A new asymmetric carbon-carbon bond forming reaction: Four-component stereoselective synthesis of (Z)-4,6-dihydroxy-3-methylalk-2-enyl methyl sulfones

Full text of DOI:10.1002/(SICI)1521-3773(20000515)39:10<1806::AID-ANIE1806>3.0.CO;2-S

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[5] T. Suzuki, J. Nishida, T. Tsuji, Angew. Chem. 1997, 109, 1387; Angew.
Chem. Int. Ed. Engl. 1997, 36, 1329.
A New Asymmetric Carbon ± Carbon Bond
Forming Reaction: Four-Component
Stereoselective Synthesis of (Z)-4,6-Dihydroxy-
3-methylalk-2-enyl Methyl Sulfones**
[6] All new compounds gave satisfactory spectral data and analytical
values. Selected 1H NMR (400 MHz, TMS) data are as follows: 1a
(CDCl3, 248C): d ˆ 7.47 (brd, J ˆ 7.8Hz, 4H), 7.40 (dd, J ˆ 7.8, 1.5 Hz,
2H), 7.21 ± 7.32 (m, 6H), 7.12 (m, 4H), 6.97 (brdd, J ˆ 7, 7 Hz, 2H),
6.87 ± 6.94 (m, 4H), 6.61 (brd, J ˆ 7.8Hz, 2H); 2a-(BF4)2 (CD3CN,
208C): d ˆ 8.48 (ddd, J ˆ 6.8, 6.8, 1.5 Hz, 4H), 8.31 (brd, J ˆ 8.3 Hz,
4H), 7.75 (ddd, J ˆ 6.8, 6.8, 1.5 Hz, 2H), 7.73 (dd, J ˆ 8.3, 1.5 Hz, 4H),
7.58(ddd, J ˆ 6.8, 6.8, 1.0 Hz, 4H), 7.47 (ddd, J ˆ 7.8, 7.8, 1.0 Hz, 2H),
7.37 (dd, J ˆ 7.8, 1.8 Hz, 2H), 7.32 (brd, J ˆ 7.8Hz, 2H).
Vera Narkevitch, Kurt Schenk, and Pierre Vogel*
Dedicated to Professor Horst Prinzbach
on the occasion of his 68th birthday
[7] H. Gilman, W. J. Trepka, J. Org. Chem. 1961, 26, 5202.
In the presence of a Lewis acid, 1-alkoxy- or 1-silyloxy-1,3-
dienes can be combined with enoxysilanes and sulfur dioxide
to generate (Z)-6-oxo-4-oxyalk-2-ene sulfinates, which react
with methyl iodide (S-alkylation) to afford the corresponding
methyl sulfones.[1, 2] We report here an asymmetric version of
this new carbon ± carbon bond forming reaction that can be
used to construct polyketide fragments stereoselectively.
Enantiomerically pure (>99% ee) diene (‡)-2 was ob-
tained by reaction of 1 with sodium (À)-(S)-1-(2,4,6-triiso-
propylphenyl)ethoxide[3] followed by Wittig methylenation
(Scheme 1).[4] In the presence of Yb(OTf)3 (Tf ˆ F3CSO2) and
[8] Comparisons of the coefficients obtained by linear combination of
atomic orbitals (LCAO) in singly occupied molecular orbitals
(SOMO) between xanthyl and thioxanthyl indicate that the consid-
erable spin exists on S in thioxanthyl whereas much larger spin density
is expected at C9 in xanthyl (K. Okada, T. Imakura, M. Oda, A.
Kajiwara, M. Kamachi, M. Yamaguchi, J. Am. Chem. Soc. 1997, 119,
5740). This fact may be related to the reason for the different number
of electrons involved in E1red of 22‡. One possible explanation might be
. .
the rapid equilibrium of 2a with some closed-shell species, which
.
‡
facilitates the disproportionation of 2a to make the Er2ed wave
. .
ambiguous. Such a process is less likely in 2b , in which the spin
density is delocalized over thioxanthyl moieties.
[9] When the dication salt 2a-(BF4)2 was reduced by SmI2 in THF
followed by quenching with air, peroxide 1a was obtained in 85%
. .
yield. This result indicates that (2-O2) is also generated by 2e
H
OR*
reduction of 2a2‡ followed by C O bond making (EEC process).
À
1. R*ONa
2. Ph3P=CH2
EtO
O
H
[10] Crystal structure analyses: 1a: C38H24O5, Mr ˆ 560.60, monoclinic,
P21/c, a ˆ 10.211(3), b ˆ 16.311(5), c ˆ 16.931(3) Š, b ˆ 103.88(2)8,
(+)-2
1
Vˆ 2737(1) Š3, Z ˆ 4, 1calcd ˆ 1.360 gcmÀ1
,
Rw ˆ 0.069. 1b ´
0.5AcOEt (À1008C): C40H28O4S2, Mr ˆ 636.78, monoclinic, C2/c,
a ˆ 31.597(1), b ˆ 10.2379(3), c ˆ 22.9976(7) Š, b ˆ 123.615(1)8, Vˆ
1. Yb(OTf)3, CH2Cl2
SO2, −90 oC, 24 h
2. Bu4NF
SO2Me
O
OR'
OSiMe3
6195.3(3) Š3, Z ˆ 8, 1calcd ˆ 1.365 gcmÀ1, Rw ˆ 0.055. Crystallographic (+)-2
data (excluding structure factors) for the structures reported in this
paper have been deposited with the Cambridge Crystallographic Data
Centre as supplementary publication nos. CCDC-136844 and -136845.
Copies of the data can be obtained free of charge on application to
CCDC, 12 Union Road, Cambridge CB21EZ, UK (fax: (‡44)1223-
336-033; e-mail: deposit@ccdc.cam.ac.uk).
+
5
(S)
R
R
3. MeI
3 R = Ph
9 R = Me
(−)-4 R = Ph, R' = R* (79%, d.r. = 25:1)
(−)-5 R = Ph, R' = H (88%)
(−)-10 R = Me, R' = R* (86%, d.r. = 5.2:1)
(−)-11 R = Me, R' = H (83%)
CF3COOH
CF3COOH
À
[11] The O O bond length in 1,4-diphenyl-2,3-dioxabicyclo[2.2.1]heptane
SO2Me
is 1.501(2) Š (D. J. Coughlin, R. S. Brown, R. G. Salomon, J. Am.
Chem. Soc. 1979, 101, 1533) and that in tetrabenzopentacene
OR' OR'
(Me4N)(AcO)3BH
(–)-5 or (–)-11
R
MeCN, AcOH
−40 o
endoperoxide is 1.496(5) Š (A. Izuoka, T. Murase, M. Tsukada, Y.
Ito, T. Sugawara, A. Uchida, N. Sato, H. Inokuchi, Tetrahedron Lett.
1997, 38, 245). Long O O distances are more common for small ring
peroxides, such as dioxiranes (1.503(5) Š for dimesityldioxirane: W.
Sander, K. Schroeder, S. Muthusamy, A. Kirschfeld, W. Kappert, R.
Boese, E. Kraka, C. Sosa, D. Cremer, J. Am. Chem. Soc. 1997, 119,
7265) or dioxetanes (1.500 and 1.55 Š in 1,6-diphenyl-2,5,7,8-tetraox-
obicyclo[4.2.0]octane derivatives: W. Adam, E. Schmidt, E.-M. Peters,
K. Peters, H. G. von Schnering, Angew. Chem. 1983, 95, 566; Angew.
Chem. Int. Ed. Engl. 1983, 22, 546). The last one is surprisingly long for
C
(−)-6 R = Ph, R' = H (79%, 99.4% ee)
12 R = Me, R' = H (22-49%, d.r. = 5:1)
18 R = Ph, R',R' = Me2C (99%)
À
(S)
H
R* =
Me
Scheme 1. Asymmetric synthesis of 4,6-anti-(Z)-4,6-dihydroxy-3-methyl-
alk-2-enyl methyl sulfones; see text for details.
À
an O O bond although the error in the determination was not given.
[12] When the similar oxidation was conducted under the presence of
tetraphenylcyclopentadienone (10 equiv) no detectable amount of cis-
dibenzoylstilbene was formed, which suggests that the major reaction
an excess of SO2, (‡)-2 reacted with enoxysilane 3 to give a
trimethylsilyl sulfinate, which was desilylated with Bu4NF and
treated with MeI to afford a 25:1 mixture of sulfone (À)-4 and
its diastereomer (79% yield, recovery of 20% of (‡)-2).[5]
1
path does not produce O2.
[13] P. M. S. Monk, R. J. Mortimer, D. R. Rosseinsky, Electrochromism:
Fundamentals and Applications, VCH, Weinheim, 1995, pp. 124 ± 182;
S. Hünig, M. Kemmer, H. Wenner, I. F. Perepichka, P. Bäuerle, A.
Emge, G. Gescheid, Chem. Eur. J. 1999, 5, 1969.
[14] Reductive oxygenation would also occur by the combination of 22‡
[*] Prof. P. Vogel, V. Narkevitch
.
À
with O2 , which is generated by 1e reduction of O2. This process
seems, however, less likely when it is considered that O2 is a weaker
Â
Section de chimie de lꢁUniversite de Lausanne, BCH
1015 Lausanne-Dorigny (Switzerland)
Fax : (‡41)21-692-39-75
electron acceptor (Ered <À 0.8V versus SCE in CH 2Cl2) than 22‡
.
E-mail: pierre.vogel@ico.unil.ch
K. Schenk
Institut de Cristallographie, BSP
Â
Universite de Lausanne, Lausanne-Dorigny (Switzerland)
[**] This work was supported by the Swiss National Science Foundation.
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Angew. Chem. Int. Ed. 2000, 39, No. 10

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Pure (À)-4 was obtained by flash chromatography on silica
gel. Trifluoroacetolysis[6] of (À)-4 gave (À)-5 (88% yield),
which was reduced with (Me4N)(AcO)3BH in MeCN/AcOH
(À408C, 15 h)[7] to produce anti-diol (À)-6 (79% yield).
Hydroboration of (À)-6 with BH3 ´ Me2S (THF, À88C, 24 h)
provided a 3.9:1 mixture of triols 7 and 8 (91% yield,
Scheme 2).
16 as the major alcohol. Further treatment of 16 with BH3 ´
THF led to a diol that gave acetonide 22 on treatment with
(MeO)2CMe2/acetone/PPTS (d ˆ 23.7, 24.9; Me), establishing
the relative configurations of 14 and 15.
An asymmetric version of our four component reaction
(1-alkoxy-1,3-diene ‡ SO2 ‡ enoxysilane ‡ alkyl iodide) has
been realized. Exploration of its versatility and its application
to the synthesis of polyketides and analogues, as well as
studies of its mechanism,[13] are underway in our laboratory.[14]
OH OR' OR'
OH OR' OR'
1. BH3•Me2S, THF
2. H2O2, NaOH
SO2Me
SO2Me
(−)-6
+
Ph
Ph
Experimental Section
7 R' = H
8 R' = H
20 R',R' = Me2C
21 R',R' = Me2C (99%)
(À)-4: A mixture of (‡)-2 (192 mg, 0.6 mmol), 3 (0.6 mL, 3 mmol), and
Yb(OTf)3 (298mg, 0.48mmol) in anhydrous CH 2Cl2 (6 mL) was degassed
on the vacuum line. SO2, purified by flowing through a column of basic
alumina (Merck, activity Is, 1.28g, 20 mmol), was added at À1968C. The
mixture was stirred at À908C for 24 h, and SO2 was pumped away at
À908C and then at À658C. 1m Bu4NF in THF (6 mL, 6 mmol) and MeI
(1.2 mL, 20 mmol) were added under an argon atmosphere, and the
mixture stirred at 08C for 1 h and then at 208C for 15 h. After addition of
H2O (30 mL), the mixture was extracted with CH2Cl2 (5 Â 20 mL). The
combined organic extracts were dried over MgSO4. Solvent evaporation
and flash chromatography on silica gel (CH2Cl2/Et2O 24/1; Rf ((À)-4) ˆ
0.35) afforded (À)-4 (244 mg, 79%) and (‡)-2 (36 mg, 20%); colorless
crystals were obtained by recrystallization from MeOH, m.p. 116 ± 1188C
(MeOH). [a]2D5 ˆ À0.7 (c ˆ 1.0, CHCl3); UV (MeCN): lmax (e) ˆ 241 (5700),
205 nm (12500); IR (KBr): nÄ ˆ 3055, 2965, 1685, 1420, 1305, 1265, 895, 745,
SO2Me
OR' OR'
Et2BOMe
NaBH4/THF
MeOH, −78 o
1. BH3•Me2S, THF
2. H2O2, NaOH
(–)-11
C
(−)-13 R' = H (83%, d.r. >99:1, 99.4% ee)
19 R',R' = Me2C (99%)
OR1 OR2 OR3
OR1 OR2 OR3
SO2Me
+
SO2Me
14 R1 = R2 = R3 = H
15 R1 = R2 = R3 = H
(+)-17 R1 = R2 = Me2C, R3 = H (99%)
(−)-16 R1 = R2 = Me2C, R3 = H
22 R1 = iPr, R2,R3 = Me2C (57%)
705 cmÀ1
;
1H NMR (400 MHz, CDCl3): d ˆ 7.86 ± 7.41 (m, 5H), 7.06 ± 6.98
(m, 2H), 5.55 (ddq, 3J(H-5,H-6) ˆ 9.4, 3J(H-5,H'-6) ˆ 4.7, 4J(H-5,Me-
Scheme 2. Synthesis of polyketides; see text for details.
3
3
C(4)) ˆ 1.3 Hz, H-5), 5.01 (q, J(H-1',H-2') ˆ 6.7 Hz, H-1'), 4.70 (dd, J(H-
3,H-2) ˆ 8.8, 3J(H-3,H'-2) ˆ 4.0 Hz, H-3), 4.03 (dd, 2J(H,H) ˆ 15.2, 3J(H-
6,H-5) ˆ 9.4 Hz, H-6), 3.93 (sept, CHiPr), 3.47 (dd, 2J(H,H) ˆ 17.3, 3J(H-
2,H-3) ˆ 8.8 Hz, H-2), 3.25 (dd, 2J(H,H) ˆ 15.2, 3J(H-6,H-5) ˆ 4.7 Hz, H'-
Under similar conditions, (‡)-2 and SO2 reacted with
enoxysilane 9 to give a 5.2:1 mixture of (À)-10 and its
diastereomer (86% yield). Pure (À)-10 was obtained by flash
chromatography on silica gel. Trifluoroacetolysis of (À)-10
gave aldol (À)-11, which was reduced with (Me4N)(AcO)3BH
in MeCN/AcOH[7] to form 12 as the major anti-diol
2
3
6), 3.19 (dd, J(H,H) ˆ 17.3, J(H-2,H-3) ˆ 4.0 Hz, H'-2), 3.12, 2.85 (2sept,
2CHiPr), 2.78(s, MeSO 2), 1.88 (d, 4J(Me-C(4),H-5) ˆ 1.3 Hz, Me-C(4)),
1.54 (d, 3J(H-1',H-2') ˆ 6.7 Hz, H3C(2')), 1.40 ± 1.13 (m, 2 Me2C), 1.26 (d,
3J(Me,CH) ˆ 6.9 Hz, iPr); elemental analysis calcd for C32H48O5S ((À)-4 ´
MeOH): C 70.55, H 8.88, S 5.88; found: C 70.86, H 8.60, S 5.99.
(À)-5. A mixture of (À)-4 (149 mg, 0.29 mmol), CH2Cl2 (4.5 mL), and
CF3COOH (0.3 mL) was stirred at 208C for 40 min. A saturated aqueous
solution of NaHCO3 (30 mL) was added, and the mixture extracted with
CH2Cl2 (3 Â 20 mL). The combined organic phases were dried over MgSO4.
Solvent evaporation and flash chromatography on silica gel (CH2Cl2/
EtOAc) afforded (À)-5 (72 mg, 88%) as a yellow oil after removal of
solvent. [a]2D5 ˆ À52 (c ˆ 1.0, CHCl3).
(Scheme 1). Alternatively, reduction of (À)-11 with Et2-
[8]
BOMe/NaBH4
afforded syn-diol (À)-13 (83% yield,
Scheme 2), the hydroboration of which with BH3 ´ Me2S in
THF (08C, 24 h) led to a 2.2:1 mixture of triols 14 and 15
(83%). Their acetonides 16 and 17, obtained under standard
conditions ((Me2O)2CMe2/acetone/pyridinium p-toluenesul-
fonate (PPTS)), could be separated by flash chromatography.
The modest diastereoselectivities for the hydroborations of
(À)-6 and (À)-13 might be due to competing effects arising
from A1,2 and A1,3 allylic strain.[9]
Received: November 25, 1999 [Z14313]
[1] B. Deguin, J.-M. Roulet, P. Vogel, Tetrahedron Lett. 1997, 32, 6197 ±
6200.
The structures of (À)-4 and (À)-10 were established by
single-crystal X-ray radiocrystallography.[10] The enantiomeric
[2] J.-M. Roulet, G. Puhr, P. Vogel, Tetrahedron Lett. 1997, 38, 6201 ± 6204.
[3] P. Delair, A. M. Kanazawa, M. B. M. de Azevedo, A. E. Greene,
Tetrahedron: Asymmetry 1996, 7, 2707 ± 2710; A. Kanazawo, P. Delair,
M. Pourashraf, A. E. Greene, J. Chem. Soc. Perkin Trans. 1 1997,
1911 ± 1912.
[4] R. Rieger, E. Breitmaier, Synthesis 1990, 697 ± 701.
[5] The use of other chiral alcohols such as (R)-1-phenyl-1-propanol, (R)-
1-(2-naphthyl)ethanol, (R)-1-phenylethanol, and (S)-1-(pentafluoro-
phenyl)ethanol led to lower diastereoselectivities.
[6] G. H. Posner, D. G. Wettlaufer, J. Am. Chem. Soc. 1986, 108, 7373 ±
7377.
[7] D. A. Evans, K. T. Chapman, E. M. Carreira, J. Am. Chem. Soc. 1988,
110, 3560 ± 3578.
[8] K. Nasaraka, F. G. Pai, Tetrahedron 1984, 40, 2233 ± 2238; K. M. Chen,
G. E. Hardtmann, K. Prasad, O. Repic, M. J. Shapiro, Tetrahedron
Lett. 1987, 28, 155 ± 158.
purity (99.4% ee) of diols (À)-6 and (À)-13 was determined
13
from the 17F NMR spectra ( C satellite for C F coupling) of
À
their Mosher diesters[11] derived from (S)-a-methoxy-a-phe-
nylacetyl chloride. The anti and syn relative configurations of
(À)-6 and (À)-13, respectively, were confirmed by the
13C NMR spectra of their acetonides 18 (d ˆ 25.0, 24.7;
Me2C) and 19 (d ˆ 30.2, 19.6; Me2C),[12] obtained upon
treatment with (MeO)2CMe2 and PPTS. Under similar con-
ditions, triols 7 and 8 were converted selectively into
acetonides 20 and 21; their 13C NMR and 2D NOESY
1H NMR spectra of the latter proved the structures of the
former. Treatment of 16 and 17 with acid (AcOH/H2O)
provided pure triols 14 and 15. Hydroboration of 19 provided
[9] R. W. Hoffmann, Chem. Rev. 1989, 89, 1841 ± 1860.
Angew. Chem. Int. Ed. 2000, 39, No. 10
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[10] Crystallographic data (excluding structure factors) for the structures
reported in this paper have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication no.
CCDC-134999 and -135000. Copies of the data can be obtained free
of charge on application to CCDC, 12 Union Road, Cambridge
CB21EZ, UK (fax: (‡44)1223-336-033; e-mail: deposit@ccdc.cam.
ac.uk).
[11] T. A. Dale, H. S. Mosher, J. Am. Chem. Soc. 1973, 95, 512 ± 519; T. A.
Dale, D. L. Dull, H. S. Mosher, J. Org. Chem. 1969, 34, 2543 ± 2549.
[12] S. D. Rychnovsky, B. N. Rogers, T. I. Richardson, Acc. Chem. Res.
1998, 31, 9 ± 17, and references therein.
We and others have recently reported an interesting class of
materials possessing organic groups fused ªwithinº the
mesoporous frameworks.[13±16] These novel organic ± inorgan-
ic hybrid materials, denoted periodic mesoporous organo-
silicas (PMOs), are prepared through the surfactant-templat-
ed condensation of bifunctional organosiloxane precursors,
(R'O)3SiRSi(OR')3.[19] This new approach extends the realm
of mesoporous materials to ªchemistry of the channel wallsº
rather than limiting it to ªchemistry of the void spaceº. In
contrast to mesoporous materials that have terminally bonded
organic groups dangling into the channels, PMOs offer a
unique opportunity to affect the chemistry of the framework
through organic transformations. The physical and chemical
properties of these materials may be modified with suitable
choice of organic and organometallic groups (R) inside the
channel wall of the PMO. Examples of PMOs containing
ethane, ethene, acetylene, ferrocene, thiophene, and benzene
inside the framework have been reported.[13±16] Here we
report the discovery of thermally robust periodic mesoporous
methylenesilica and demonstrate a unique thermal trans-
formation in which bridging methylene groups ªinside the
channel wallsº convert into terminally bound methyl groups
residing ªwithin the channel spacesº.
Â
[13] For preliminary studies, see T. Fernandez, J. A. Sordo, F. Monnat, B.
Deguin, P. Vogel, J. Am. Chem. Soc. 1998, 120, 13276 ± 13277; T.
Â
Â
Fernandez, D. Suarez, J. A. Sordo, F. Monnat, E. Roversi, A.
EstrelladeCastro, K. Schenk, P. Vogel, J. Org. Chem. 1998, 63,
Ä
9490 ± 9499; E. Roversi, F. Monnat, K. Schenk, P. Vogel, P. Brana, J. A.
Sordo, Chem. Eur. J., in press.
[14] Preliminary experiments have shown that (E)-1-alkoxybutadienes and
(E,E)-1-alkoxy-2-methylpenta-1,3-dienes can be combined with enoxy-
silanes 3, 9, and others, and with carbon electrophiles different from
MeI.
Methylene-bridged PMOs are also an interesting class of
materials from the point of view of fundamental theory and
applications. As the simplest organic group, methylene is a
useful moiety to study for sophisticated ab initio calcula-
tions.[20, 21] Methylene is also useful for the preparation of
silicon carbides and oxycarbides.[22, 23] Since methylene is
isoelectronic with oxygen, periodic mesoporous methylene-
silica is a useful analogue for structural, mechanical, and
electronic comparison with the widely studied periodic
mesoporous silica. Moreover, periodic mesoporous methyl-
enesilica may be useful as a precursor for additional chemical
modifications.
To prepare hexagonal mesoporous methylenesilica, we
used a procedure similar to that of other PMOs.[13, 14] With a
surfactant as the template, samples were synthesized with
different proportions of methylene groups (Scheme 1). For
this, a mixture of two precursors was used: bis(triethoxysilyl)-
methane (1), containing the bridging methylene groups, and
tetraethoxysilane (2). The cationic cetyltrimethylammonium
surfactant template was then removed from the samples by
solvent extraction with methanol/hydrochloric acid.
Metamorphic Channels in Periodic Mesoporous
Methylenesilica**
Tewodros Asefa, Mark J. MacLachlan,
Hiltrud Grondey, Neil Coombs, and Geoffrey A. Ozin*
Since the discovery of mesoporous silica, MCM-41, in
1992,[1, 2] the synthesis of mesoporous inorganic materials
using supramolecular organic templates continues to draw a
great deal of attention due to the potential application of
these materials in catalysis,[3] nanoelectronics,[4] separation
science,[5] and environmental remediation.[6] The composition
of mesoporous materials span a variety of inorganic com-
pounds, including a range of oxides,[7, 8] Pt metal,[9] phos-
phates,[10] CdS,[11] and M/Ge4S10,[12] but, until very recent-
ly,[13±16] none have included organic moieties as a structural
component of the framework.
A vast number of organic, inorganic, organometallic, and
polymeric species have been included inside the periodic
hexagonal channels of MCM-41.[17] In particular, many species
have been anchored or grafted to the channel wall of the silica
by synthesis or postsynthesis treatment with RSi(OR')3
compounds.[17, 18] These organic groups, which protrude into
the channels, have potential for many useful transformations,
catalysis, separations, and other interesting chemistry.
The mesoporous methylenesilica materials were investigat-
ed by powder X-ray diffraction (PXRD) and transmission
electron microscopy (TEM) before and after solvent extrac-
[*] Prof. G. A. Ozin, T. Asefa, Dr. M. J. MacLachlan, Dr. H. Grondey,
Dr. N. Coombs
Materials Chemistry Research Group, Department of Chemistry
University of Toronto
Toronto, Ontario M5S 3H6 (Canada)
Fax : (‡1)416-971-2011
E-mail: gozin@alchemy.chem.utoronto.ca
[**] This work was supported by the NSERC of Canada. M.J.M. is grateful
to NSERC for postgraduate (1995 ± 1999) and postdoctoral fellow-
ships (1999 ± 2001). G.A.O. thanks the Killam Foundation for the
award of an Isaac Walton Killam research fellowship (1995 ± 1997).
Scheme 1. Synthesis of the hexagonal mesoporous methylenesilica. The
ratio of 1 and 2 corresponds to the molar contribution of Si from each
reagent (i.e., 5 was prepared from BTM 1 and TEOS 2 in a molar ratio of
1:6; see the Experimental Section).
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Angew. Chem. Int. Ed. 2000, 39, No. 10