Electronic effects and the stereochemistries in rearrangement-displacement reactions of triaryl(halomethyl)silanes with fluoride and with alkoxide ions

Article abstract of DOI:10.1021/jo010471j

Tetrabutylammonium fluoride (TBAF) reacts with (halomethyl)diphenyl(para-substituted-phenyl)silanes (13, X = Cl), 14 (X = Br), and 15 (X = I) in ether solvents to give fluorodiphenyl(parasubstituted-phenylmethyl)silanes (17a) and fluorophenyl(phenylmethyl)(para-substituted-phenyl)silanes (20a) by attack on silicon and migrations of the phenyl or the para-substituted-phenyl groups to C-1 with displacement of chloride ion. Sodium methoxide in dioxane effects rearrangement displacements of 14 (X = Br) to yield methoxydiphenyl(para-substituted-phenylmethyl)silanes (17b) and methoxyphenyl(phenylmethyl)(para-substituted-phenyl)silanes (20b). The migratory aptitudes of the varied phenyl groups in rearrangement-displacements of 13 with F^- at 25°C are p-CF₃-Ph, 2.72 > p-Cl-Ph, 1.67 > Ph, 1.00 > p-CH₃-Ph, 0.91 > p-CH₃O-Ph, 0.58 > p-(CH₃)₂N-Ph, 0.55. For reactions of 14 with sodium methoxide in dioxane, the migratory aptitudes at 23°C are p-CF₃-Ph, 2.53 > p-Cl-Ph, 1.64 > Ph, 1.00 > p-CH₃O-Ph, 0.84 > p-CH₅-Ph, 0.79 > p-(CH₃)₂N-Ph, 0.68. The migratory aptitudes in the above rearrangement-displacements are increased by electron withdrawing substituents, and logarithms of the migratory aptitudes give satisfactory linear correlations with σ and/or σ-zero values of the phenyl substituents. Hammett correlations however of the migratory aptitudes from reactions of F^- with 13 (X = Cl) at 0 and -20°C, 14 (X = Br) at 23, 0, and -20°C, and 15 (X = I) at 23°C are not linear. (+)-(Bromomethyl)methyl-1 naphthylphenylsilane (23, [α]_D²³ +8.29°, cyclohexane) reacts with CsF and with TBAF in THF to give benzylfluoromethyl-1-naphthylsilane (51, [α]_D²⁵ = 0.00°, cyclohexane) and fluoromethyl-(1 naphthylmethyl)phenylsilane (52, impure) in 10.4:1 ratio along with unchanged 23 ([α]_D²³ 8.29°, cyclohexane). Sodium methoxide and (+)-23 in dioxane at 25°C and at 0°C yield (+)benzylmethoxymethyl-1-naphthylsilane (64) and (+)-methoxymethyl(1-naphthylmethyl)phenylsilane (65) in ～9:1 ratio. The conversions of (+)-23 to (+)-64 occur with <93% inversion about silicon. Reaction of (+)-23 with sodium methoxide at 25°C to give (+)-65 also occurs with inversion. Further, sodium ethoxide and sodium 2-propoxide react with (+)-23 at 20-25°C by rearrangement displacements on silicon with phenyl migrations to yield (+)-benzylethoxymethyl-1-naphthylsilane (69) and (+)-benzylmethyl-1-naphthyl-2-propoxysilane (70), respectively, each with <95% inversion about silicon. The mechanisms of rearrangement-displacements of 13-15 and (+)-23 by fluoride and by alkoxide ions are discussed.

Full text of DOI:10.1021/jo010471j

J . Org. Chem. 2002, 67, 3561-3574
3561
Electr on ic Effects a n d th e Ster eoch em istr ies in
Rea r r a n gem en t-Disp la cem en t Rea ction s of
Tr ia r yl(h a lom eth yl)sila n es w ith F lu or id e a n d w ith Alk oxid e Ion s
J ohn M. Allen,† Steve L. Aprahamian,‡ Esther A. Sans,§ and Harold Shechter*
Department of Chemistry, The Ohio State University, Columbus, Ohio 43210
shechter@chemistry.ohio-state.edu
Received May 7, 2001
Tetrabutylammonium fluoride (TBAF) reacts with (halomethyl)diphenyl(para-substituted-phenyl)-
silanes (13, X ) Cl), 14 (X ) Br), and 15 (X ) I) in ether solvents to give fluorodiphenyl(para-
substituted-phenylmethyl)silanes (17a ) and fluorophenyl(phenylmethyl)(para-substituted-phenyl)-
silanes (20a ) by attack on silicon and migrations of the phenyl or the para-substituted-phenyl groups
to C-1 with displacement of chloride ion. Sodium methoxide in dioxane effects rearrangement-
displacements of 14 (X ) Br) to yield methoxydiphenyl(para-substituted-phenylmethyl)silanes (17b)
and methoxyphenyl(phenylmethyl)(para-substituted-phenyl)silanes (20b). The migratory aptitudes
of the varied phenyl groups in rearrangement-displacements of 13 with F- at 25 °C are p-CF3-Ph,
2.72 > p-Cl-Ph, 1.67 > Ph, 1.00 > p-CH3-Ph, 0.91 > p-CH3O-Ph, 0.58 > p-(CH3)2N-Ph, 0.55. For
reactions of 14 with sodium methoxide in dioxane, the migratory aptitudes at 23 °C are p-CF3-Ph,
2.53 > p-Cl-Ph, 1.64 > Ph, 1.00 > p-CH3O-Ph, 0.84 > p-CH5-Ph, 0.79 > p-(CH3)2N-Ph, 0.68. The
migratory aptitudes in the above rearrangement-displacements are increased by electron-
withdrawing substituents, and logarithms of the migratory aptitudes give satisfactory linear
correlations with σ and/or σ-zero values of the phenyl substituents. Hammett correlations however
of the migratory aptitudes from reactions of F- with 13 (X ) Cl) at 0 and -20 °C, 14 (X ) Br) at
23, 0, and -20 °C, and 15 (X ) I) at 23 °C are not linear. (+)-(Bromomethyl)methyl-1-
naphthylphenylsilane (23, [R]2D3 +8.29°, cyclohexane) reacts with CsF and with TBAF in THF to
give benzylfluoromethyl-1-naphthylsilane (51, [R]2D5 ) 0.00°, cyclohexane) and fluoromethyl-(1-
naphthylmethyl)phenylsilane (52, impure) in 10.4:1 ratio along with unchanged 23 ([R]2D3 8.29°,
cyclohexane). Sodium methoxide and (+)-23 in dioxane at 25 °C and at 0 °C yield (+)-
benzylmethoxymethyl-1-naphthylsilane (64) and (+)-methoxymethyl(1-naphthylmethyl)phenylsilane
(65) in ∼9:1 ratio. The conversions of (+)-23 to (+)-64 occur with >93% inversion about silicon.
Reaction of (+)-23 with sodium methoxide at 25 °C to give (+)-65 also occurs with inversion. Further,
sodium ethoxide and sodium 2-propoxide react with (+)-23 at 20-25 °C by rearrangement-
displacements on silicon with phenyl migrations to yield (+)-benzylethoxymethyl-1-naphthylsilane
(69) and (+)-benzylmethyl-1-naphthyl-2-propoxysilane (70), respectively, each with >95% inversion
about silicon. The mechanisms of rearrangement-displacements of 13-15 and (+)-23 by fluoride
and by alkoxide ions are discussed.
Fluoride1 and alkoxide reagents2 (2, Scheme 1) in
Sch em e 1
aprotic environments react with (chloromethyl)silanes 1
by nucleophilic attack on silicon possibly as in 3 to give
(1) rearrangement-displacement products 4 and 5 aris-
ing from competitive migrations of the phenyl (Ph-Z) and
the methyl groups to C-1 with displacement of chloride
ion and (2) silyl derivatives 6 by loss of chloromethide
* Phone: (614)292-6300. Fax: (614)292-1685.
† Present address: Ahlstrom Dexter LLC, Windsor Lock, CT 06096.
‡ Present address: Mobay Chemical Corporation, Pittsburgh, PA
15317.
§ Present address: Pacemaker Inc., Buffalo, NY 21300.
(1) (a) Damrauer, R.; Danahey, S. E.; Yost, V. E. J . Am. Chem. Soc.
1984, 106, 7633. (b) Damrauer, R.; Yost, V. E.; Danahey, S. E.;
O’Connell, B. K. Organometallics 1985, 4, 1779.
(2) (a) Eaborn, C.; J effrey, J . C. Chem. Ind. 1955, 1041. (b) Eaborn,
C.; J effrey, J . C. J . Chem. Soc. 1957, 137. (c) In reactions of 1 with
sodium ethoxide in ethanol, nucleophilic displacements of chloride ion
at C-1 also occur by SN2 processes to give (ethoxymethyl)dimethyl-
(substituted-phenyl)silanes. However, in aprotic solvents sodium,
potassium, and cesium alkoxides react essentially totally on silicon as
ion. The effects of phenyl substituents (Z in Ph-Z) on
increasing the rates of disappearance of silanes 1 in
reactions with potassium fluoride (2, Nuc- ) F-) in
in Scheme 1.2d,e (d) Sans, E. A. Ph.D. Dissertation, The Ohio State
University, Columbus, Ohio, 1981. (e) Kreeger, R. L.; Menard, P. R.;
Sans, E. A.; Shechter, H. Tetrahedron Lett. 1985, 26, 1115.
10.1021/jo010471j CCC: $22.00 © 2002 American Chemical Society
Published on Web 05/04/2002

3562 J . Org. Chem., Vol. 67, No. 11, 2002
Allen et al.
mesitylene at 85 °C are Z ) m-CF3 > p-Cl > p-F > H >
p-CH3.1b In rearrangement-displacements of 1 (Scheme
1) by sodium ethoxide (2, Nuc- ) C2H5O-) in ethanol at
78 °C, substituents (Z) in the phenyl groups increase the
rates of reactions in the order Z ) p-Cl > H > p-CH3 >
p-CH3O.2a,b The overall rearrangement-displacement
reactions are accelerated when the substituents in the
phenyl groups in 1 are electron-withdrawing. The rate-
determining steps in the above reactions of 1 have been
presumed to involve transition states close in structure
to pentacoordinate silylanionic intermediates 3 (Scheme
1) that are stabilized by electron-withdrawing substitu-
ents in the phenyl groups.1b,2a,b
Of present interest is that the reactions of 1 with
potassium fluoride (2, Nuc- ) F-) in toluene at 55 °C to
yield 4 (Nuc ) F) give migratory aptitudes of the phenyl
groups in the order Ph > p-CH3-Ph > m-CF3-Ph > p-Cl-
Ph > p-F-Ph, and the phenyl groups all migrate much
more rapidly than do the methyl groups.1b Further, the
migratory aptitudes in reactions of 1 with sodium meth-
oxide in dioxane at 60 °C to yield 4 (Nuc ) CH3O) are
found to be p-CF3-Ph > m-Cl-Ph > p-Cl-Ph > p-CH3-Ph
> p-CH3O-Ph > Ph, and the migratory aptitudes of the
varied phenyl groups compared to the methyl range from
26 to 5:1.2d There are thus no simple interpretations of
the electronic effects on migration of the phenyl groups
in the rearrangement-displacement processes of 1 as in
Scheme 1.1b,2d The selectivities and the stereochemistries
of rearrangement-displacements of (halomethyl)silanes
with nucleophiles3 including the possibilities of pseu-
dorotation with nucleophiles are also intriguing ques-
tions.2d,3d An important relevant example of the specificity
of rearrangement in reactions of (halomethyl)silanes is
cyclization of lithium 3-[(chloromethyl)silyl]-1-propoxide
7 (eq 1) with phenyl migration (>90%) and displacement
of chloride ion possibly via 8 to yield oxasilacyclopentane
9.4a,b The ring-closure of [(chloromethyl)dimethylsilyl]-
alkoxide 10 at -78 °C in THF takes place, however, by
reaction on silicon (eq 2) with rearrangement-displace-
ment involving methyl migration to give oxasilacyclo-
pentane 12 (>90%).4c Oxasilacyclopentane 12 is surmized
to result upon selective formation and then apical rear-
rangement-decomposition of the highly strained trigonal
bipyramidal intermediate 11.4c Phenyl migration is not
observed.4c-e
Sch em e 2
Sch em e 3
(bromomethyl)silane 236 with fluoride and with alkoxide
reagents in ether solvents at various temperatures. The
experiments and results are described as follows.
Studies are now reported of (1) the migratory aptitudes
of varied phenyl groups in the reactions of (halomethyl)-
silanes 13a -f, 14a -f, and 15a -f with tetrabutylammo-
nium fluoride5a,b (TBAF, > 2 equiv) at 25 to -20 °C in
THF and of 14a -f with sodium methoxide in dioxane at
23 °C as in Scheme 2 and (2) the stereochemistries of
rearrangement-displacement reactions of optically active
Resu lts a n d Discu ssion
A. Migr a tor y Ap titu d es in Rea r r a n gm en t-Dis-
p la cem en t Rea ction s of Sila n es 13-15 w ith F lu o-
r id e Ion . The reactions of fluoride ion with (halomethyl)-
silanes 13-15 (Scheme 2), synthesized as in Schemes 3
and 4,7-9 have been investigated in detail. Potassium

Rearrangement-Displacement Reactions
J . Org. Chem., Vol. 67, No. 11, 2002 3563
Sch em e 4
toluenes 18 and 21 essentially quantitatively upon
formation and then cleavage of 17a and 20a by fluoride
ion followed by protolysis. Displacements of (halomethyl)-
silanes 13-15 by TBAF (eq 6) by attack on silicon to give
fluorosilanes 31 and halomethide ion (32), and products
thereof do not occur. The migratory aptitudes in rear-
rangement-displacement reactions of 13-15 with fluo-
ride ion were determined simply in each experiment from
the para-substituted-toluene (18) and the toluene (21)
formed as in Scheme 2. The analytical and the statistical
methods used are described in the Experimental Sec-
tion.10
The behaviors of (chloromethyl)silanes 13a -f with
TBAF in THF were first studied at 25 °C. The migratory
aptitudes (p-Z-Ph/Ph) for rearrangements of the varied
phenyl groups as in Scheme 2 are summarized in Table
1. The results show that para-substituents that are
electron-attracting (Z-p; CF3 > Cl) speed whereas those
that are usually electron-donating [Z-p; (CH3)2N > CH3O
> CH3] slow migration of the phenyl groups. Of note is
that the substituent effects on the relative rates of
rearrangement of the varied phenyl groups range from
2.72 to 0.55, a factor of only ∼5. The migratory aptitudes
in the rearrangement-displacements are interpretable,
however, on the basis that the transition states for
rearrangement are close in structure to pentacoordinate
intermediates 16 (Nuc ) F) and/or other polycoordinate
silylanionic intermediates as will be discussed and reflect
the abilities of the phenyl groups which migrate to
remove electrons from silylanionic centers. Further, the
Hammett free energy correlations11,12 obtained upon
plotting the logarithms of the migratory aptitudes (F-Z-
C6H4/C6H5) against σ (Figure 1a: rho (F) ) 0.64, corr.
coeff. ) 0.964, aver. std. deviation ( 0.065) and σ-zero
(Figure 1b; F ) 0.84, corr. coeff. ) 0.964, aver. std.
deviation ( 0.065) substituent values are satisfactorily
linear12 and consistent with the conclusion that the
transition states for rearrangement-displacements in 16
(Nuc ) F)1 or other controlling silylanionic intermediates
that are involved are favored at 25 °C by electron-
withdrawing substituents in the phenyl groups which
migrate.
fluoride (KF) and cesium fluoride (CsF) are insoluble in
various ether solvents and react slowly with 13-15 at
-20 to 25 °C. Commercial TBAF5b is soluble in THF and
is excellent for reactions with 13-15. The behaviors of
13-15 with 1 equiv of commercial TBAF in THF are
complicated however (Scheme 2) in that rearrangement-
displacement products 17a and 20a are partly converted
to para-substituted-toluenes (18) and difluorodiphenyl-
silane (19a ) and to toluene (21) and difluorophenyl (para-
substituted-phenyl)silanes (22a ) by reactions with fluo-
ride ion and then H2O in the reagent. Under proper
conditions however, 13-15 and TBAF (>2 equiv) yield
(3) (a) For further examples and references to such rearrangement-
displacement reactions see ref 1b, 2e, and 3b-f. (b) Corey, J . Y.; Corey,
E. R.; Chang, V. H. T.; Hauser, M. A.; Leiber, M. A.; Reinsel, T. E.;
Riva, M. E. Organometallics 1984, 3, 1051. (c) Sans, E. A.; Shechter
H. Tetrahedron Lett. 1985, 26, 1119. (d) Aprahamian, S. L.; Shechter,
H. Tetrahedron Lett. 1990, 31, 1080. (e) Hudrlik, P. F.; Abdallah, Y.
M.; Kulkarni, A. K.; Hudrlik, A. M. J . Org. Chem. 1992, 57, 6552. (f)
Eisch, J . J .; Chiu, C. S. Heteroatom Chem. 1994, 5, 265.
(4) (a) Hudrlik, P. F.; Abdallah, Y. M.; Hudrlik, A. M. Tetrahedron
Lett. 1992, 33, 6743. (b) Oxasilacyclopentane 9 is unstable and was
converted by CH3Li/Et2O and neutralization to benzyl(3-hydroxy-1-
propyl)methylphenylsilane. (c) Hijji, Y. M.; Hudrlik, P. F.; Hudrlik, A.
M. J . Chem. Soc., Chem. Commun. 1998, 1213. (d) The importance of
steric and strain factors in rearrangement-displacements of halo-
methylsilanes is illustrated further by reactions of 1-(1-iodoalkyl)-1-
phenyl-1-silacyclobutanes with potassium tert-butoxide to give 2-alkyl-
1-tert-butoxy-1-phenyl-1-silacyclopentanes exclusively.4e Migrations of
the phenyl groups do not occur.4e (e) Matsumoto, K.; Miura, K.; Oshima,
K.; Utimoto, K. Tetrahedron Lett. 1991, 32, 6383.
(5) (a) The migratory aptitudes of various phenyl groups in reactions
of 13a -f with fluoride ion were initially studied by Aprahamian, S.
L., Ph.D. Dissertation, The Ohio State University, Columbus, Ohio,
1986, and have been reported in part in ref 3d. (b) Commercial TBAF
contains <5% H2O. The H2O leads to the silico-protolytic cleavage
reactions as in Scheme 2.
Reactions of (chloromethyl)silanes 13a -f with TBAF
in THF were then investigated at 0 °C and at -20 °C in
efforts to spread the migratory abilities of the varied
phenyl groups in the rearrangement-displacements
(Scheme 2). The yields of 18 and 21 (Scheme 2) in
(6) Brook, A. G.; Duff, J . M.; Anderson, D. G. J . Am. Chem. Soc.
1970, 92, 7567.
(7) (a) Smetankina, N. P.; Miryan, N. I. J . Gen. Chem. USSR 1967,
37, 1309. (b) Belyakova, Z. V.; Golubtsov, S. A. J . Gen. Chem. USSR
1961, 31, 2966. (c) Motsarev, G. V.; Rosenberg, V. R. J . Appl. Chem.
USSR 1964, 37, 395.
(8) (a) Silanes 14a ,b,d ,e were synthesized upon modification of the
method for 14c by Brook, A. G.; Duff, J . M.; Anderson, D. G. Can. J .
Chem. 1970, 48, 561. (b) Silanes 28b-e were obtained as described
by Gilman, H.; Dunn, G. E. J . Am. Chem. Soc. 1951, 73, 3404. Silane
28a has not been previously reported. (c) The syntheses of 29a ,b,d ,e
are extensions of that for 29c by Seyferth, D.; Burtlich, J . J . Am. Chem.
Soc. 1963, 85, 2667 and Seyferth, D.; Burtlich, J .; Dertouzos, H.;
Simmons, H. D. J . Organomet. Chem. 1967, 7, 405.
(10) (a) J ones, R. A. An Introduction to Gas-Liquid Chromatogra-
phy; Academic Press: New York, 1970; p 77. (b) Young, H. D. Statistical
Treatment of Experimental Data; McGraw-Hill: New York, 1962; p 2.
(c) The various analyses, experimental errors, standard deviations,
statistical details, and the varied attempted correlations of the
migratory aptitudes in reactions of 13a -f with F- are discussed in
depth in ref 5a.
(11) (a) Hammett, L. P. Physical Organic Chemistry, 2nd ed.;
McGraw-Hill: New York, 1970; Chapter 11, p 347. (b) Exner, O.
Advances in Linear Free Energy Relationships; Chapman, N. B.,
Shorter, J ., Eds.; Plenum Press: New York, 1972, Chapter 1; p 191.
(c) J affee, H. H. Chem. Rev. 1953, 53, 191.
(9) (a) (Bromomethyl)silane 30 was prepared from (bromomethyl)-
trichlorosilane9b,c and phenylmagnesium bromide (2 equiv) in Et2O (see
Suppporting Information). (b) Speier, J . L. J . Am. Chem. Soc. 1951,
73, 826. (c) Khimicheskaya Seriya, Invest. Akad. USSR. 1978, 10, 2366.
(12) Shorter, J . Correlation Analysis in Organic Chemistry; An
Introduction to Linear Free-Energy Relationships; Clarendon Press:
Oxford, 1973; p 105.

3564 J . Org. Chem., Vol. 67, No. 11, 2002
Allen et al.
Ta ble 1. Migr a tor y Ap titu d es of Su bstitu ted -P h en yl Gr ou p s (p-Z-P h /P h ) in Rea r r a n gem en t-Disp la cem en t Rea ction s of
TBAF w ith 13a -f in THF a t 25°, 0°, a n d -20 °C, Resp ectively
13, p-Z-Ph-
corrected (p-Z-Ph/Ph)a, 25 °C
corrected (p-Z-Ph/Ph)a, 0 °C
corrected (p-Z-Ph/Ph)a -20 °C
13a , p-CF3-Ph-
13b, p-Cl-Ph-
13c, Ph-
13d , p-CH3-Ph-
13e, p-CH3O-Ph-
13f, p-(CH3)2N-Ph-
2.72 ( 0.27
1.67 ( 0.17
1.00 ( 0.10
0.906 ( 0.091
0.58 ( 0.12
0.550 ( 0.095
3.00 ( 0.30
2.01 ( 0.20
3.20 ( 0.32
2.07 ( 0.20
1.00 ( 0.10
0.974 ( 0.097
0.906 ( 0.091
1.09 ( 0.19
1.00 ( 0.10
0.981 ( 0.098
0.974 ( 0.0970
1.13 ( 0.17
a
Mean values and the errors in the migratory aptitudes of the various substituted-phenyl groups.
F igu r e 1. Plots of the logarithms of the migratory aptitudes (F-Z-Ph/Ph) versus substituent values (σ or σ-zero) for reactions of
(halomethyl)silanes 13a -f, 14a -f, and 15a -f with TBAF or NaOCH3 in the solvent and at the temperature indicated: (a) 13a -
f, σ, TBAF/THF, 25 °C; (b) 13a -f, σ-zero, TBAF/THF, 25 °C; (c) 13a -f, σ, TBAF/THF, 0 °C; (d) 14a -f, σ, TBAF/THF, 23 °C; (e)
15a -f, σ, TBAF/THF, 23 °C; (f) 14a -f, σ, NaOCH3, dioxane, 23 °C.
reactions at 0 °C and at -20 °C are ∼100%. The
migratory aptitudes at 0 °C and -20 °C are listed in
Table 1. The study shows, however, that (1) as the
reaction temperatures are lowered, the spreads in the
migratory aptitudes are reduced rather than increased,
(2) the migratory abilities of phenyl groups containing
strong electron donors [13, Z-p ) N(CH3)2 and OCH3] are
increased rather than decreased, and (3) the increases in
the migratory aptitudes of phenyl groups substituted by
electron-withdrawing substituents (13, Z-p ) CF3 and Cl)
are small and probably insignificant statistically. Regres-
sion analyses of logarithms of the migratory aptitudes
of the phenyl groups versus σ constants result in positive
F values (0 °C, F ) 0.44, corr. coeff. ) 0.805; -20 °C, F )
0.45, corr. coeff. ) 0.8107) for the rearrangement-
displacements but the Hammett plots as in Figure 1c and
Supporting Information are curved, and the correlations
are deemed to be poor because of mechanism differences
rather than experimental errors.10c,11,12 Strong para
electron-withdrawing groups increase the migratory
aptitudes of phenyl groups in reactions of 13a -f with
fluoride ion at all temperatures studied.
The behaviors of (bromomethyl)silanes 14a -f and
(iodomethyl)silanes 15a -f with TBAF (2.3 equiv) in THF
were studied to determine if there are significant differ-
ences in the migratory aptitudes from that for (chlorom-
ethyl)silanes 13a -f. In reactions of 14a -f with TBAF
at 23 °C phenyl groups with electron-withdrawing para-
substituents (Z-p ) CF3 and Cl) again migrate signifi-
cantly faster (Table 2) than phenyl. When the para-

Rearrangement-Displacement Reactions
J . Org. Chem., Vol. 67, No. 11, 2002 3565
Ta ble 2. Migr a tor y Ap titu d es of Su bstitu ted -P h en yl Gr ou p s (p-Z-P h /P h ) in Rea r r a n gem en t-Disp la cem en t Rea ction s of
TBAF in THF w ith 14a -f a t 23, 0, a n d -20 °C, Resp ectively, a n d 15a -f a t 23 °C
14 or 15, p-Z-Ph-
corrected (p-Z-Ph/Ph),a 23 °C
corrected (p-Z-Ph/Ph),a 0 °C
corrected (p-Z-Ph/Ph),a -20 °C
14a , p-CF3-Ph-
14b, p-Cl-Ph-
14c, Ph-
14d , p-CH3-Ph-
14e, p-CH3O-Ph-
14f, p-(CH3)2N-Ph-
15a , p-CF3-Ph-
15b, p-Cl-Ph-
15c, Ph-
2.43 ( 0.24
1.79 ( 0.18
1.00 ( 0.10
0.967 ( 0.097
1.00 ( 0.10
1.30 ( 0.13
2.46 ( 0.25
1.65 ( 0.17
1.00 ( 0.10
0.96 ( 0.10
1.07 ( 0.10
1.43 ( 0.14
2.77 ( 0.28
1.92 ( 0.19
1.00 ( 0.10
0.96 ( 0.10
1.05 ( 0.11
1.34 ( 0.13
2.96 ( 0.30
1.96 ( 0.20
1.00 ( 0.10
0.97 ( 0.10
0.97 ( 0.10
1.36 ( 0.14
15d , p-CH3-Ph-
15e, p-CH3O-Ph-
15f, p-(CH3)2N-Ph-
a
Mean values and the errors in the migratory aptitudes of the various substituted-phenyl groups at the indicated temperatures.
substituents are electron-donating (Z-p ) CH3 and OCH3)
the migratory aptitudes of the substituted phenyl groups
are essentially the same as for phenyl. For 14f [Z-p )
N(CH3)2], however, the migratory aptitude of the p-
dimethylaminophenyl group is somewhat larger than for
the phenyl group. The Hammett plot in Figure 1d thus
does not give a satisfactory linear correlation.11,12 The
p-dimethylamino group does not behave simply as an
electron donor in the migrations in reactions of 14f with
fluoride ion.
possible 33 present to 14f. The migratory aptitude for
the “p-dimethylaminophenyl group” in the above experi-
ment is 1.37 and therefore similar to that for 14f in the
absence of the proton scavenger base, tributylamine.
Rearrangement-displacement of 33 by fluoride ion in the
above experiment is not likely.
The migratory aptitudes in reactions of 14f in dioxane
at 23 °C with TBAF (3 equiv) in the presence of sodium
methoxide (16 equiv) were determined. The migratory
aptitude for the p-dimethylaminophenyl group is 1.19
and similar to that (1.24) for 14f with TBAF in dioxane.
Since TBAF effects complete rearrangement-displace-
ment of 14f in less than 3 min whereas ∼36 h are
necessary for sodium methoxide, 14f in the presence of
the fluoride and methoxide reacts essentially totally with
fluoride ion. The sodium methoxide ensures that 14f is
not converted to 33 which then undergoes rearrange-
ment-displacements as in Scheme 2 or related processes.
Reactions of 14f were also effected with CsF in THF.
Although highly insoluble, CsF (9.5 equiv) reacts ef-
fectively with 14f in THF at 23 °C and results in a
migratory aptitude of the p-dimethylaminophenyl group
of 1.63.
The effects of solvents and experimental differences on
rearrangement-displacements of 14f by fluoride ion at
23 °C were then studied. The migratory aptitude of the
p-dimethylaminophenyl group in reactions of 14f with
TBAF in dioxane (1.24) is similar to that in THF (1.30,
Table 2). Further, with 14f and TBAF in 96% hexane-
4% THF, the migratory aptitude of the p-dimethylami-
nophenyl group is 1.66. There is thus no large effect of
solvent on the migratory aptitude of the p-dimethylami-
nophenyl group, but the group migrates faster than
phenyl, p-tolyl, or p-anisyl under identical conditions.
The effects of concentration of fluoride ion on the
migratory aptitudes in rearrangement-displacements of
14b and of 14f in THF at 23 °C were also investigated.
The migratory aptitudes from these experiments are
summarized in Supporting Information. For 14b, in-
creasing the fluoride ion concentration from 0.095 to 2.44
M causes little change in the migratory aptitude of the
p-chlorophenyl group. Raising the TBAF from 0.004 to
2.44 molar in reactions of 14f, however, results in an
increase in the migratory aptitude of the p-dimethylami-
nophenyl group from 1.23 to 1.51. That the migratory
ability of the p-dimethylaminophenyl group increases
with TBAF equivalents raises the possibility that the
fluoride reagent contains acid (HF) which converts 14f
extensively to its ammonium salt 33. Thus in rearrange-
ment-displacements of 33 by fluoride ion containing acid
The rearrangement-displacement behaviors of (bro-
momethyl)silanes 14a -f with TBAF (2.3 equiv) in THF
were then investigated at 0 °C and -20 °C (Table 2).
Lowering the reaction temperatures does not affect the
migratory aptitudes of the phenyl groups greatly. Plots
(see Supporting Information) of the logarithms of the
migratory aptitudes (p-Z-Ph/Ph) at 0 °C and at -20 °C
versus σ-zero values are not satisfactorily linear and are
similar to that in Figure 1d for reactions at 23 °C. The
acceleration of the migratory aptitude by the p-(CH3)2N
group continued to be of interest.
The rearrangement-displacement reactions of (iodom-
ethyl)silanes 15a -f with fluoride ion (2.3 equiv) were also
studied (Scheme 2) in THF at 23 °C. The TBAF reagent
converts 15a -f (Scheme 2) quantitatively to para-
substituted-toluenes (18) and toluene (21). The rear-
rangement-displacement results (Table 2) show trends
essentially identical to those for 13a -f and 14a -f. The
plot (Figure 1e) of the logarithms of the migratory
aptitudes in Table 2 versus appropriate σ-zero substitu-
ent values is curved. The overall behaviors of (halom-
ethyl)silanes 13a -f, 14a -f, and 15a -f with fluoride in
THF are thus similar. The questions of concern are (1)
why are the attempted free energy correlations nonlinear,
(2) what are the mechanisms of rearrangement-displace-
ments of 13a -f, 14a -f, and 15a -f by fluoride ion, and
the p-dimethylammoniumphenyl group will be relatively
highly electron-deficient and be expected to migrate with
its electrons more readily than phenyl. To evaluate that
rearrangement-displacements might have involved 33,
reactions of 14f with TBAF (3 equiv) were conducted in
the presence of excess tributylamine (3.5 equiv). The
purpose of the tributylamine was to deprotonate the

3566 J . Org. Chem., Vol. 67, No. 11, 2002
Allen et al.
Sch em e 5
(3) why does the p-dimethylaminophenyl group migrate
as rapidly as found.
The Hammett equation assumes that the reaction
constant, rho (F), is independent of sigma (σ) or sigma-
zero (σ°) substituent constants.11,12 Curved Hammett
plots are theorized to arise because the requirements for
breaking bonds in a series of intermediates as in 16 (Nuc
) F, Scheme 2) are not constant and F is σ constant
dependent (F ) Fo + τσ in which Fo is the reaction constant
independent of the substituent and τ is dependent on the
structure of the reaction center and reflects the difference
between transition state and ground-state effects).13 On
the basis that the F values for the observed relative
migratory aptitudes in reactions of 13a -f with fluoride
ion are σ constant dependent, second-order least-squares
regressions result in calculated values for F for substi-
tuted phenyl groups at 0 °C (corr. coeff. ) 0.971) and -20
°C (corr. coeff. ) 0.976) as follows: p-CF3-C6H4, 0.85, 0.92;
p-Cl-C6H4, 0.65, 0.70; C6H5, 0.47, 0.52; p-CH3-C6H4, 0.37,
0.41; p-CH3O-C6H4, 0.27, 0.31; p-(CH3)2N-C6H4, 0.03, 0.04.
The results are (1) the free energy correlation lines are
still curved, (2) the calculated F values are all greater
than zero and in agreement with expectations that
transition states such as from 16 (Nuc ) F) are always
negative (silicanionic), and (3) as the σ constants get
larger, the calculated F values and the electronic de-
mands during rearrangement decrease.
inversion14 as in Scheme 5 or to give substitution
products which are partly or totally racemic.14 Displace-
ments with inversion on silicon are usually presumed to
involve transition states from distorted trigonal bipyra-
midal intermediates 40 involving backside attack in
which the entering (Nuc) and leaving groups (LG) are
both apical.14 In substitution processes resulting in
retention in stereochemistry it has been theorized that
(1) the incoming nucleophile enters equatorially as in 41,
the leaving group is expelled axially, and the nucleophile
takes the position initially occupied by the leaving group,
(2) the entering nucleophile attacks from an axial position
as in 42 with equatorial displacement of the leaving
group and the nucleophile taking its place, or (3) reaction
occurs as in 43-45 (Figure 2) in which the incoming
nucleophile is axial and the leaving group is equatorial,
pseudorotation occurs in which the nucleophile becomes
equatorial and the group to depart is axial, and then the
leaving group is expelled.14 Partial or total racemization
can occur upon extension of the pseudorotational pro-
cesses.14 Further possibilities include attack of nucleo-
philes on 40-42 to give dinegatively charged hexacoor-
The electrical effects on the migratory aptitudes and
the satisfactory and the deviant free energy correlations
for rearrangement-displacements of 13-15 by F- at
various temperatures are consistent, however, with the
presumption that there are differences in the transition
states of the pentacoordinate silicanionic processes as in
dinate intermediates (or transition states) such as 46-
48 and/or their isomers14 that lose their leaving groups
and a nucleophile to give displacement products with
retention (39), inversion (37), or partial or total racem-
ization.
34-36. In 34-36 fluorine and the migrating phenyl
group are apical, displacement occurs on silicon with
inversion, and halogen is expelled by backside attack of
the migrating phenyl group on carbon of the equatorial
halomethyl substituent. As the lengths of the carbon-
halogen bonds in 34-36 increase, the transition states
become more neutral as in 35, and the electronic de-
mands from the phenyl substituents during rearrang-
ment are lowered. Further, when there is greater het-
erolytic breaking of a C-X bond as in 36 in which Z is
highly electron donating (Z ) N(CH3)2 or OCH3), the
greater is the electronic compensation by participation
of the migrating phenyl group.
In the rearrangement-displacement reactions of (ha-
lomethyl)silanes with F- as in Scheme 2 or if there is
attack on silicon as in 40-48 et al. in such processes,
backside attack of the migrating group on carbon (C-1)
from which the leaving group is expelled is expected.15
What the stereochemistries will be, however, at the silyl
centers in the rearrangement-displacement acts in 13-
15 are not obvious.14 Of further concern are the differ-
Although the behaviors of 13-15 with F- can be
rationalized as in 34-36, the linear and the unsatisfac-
tory Hammett correlations obtained might have origins
quite different than as proposed above. The stereochem-
istries of nucleophilic displacements on silicon can be
complicated, much more so than on carbon. Of relevance
is that chiral tertiary silanes undergo bimolecular dis-
placements by nucleophiles with complete retention or
(14) The stereochemistries of displacement reactions of silanes by
nucleophiles and formation, fluxional behavior, and pseudorotation of
silylanionic complexes have been reviewed in (a) The Chemistry of
Organosilicon Compounds; Rappoport, Z., Apeloig, Y. J ., Eds.; Wiley
& Sons: Chichester, 1998 by (1) Bassindale, A. R.; Glynn, S. J .; Taylor,
P. G., Chapter 9, p 495 and (2) Kost, D.; Kalikhman, I., Chapter 23, p
1339, (b) Chuit, C.; Corriu, J . P.; Reye, C.; Young, J . C. Chem. Rev.
1993, 93, 1371, (c) Holmes, R. R. Chem. Rev. 1990, 90, 17, (d) The
Chemistry of Organosilicon Compounds; Patai, S., Rappoport, Z. J .,
Eds.; Wiley & Sons: Chichester, 1989 by (1) Corey, J . Y., Chapter 1,
p 1, (2) Corriu, R. J . P.; Guerin, C.; Moreau, J . J . E., Chapter 3, p 305,
(3) Bassindale, A. R.; Taylor, P. G., Chapter 13, p 839, and (4) Corriu,
R. J . P.; Young, J . C., Chapter 20, p 1289, and (e) Corriu, R. J . P.;
Guerin, C. J . Organomet. Chem. 1980, 198, 231.
(13) (a) Swain, C. G.; Langsdorf, W. P. J . Am. Chem. Soc. 1951, 73,
2813. (b) Westaway, K. C.; Waszczylo, Z. Can. J . Chem. 1982, 60, 2500.

Rearrangement-Displacement Reactions
J . Org. Chem., Vol. 67, No. 11, 2002 3567
F igu r e 2. Pseudorotation in trigonal bipyramidal silicon intermediates 43 and 45. In 43 groups R1, R2, and LG are equatorial,
and R3 and Nuc are axial. In 45, R1, R3, and Nuc are equatorial, and R2 and LG are axial. Group R1 is the pivot in the
pseudorotational processes.
Sch em e 6
of 1-naphthyl migration, is obtained only in small quanti-
ties from (+)-23 and does not chromatograph well, its
optical properties could not be determined accurately. In
reactions with TBAF or CsF in THF in which (+)-23
([R]2D5 + 8.29°, cyclohexane) is in excess, the recovered
(bromomethyl)silane (+)-23 is not changed stereochemi-
cally. Silane (+)-23 is not racemized prior to or during
its rearrangement-displacement reactions with fluoride
ion.
ences in the reaction mechanisms when the migratory
aptitudes and the free energy correlations change as has
now been found. In efforts to clarify some of the above
questions, the stereochemical behavior of (+)-23 with
fluoride ion has been investigated.
B. Stu d y of th e Ster eoch em istr y of Rea ction s of
(+)-23 w ith F lu or id e Ion . Silane (+)-23 ([R]2D3 + 8.29°,
cyclohexane),6 prepared as in Scheme 6,16a,b reacts quickly
(2-3 min) in THF with TBAF and with CsF (heteroge-
neous, 9 h) at 20-25 °C as in eq 7 to give, after rapid
workup and chromatography of the reaction products on
silica gel, optically inactive benzylfluorosilane 51 [R]D25
) 0.00°, cyclohexane; 28%)] and impure fluoro-(1-naph-
thylmethyl)silane 52. As a check of its lack of optical
activity, crude 51, as obtained from (+)-23 and CsF in
THF at 23 °C with minimum handling, was treated with
phenyllithium (eq 8).17 Optically inactive benzylsilane 53
([R]2D5 ) 0.00°, cyclohexane) was obtained.17 To verify its
structure (+,-)-benzylfluorosilane 51 was synthesized (eq
9) from (+,-)-benzylmethoxysilane 5418 and BF3 etherate.
From experiments in which (+)-23 reacts with TBAF (2
equiv) at 25 °C in THF and the 51 and 52 formed are
protolytically cleaved by TBAF/H2O to 21 and 1-meth-
ylnaphthalene (1-CH3-Np), respectively, the migratory
aptitudes for the phenyl and the 1-naphthyl groups as
in eq 7 are ∼10.4:1.19 Since fluorosilane 52, the product
In a further attempt to obtain 51 with optical activity,
(+)-23 ([R]2D3 + 8.29°, cyclohexane) in THF was treated
with TBAF (1 equiv) in THF for 10 s (or less) at room
temperature. The mixture was immediately diluted,
rapidly cooled by addition of cold pentane (-78 °C), and
then filtered quickly to remove the TBABr and the TBAF
precipitated. Rapid concentration of the cold reaction
solution at reduced pressure followed by rapid chroma-
tography on silica gel gave a mixture of (+)-23 and 51
with an observed rotation of R2D5 ) +0.100° (cyclohex-
ane) as the major product. The product was shown by
1H NMR to be a 1:4 mixture of 23 and 51, and therefore
its optical activity is due to initial (+)-23.
Experiments were then executed with TBAF and
excess (+)-23 as in eq 7 in which the times for rearrange-
ment-displacements of the (+)-23, exposure of the 51
and 52 formed to F-, and handling of the reaction
mixtures were greatly minimized The optical proper-
ties of the 51 formed were then estimated as quickly
as practical without the product being separated from
the reaction solutions. Reactions were conducted in 5-10
min in THF at 23 °C in which the equivalents of (+)-23
([R]2D3 +8.29°, cyclohexane) to TBAF ranged from 1.0 to
0.25-0.98 [(+)-23 was always in excess], the solutions
were then rapidly filtered and quickly diluted to volume,
and their optical rotations were immediately determined
(15) Larson, G. L.; Klesse, R.; Cartledge, F. K. Organometallics 1987,
6, 2250 report that thermolysis of (S,S)-(1-chloroethyl)methyl(1-
naphthyl)phenylsilane at 280 °C results in rearrangements in which
the phenyl and the 1-naphthyl groups migrate from silicon by backside
processes (95%) resulting in inversion about C-1 of the 1-chloroethyl
group along with migrations of chlorine to silicon to yield chlorosilanes
in which the stereochemistry about silicon is racemic. The mechanism
by which loss of stereochemistry about silicon occurs has not been
established.
(16) (a) Sommer, L. H.; Fyre, C. L.; Parker, G. A.; Michael, K. W. J .
Am. Chem. Soc. 1964, 86, 3271. (b) Sommer, L. H.; Ulland, L. A.;
Parker, G. A. J . Am. Chem. Soc. 1972, 94, 3469.
(17) (a) Chiral tert-fluorosilanes undergo bimolecular displacement
by aryllithium reagents to give substitution products with high-order
retention in stereochemistry.17b-d (b) Sommer, L. H.; Korte, K. D.;
Rodewald, P. G. J . Am. Chem. Soc. 1967, 89, 862. (c) Sommer, L. H.;
Rodewald, P. G. J . Am. Chem. Soc. 1967, 89, 5802. (d) Corriu, R. J . P.;
Royo, G. Bull. Soc. Chem. Fr. 1972, 1497.
(18) (+,-)-Methoxysilane 54 was prepared by rearrangement-
displacement reaction of (+,-)-23 with sodium methoxide in THF.
(19) Reaction of (+,-)-51 with TBAF (1 equiv) gives 21 quantita-
tively and presumably difluoromethyl-1-naphthylsilane. With ad-
ditional TBAF conversion of the difluoromethyl-1-naphthylsilane to
naphthalene occurs. Similarly, 52 is converted by excess TBAF to
1-methylnaphthalene and to benzene.

3568 J . Org. Chem., Vol. 67, No. 11, 2002
Allen et al.
without further workup. As detailed in Supporting
Information, what is learned from these experiments is
that the optical rotations of the reaction mixtures before
any workup correspond quite well to the (+)-23 expected
to be present, and the contributions of 51 to the optical
activities are nonexistent or at best small. Further, rapid
workup of the reaction mixture from (+)-23 and TBAF
in a 1.00:0.25 mole ratio reveals that the 51 in the
product is optically inactive.
59 upon exposure to TBAF at room temperature (see
Experimental Section).21 The questions thus still remain
as to whether the (+,-)-51 obtained from (+)-23 and F-
results from (1) racemization of optically active 51 via
pentacoordinate intermediate 5721e (or/and its hexacoor-
dinate derivatives), (2) rearrangement-displacement of
pentacoordinate silylanionic intermediates such as 60 in
which there has been racemizing pseudorotation,21e or/
and (3) formation and decomposition of optically inactive
hexacoordinate silyldianionic intermediates such as 61.
The stereochemical behavior of (+)-23 or other chiral
(halomethyl)silanes, and their products with F- at very
low temperatures, possibly shorter reaction times, and
using better rapid techniques, will have to be studied to
answer the above questions. In efforts to clarify the
mechanisms of rearrangement-displacement reactions
of (halomethyl)silanes with other nucleophiles,2d,f the
behaviors of 14 and (+)-23 with alkoxides in aprotic
environments have been investigated.
From the above experiments with (+)-23 and F- it
cannot be concluded whether the optically inactive 51 is
formed during or/and after rearrangement-displace-
ments. Fluorosilanes such as 55 are known to react with
fluoride donors (metal fluorides, ammonium fluoride,
and tetraalkylammonium fluorides) in protic, aprotic,
crown ether, or (best) cryptand environments to give
the corresponding difluorosilicate ions 56.14b,20 Difluoro-
- 20a,d,f,h
- 20b
silicate ions such as Ph3SiF2
,
1-NpPh2SiF2 ,
- 20h
- 20c,e
Ph2(CH3)SiF2
,
and (CH3)3SiF2
have trigonal py-
ramidal structures as in 56 in which the fluorines, the
C. Migr a tor y Ap titu d es in Rea r r a n gem en t-Dis-
p la cem en t Rea ction s of Sila n es 14 w ith Sod iu m
Meth oxid e. Study has been made of the migratory
aptitudes in rearrangement-displacements of 14a -f
with sodium methoxide (Scheme 2, Nuc- ) CH3O-, 10-
12 equiv) in dioxane and in THF at 23 °C. Sodium
methoxide reacts slowly with 14 by attack on silicon
(Scheme 2) to give methoxysilanes 17b and 20b, presum-
ably upon formation and collapse of pentacoordinate
silylanionic intermediates 16b or (less likely) related
hexacoordinate anionic intermediates. Rearrangement-
displacement products 17b (Z-p ) Cl and CH3) and 20b
(Z-p ) Cl, H, and CH3) were synthesized from dimethox-
ysilanes 6222a,b and 63, respectively, as in Schemes 7 and
8 (see Supporting Information).
most electronegative substituents, are in the axial posi-
tions. Silicanions such as 56 will be optically inactive.20
In the present experiments, if reactions of (+)-23 with
F- were to give optically active 51 and then addition of
F
- to the 51 to form difluorosilicate ion 57 occurs rapidly
and reversibly, racemic 51 will be the product. In support
of such a possibility for racemization of (+)-23 by F-, (-)-
fluoromethyl-1-naphthylphenylsilane (58, a close ana-
logue of (+)-23)20 in THF has been presently found to
rapidly lose its optical activity completely possibly via
Sch em e 7
(20) (a) Damrauer, R.; Danahey, S. E. Organometallics 1986, 5, 1490.
(b) Harland, J . J .; Payne, J . S.; Day, R. O.; Holmes, R. R. Inorg. Chem.
1987, 26, 760. (c) Scherbaum, F.; Huber, B.; Muller, G.; Schmidbaur,
H. Angew. Chem., Int. Ed. Engl. 1988, 27, 1542. (d) Damrauer, R.;
O’Connell, B.; Danahey, S. E.; Simon, R. Organometallics 1989, 8, 1167.
(e) Dixon, D. A.; Farnham, W. B.; Heilemann, W.; Mewa, R.; Noble-
meyer, M. Heteroat. Chem. 1993, 4, 287. (f) Pilcher, A. S.; Ammon, H.
L.; DeShong, P. J . J . Am. Chem. Soc. 1995, 117, 5166. (g) Albanese,
D.; Landini, D.; Penso, M. Tetrahedron Lett. 1995, 36, 8865. (h)
Yamaguchi, S.; Akiyama, S.; Tamoa, K. Organometallics 1999, 18,
2851.
Sch em e 8
(21) (a) (-)-Fluorosilane 58 has been prepared from (-)-[(-)-
menthoxy]methyl-1-naphthylphenylsilane and BF3 in Et2O by Sommer,
L. H.; Frye, C. L.; Parker, G. A.; Michael, K. W. J . Am. Chem. Soc.
1964, 86, 3271. (b) (-)Silane 58 has also been obtained21c by treating
(-)-bromo(methyl)-R-naphthylphenylsilane in CHCl3 (11.5 mL) with
solid cyclohexylammonium fluoride at room temperature as follows.
Upon immediately stirring the mixture for a few seconds the fluoride
salt dissolved. The reaction system was immediately quenched by rapid
addition of pentane (200 mL) cooled to ∼-78 °C. The (-)-58 isolated
was obtained in 96.2% yield, 92% optically pure with 96% net inversion
of configuration.21c (c) Sommer, L. H.; Parker, G. A.; Lloyd, N. C.; Frye,
C. L.; Michael, K. W. J . Am. Chem. Soc. 1967, 89, 857. (d) The above
techniques for synthesis of (-)-5821b,c are essentially identical to those
presently used with (+)-23 and TBAF for 10 s (or less). (e) The rate
constants and the probable reaction mechanisms for racemization of
dilute solutions of 58 (0.047 M) by cyclohexylammonium fluoride (5 ×
10-6 to 1 × 10-4 M) at 24.4 °C in CCl4 containing alcohols in various
(small) concentrations have been studied by Sommer, L. H.; Bauman,
D. L. J . Am. Chem. Soc. 1969, 91, 7045.
Gas chromatographic analyses of reaction mixtures
from 14f and sodium methoxide in dioxane at 23 °C
reveal that the initial rearrangement-displacement prod-
ucts, 17b [Z-p ) (CH3)2N] and 20b [Z-p ) (CH3)2N], are
converted in part to p-dimethylaminotoluene [18, Z-p )
(22) (a) Hiratsuka, K. J pn. Pat. 5330, Sept. 15, 1951; Chem. Abst.
1953, 47, 9345. (b) Tacke, R.; Strecker, M.; Sheldrick, W. S.; Heeg, E.;
Berndt, B.; Knapstein, K. M. Z. Naturforsch. Teil B 1979, 34B, 1279.

Rearrangement-Displacement Reactions
J . Org. Chem., Vol. 67, No. 11, 2002 3569
Ta ble 3. Migr a tor y Ap titu d es of Su bstitu ted -P h en yl
Gr ou p s (p-Z-P h /P h ) in Rea r r a n gem en t-Disp la cem en ts of
14a -f w ith Sod iu m Meth oxid e in Dioxa n e a t 23 °C
Sch em e 10
corrected
corrected
14, p-Z-Ph-
(p-Z-Ph/Ph)a
14, p-Z-Ph-
(p-Z-Ph/Ph)a
14a , p-CF3-Ph- 2.53 ( 0.25 14d , p-CH3-Ph-
0.79 ( 0.08
0.84 ( 0.08
1.00 ( 0.10 14f, p-(CH3)2N-Ph- 0.68 (0.69)b ( 0.07
14b, p-Cl-Ph-
14c, Ph-
1.64 ( 0.16 14e, p-CH3O-Ph-
a
Mean values of the migratory aptitudes of the various sub-
and 1-naphthyl migrations, respectively, were identified
from their analyses and spectra, and/or upon comparison
with authentic racemic samples (see Experimental Sec-
tion).24
b
stituted-phenyl groups. The migratory aptitude from reaction of
14f with sodium methoxide in THF at 23 °C.
Sch em e 9
The stereochemistry of phenyl migration in rearrange-
ment-displacement of (+)-23 to yield (+)-64 was deter-
mined from results summarized in Scheme 9. First,
methoxysilane (+)-64 (Scheme 9) is converted by phe-
nyllithium in Et2O to the displacement product, (-)-
benzylphenylsilane 66 ([R]2D3 -5.25°, cyclohexane). Since
all previous chiral alkoxysilanes including 38 (X ) OR,
eq 10) react with aryllithium and alkyllithium reagents
in ether solvents to give displacement products 67 with
retention of configuration,16a,17c (-)-66 is concluded to be
formed (Scheme 9) from (+)-64 and phenyllithium with
retention. Correlation of the stereochemistry of (-)-66
with (+)-23 was then accomplished upon reaction of (+)-
23 with phenylmagnesium bromide (Scheme 9) in the
presence of cuprous iodide to give (+)-66, [R]2D3 + 6.15°
(cyclohexane). Since no silicon-carbon bonds are broken
in the coupling reaction of (+)-23 with phenylmagnesium
bromide and cuprous iodide, (+)-66 is formed with
retention of configuration. Therefore, for conversion of
(+)-49 to (-)-66 as in Schemes 6 and 9, reaction of (+)-
23 with sodium methoxide to give (+)-64 must occur with
>93% inversion on silicon.
(CH3)2N] and toluene (21). Fluoride ion, however, is
excellent for cleaving methoxysilanes 17b and 20b.
Excess TBAF (2.3 equiv) was thus added to each reaction
mixture from 14a -f and sodium methoxide after TLC
revealed total depletion of the initial halides by the
sodium methoxide. The reaction mixtures were then
worked up for toluenes 18 and 21 as previously described.
The experimental results are highly reproducible and the
migratory aptitudes determined are summarized in Table
3. This study shows that (1) substituent effects on the
migratory aptitudes are small, (2) para electron-with-
drawing substituents (Z-p ) CF3 and Cl) accelerate
rearrangements of phenyl groups, (3) p-(CH3)2N, p-CH3O,
and p-CH3 substituents behave as traditional electron-
donors with respect to migratory aptitudes, and (4) the
migratory ability of the p-dimethylaminophenyl group in
reactions of 14f with methoxide ion is approximately half
that with fluoride ion. Of particular note is that the
Hammett plot (Figure 1f) of logarithms of the migratory
aptitudes and σ-zero substituent values for rearrange-
ment-displacement reactions of 14a -f with methoxide
ion has a F value of 0.72 with a correlation coefficient of
0.97, is more linear than for such reactions of 14a -f with
fluoride ion, and is clearly satisfactory.12 The behaviors
of 14a -f with methoxide ion appear simpler than with
fluoride ion.
D. Th e Ster eoch em istr ies of Rea ction s of (+)-23
w ith Alk oxid e Ion s. The stereochemistries of reactions
of (+)-23 with alkoxide reagents have been studied as
follows. Bromomethylsilane (+)-23 ([R]2D3 +8.29°, cyclo-
hexane) reacts with sodium methoxide (1.0 equiv) in
dioxane by rearrangement-displacements (Scheme 9) at
25 °C to yield (+)-benzylmethoxysilane 64 ([R]2D3 +39.5°,
cyclohexane) and (+)-methoxy(1-naphthylmethyl)silane
65 in ∼9.5:1 ratio.23 The behavior of (+)-23 with sodium
methoxide/dioxane at 0 °C to give (+)-64 ([R]2D3 + 38.8°,
cyclohexane) and (+)-65 is essentially identical to that
at 25 °C. Silanes (+)-64 and (+)-65, products of phenyl
The stereochemical conclusion for conversion of (+)-
23 to (-)-66 as in Scheme 9 is also consistent with
observations (Scheme 10) that (1) chlorination (Cl2) of (+)-
49 ([R]2D3 +33.2°, cyclohexane, Scheme 6) yields (+)-
chlorosilane 68 ([R]2D3 -6.22°, cyclohexane) with reten-
tion and benzyllithium or benzylsodium then converts the
(-)-68 to (-)-66 ([R]2D3 -6.68°, cyclohexane) by inver-
sion.17c The overall stereochemistries of conversions of
(+)-49 to (-)-66 in Schemes 6 and 9 and in Scheme 10
are thus identical and involve single inversions. Further,
there is no significant difference in the stereochemistry
of reactions of (+)-23 with sodium methoxide at 25 °C
and 0 °C and therefore, under the conditions studied,
there is no evidence for pseudorotation during formation
of (+)-64 (Scheme 9). The exact stereospecificity in
reaction of (+)-23 with sodium methoxide resulting in
(23) The phenyl/1-naphthyl migratory aptitudes were determined
by decomposing the 64 and 65 with excess TBAF/H2O and determining
by GLC the 21 and 1-methylnaphthalene formed.
(24) (a) Authentic methoxysilane (+,-)-64 was prepared (see Ex-
perimental Section) by reaction of trimethoxymethylsilane and 1-naph-
thylmagnesium bromide and then displacement of the resulting
dimethoxymethyl-1-naphthylsilane with benzylmagnesium chloride. (b)
Methoxysilane (+,-)-65 was synthesized (see Experimental Section)
by coupling dimethoxymethylphenylsilane with 1-naphthylmethyl-
magnesium chloride.

3570 J . Org. Chem., Vol. 67, No. 11, 2002
Allen et al.
Sch em e 11
possibly as in 71 (and/or 72) and 73 or otherwise. In
trigonal bipyramidal processes 71 can be favored over 73
because the constraints during formation or (and) rear-
rangement-displacements will be less when the smaller,
more mobile phenyl group is in an apical position and
the relatively bulky 1-naphthyl group is basal. Of par-
ticular interest is that the stereochemistries of rear-
rangement-displacements of (+)-23 with alkoxides as in
71 are also consistent with behavior expected for pyra-
midal transition states 74 and 75 in reactions of 14a -f
with sodium methoxide in that electron-withdrawing
substituents increase the migratory aptitudes of phenyl
groups and the F value in the linear free energy correla-
tion as in Figure 1f is small and positive. It is presently
clear that the mechanistic details of rearrangement-
displacements of (halomethyl)silanes by alkoxides are
considerably simpler and better understood than with
fluorides.
migration of the 1-naphthyl group was not determined
because (+)-65 is formed in low yield, and the product
could not be purified completely. It is clear, however, from
the sign of its rotation that (+)-65 (Scheme 9) is formed
from (+)-23 with overall inversion.
Rearrangement-displacements (Scheme 11) of (+)-23
[[R]2D3 -8.29°, cyclohexane]] also occur with sodium
ethoxide and with sodium 2-propoxide in dioxane at 23
°C. (+)-Benzylethoxysilane 69 ([R]2D3 + 39.4°, cyclohex-
ane) and (+)-benzyl-2-propoxysilane 70 ([R]2D3 +28.1°,
cyclohexane), respectively, are formed by phenyl migra-
tions. 1-Naphthyl migrations in these experiments are
very small. The gross structures of (+)-69 and (+)-70 are
assigned upon direct comparison with racemic 69 and 70,
respectively, prepared by reactions of (+,-)-64 with
ethanol and 2-propanol at 80 °C in toluene containing
potassium hydroxide. Displacements of the (+)-69 and
the (+)-70 with phenyllithium (Scheme 11) in Et2O then
occur with retention16a,17c to give (-)-66 of [R]2D3 -5.50°
and -5.57°, respectively, in cyclohexane. Rearrange-
ment-displacements of (+)-23 by sodium ethoxide and
sodium 2-propoxide to give (+)-69 and (+)-70, respec-
tively, are thus concluded to occur with (at least) 95%
inversion at silicon, and pseudorotation is insignificant
in these reactions.
Studies of synthesis and nucleophilic rearrangement-
displacements of 2-halo-1-methyl-1-phenylsilacycloal-
kanes of fixed stereochemistries have been initiated.
Su m m a r y
In reactions of 13 (X ) Cl) and F- in THF at 25 °C,
electron-withdrawing substituents increase the migratory
aptitudes of the phenyl groups and correlations of
logarithms of the migratory aptitudes with σ and with
σ-zero substituent values are linear. Such correlations
for F- with 13 (X ) Cl) at lower temperatures and 14 (X
) Br) and 15 (X ) I) at various temperatures, however,
are unsatisfactory. Electron-donor groups have little
effect or even accelerate aryl migrations in these latter
systems. Rearrangement-displacements of (+)-23 with
The inversions in the rearrangement-displacements
of (+)-23 by alkoxides to give (+)-64, (+)-69, and (+)-70
are understandable on the basis of nucleophilic attack
on silicon from a direction opposite the phenyl group via
pyramidal (pentacoordinate) intermediates and/or transi-
tion states as pictured in 71. Expulsion of bromide ion
with migration of the phenyl group to C-1 therefore
F
- yield optically inactive 51; the migratory aptitudes of
the phenyl group are much greater (∼10.5:1) than for
1-naphthyl. For 14 (X ) Br) and sodium methoxide in
dioxane at 0 °C, electron-withdrawing substituents ac-
celerate migration of the varied phenyl groups and the
migratory aptitudes correlate well. Further, reactions of
(+)-23 with sodium methoxide, sodium ethoxide, and
sodium 2-propoxide in dioxane involving phenyl migra-
tions yield (+)-64, (+)-69, and (+)-70, respectively, with
>93-95% inversion about silicon. 1-Naphthyl migrations
in rearrangement-displacements of (+)-23 with sodium
methoxide to give (+)-65 also occur with inversion. The
migratory aptitudes of the phenyl and the 1-naphthyl
groups in reactions of (+)-23 and sodium methoxide are
∼9:1. Rearrangement-displacements in distorted trigo-
nal bipyramidal (pentacoordinate) silicanionic intermedi-
ates such as 71 (and/or closely related transition states)
in which the entering nucleophile is apical to silicon and
backside to the migrating aryl group in the remaining
apical position will give the inversions found for (+)-23
with alkoxides. Pseudorotation in reactions of (+)-23 with
alkoxides is not evident. In rearrangement-displace-
ments of 14 (X ) Br) by sodium methoxide, phenyl groups
results in inversion of the configuration about silicon and
corresponds to traditional Walden inversions in bimo-
lecular rearrangement-displacements reactions of varied
carbon compounds. Though probably less likely to occur,
hexacoordinate processes such as in 72 will also result
in inversion about silicon.
Of note is that phenyl migrates much more readily
(∼10.5:1) than 1-naphthyl in reactions of (+)-23 with
alkoxides. This fact implies that there are important
steric and conformational effects in formation and de-
composition in pentacoordinate silylanionic processes

Rearrangement-Displacement Reactions
J . Org. Chem., Vol. 67, No. 11, 2002 3571
Reactions of 26 as in Procedure A with p-chlorophenyl-
lithium and p-methoxyphenyllithium were used for prepara-
tion (see Supporting Information) of chloromethyl(p-chlorophe-
nyl)diphenylsilane (13b, 54%) and chloromethyl(p-methoxy-
phenyl)diphenylsilane (13e, 30%), respectively.
which are relatively electron-deficient presumably occupy
apical positions preferentially and migrate nucleophili-
cally with displacement of Br-. Further, the facts that
the migratory aptitudes of the phenyl group are much
larger than for 1-naphthyl in reactions of (+)-23 with F-
and CH3O- indicate that primarily because of steric
effects in the rearrangement-displacement acts the
phenyl group is preferentially apical and attack on C-1
is less hindered than for such behavior of the 1-naphthyl
group.
(Ch lor om eth yl)[4-d im eth yla m in o)p h en yl]d ip h en ylsi-
la n e (13f). P r oced u r e B. To a suspension of freshly cut
lithium chips (0.23 g, 33 mmol) in Et2O (5 mL) was added
bromo(4-dimethylamino)benzene (0.30 g, 15 mmol) in Et2O (20
mL) at a rate (∼30 min) to cause reflux. The reaction mixture
was refluxed 2 h and then added to a stirred solution of 26
(3.5 g, 13 mmol) in Et2O (10 mL) at room temperature. The
mixture was refluxed until the Gilman test25a for organo-
lithium reagents was negative (∼1 h). After addition of H2O,
the ethereal solution was dried, concentrated, and cooled. The
slightly yellow solid which separated was recrystallized from
methylene chloride at -78 °C and then from hexane to give
Exp er im en ta l Section
Gen er a l In for m a tion . Reactions were conducted in oven-
dried glassware under dry argon. Migratory aptitude experi-
ments were conducted in sealed sample vials. Gas chromato-
graphic yields were determined using internal standards and
peak areas were corrected for response factors of the flame
ionization detector. The GC capillary column consisted of a
15 m × 0.53 mm bonded FSOT and a polyphenylmethylsilox-
ane 1.2 µm stationary phase. 1H NMR spectra (250 MHz) were
obtained in DCCl3. Proton NMR peaks are reported in parts
per million using HCCl3 resonance at 7.26 ppm as the
standard. Melting points were obtained on a capillary melting
point unit and are uncorrected. MS values are based on 35Cl,
79Br, and 29Si. Optical rotations were determined in a 1 dm
cell using Na/cont light (589 nm) at 23 °C. Carbon and
hydrogen combustion analyses were performed by Atlantic
Microlab, Inc., Norcross, GA.
Ch lor o(ch lor om eth yl)d ip h en ylsila n e (26) a n d (Ch lo-
r om eth yl)tr ip h en ylsila n e (13c). Phenylmagnesium bromide
(25, freshly prepared, 250 mL of a 2.35 M solution in Et2O,
0.588 mol) was added dropwise to trichloro(chloromethyl)-
silane7c (24, 54.1 g, 0.294 mol) in anhydrous Et2O (100 mL) at
room temperature. The mixture was refluxed 5 h and then
filtered through Celite. The magnesium salts were rinsed with
anhydrous Et2O. Concentration in vacuo followed by rapid
distillation from the remaining magnesium salts gave a liquid
(bp 96-155 °C/3 Torr) which was redistilled through a stain-
less steel column to yield 26 (53.3 g, 0.199 mol, 68%) as a clear
liquid: bp 136-140 °C/2.5 Torr [lit.7b 187-192 °C/10 Torr];
1H NMR (CDCl3) δ 7.80-7.25 (m, 10H), 3.40 (s, 2H); exact
mass calcd for C13H12Cl2Si m/e 266.006; found 266.0164.
1
white needles of 13f: yield (30%); mp 106-110 °C; H NMR
(CDCl3) δ 7.55-6.55 (m, 14H), 3.40 (s, 2H), 2.95 (s, 6H); exact
mass calcd for C21H22ClNSi m/e 351.1213, found 351.1163.
Anal. Calcd for C21H22ClNSi: C, 71.69; H, 6.26. Found: C,
71.49; H, 6.23.
(Chloromethyl)(p-methylphenyl)diphenylsilane (13d , see
Supporting Information) was prepared (54%) from 27 (Z-p )
CH3) and 26 as in Procedure B.
(Dibr om om eth yl)d ip h en yl(p-tr iflu or om eth ylp h en yl)-
sila n e (29a ), P r oced u r es C a n d D. n-BuLi (8.9 mL, 2 M in
hexane, 0.022 mol) was added in Procedure C in 15 min to
p-bromobenzotrifluoride (5.0 g, 0.022 mol) in dry Et2O (25 mL)
under argon at -40 °C. The solution was stirred 10 min,
warmed to room temperature, added dropwise to dichlo-
rodiphenylsilane (6.3 g, 0.025 mol) in Et2O (20 mL), and
refluxed 8 h. The Et2O was removed by distillation while
adding benzene (100 mL) until the stillhead temperature
reached 78 °C. The mixture was filtered and concentrated at
reduced pressure to give (chloro)diphenyl(p-trifluorometh-
ylphenyl)silane, an orange oil (11.0 g), that was dissolved in
Et2O (40 mL) and added at 0 °C to LiAlH4 (0.60 g, 0.016 mol)
in Et2O (20 mL). The solution was refluxed overnight, quenched
at 0 °C with Et2O saturated with H2O, and treated with 10%
acetic acid (45 mL). The organic layer was separated, washed
with 10% acetic acid (50 mL), H2O, and brine, dried over
sodium sulfate, filtered, and fractionally distilled to yield
diphenyl(p-trifluoromethylphenyl)silane (28a , 5.1 g, 0.016 mol,
1
70%): bp 145-150 °C/0.05 Torr; H NMR (CDCl3) δ 7.7-7.3
(m, 14H), 5.50 (s, 1H).
Addition of absolute ethanol (30 mL) to the pot residue from
distillation of 26 led to crystallization of an off-white solid.
Recrystallization from petroleum ether gave 13c (3.2 g, 10
mmol, 4%) as white plates: mp 113-116 °C, lit.7a 112-115
A stirred solution of 28a (4.93 g, 0.015 mol) and phenyl-
(tribromomethyl)mercury (7.94 g, 0.015 m) in benzene (75 mL)
in Procedure D was heated at 85 °C for 4 h. The mixture was
filtered, concentrated at reduced pressure, dissolved in pen-
tane, filtered, evaporated, and then chromatographed on silica
gel using 90% hexane/10% benzene as the eluent. Isolation and
crystallization of the product from hexane yielded 29a (3.1 g,
0.0062 mol, 41%): white crystals; mp 108-109.5 °C; 1H NMR
(CDCl3) δ 7.86-7.40 (m, 14H), 5.76 (s, 1H); MS (no M+ was
1
°C; H NMR (CDCl3) 7.65-7.25 (m, 15H), 3.45 (s, 2H); exact
mass calcd for C19H17ClSi m/e 308.0789, found 308.0745.
(Ch lor om eth yl)d ip h en yl(p-tr iflu or om eth ylp h en yl)si-
la n e (13a ), P r oced u r e A. A solution of n-BuLi (15 mmol) in
hexanes (15 mmol) was added (∼30 min) to bromo(p-trifluo-
romethyl)benzene (0.33 g, 15 mmol) in Et2O (20 mL) at -40
°C. The mixture was allowed to warm gradually to ∼15 °C
until testing25a revealed that all of the n-BuLi had reacted.
The (p-trifluoromethyl)phenyllithium solution was added to
26 (3.5 g, 13 mmol) in Et2O (10 mL) at -40 °C. The mixture
was allowed to warm to room temperature (∼1 h) until the
lithium reagent had completed its reactions. Water (30 mL)
was added. The mixture was separated and extracted twice
with Et2O. The Et2O solutions were combined, washed with
H2O and saturated aqueous NaCl, and dried over anhydrous
MgSO4. After filtration and concentration in vacuo, a white
solid was obtained. Recrystallizations from Et2O and from
hexane gave 13a : white needles (51%); mp 98-100 °C; 1H
NMR (CDCl3) δ 7.65-7.20 (m, 14H), 3.45 (s, 2H); exact mass
calcd for C19H14F3Si [M+ - (CH2Cl)] m/e 327.0817, found
327.0802. Anal. Calcd for C20H16ClF3Si: C, 63.74; H, 4.25.
Found: C, 64.00; H, 4.29.
observed) 327.0832 (C19H14F3Si, 100%). Anal. Calcd for C20H15
Br2F3Si: C, 48.02%; H, 3.02%. Found: 47.92%, H, 3.05%.
-
(p-Chlorophenyl)(dibromomethyl)diphenylsilane (29b, 42%),
(dibromomethyl)triphenylsilane (29c, 30%), (dibromomethyl)-
(p-methylphenyl)diphenylsilane (29d , 53%), and (dibromom-
ethyl)(p-methoxyphenyl)diphenylsilane (29e, 58%) were pre-
pared from (p-chlorophenyl)diphenylsilane (28b), triphenylsilane
(28c), (p-methylphenyl)diphenylsilane (28d ), and (p-methox-
yphenyl)diphenylsilane (28e), respectively, upon extension of
Procedure D.
(Br om om eth yl)d ip h en yl(p-tr iflu or om eth ylp h en yl)si-
la n e (14a ), P r oced u r e E. n-BuLi (1.05 mL, 2.5 M, 2.6 mmol)
in hexane was added in 5 min to 29a (1.25 g, 2.5 mmol) in
Et2O (48 mL) at -78 °C under argon. The solution was stirred
10 min at -78 °C and then treated with gaseous HBr for 10 s.
The mixture was warmed to room temperature, and H2O was
added. The organic layer was washed with brine, dried (Na2-
SO4), filtered, and concentrated under reduced pressure.
Chromatography of the residue on silica gel using 90% hexane/
10% benzene as eluent, solution of the product in pentane, and
(25) (a) Gilman, H.; Schulze, F. J . Am. Chem. Soc. 1925, 47, 2002.
(b) Gilman, H.; Swiss, J . J . Am. Chem. Soc. 1940, 62, 1847.

3572 J . Org. Chem., Vol. 67, No. 11, 2002
Allen et al.
crystallization at -10 °C yielded 14a (0.60 g, 1.4 mmol, 56%):
phenyl group.10b,c The standard deviations in the migratory
aptitudes for the p-methoxyphenyl and the p-dimethylami-
nophenyl groups in reactions of 13e and 13f are slightly larger
than the minimum errors ((10%) because the GC peak areas
for the substituted-toluenes (18e and 18f) are small and broad
compared to 21 and the standard.10b,c The errors in the
migratory aptitudes for these substituted-phenyl groups are
assumed to be the standard deviations of their mean migratory
aptitudes.10b,c The mean values for the migratory aptitudes for
all of the other substituted-phenyl groups in reactions of 13
and fluoride ion have standard deviations smaller than the
minimum error ((10%) and thus the errors are assumed to
be (10%.10b,c The average relative error for all the migratory
aptitudes is only (13%.10b,c
Rea ction s of 14f w ith TBAF in 96% Hexa n e-4% THF
a n d in Dioxa n e. Silane 14f (0.0517 g, 0.1304 mol) was added
to a mixture prepared from TBAF in THF (0.160 mL, 2.44 µL)
and hexane (4 mL). The TBAF was quite insoluble in the
reaction mixture. The solution was stirred for 2 weeks at ∼25
°C, and anisole (0.0134 g) was added. Gas chromatographic
analysis of the reaction mixture revealed the presence of (1)
21 (0.0655 mmol, 50%), (2) anisole (standard), and (3) 18, Z-p
) N(CH3)2 (0.0543 mmol, 42%).
1
white crystals; mp 73-74 °C; H NMR (CDCl3) δ 7.74-7.38
(m, 14H), 3.20 (s, 2H); MS M+ 420.1286 (C20H16BrF3Si, 0.38%),
327.0878 (C19H14F3Si, 100%). Anal. Calcd for C20H16BrF3Si: C,
57.01%, H, 3.83%. Found. C, 57.10%; H, 3.87%.
(Bromomethyl)(p-chlorophenyl)diphenylsilane (14b, 67%),
(bromomethyl)triphenylsilane (14c, 44%), (bromomethyl)(p-
methylphenyl)diphenylsilane (14d , 45%), and (bromomethyl)-
(p-methoxyphenyl)diphenylsilane (14e, 39%) were prepared by
reactions of 29b-e, respectively, with n-BuLi and then HBr
as in Procedure E for 14a .
(Br om om et h yl)(p -d im et h yla m in op h en yl)d ip h en ylsi-
la n e (14f). Bromo(p-dimethylamino)benzene (1.96 g, 9.8 mmol)
in THF (10 mL) was added in 30 min to magnesium (0.25 g,
10 mmol) in THF (10 mL) at room temperature. After being
stirred for 2 h, the mixture was added to (bromomethyl)-
chlorodiphenylsilane (3.05 g, 9.8 mmol) in THF (15 mL). The
resulting solution was stirred for 8 h, concentrated at reduced
pressure, and taken up in Et2O/H2O. The organic layer was
washed with brine, dried (Na2SO4), filtered, and vacuum-
concentrated. The oily residue was chromatographed on silica
gel (150 g) using 98% hexane/2% ethyl acetate as eluent.
Isolation and crystallization of the product from hexane gave
14f (1.62 g, 0.004 mol, 41%): white crystals; mp 105-107 °C;
1H NMR (CDCl3) δ 7.62-7.33 (m, 12H), 6.75-6.72 (d, 2H), 3.16
(s, 2H), 2.99 (s, 6H); MS M+ 395.0722 (C21H22BrNSi, 10.36%),
302.1412 (C20H20NSi, 100%). Anal. Calcd for C21H22NSi: C,
63.63%, H, 5.59%. Found. C, 63.48%; H, 5.64%.
(Iod om e t h yl)d ip h e n yl(p -t r iflu or om e t h ylp h e n yl)si-
la n e (15a ), P r oced u r e F . A solution of 13a (0.90 g, 2.4 mmol)
and sodium iodide (1.44 g, 0.96 mmol) in anhydrous acetoni-
trile (20 mL) was heated at 82 °C for 48 h. The mixture was
cooled to room temperature, diluted with Et2O, filtered, and
concentrated at reduced pressure. The residue was dissolved
in hexane, filtered, and evaporated to an oil that was chro-
matographed on silica gel using 90% hexane/10% benzene as
eluent. Isolation after recrystallization from hexane yielded
15a (0.73 g, 1.56 mmol, 65%): white crystals; mp 67-68.5 °C;
1H NMR (CDCl3) δ 7.74-7.37 (m, 14H), 2.72 (s, 2H); MS M+
467.9978 (C20H16F3ISi, 2.87%), 327.0822 (C19H14F3Si, 100%).
Anal. Calcd for C20H16F3ISi: C, 51.29%; H, 3.44%. Found: C,
51.34%; H, 3.45%.
(p-Chlorophenyl)(iodomethyl)diphenylsilane (15b, 29%), (io-
domethyl)triphenylsilane (15c, 60%), (iodomethyl)(p-methyl-
phenyl)diphenylsilane (15d , 49%), iodomethyl(p-methoxy-
phenyl)diphenylmethane (15e, 39%) and (p-dimethylamino-
phenyl)(iodomethyl)diphenylsilane (15f, 55%) were prepared
from 13b-e and 14f, respectively, by reactions with KI upon
extension of Procedure E.
Migr a tor y Ap titu d es fr om Rea ction s of 13a -f, 14a -f,
a n d 15a -f, w ith TBAF . Gen er a l Meth od : The halosilane
(13a -f, 14a -f, and 15a -f, 0.15-0.22 mmol) in THF (0.3 mL)
was added in 2 min to a 1.0 M solution of TBAF (0.35 mL,
0.35 mmol). The mixture was stirred until TLC revealed that
reaction of the halosilane was complete (25 °C, ∼8 h; 0 °C,
10-15 days; -20 °C 18-24 days). Water (2.0-2.5 mL) and
then pentane (0.2-0.3 mL) were added. The mixture was
separated and extracted with pentane (4 × 0.30 mL). Anisole,
an internal standard, was added at the beginning of an
experiment or during workup of the products. The pentane
fractions were combined and analyzed.
In a similar experiment a solution of 14f (0.0581 g, 0.147
mmol) and anisole (0.0135 g) in dioxane (0.2 mL) was added
in 2 min to TBAF (1 M, 0.34 mL, 0.34 mmol) in dioxane at 23
°C. The solution was stirred 18 h and worked-up as in the
General Method. The analytical results are (1) 21 (0.0886
mmol, 60%), (2) anisole (standard), and (3) 18, Z-p ) N(CH3)2
(0.0539 mmol, 37%).
Rea ction of (+)-23 w ith CsF . A mixture of (+)-23 (0.112
g, 0.328 mmol; [R]2D3 + 8.29°, cyclohexane)6 and CsF (0.228 g,
1.50 mmol) in dry THF (4 mL) was stirred overnight at room
temperature, diluted with hexane, filtered, and concentrated
at reduced pressure. The residue, on chromatography on silica
gel using 75% hexane/25% benzene as eluent, yielded fluo-
rosilane (+,-)-51 (0.034 g, 0.1213 mmol, 37%; [R]2D5 + 0.00°,
1
cyclohexane); H NMR (CDCl3) δ 8.05-7.00 (m, 12H), 2.74-
2.55 (octet, 2H), 0.60-0.57 (d, 3H); MS M+ 280.1051 (C18H17
-
FSi, 36.8%), 189.0596 (C11H10FSi, 100%). The product is
essentially identical with (+,-)-51 prepared from (+,-)-54 and
BF3 etherate as described later.
Rea r r a n gem en t-Disp la cem en t of (+)-23 w ith CsF .
Rea ction of 51 w ith P h en yllith iu m . Reaction of (+)-23
(0.1122 g, 0.3287 mmol; [R]2D3 +8.29°, hexane)16b and CsF
(0.220 g, 0.00151 mol) was effected as in the previous experi-
ment. After concentration at reduced pressure, the residue (51)
was dissolved in Et2O (4 mL), treated with 1.8 M phenyl-
lithium (0.54 mmol), stirred overnight, concentrated, and
filtered. Chromatography on silica gel (90% hexane/10%
benzene as eluent) gave (+,-)-53 (0.031 g, 0.0916 mmol, 28%;
[R]2D5 + 0.00°, cyclohexane), an optically inactive product
identical with authentic (+,-)-53.
Rea ction of (+)-23 w ith TBAF . Silane (+)-23 (0.126 g,
0.369 mmol, [R]2D3 + 8.29°, cyclohexane) in THF (2 mL) was
treated with TBAF solution (1 M, 0.40 mL, 0.40 mmol) in THF
(5 mL) for 10 s at room temperature and immediately diluted
with pentane (100 mL) cooled to -78 °C. The solution was
filtered, and the cold solvent was removed quickly at reduced
pressure. The residue was chromatographed rapidly on silica
gel using 75% hexane/25% hexane as eluent to give a mixture
(0.0511 g) of 51 and 23 which in cyclohexane (1 mL) had an
observed optical rotation of R2D5 ) 0.110°. 1H NMR integration
of the mixture in cyclohexane revealed 23 and 51 to be present
in a ratio of 1:4. From the 1H NMR analysis the optical
rotation of the mixture was calculated to be due to initial (+)-
23.
The amounts of 18 and 21 produced in each experiment
were determined chromatographically. The migratory apti-
tudes were calculated from the 18 and 21 formed in each
experiment and incorporate statistics in that each initial
(halomethyl)silane (13-15) contains two phenyl groups and
one para-substituted-phenyl group. The GC analysis for an
individual toluene (18 and 21) is accurate to ∼( 5%,10a and
thus the minimum error in the determinations of the migra-
tory aptitudes in each experiment is ∼( 10%.10a-c The reac-
tions for almost every (halomethyl)silane (13-15) with TBAF
at a single temperature were conducted from 3 to 11 times,
and the total yields of 18 and 21 in all experiments ranged
from 93 to 106%. The mean and the standard deviation were
calculated for the migratory aptitude of each substituted-
Syn th esis of (+,-)-Ben zylflu or om eth yl-1-n a p h th ylsi-
la n e (51). A mixture of (+,-)-54 (0.75 g, 2.56 mmol) and BF3
etherate (0.5 mL) in Et2O (10 mL) was stirred 4 h and
concentrated under vacuum. Recrystallization of the residue
from hexane gave (+,-)-51 (0.26 g, 0.928 mmol, 36%): white
crystals; mp 70.5-73 °C; 1H NMR (CDCl3) δ 8.04-7.00 (m,
12H), 2.73-2.54 (octet, 2H), 0.60-0.57 (d, 3H); MS M+

Rearrangement-Displacement Reactions
J . Org. Chem., Vol. 67, No. 11, 2002 3573
280.1079 (C18H17FSi, 31.77%), 189.0593 (C11H10FSi, 100%).
Anal. Calcd for C18H17FSi: C, 77.10%; H, 6.11%. Found: C,
77.03%; H, 6.15%.
Rea ction s of (+)-23 w ith Sod iu m Meth oxid e. Bromosi-
lane (+)-23 [0.90 g, 2.64 mmol, [R]D
23 + 8.29° (0.0135 g in 1 mL
of cyclohexane), lit [[R]2D3 + 9.15°]16d was added to sodium
methoxide (0.25 g, 0.046 mol) in dry dioxane (16 mL) under
argon at room temperature. The solution was stirred 2 h while
the reactions were followed by TLC. The mixture was diluted
with hexane, filtered, concentrated, and chromatographed on
silica gel. The eluent, 85% hexane/15% benzene, led to recovery
of (+)-23 [0.039 g, 1.04 mol, 43% recovery, [R]2D3 +8.21°
(0.0195 g in 1 mL of cyclohexane)]. Use of the eluent, 97%
hexane/3% ethyl acetate, allowed isolation of (+)-64 and (+)-
Migr ator y Aptitu des in Reaction s of (+)-23 with TBAF.
To (+)-23 (0.0547 g, 0.1603 mol) in THF (0.20 mL) was added
1 M TBAF (0.40 mL, 0.4 mmol) in THF. The mixture was
stirred overnight, worked-up upon addition of H2O (2 mL), and
extracted with pentane (4 × 0.4 mL). Anisole was added as
an internal standard to the combined extract. The solution was
analyzed by GC methods. The analysis revealed (1) 21 (0.1333
mol, 83%), (2) anisole (standard), and (3) 1-methylnaphthalene
(0.012 mol, 8%). The mole ratio of 21 to 1-methylnaphthalene
and thus the migratory ratio of the phenyl and the 1-naphthyl
groups from reactions of (+)-23 with F- is 10.4:1. Benzene and
naphthalene are also produced in cleavage of 52 and 51 by F-
and protonation. The ratio of benzene to naphthalene was not
quantified.
1
65 in a 10.5:1 ratio (by H NMR). Further chromatography of
(+)-23 and (+)-64 on silica gel resulted in separation of (+)-
23 [0.112 g, 0.397 mol, 15%; [R]2D3 +39.5° (0.112 g in 5 mL of
cyclohexane)]: 1H NMR (CDCl3/CHCl3) δ 8.29-6.95 (m, 12H),
3.45 (s, 3H), 2.66-2.51 (q, 2H), 0.47 (s, 3H); MS M+ 292.1257
(C19H20OSi, 8.69%), 201.0741 (C12H13OSi, 100%). The chro-
matographic and 1H NMR properties of (+)-64 are identical
with those of (+,-)-64 prepared as follows.
Syn th esis of Ra cem ic Ben zylm eth oxym eth yl-1-n a p h -
th ylsila n e [(+,-)-64].24 Benzylmagnesium chloride, prepared
from benzyl chloride (1.28 g, 0.055 mol) and magnesium (1.28
g, 0.055 mol) in Et2O (12 mL), was added to dimethoxymethyl-
1-naphthylsilane8a (16.33 g, 0.07 mol) in dry Et2O (25 mL).
The mixture was refluxed 5 h, cooled, filtered, concentrated,
and vacuum-distilled to give (+,-)-64 (9.0 g, 0.031 mol, 62%)
as an oil: bp 149-154 °C (0.05 Torr); 1H NMR (CDCl3) δ 8.36-
7.00 (m, 12H), 3.49 (s, 3H), 2.71-2.55 (q, 4H), 0.52 (s, 3H);
MS M+ 292.1276 (C19H22OSi, 7.94%), 201.0756 (C12H13OSi,
100%). Anal. Calcd for C19H20OSi; 78.03%; H, 6.89%; Found
C, 78.16; H, 6.90.
Ra cem iza tion of (-)-F lu or om eth yl-1-n a p h th ylp h en yl-
sila n e (58) by TBAF in THF . Experiment 1: a solution of
58 (0.0147 g, 6.17 × 10-2 mmol) in THF (1 mL) in an optical
cell at room temperature had a rotation (R) of -0.631° (RD).
To the cell was added 0.01 mL of 1 M TBAF in THF. The cell
was immediately placed in a polarimeter and in ∼10 s gave a
rotation (R) of -0.556° (RD). The rotations (R) of the partially
heterogeneous solution as monitored every 5 s during the next
80 s dropped progressively from -0.544° (RD) to -0.412° (RD).
Upon then stirring the cell contents quickly, the mixture
became completely homogeneous and gave an immediate
rotation of R ) 0.00° (RD). Experiment 2: a solution of (-)-58
(0.0236 g, 9.9 × 10-2 mmol) in THF (1 mL) at room temper-
ature had a rotation of R ) -0.734° (RD). The solution, after
addition of 1 M TBAF (0.01 mL), rapid stirring, and immediate
measurement, was optically inactive (R ) 0.00° (RD)).
Dim et h oxyp h en yl(p h en ylm et h yl)sila n e (63). Benzyl
chloride (40.0 mL, 44.0 g, 0.348 mol) in Et2O (50 mL) was
added to a stirred suspension of magnesium turnings (10.0 g,
0.411 mol) in Et2O (150 mL), and the mixture was refluxed 2
h. An aliquot of the benzylmagnesium chloride solution (175
mL, 1.42 M; 0.248 mol) was added (∼2 h) to trimethoxyphe-
nylsilane27 (49.0 g, 0.247 mol) in Et2O (100 mL) under argon.
The mixture was refluxed until the test for the Grignard
reagent25a was negative (∼5 h) and then cooled. Hydrochloric
acid (10%) and water were added. The aqueous layer was
separated and extracted with Et2O. The combined Et2O
extracts were washed with H2O and saturated aqueous NaCl,
dried over MgSO4, filtered, concentrated in vacuo, and distilled
through a glass column packed with stainless steel staples to
yield 63, a clear colorless liquid (34.6 g, 0.134 mol, 54%): bp
Syn th esis of Ra cem ic Meth oxym eth yl-(1-n a p h th ylm -
et h yl)p h en ylsila n e [(+,-)-65]. 1-Naphthylmethylmagne-
sium chloride, prepared from 1-chloromethylnaphthalene (8.83
g, 0.05 mol), magnesium (1.28 g, 0.53 mol), Et2O (22.5 mL),
and benzene (25 mL), was added dropwise to dimethoxymeth-
ylphenylsilane (9.12 g, 0.05 mol) in Et2O (25 mL). The mixture
was heated at 55 °C for 3 h, cooled, filtered, and distilled to
1
give (+,-)-65: bp 145-149 °C/0.05 Torr; H NMR (CDCl3) δ
8.01-7.21 (m, 12H), 3.44 (s, 3H), 3.03-2.83 (q, 2H), 0.29 (s,
3H); MS M+ 292.1259 (C19H20Osi, 13.13%), 151.0605 (C8H11
-
OSi, 100%). Anal. Calcd for C19H20OSi: C, 78.03%; H, 6.98%.
Found: C, 78.04%; H, 6.93%.
Con ver sion of (+)-64 by P h en yllith iu m to (-)-Ben zyl-
m eth yl-1-n a p h th ylp h en ylsila n e [(-)-66]. Phenyllithium
(0.13 mL, 1.8 M in Et2O/cyclohexane) was added to (+)-64
(0.0580 g, 0.198 mmol; [R]2D3 +39.5°, cyclohexane) in Et2O
(4 mL). The mixture was stirred 2 h, diluted with hexane,
filtered, and concentrated at reduced pressure. Chromatogra-
phy of the residue on silica gel using 90% hexane/10% ben-
zene as eluent yielded (-)-66 [0.0606 g, 0.179 mmol, 90%;
[R]2D3 -5.25° (0.0606 g in 1 mL of cyclohexane)]: 1H NMR
(CDCl3) δ 7.93-6.80 (m, 17H), 2.90-2.77 (q, 2H), 0.58 (s, 3H);
MS M+ 338.1498 (C24H22Si, 6.23%), 247.0974 (C17H15Si, 100%).
By the above procedure (+,-)-64 was converted to (+,-)-
1
105-120 °C/0.4 Torr; H NMR δ 7.50-6.90 (m, 10H), 3.50 (s,
6H), 2.30 (s, 2H); exact mass calcd for C15H18O2Si m/e 258.1076,
found 258.1082. Anal. Calcd for C15H18O2Si: C, 69.77; H, 6.98.
Found: C, 69.98; H, 6.89.
Migr a tor y Ap titu d es for Rea ction s of 14a -f w ith
Sod iu m Meth oxid e. Gen er a l Meth od . The migratory ap-
titudes in reactions of bromosilanes 14a -f with sodium
methoxide were determined as follows. The bromosilane (14a -
f, 0.15 mmol) was added to sodium methoxide (generally 0.11
g, 2.0 mmol) in purified dioxane (0.40 mL). The resulting
mixture was vigorously stirred at ∼25 °C until TLC indicated
no 14a -f remained. The mixture was then treated with TBAF
(2.3 equiv, 1 M in THF) and stirred at 25 °C for 8 h. [The excess
fluoride ion assured cleavage of 17b (Nuc ) CH3O) and 20b
(Nuc ) CH3O); fluoride attacks silicon in 17b and 20b much
more rapidly than does methoxide]. The mixture was worked-
up by addition of H2O and extraction with pentane (4 × 0.3
mL). A known amount of the internal standard, anisole, was
added to the combined pentane extracts, and the solution was
analyzed by capillary GC as described previously. Similar
experiments were executed using CsF in THF.
1
66 (58%) whose IR, H NMR, and MS are identical with that
of (-)-66 as prepared from (+)-64. Anal. Calcd for C24H22Si:
C, 85.13%; H, 6.55%. Found: C, 85.17%; H, 6.55%.
Rea ction of (+)-23 w ith P h en ylm a gn esiu m Br om id e/
Cu p r ou s Iod id e To Give (+)-66. Phenylmagnesium bromide
(0.3245 g, 1.79 mmol) in THF (10 mL) was added to (+)-23
(0.550 g, 1.60 mmol, [R]2D3 +8.29°, cyclohexane) in THF (4 mL)
containing a small amount of cuprous iodide. The resulting
mixture was refluxed 6 h and cooled, and the solvent was
removed at reduced pressure. The remaining material was
chromatographed on silica gel using 90% hexane/10% benzene
as eluent to give (+)-66 (0.4518 g, 1.33 mmol), [R]2D3 +6.15°
(0.3497 g in 5 mL of cyclohexane): 1H NMR (CDCl3) δ 7.90-
6.82 (m, 17H), 2.91-2.79 (q, 2H), 0.59 (s, 3H); MS M+ 338.1492
(C24H22Si, 5.72%), 247.0993 (C17H15Si, 100%).
(26) Gilman, H.; Aoki, D. J . Organomet. Chem. 1964, 1, 449.
(27) Kantor, S. W. J . Am. Chem. Soc. 1953, 75, 2712.
(28) (a) Previously prepared by reaction of chlorodiphenyl(phenyl-
methyl)silane and methanol in the presence of pyridine.28b (b) Brook,
A. G.; Peddle, G. J . D. Can. J . Chem. 1963, 41, 2351.
Migr a tor y Ap titu d es in Rea ction s of (+)-23 w ith So-
d iu m Meth oxid e. Bromosilane (+)-23 (0.0630 g, 0.185 mmol)
and sodium methoxide (0.119 g, 2.20 mmol) were added to
dioxane (0.40 mL). The mixture was stirred 48 h. TLC revealed

3574 J . Org. Chem., Vol. 67, No. 11, 2002
Allen et al.
that no (+)-23 remained. A solution of 1 M TBAF (0.60 mL,
0.60 mmol) in THF was added, and the mixture was stored
overnight. Anisole (0.0158 g) was added as an internal
standard, and the mixture was worked-up by addition of H2O
and extraction with pentane (4 × 0.4 mL portions). GLC
analysis revealed the presence of 21 (0.149 mmol, 81%), anisole
(standard), and 1-methylnaphthalene (0.0157 mol, 9%). The
mole ratio of 21 to 1-methylnaphthalene, and thus the migra-
tory ratio of the phenyl and the 1-naphthyl groups from
reaction of (+)-23 with sodium methoxide is 9:1. [In reactions
of (+)-23 with sodium methoxide and then protonation,
benzene and naphthalene are produced as very minor prod-
ucts].
and 2-propanol (2 mL). After the excess 2-propanol had been
removed at reduced pressure, the sodium 2-propoxide was
placed under argon and (+)-23 (0.65 g, 1.90 mmol, [R]D23
+8.29°, cyclohexane) in dioxane (15 mL) was added. After
being stirred 3 h at 23 °C, the mixture was diluted with
hexane, filtered, and concentrated at reduced pressure. Chro-
matography of the remaining oil on silica gel with 90% hexane/
10% benzene as eluent yielded (+)-23 (0.36 g, 1.05 mmol, 55%
recovery). Use of 98% hexane/2% ethyl acetate as eluent gave
(+)-70 [0.031 g, 0.0967 mmol, 11.4%; [R]2D3 28.1° (0.031 g in 2
mL of cyclohexane)]: 1H NMR (CDCl3) δ 8.41-6.90 (m, 12H),
4.1-3.9 (septet, 1H), 2.64-2.51 (q, 2H), 1.17-1.10 (q, 6H), 0.49
(s, 3H).
Rea ction of (+)-23 w ith Sod iu m Eth oxid e to Yield (+)-
Ben zyleth oxym eth yl-1-n aph th ylsilan e (69). Sodium (0.0608
g, 2.64 mmol) was added to anhydrous ethanol. After depletion
of the sodium, the excess ethanol was removed under high
vacuum. The residue was placed under argon and (+)-23 (0.65
g, 1.90 mmol, [R]2D3 +8.29°, cyclohexane) in dry dioxane (10
mL) was added. The mixture was stirred 4 h at 23 °C, diluted
with hexane, filtered, and concentrated at reduced pressure.
The oily residue, on chromatography on silica gel with 90%
hexane/10% benzene as eluent, yielded initial (+)-23 (0.3182
g, 0.9323 mmol, 49%). Using 97% hexane/3% ethyl acetate as
eluent gave (+)-69 [(0.0571 g, 0.186 mmol, 19%, [R]2D3 39.4°
(0.0571 g in 3 mL of cyclohexane)]: 1H NMR (CDCl3, TMS
0.0817) δ 8.34-6.93 (m, 12H), 3.69-3.66 (q, 2H), 2.64-2.52
(q, 2H), 1.20-1.14 (t, 3H), 0.46 (s, 3H); MS M+ 306.1434
(C20H22OSi, 14.38%), 215.0856 (C13H15OSi, 100%).
Con ver sion of (+,-)-64 by Sod iu m Eth oxid e to (+,-)-
69. To ethanol (3 mL) in toluene (20 mL) were added (+,-)-
64 (0.62 g, 2.10 mmol) and a small amount of KOH. The
solution was heated at 80 °C for 4 h, cooled to room temper-
ature, filtered, and concentrated. Chromatography of the
remaining oil on silica gel (8% hexane/2% ethyl acetate as
eluent) yielded (+,-)-69 (0.30 g, 0.98 mmol, 46%): 1H NMR
(CDCl3, TMS 0.0011) δ 8.35-6.93 (m, 12H), 3.70-3.67 (q, 2H),
2.66-2.51 (q, 2H), 1.21-1.15 (t, 3H), 0.47 (s, 3H); MS M+
306.1453 (C20H22OSi, 10.35%), 215.0908 (C13H15OSi, 100%).
Anal. Calcd for C20H22OSi, 78.12%; H, 7.54%. Found: C,
78.31%; H, 7.29%.
Con ver sion of (+)-70 by P h en yllith iu m to (-)-66. Phe-
nyllithium (0.06 mL, 1.8 M in Et2O/cyclohexane, 0.108 mmol)
was added to (+)-70 (0.031 g, 0.0967 mmol, [R]2D3 +28.1°,
cyclohexane) in Et2O (5 mL). After 2 h, the solution was diluted
with hexane, filtered, and concentrated at reduced pressure.
The residue was chromatographed on silica gel using 90%
hexane/10% benzene as eluent to yield (-)-66 (0.0294 g, 0.0868
mmol, 90%; [R]2D3 -5.57°, 0.0294 g in 1 mL of cyclohexane):
1H NMR (CDCl3) δ 7.93-6.80 (m, 17H), 2.90-2.77 (s, 3H), 0.58
(s, 3H).
Con ver sion of (+,-)-64 b y Sod iu m 2-P r op oxid e t o
(+,-)-70. 2-Propanol (6 mL) and KOH (a small amount) were
added to (+,-)-64 (0.62 g, 2.12 mmol) in toluene (25 mL). The
stirred solution was heated to 80 °C for 2 days. Chromatog-
raphy with 97% hexane/3% ethyl acetate yielded (+,-)-70 (0.10
g, 0.31 mol, 15%): 1H NMR (CDCl3) δ 8.40-6.91 (12H), 4.08-
4.00 (septet, 1H), 2.64-2.52 (q, 2H), 1.17-1.11 (q, 6H), 0.49
(s, 3H). The 1H NMR of the (+,-)-70 is essentially identical
with that of (+)-70 prepared previously.
Ack n ow led gm en t. This research was generously
supported by the National Science Foundation.
Su p p or tin g In for m a tion Ava ila ble: Plots of the loga-
rithms of the migratory aptitudes (p-Z-Ph/Ph) versus (1) σ-zero
substituent values for reactions of 13a -f with TBAF/THF at
0 °C and -20 °C, respectively, (2) σ substituent values for
13a -f with TBAF/THF at -20 °C, and (3) σ-zero substituent
values for 14a -f with TBAF/THF at 0 °C and -20 °C,
respectively, a table and discussion of the migratory aptitudes
of the p-Cl-Ph- and the p-(CH3)2N-Ph- groups, respectively, in
reactions of 14b and 14f in THF at 23 °C with TBAF at various
concentrations, a summary and discussion of the optical
behaviors of solutions of (+)-23 with varied equivalents of
TBAF at 23 °C, and procedures or directions for preparation
of silanes 13b,d ,e, 14b-e, 15b-f, 17b (Z-p ) Cl), 17b (Z-p )
CH3), 20b (Z-p ) Cl), 20b (Z-p ) H), 20b (Z-p ) CH3), 28a ,
29b-e, and 30. This material is available free of charge via
the Internet at http://pubs.acs.org.
Con ver sion of (+)-69 by P h en yllith iu m to (-)-66. Phe-
nyllithium (0.11 mL, 1.8 M, 0.20 mmol) in Et2O/cyclohexane
was added to (+)-69 (0.055 g, 0.18 mmol, [R]2D3 39.4°, cyclo-
hexane) in anhydrous Et2O (5 mL). The mixture was stirred 6
h, concentrated at reduced pressure, and chromatographed on
silica gel (90% hexane/10% benzene as eluent) to give (-)-66
[(0.0521 g, 0.159 mmol, 85%), [R]2D3 -5.50° (0.040 g in 1 mL of
cyclohexane)]: 1H NMR (CDCl3) δ 7.93-6.80 (m, 17H), 2.90-
2.77 (q, 2H), 0.58 (s, 3H). The spectral properties of (-)-66 are
identical with previous samples.
Rea ction of (+)-23 w ith Sod iu m 2-P r op oxid e To Give
(+)-Ben zylm eth yl-1-n a p h th yl-2-p r op oxysila n e 70. Sodium
2-propoxide was prepared from sodium (0.0645 g, 2.80 mmol)
J O010471J