phenyl bis(trifluoromethanesulfoneimide) (20
mmol, 7.15 g) was added dropwise. The reaction was continued
overnight, while slowly warming to room temperature, and then
quenched by addition of 1 M HCl aq. Extraction with ether, dry-
ing of the organic layer, concentration on a rotary evaporator, and
chromatographic purification of the residue using hexane as an
eluant gave the corresponding enol triflate as a colorless oil (3.99
g, 82%). This material is stereochemically pure and, unlike men-
thenyl iodide and bromide, is stable at room temperature under
light. 300 MHz 1H NMR (CDCl3) δ 5.64 (1H, br s, CHwC), 2.42–
2.53 (1H, m, CH), 2.26–2.41 (1H, m, CH), 2.07–2.22 (1H, m,
CH), 1.75–1.88 (2H, m, CH,), 1.34–1.50 (1H, m, CH), 1.06–1.25
(1H, m, CH), 1.04 (3H, d, J = 7.2 Hz, CH3), 0.95 (3H, d, J = 7.2
Hz, CH3), 0.82 (3H, d, J = 6.9 Hz, CH3); 75 MHz 13C NMR
(CDCl3) δ 151.80, 125.93, 118.58 (JC–F = 320 Hz), 43.08, 30.62,
29.95, 27.30, 22.44, 21.19, 19.78, 16.27; 282 MHz 19F NMR
(CDCl3) δ −74.99.
and 13C spectra were referenced to internal solvent resonances and
are reported relative to tetramethylsilane. 19F NMR spectra were
referenced to external CF3C6H5 (−64 ppm). Oxygen- and mois-
ture-sensitive NMR samples were prepared in a glovebox and
sealed with Teflon caps. Elemental analyses were performed at
the School of Agriculture, Nagoya University. For 13C NMR anal-
yses of poly(vinyl ether) microstructures, 100–150 mg of polymer
samples were completely dissolved in C6D6 (0.6 mL) with a heat
gun in a 5-mm NMR tube, and the samples were transferred to the
NMR spectrometer with the probehead preequilibrated at 70 °C.
A 45° pulse width and 1.30 s acquisition time were used with a
pulse delay of 5.0 s. Triad signals were assigned according to lit-
erature criteria,22 and the stereoregularities of some isotact-rich
samples were further confirmed by 13C NMR analyses of PVA
(10% in DMSO-d6 at 50 °C with an acquisition time and a pulse
delay of 1.64 s and 1.80 s, respectively) obtained after cleavage of
ethers.7b,23 Infrared (IR) spectra were measured on a Shimadzu
FTIR-9100 spectrometer. Separation of 2-menthyl- and 2-neo-
menthylphenols was achieved by recycling preparative HPLC on a
Japan Analytical Industry Co., Ltd. LC-908 equipped with an RI-5
detector and a JAIGEL-SIL, s-043-15 column (250 mm length ×
20 mm inner diameter). Optical rotations were measured on a
JASCO DIP-1000 digital polarimeter. Reaction products of small
moisture-insensitive molecules were purified by flash chromatog-
raphy on silica gel E. Merck 9385 or silica gel 60 extra pure. An-
alytical thin-layer chromatography (TLC) was performed on Mer-
ck precoated TLC plates (silica gel 60 GF254, 0.25 mm). Gel per-
meation chromatography (GPC) analyses of polymer samples
were carried out with a JASCO PU-980 pump and a JASCO RI-
930 detector using Tosoh TSKgel GMHHR-H and TSKgel
G3000HHR (300 mm length × 7.8 mm inner diameter) in series.
Solutions of polymer samples dissolved in THF were filtered
through a Dismic-13JP PTFE 0.5 µm filter. All GPC data were
analyzed using JASCO Borwin Ver. 1.21 software. The molecular
weight calibration curve was obtained using standard polysty-
renes.
Synthesis of (+)-2-Menthenylphenyl Methoxymethyl Ether
(2a). To a solution of 1a (20 mmol, 2.8 g) in THF (40 mL) was
added n-BuLi (1.6 M in hexane, 13 mL) at 0 °C under Ar. The
suspension was stirred at 0 °C for 2 h. B(OMe)3 (30 mmol, 3.4
mL) was added in one portion and the resulting clear solution was
stirred for 1 h, and then for another 1 h after the addition of sat.
NH4Cl aq. The product was extracted with EtOAc (2 times) and
the combined extracts were dried over MgSO4. Solvents were re-
moved by evaporation and in vacuo to give a mixture of the de-
sired arylboronic and diarylborinic acids, which can be used with-
out further purification. They should not be allowed to stand long-
er at ambient temperature because of the slow deprotection of
methoxymethyl ether. The mixture was dissolved in DME–H2O
(50 mL/8 mL). Menthenyl triflate (15 mmol, 4.3 g) and Cs2CO3
(18 mmol, 5.9 g) were added and the reaction solution was de-
gassed and filled with argon, and [Pd(PPh3)4] (0.1 mmol, 116 mg)
was then added. The mixture was heated at 80 °C for 12 h. After
the usual work-up and purification by column chromatography on
silica gel (EtOAc/hexane = 1:20), the desired coupling product
was obtained (4.1 g, 99.6%). [α]2D9 +58.4 (c 0.56, CHCl3); 300
i
Me3Al, Bu3Al, Et2AlF, and B(C6F5)3 were provided by Toso-
Akzo Chem. Co. Ltd., Japan. (BHT)2AlH•OEt2,15 (BHT)2AlMe
(MAD),24 (4-Br-2,6-tBu2C6H2O)2AlMe (MABR),25 (2,6-Ph2C6H3-
O)3Al (ATPH),26 (4-Br-2,6-Ph2C6H3O)3Al (ATPH-Br),27 (BHT)2-
AlBui,16 (2,4,6-tBu3C6H2O)2AlBui,16 B(C12F9)3,8a,c Al(C6F5)3,28
(R)-(+)-3,3ꢀ-(R3Si)2-1,1ꢀ-bi-2-naphthol (R = iPr, Ph; R3Si = tBu-
Ph2Si),29 and (R)-(+)-3,3ꢀ-bis[tris(3,5-diethylphenyl)silyl]-1,1ꢀ-bi-
2-naphthol30 were prepared as described in the literature. All oth-
er chemicals were purchased from commercial suppliers.
1
MHz H NMR (CDCl3) δ 7.12–7.20 (2H, m, Ar–H), 6.92–7.04
(2H, m, Ar–H), 5.55 (1H, dd, J = 1.8, 3.6 Hz, CwCH), 5.19 (1H,
d, Jgem = 6.6 Hz, OCHHO), 5.13 (1H, d, Jgem = 6.6 Hz, OCHHO),
3.48 (3H, s, OCH3), 2.82–2.91 (1H, m, CHCwC), 2.17–2.32 (1H,
m, CHCwC), 1.83–1.93 (1H, m, CH), 1.72–1.83 (1H, m, CH),
Preparation of Trityl Fluoride (TrF). Several methods have
been reported for the synthesis of TrF,31 most of which produce
much more crystalline triphenylmethanol (TrOH) as a residual
starting material or a byproduct; this disturbs the crystallization/

1452 Bull. Chem. Soc. Jpn., 74, No. 8 (2001)
Cationic Polymerization
1.58–1.69 (1H, m, CH), 1.31–1.46 (1H, m, CH), 1.13–1.30 (1H,
m, CH), 0.99 (3H, d, J = 6.9 Hz, CH3), 0.85 (3H, d, J = 6.9 Hz,
CH3), 0.58 (3H, d, J = 6.9 Hz, CH3); 75 MHz 13C NMR (CDCl3)
δ 154.17, 141.06, 135.52, 133.58, 130.38, 127.41, 121.84, 114.17,
94.42, 55.89, 42.34, 31.58, 31.51, 28.62, 22.11, 21.72, 20.93,
15.75; IR (liquid film) 2955, 1597, 1487, 1244, 1154, 1078, 1005,
924, 864, 752 cm−1; Anal. Calcd for C18H26O2: C, 78.79; H, 9.55
%. Found: C, 78.92; H, 9.50%.
2.09 (1H, m, CH), 1.82–1.96 (2H, m, 2CH), 1.64–1.79 (3H, m,
3CH), 1.35–1.58 (2H, m, 2CH), 1.04 (1H, qd, J = 12.6, 3.6 Hz,
CH), 0.93 (3H, d, J = 6.3 Hz, CH3), 0.90 (3H, d, J = 6.9 Hz,
CH3), 0.84 (3H, d, J = 6.9 Hz, CH3); 75 MHz 13C NMR (CDCl3)
δ 156.71, 128.81, 128.14, 125.93, 119.24, 117.67, 83.83, 49.89,
49.69, 34.53, 28.04, 26.64, 23.69, 21.92, 20.70, 18.61. Com-
pound 4 was heated with 1,1ꢀ-thiocarbonyldiimidazole in THF
overnight. Usual work-up and chromatographic purification
(EtOAc/hexane = 1:20) gave the desired cyclic thiocarbonate 5 as
a crystalline solid (1.31 g, overall yield: 45%). [α]2D9 +2.85 (c
0.57, CHCl3); 300 MHz 1H NMR (CDCl3) δ 7.35 (1H, m, Ar-H),
7.24 (1H, m, Ar-H), 7.15 (1H, d, J = 8.4 Hz, Ar-H), 7.09 (1H, d, J
= 7.5 Hz, Ar-H), 1.68–2.19 (7H, m, 7CH), 1.30 (1H, dd, J = 14.4,
12.0 Hz, CH), 0.97–1.15 (1H, m, CH), 0.85 (3H, d, J = 6.0 Hz,
CH3), 0.89 (3H, d, J = 6.9 Hz, CH3), 0.84 (3H, d, J = 6.9 Hz,
CH3); 75 MHz 13C NMR (CDCl3) δ 184.33, 146.79, 129.06,
125.77, 124.13, 123.07, 115.50, 91.32, 48.60, 47.36, 33.77, 26.75,
26.56, 23.24, 21.30, 19.97, 17.14; IR (KBr) 2961, 1489, 1374,
1323, 1283, 1235, 1217, 1128, 911, 770 cm−1; Anal. Calcd for
C17H22O2S: C, 70.31; H, 7.64%. Found: C, 70.31; H, 7.55%.
n-Bu3SnH Reduction of 5. To a reflux solution of n-Bu3SnH
in o-xylene was added an o-xylene solution of 5 (0.5 mmol, 145
mg) over 1 h. After the addition of 5, the reaction was allowed to
continue for an additional 30 h. The solution was cooled, washed
with ice water and extracted with ether. The organic layer was
dried over MgSO4, and filtered through a celite pad. Evaporation
of solvents and purification by preparative HPLC (EtOAc/H =
1:100) furnished 6, 7, and 8 in respective yields of 53, 32, and
20%. The absolute configurations of 6 and 7 were confirmed by a
diffraction study of p-nitrobenzoate ester of 6. The ester was re-
crystallized from EtOH to give a cubic crystal suitable for X-ray
analysis.
Synthesis of (+)-2,6-Dimenthenylphenol (3a). A second at-
tempt to introduce a menthenyl group into the 6 position of 2a was
made in the same manner as described above through the forma-
tion of boronic and borinic acids followed by Suzuki coupling
with menthenyl triflate. The obtained methoxymethyl ether was
deprotected in 3 M HCl/THF/H2O at reflux to give the corre-
sponding phenol (68%). mp 98–101 °C; [α]2D9 +91.9 (c 0.53,
1
CHCl3); 300 MHz H NMR (CDCl3) δ 9.46 (2H, d, J = 7.5 Hz,
Ar-H), 6.80 (1H, t, J = 7.5 Hz, Ar-H), 5.95 (1H, s, OH), 5.68 (2H,
s, CwCH), 2.63–2.76 (2H, m, CH-CwC), 2.20–2.36 (2H, m, CH-
CwC), 1.75–1.96 (4H, m, CH), 1.57–1.72 (2H, m, CH), 1.36–1.51
(2H, m, CH), 1.15–1.31 (2H, m, CH), 1.01 (6H, d, J = 6.9 Hz,
CH3), 0.84 (6H, d, J = 6.9 Hz, CH3), 0.59 (6H, d, J = 6.9 Hz,
CH3); 75 MHz 13C NMR (CDCl3) δ 148.80, 139.48, 135.75,
128.88, 127.16, 119.38, 42.93, 31.31, 28.51, 21.92, 21.78, 20.90,
15.96; IR (KBr) 3499, 2955, 1603, 1439, 1331, 1262, 1225, 1090,
1021, 795, 749 cm−1; Anal. Calcd for C26H38O: C, 85.19; H,
10.45%. Found: C, 85.08; H, 10.53%.
Synthesis of (+)-4-Chloro-2,6-dimenthenylphenol (3b).
The p-chloro analogue was synthesized from 1b by repeated bo-
ronic acid formation followed by a cross-coupling reaction and fi-
nal removal of a methoxymethyl group in the same manner as
shown for 3a (51%).
4-Chloro-2-menthenylphenyl Methoxymethyl Ether (2b):
300 MHz 1H NMR (CDCl3) δ 7.10–7.14 (2H, m, Ar-H), 6.96 (1H,
d, J = 9.3 Hz, Ar-H), 5.57 (1H, br, CwCH), 5.15 (1H, d, J = 6.6
Hz, Ar-O-CHH), 5.10 (1H, d, J = 6.6 Hz, Ar-O-CHH), 3.46 (3H,
s, OCH3), 2.77–2.88 (1H, m, CH-C(Ar)wC), 2.15–2.30 (1H, m,
CH-CwC-Ar), 1.83–1.93 (1H, m, CHH-C(Me)-CwC), 1.73–1.82
(1H, CHH-C-C(Me)-C), 1.53–1.70 (1H, m, CHMe2), 1.30–1.45
(1H, m, CHH-C-C(Me)-C), 1.10–1.25 (1H, m, CHH-C(Me)-
CwC), 1.00 (3H, d, J = 7.2 Hz, CH3-CHCwC), 0.86 (3H, d, J =
6.9 Hz, CH3), 0.59 (3H, d, J = 6.6 Hz, CH3). 3b: [α]2D9+101.2 (c
(+)-2-Neomenthylphenol (6). [α]2D9 +41.2 (c 0.51, CHCl3);
300 MHz 1H NMR (CDCl3) δ 7.48 (1H, dd, J = 1.5, 7.5 Hz, Ar-
H), 7.06 (1H, td, J = 7.8, 1.5 Hz, Ar-H), 6.83 (1H, t, J = 7.8 Hz,
Ar-H), 6.76 (1H, dd, J = 1.5, 7.8 Hz, Ar-H), 4.66 (1H, s, OH),
3.56 (1H, td, J = 5.4, 2.4 Hz, ArCH), 1.81–1.98 (2H, m, 2CH),
1.65–1.77 (2H, m, 2CH), 1.41–1.61 (2H, m, 2CH), 1.23–1.39 (2H,
m, 2CH), 1.01 (1H, qd, J = 12.3, 1.5 Hz, CH), 0.89 (3H, d, J =
6.6 Hz, CH3), 0.80 (3H, d, J = 6.3 Hz, CH3), 0.72 (3H, d, J = 6.3
Hz, CH3). 75 MHz 13C NMR (CDCl3) δ 153.21, 131.15, 130.57,
126.30, 119.66, 115.40, 46.72, 41.00, 35.28, 32.88, 29.91, 27.35,
25.88, 22.64, 21.42, 21.13; IR (liquid film) 3100–3800, 2800–
3030, 1607, 1586, 1385, 1269, 1098, 936, 820, 750 cm−1; Anal.
Calcd for C16H24O: C, 82.70; H, 10.41%. Found: C, 82.65; H,
10.13%.
1
0.57, CHCl3); 300 MHz H NMR (CDCl3) δ 6.92 (2H, s, Ar-H),
5.88 (1H, s, OH), 5.68 (2H, s, CwCH), 2.60–2.71 (2H, m, CH-
CwC), 2.18–2.34 (2H, m, CH-CwC), 1.75–1.95 (4H, m, CH),
1.53–1.70 (2H, m, CH), 1.35–1.51 (2H, m, CH), 1.13–1.34 (2H,
m, CH), 1.01 (6H, d, J = 6.9 Hz, CH3), 0.85 (6H, d, J = 6.9 Hz,
CH3), 0.60 (6H, d, J = 6.9 Hz, CH3); 75 MHz 13C NMR (C6D6) δ
148.94, 139.85, 137.41, 131.75, 127.86, 125.63, 43.79, 32.15,
29.57, 22.69, 22.62, 21.69, 16.87; IR (KBr) 3484, 2959, 1595,
1435, 1325, 1221, 1130, 965, 872, 689 cm−1; Anal. Calcd for
C26H37ClO: C, 77.87; H, 9.30%. Found: C, 77.87; H, 9.49%.
(+)-Thiocarbonate (5): To a solution of 1a (10 mmol, 1.3
mL) in THF (20 mL) was added n-BuLi (1.6 M in hexane, 6.25
mL) at 0 °C under Ar. The suspension was stirred at 0 °C for 2 h.
(−)-Menthone (9.3 mmol, 1.44 mL) was added at −78 °C. After
10 min, the cooling bath was removed to allow the mixture to
warm to room temperature. Next, 3 M HCl was added and the re-
sulting mixture was refluxed overnight to complete cleavage of
MOM ether. After acidic work-up, the corresponding crude diol 4
was obtained. 300 MHz 1H NMR (CDCl3) δ 9.79 (1H, s, Ar-OH),
7.12 (1H, td, J = 7.5, 1.5 Hz, Ar-H), 6.97 (1H, dd, J = 7.8, 1.5
Hz, Ar-H), 6.77–6.87 (2H, m, 2Ar-H), 2.48 (1H, s, OH), 2.00–
(−)-2-Menthylphenol (7). [α]2D9 −48.8 (c 0.40, CHCl3); 300
1
MHz H NMR (CDCl3) δ 7.14 (1H, d, J = 7.5 Hz, Ar-H), 7.04
(1H, t, J = 7.5 Hz, Ar-H), 6.91 (1H, t, J = 7.5 Hz, Ar-H), 6.74
(1H, d, J = 7.5 Hz, Ar-H), 4.60 (1H, s, OH), 2.90 (1H, m, ArCH),
1.69–1.86 (3H, m, 3CH), 1.40–1.60 (3H, m, 3CH), 0.98–1.28 (3H,
m, 3CH), 0.89 (3H, d, J = 6.3 Hz, CH3), 0.81 (3H, d, J = 6.9 Hz,
CH3), 0.69 (3H, d, J = 6.6 Hz, CH3); 75 MHz 13C NMR (CDCl3)
δ 152.77, 132.21, 127.41, 126.17, 121.03, 115.25, 46.77, 44.56,
38.19, 35.27, 33.21, 27.53, 24.65, 22.47, 21.62, 15.77; IR (liquid
film) 3100-3700, 2800–3030, 1590, 1456, 1370, 1267, 1086, 938,
833, 750 cm−1; Anal. Calcd for C16H24O: C, 82.70; H, 10.41%.
Found: C, 82.67; H, 9.79%.
1
2-Menthenylphenol (8). 300 MHz H NMR (CDCl3) δ 7.12
(1H, t, J = 7.5 Hz, Ar-H), 7.04 (1H, d, J = 7.5 Hz, Ar-H), 6.92
(1H, d, J = 7.5 Hz, Ar-H), 6.68 (1H, d, J = 7.5 Hz, Ar-H), 5.73
(1H, br s, CwCH), 5.64 (1H, s, OH), 2.50–2.62 (1H, m, CwC-CH),

M. Oishi et al.
Bull. Chem. Soc. Jpn., 74, No. 8 (2001) 1453
2.23–2.39 (1H, m, CwC-CH), 1.79–1.98 (2H, m, 2CH), 1.66–1.79
(1H, m, CH), 1.40–1.57 (1H, m, CH), 1.14–1.30 (1H, m, CH),
1.01 (3H, d, J = 7.2 Hz, CH3), 0.85 (3H, d, J = 6.9 Hz, CH3), 0.63
(3H, d, J = 6.6 Hz, CH3); 75 MHz 13C NMR (CDCl3) δ 152.15,
137.90, 136.70, 128.23, 128.08, 127.68, 119.88, 115.41, 43.39,
31.05, 31.01, 28.39, 21.78, 21.59, 20.95, 16.13
toluene (10 mL) was condensed at −78 °C under 10−4 Torr. To
this solution was added a solution of Me3Al (0.5 M in hexane,
0.20 mL) at room temperature under Ar. After stirring for 1h, a
slightly yellow solution of 15 was formed with the extrusion of
methane gas. For a polymerization study this solution was used
without any special treatment. Compound 15 can also be prepared
in dry hexane. Careful concentration and crystallization of the
saturated solution at room temperature gave rise to a colorless
crystal, which was characterized by X-ray diffraction study be-
Hydrogenation of 2a. Compound 6 can be stereoselectively
obtained by hydrogenation and successive deprotection. A sus-
pension of 2a (0.52 mmol, 142 mg) and Raney® nickel (H2O dis-
persion, 50 mg) in EtOH (10 mL) was stirred at room temperature
under hydrogen (1 atm). After being stirred for 96 h, the mixture
was filtered through a celite pad. The filtrate was concentrated
and the residue was subjected to column chromatography on silica
gel (EtOAc/hexane = 1:10) to give the corresponding MOM ether
(72 mg, 50%). The stereoselectivity was determined by 1H NMR
1
cause H and 13C NMR analyses of 15 in C6D6 gave very broad
signals.
General Procedure for Polymerization Using a Lewis Acid
and TrF (1:1) System. To a solution of a Lewis acid (0.1
mmol) in dry toluene (10 mL) was added TrF (0.1 mmol, 26 mg)
at −78 °C under argon. After several minutes, t-butyl vinyl ether
(10.0 mmol, 1.31 mL) was added via a syringe dropwise. Poly-
merization was continued under the conditions stated in Tables 1
and 4, and MeOH (0.5 mL) and pyridine (0.2 mL) were then add-
ed to quench the reaction. The mixture was poured into MeOH
(500 mL) with vigorous stirring. The white precipitate was col-
lected by filtration and dried in vacuo (25 °C/10−4 Torr) to give
poly(t-butyl vinyl ether) as a white powdery solid.
Typical Polymerization Procedure Using a Lewis Acid–TrF
(1:2) System. To a solution of a Lewis acid (0.1 mmol) in dry
toluene (10 mL) was added TrF (0.2 mmol, 52 mg) at 25 °C under
argon. After several minutes, the reaction vessel was cooled at
−78 °C and t-butyl vinyl ether (10.0 mmol, 1.31 mL) was added
via a syringe dropwise. Polymerization was continued under the
conditions Tables 3 and 5, and MeOH (0.5 mL) and pyridine (0.2
mL) were then added to quench the reaction. The subsequent pro-
cedure is the same as described above.
1
analysis to be > 99:1. 300 MHz H NMR (CDCl3) δ 7.50 (1H,
dd, J = 1.2, 7.8 Hz, Ar-H), 7.06–7.16 (2H, m, Ar-H), 6.89 (1H, dt,
J = 1.8, 7.2 Hz, Ar-H), 5.22 (1H, d, J = 6.6 Hz, OCHHO), 5.19
(1H, d, J = 6.6 Hz, OCHHO), 3.71–3.78 (1H, m, Ar-CH), 3.49
(3H, s, OCH3), 1.81–1.97 (2H, m, CH), 1.22–1.75 (6H, m, 6CH),
1.00 (1H, dq, J = 4.8, 12.9 Hz, CH), 0.88 (3H, d, J = 6.3 Hz,
CH3), 0.78 (3H, d, J = 6.3 Hz, CH3), 0.70 (3H, d, J = 6.3 Hz,
CH3); 75 MHz 13C NMR (CDCl3) δ 154.91, 134.12, 130.29,
126.20, 120.36, 113.87, 94.31, 55.84, 46.78, 41.37, 35.38, 32.50,
29.92, 27.34, 25.81, 22.70, 21.40, 21.17
(+)-2,4-Dibromo-6-neomenthylphenol (9). Compound
6
(0.87 mmol, 202 mg) was treated by the dropwise addition of bro-
mine (2.2 mmol, 0.11 mL) in CH2Cl2 at 0 °C. The mixture was
warmed to room temperature and stirred for 3 h. The reaction
mixture was diluted with ether, poured into a separatory funnel,
and washed with brine. The organic extract was then dried over
MgSO4. After filtration and evaporation of the solvents, the resi-
due was subjected to chromatographic purification (silica gel, hex-
ane only) to give dibromophenol 9 as a white solid (216 mg,
64%). [α]2D9+27.3 (c 0.49, CHCl3); 300 MHz 1H NMR (CDCl3) δ
7.53 (1H, d, J = 2.4 Hz, Ar-H), 7.44 (1H, d, J = 2.4 Hz, Ar-H),
5.61 (1H, s, OH), 3.66 (1H, td, J = 5.1, 2.1 Hz, ArCH), 1.82–1.98
(2H, m, CH), 1.62–1.72 (1H, m, CH), 1.22–1.52 (5H, m, CH),
0.90–1.08 (1H, m, CH), 0.90 (3H, d, J = 6.6 Hz, CH3), 0.81 (3H,
X-ray Crystallographic Analysis. Crystals of p-nitrobenzo-
ic acid ester of 6 and 15 were grown from saturated solution in
EtOH and dry hexane, respectively. The former sample was
mounted on a glass fiber. The crystal of 15 was carefully handled
Table 7. Crystallographic Data for Ester from 6 and 15
Compound
ester from 6
15
d, J = 6.6 Hz, CH3), 0.70 (3H, d, J = 6.3 Hz, CH3); 75 MHz 13
C
Formula
Formula weight
Crystal color, habit
Crystal system
Space group
a/Å
C23H27NO4
381.72
colorless, platy
Orthorthombic
P212121
7.5290(2)
20.4320(15)
27.8630(21)
4286.2(8)
8
C53H77AlO2
773.18
colorless, cube
Orthorthombic
P212121
12.6330(2)
17.0840(3)
22.6770(4)
4894.2(2)
5
NMR (CDCl3) δ 149.20, 134.80, 132.56, 130.82, 111.43, 111.05,
46.49, 40.45, 35.06, 34.13, 29.80, 27.13, 25.84, 22.50, 21.46,
21.09; IR (KBr) 3513, 2953, 1561, 1453, 1316, 1231, 1171, 1130,
849, 716 cm−1; Anal. Calcd for C16H22Br2O: C, 49.26; H, 5.68%.
Found: C, 49.24; H, 5.69 %.
(−)-2,4-Dibromo-6-menthylphenol (10). Compound 7 was
brominated in the identical manner as described for 9 to afford the
desired phenol as a colorless oil (85%). [α]2D9 −37.1 (c 0.52,
b/Å
c/Å
V/Å3
1
CHCl3); 300 MHz H NMR (CDCl3) δ 7.41 (1H, d, J = 2.1 Hz,
Z
Dx/Mg m−3
F(000)
1.53
408
0.0801
298
1.31
848
0.0971
193
Ar-H), 7.19 (1H, d, J = 2.1 Hz, Ar-H), 5.51 (1H, s, OH), 3.07
(1H, td, J = 11.7, 3.3 Hz, ArCH), 1.69–1.86 (3H, m, CH), 1.34–
1.60 (3H, m, CH), 1.08–1.28 (1H, m, CH), 0.88–1.08 (2H, m,
CH), 0.89 (3H, d, J = 6.6 Hz, CH3), 0.83 (3H, d, J = 6.9 Hz,
CH3), 0.69 (3H, d, J = 6.9 Hz, CH3); 75 MHz 13C NMR (CDCl3)
δ 148.90, 136.03, 130.71, 129.88, 112.78, 110.99, 46.96, 44.30,
39.32, 35.09, 33.07, 27.68, 24.49, 22.42, 21.59, 15.78; IR (KBr)
µ/mm−1
T/K
θmax
0
/
23.62
24.84
Limiting indices
0 ꢀ h ꢀ 8
0 ꢀ k ꢀ 23
0 ꢀ l ꢀ 32
3323
−15 ꢀ h ꢀ 15
−20 ꢀ k ꢀ 20
−27 ꢀ l ꢀ 27
4563
3515, 2953, 1703, 1566, 1321, 1252, 1142, 1001, 853, 696 cm−1
;
Anal. Calcd for C16H22Br2O: C, 49.26; H, 5.68%. Found: C,
49.26; H, 5.56%.
Independent reflections
Observed reflections
2366
4431
Synthesis of 15. A magnetic stirrer bar and 3a (0.20 mmol,
73 mg) were charged in a flame-dried 100 mL Schlenk flask. Dry
R; ωR
S
0.039, 0.036
1.487
0.043, 0.060
2.960

1454 Bull. Chem. Soc. Jpn., 74, No. 8 (2001)
Cationic Polymerization
in a glovebox and fixed in a glass capillary tube. X-ray data were
collected on a MacScience DIP Image plate diffractometer with
λ(MoKα) = 0.7107 Å, and solved by direct methods, followed by
full-matrix least squares refinement with all non-hydrogen atoms
anisotropic and hydrogen atoms isotropic (Table 7). Reflection
data with |I| > 3σ (I) were used. The function minimized was
Σω(|Fo|−|Fc|)2, where ω = 1.0/[σ2(Fo) + 0.03[Fc]2]. Crystallo-
graphic data for the ester of 6 and 15 have been deposited at the
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK and copies can
be obtained on request, free of charge, by quoting the publication
citation and the deposition numbers CCDC NO. 154117 and
154118, respectively. The details of structures have been deposit-
ed as Document No. 74043 at the Office of the Editor of Bull.
Chem. Soc. Jpn.
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