Syntheses, structures, and thermolyses of pentacoordinate 1,2-oxastibetanes: Potential intermediates in the reactions of stibonium ylides with carbonyl compounds

Article abstract of DOI:10.1021/jo0520700

Pentacoordinate 1,2-oxastibetanes 14a-d, which are formal [2 + 2]-cycloadducts of the reactions of stibonium ylides with carbonyl compounds, were successfully synthesized by the reactions of the corresponding bromo-2-hydroxyalkylstiboraiies with NaH. The

Full text of DOI:10.1021/jo0520700

Syntheses, Structures, and Thermolyses of Pentacoordinate
1,2-Oxastibetanes: Potential Intermediates in the Reactions of
Stibonium Ylides with Carbonyl Compounds
Yosuke Uchiyama, Naokazu Kano, and Takayuki Kawashima*
Department of Chemistry, Graduate School of Science, The UniVersity of Tokyo,
7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
takayuki@chem.s.u-tokyo.ac.jp
ReceiVed October 3, 2005
Pentacoordinate 1,2-oxastibetanes 14a-d, which are formal [2 + 2]-cycloadducts of the reactions of
stibonium ylides with carbonyl compounds, were successfully synthesized by the reactions of the
corresponding bromo-2-hydroxyalkylstiboranes with NaH. The crystal structures of 14a and 14c were
established by X-ray crystallographic analyses, showing their distorted trigonal bipyramidal structures
and smaller C-Sb-O angles of the four-membered ring around antimony than the C-P-O angle of
pentacoordinate 1,2-oxaphosphetane 3. The 1H, 13C, and 19F NMR spectra of 14a-d are consistent with
the trigonal bipyramidal structure in the solution state. Although 14a did not decompose at all at 220 °C
in o-xylene-d10, the thermolyses of 3-phenyl-1,2-oxastibetane 14c were carried out at 220 °C in o-xylene-
d
10 and at 140 °C in acetonitrile-d3 to give the corresponding oxirane 28 with retention of configuration
and cyclic stibinite 25. The formation of 28 is explained by apical-equatorial ligand coupling around
antimony via a polar transition state, which is more favorable than olefin formation. In contrast, the
thermolyses of 14c in the presence of LiBr and LiBPh4 gave oxirane 29 with inversion of configuration
and the olefin 30, respectively. The formation of 29 and 30 is considered to proceed via an anti-betaine-
type intermediate and hexacoordinate 1,2-oxastibetanide 36, respectively. Selective formation of 28, 29,
and 30 in the thermolyses of 14c, which is regarded as an intermediate in the reaction of an R-phenyl-
substituted stibonium ylide with a carbonyl compound, showed that the change of the reaction conditions
controls the reactivity of a 1,2-oxastibetane compound.
SCHEME 1
Introduction
The Wittig reaction, the reaction of a phosphonium ylide with
a carbonyl compound giving an olefin, is one of the most
important organic transformations.1 In contrast to the Wittig
reaction, the reaction of a stibonium ylide with a carbonyl
compound provides the corresponding olefin and/or oxirane,
depending on the ylides and the substrates (Scheme 1).2 The
reaction of a stabilized stibonium ylide, which has a carbonyl
group at the R-position of the antimony atom, with a carbonyl
compound afforded the corresponding olefin as the sole
product,3 whereas a semistabilized stibonium ylide, which has
a phenyl group on the R-carbon of the antimony atom, afforded
both the olefin and the oxirane.4 A nonstabilized stibonium ylide
bearing no substituents was reacted with benzophenone to give
an aldehyde via an oxirane.5
(1) (a) Maryanoff, B. E.; Reitz, A. B. Chem. ReV. 1989, 89, 863. (b)
Edmonds, M.; Abell, A. In Modern Carbonyl Olefination; Takeda, T., Ed.;
Wiley-VCH: Weinheim, Germany, 2004; pp 1-17.
(2) Lloyd, D.; Gosney, I.; Ormiston, R. A. Chem. Soc. ReV. 1987, 16,
45.
(3) (a) Chen, C.; Huang, Y.-Z.; Shen, Y.; Liao, Y. Heteroat. Chem. 1990,
1, 49. (b) Liao, Y.; Huang, Y.-Z.; Zhang, L.-J.; Chen, C. J. Chem. Res. (S)
1990, 388. (c) Matano, Y. J. Chem. Soc., Perkin Trans. 1 1994, 2703.
(4) Huang, Y.-Z.; Liao, Y.; Chen, C. J. Chem. Soc., Chem. Commun.
1990, 85.
10.1021/jo0520700 CCC: $33.50 © 2006 American Chemical Society
Published on Web 12/20/2005
J. Org. Chem. 2006, 71, 659-670
659

Uchiyama et al.
SCHEME 2
CHART 1. Examples of Spectroscopically Observed and
Isolated Pentacoordinate 1,2-Oxaphosphetanes
Extensive investigations on the mechanism of the Wittig
reaction have been carried out, and pentacoordinate 1,2-
oxaphosphetanes have been accepted as an intermediate by
NMR studies.6 In contrast, mechanistic studies on the reactions
of a stibonium ylide with a carbonyl compound have been much
less explored despite a variety of reactivities, and there has been
no report of the isolation of an intermediate such as a
pentacoordinate 1,2-oxastibetane and an anti-betaine. Indeed,
there has been only one report of the trapping reaction of a
betaine intermediate with chlorotrimethylsilane at -78 °C
(Scheme 2).3b Another report used the results of theoretical
calculations on the reaction mechanism to suggest different
formation routes for the olefin and the oxirane.7 The olefin was
assumed to be formed by way of a pentacoordinate 1,2-
oxastibetane as in the Wittig reaction, whereas the oxirane was
assumed to be formed by the backside attack of oxide anion on
the R-carbon atom of an anti-betaine intermediate as in the case
of the Corey-Chaykovsky reaction, which is the reaction of a
sulfonium ylide with a carbonyl compound to give an oxirane.7,8
We previously reported the oxirane formation reaction of
highly coordinate 1,2-oxachalcogenetanes,9 which are formal
[2 + 2]-cycloadducts of chalcogenonium ylides with carbonyl
compounds, and proposed the possibility of involvement of such
1,2-oxachalcogenetanes in the Corey-Chaykovsky reaction.
These results encouraged us to explore the reactivities of
pentacoordinate 1,2-oxastibetanes, which are antimony ana-
logues of 1,2-oxaphosphetanes and 1,2-oxachalcogenetanes, to
elucidate the relationship between 1,2-oxastibetanes and the
reaction mechanism of olefin and/or oxirane formation in the
reactions of a stibonium ylide with a carbonyl compound.
Pentacoordinate 1,2-oxastibetanes were considered to be
thermally labile and unstable to moisture, as is the case of most
pentacoordinate 1,2-oxaphosphetanes. Although most of the
pentacoordinate 1,2-oxaphosphetanes are thermally labile, sev-
eral examples such as 1 and 2 have been synthesized by taking
advantage of some stabilizing groups (Chart 1).10,11 One of the
successful methods for stabilization of a pentacoordinate 1,2-
oxaphosphetane is to introduce an electron-withdrawing group
such as an electron-deficient alkoxy group and trifluoromethyl
a
SCHEME 3
a Reagents and conditions: (i) n-BuTeCH2Li (1.2 equiv), THF, -78 °C,
10 min; (ii) n-BuLi (1.2 equiv), THF, -78 °C, 10 min; (iii) (F3C)2CdO or
Ph(F3C)CdO (excess), THF, -78 °C to rt; (iv) H3O+.
group on the phosphorus atom and/or the carbon atom at the
4-position.10 Another method is to introduce a bidentate ligand
on the phosphorus atom such as the 2,2′-biphenylylene group.11
We previously reported the synthesis of isolable pentacoordinate
1,2-oxaphosphetanes 3-5,12 which are thermally stable and
tolerant to moisture, by taking advantage of the Martin ligand.13
The introduction of the Martin ligand has been found to stabilize
the pentacoordinate 1,2-oxaphosphetanes effectively.
We previously reported the synthesis and thermolysis of
pentacoordinate 3-phenyl-1,2-oxastibetanes bearing the Martin
ligand as a preliminary communication.14 In this report, we
describe the syntheses, structures, and thermolyses of pentaco-
ordinate 1,2-oxastibetanes in detail as well as the reaction
mechanism for the thermolyses.
Results and Discussion
Syntheses. Pentacoordinate 1,2-oxastibetanes were synthe-
sized by stepwise methods. Successive treatment of chlorostibo-
rane 6 bearing the Martin ligand, which was prepared similarly
to a reported procedure,15 with lithium butyltelluromethylide
(1.2 equiv), n-BuLi (1.2 equiv), hexafluoroacetone (denoted as
HFA hereafter) (excess), and aqueous NH4Cl gave the corre-
sponding 2-hydroxyalkylstiborane 7a (11%) together with
diaryl(methyl)stiborane 8 (10%) and bis(stibonyl)methane 9
(18%) (Scheme 3).16 A similar reaction with excess trifluoro-
acetophenone instead of HFA gave 7b (10%), 8 (5%), and 9
(18%). Intramolecular hydrogen bonds between the hydroxy
group and the oxygen atom of the Martin ligand were observed
(5) Henry, M. C.; Wittig, G. J. Am. Chem. Soc. 1960, 82, 563.
(6) (a) Vedejs, E.; Snoble, K. A. J. J. Am. Chem. Soc. 1973, 95, 5778.
(b) Vedejs, E.; Meier, G. P.; Snoble, K. A. J. J. Am. Chem. Soc. 1981, 103,
2823.
(7) Naito, T.; Nagase, S.; Yamataka, H. J. Am. Chem. Soc. 1994, 116,
10080.
(8) (a) Johnson, A. W.; LaCount, R. B. J. Am. Chem. Soc. 1961, 83,
417. (b) Corey, E. J.; Chaykovsky, M. J. Am. Chem. Soc. 1962, 84, 3782.
(c) Aube´, J. In ComprehensiVe Organic Synthesis: SelectiVity, Strategy, and
Efficiency in Modern Synthetic Chemistry; Trost, B. M., Fleming, I., Eds.;
Pergamon: Oxford, UK, 1991; pp 819-842.
in the IR spectra of 7a and 7b (ν ) 3073 and 3068 cm-1
,
(12) (a) Kawashima, T.; Kato, K.; Okazaki, R. J. Am. Chem. Soc. 1992,
114, 4008. (b) Kawashima, T.; Kato, K.; Okazaki, R. Angew. Chem., Int.
Ed. Engl. 1993, 32, 869.
(9) (a) Ohno, F.; Kawashima, T.; Okazaki, R. J. Am. Chem. Soc. 1996,
118, 697. (b) Kawashima, T.; Ohno, F.; Okazaki, R.; Ikeda, H.; Inagaki, S.
J. Am. Chem. Soc. 1996, 118, 12455. (c) Ohno, F.; Kawashima, T.; Okazaki,
R. Chem. Commun. 1997, 1671. (d) Ohno, F.; Kawashima, T.; Okazaki, R.
Chem. Commun. 2001, 463. (e) Kano, N.; Takahashi, T.; Kawashima, T.
Tetrahedron Lett. 2002, 43, 6775.
(10) Ramirez, F.; Smith, C. P.; Pilot, J. F. J. Am. Chem. Soc. 1968, 90,
6726.
(11) Vedejs, E.; Marth, C. Tetrahedron Lett. 1987, 28, 3445.
(13) Perozzi, E. F.; Michalak, R. S.; Figuly, G. D.; Stevenson, W. H.,
III; Dess, D. B.; Ross, M. R.; Martin, J. C. J. Org. Chem. 1981, 46, 1049.
(14) Uchiyama, Y.; Kano, N.; Kawashima, T. J. Am. Chem. Soc. 2003,
125, 13346.
(15) (a) Akiba, K.-y.; Fujikawa, H.; Sunaguchi, Y.; Yamamoto, Y. J.
Am. Chem. Soc. 1987, 109, 1245. (b) Yamamoto, Y.; Fujikawa, H.;
Fujishima, H.; Akiba, K.-y. J. Am. Chem. Soc. 1989, 111, 2276.
(16) Hiiro, T.; Atarashi, Y.; Kambe, N.; Fujiwara, S.; Ogawa, A.; Ryu,
I.; Sonoda, N. Organometallics 1990, 9, 1355.
660 J. Org. Chem., Vol. 71, No. 2, 2006

Pentacoordinate 1,2-Oxastibetanes
SCHEME 4
(SiO2) to afford 7c (40%) and 7d (28%). The stereochemistry
of 7c and 7d was deduced from the relative stereochemistry of
the finally obtained 1,2-oxastibetane, whose structure was
determined by X-ray crystallographic analysis (see below).
Treatment of 2-hydroxyalkylstiboranes 7a and 7b with
bromine (1.2 equiv) in CHCl3 resulted in quantitative formation
of the corresponding bromo(2-hydroxyalkyl)stiboranes 13a and
13b, respectively (Scheme 5).15,17 4-Bromo-tert-butylbenzene
was detected by 1H NMR spectroscopy and GC-MS. Aromatic
electrophilic substitution took place at the ipso-position of the
aryl group attached to the antimony to give bromo(2-hydroxy-
alkyl)stiboranes 13a and 13b, as in the formation of chlorostibo-
rane 6.15 The substitution of the aryl group instead of the alkyl
group is in marked contrast to the reaction of diaryl(methyl)-
bismuthane bearing the Martin ligand with sulfuryl chloride and
bromine giving diarylchloro- and diarylbromobismuthane, re-
spectively.15 Similarly to the syntheses of 13a and 13b, 7c and
7d were converted to bromo(2-hydroxyalkyl)stiboranes 13c
(57%) and 13d (72%), respectively.
a
SCHEME 5
Treatment of bromo(2-hydroxyalkyl)stiboranes 13a, 13b, 13c,
and 13d with excess NaH in THF provided the corresponding
1,2-oxastibetanes 14a (86%), 14b (77%), 14c (98%), and 14d
(90%), respectively (Scheme 5). Although 14a and 14c were
stable in air, 14b and 14d were somewhat unstable to moisture.
In contrast to 1,2-oxastibetanes 14a and 14c, 14b and 14d came
to equilibrium in CDCl3 with hydroxystiboranes 15b and 15d,
a Reagents and conditions: (i) PhCH2MgCl (1.2 equiv), Et2O, 0 °C, 2
h; (ii) LiTMP (2.2 equiv), benzene, rt, 12 h; (iii) Ph(F3C)CdO (2.2 equiv),
rt, 30 min; (iv) H3O+; (v) column chromatography (SiO2); (vi) Br2 (2.0
equiv), CHCl3, rt, 1 h; (vii) NaH (4.0 equiv), THF, rt, 2 h; (viii) H2O.
1
respectively, which were observed in the H and 19F NMR
spectra. The equilibrium ratios of 14b to 15b in CDCl3 were
1.8:1 at room temperature and 18:1 at 60 °C, suggesting that
the dehydration of 15b tends to proceed at higher temperature.
These results indicated that the number and relative configu-
ration of electron-withdrawing trifluoromethyl groups at the
4-position of 1,2-oxastibetane are important for the stability to
water.
respectively). We propose a reaction mechanism for the forma-
tion of 7a, 7b, 8, and 9: Chlorostiborane 6 is first substituted
nucleophilically by butyltelluromethylide to give butyltelluro-
methylstiborane 10 (Scheme 4), which undergoes Te-Li
exchange with n-BuLi to give lithium stibonylmethylide 11.16
Addition reaction of stibonylmethylide 11 with the ketones
followed by protonation gave 7a or 7b, whereas its hydrolysis
and its addition to chlorostiborane 6 gave undesired products 8
and 9, respectively.
Synthesis of (2-hydroxy-1-phenylalkyl)stiboranes 7c and 7d
required a new synthetic method different from that used for
the syntheses of 7a and 7b because the corresponding lithium
butyltellurobenzylide was not available. Benzylstiborane 12,
which was easily prepared by the reaction of chlorostiborane 6
with benzylmagnesium chloride (1.2 equiv) in 72% yield, was
reacted successively with lithium tetramethylpiperidide (denoted
as LiTMP hereafter) (2.2 equiv) in benzene at room temperature
for 12 h, trifluoroacetophenone (2.2 equiv), and aqueous NH4Cl
(Scheme 5). A mixture of the diastereomers of 2-hydroxyalkyl-
stiboranes 7c and 7d was separated by column chromatography
1
All the products 6-9 and 12-14 were characterized by H,
13C, and 19F NMR spectroscopy, FAB-MS, and elemental
analyses. The stereochemistry of 1,2-oxastibetane 14c was
determined by X-ray crystallographic analysis (Figure 1). In
contrast, 14b and 14d could not be isolated due to their
instability to moisture and the equilibrium with 15b and 15d,
respectively. Their stereochemistry at the 3-position of the 1,2-
oxastibetane ring was inferred by analogy with spectral data
for the 1,2-oxathietanes and comparison with those of 14c.9b
The yields of 1,2-oxastibetane 14b and 14d were estimated by
19F NMR spectroscopy.
Another synthetic route to the pentacoordinate 1,2-oxastibe-
tane is a direct reaction of a stibonium ylide with a ketone.
Benzylstiborane 12 was allowed to react with bromine to afford
benzylbromostiborane 16 (98%). Treatment of 16 with silver
FIGURE 1. ORTEP drawings of 1,2-oxaphosphetane 3 (left) and 1,2-oxastibetanes 14a (center) and 14c (right) with thermal ellipsoid plots (50%
probability). Hydrogen atoms are omitted for clarity.
J. Org. Chem, Vol. 71, No. 2, 2006 661

Uchiyama et al.
a
TABLE 2. Selected Bond Lengths (Å) and Angles (deg) of 3, 14a,
and 14c
SCHEME 6
3 (Pn ) P)
14a (Pn ) Sb)
14c (Pn ) Sb)
Pn1-O1
Pn1-O2
Pn1-C1
Pn1-C3
Pn1-C4
C1-C2
O1-C2
1.779(2)
1.722(2)
1.827(3)
1.805(3)
1.814(3)
1.541(4)
1.408(3)
2.075(2)
2.024(2)
2.118(3)
2.080(3)
2.086(3)
1.543(4)
1.406(4)
2.059(5)
2.039(5)
2.132(7)
2.103(8)
2.110(7)
1.587(10)
1.437(8)
O1-Pn1-O2
O1-Pn1-C1
O1-Pn1-C3
O1-Pn1-C4
O2-Pn1-C1
O2-Pn1-C3
O2-Pn1-C4
C1-Pn1-C3
C1-Pn1-C4
C3-Pn1-C4
Pn1-C1-C2
Pn1-O1-C2
C1-C2-O1
168.5(1)
76.5(1)
93.4(1)
94.4(1)
92.9(1)
88.9(1)
94.6(1)
124.9(1)
117.2(1)
117.5(1)
89.3(2)
95.7(2)
98.4(2)
166.17(9)
68.2(1)
95.7(1)
97.5(1)
101.4(1)
82.1(1)
95.3(1)
122.7(1)
115.7(1)
121.0(1)
89.7(2)
95.4(2)
105.7(3)
165.4(2)
69.8(2)
99.4(3)
97.9(2)
97.4(2)
81.3(3)
94.7(2)
122.9(3)
120.4(3)
116.5(3)
89.0(4)
96.3(4)
104.9(5)
a Reagents and conditions: (i) Br2 (1.2 equiv), CHCl3, rt, 0.5 h; (ii)
AgOTf (1.2 equiv), THF, rt, 4 h; (iii) LiTMP (2.0 equiv), THF, -78 °C, 4
h; (iv) (CF3)2CdO (excess).
TABLE 1. Crystallographic Data of 3, 14a, and 14c
3
14a
14c
formula
FW
cryst System
a/Å
b/Å
c/Å
R/deg
â/deg
γ/deg
V/Å3
C19H11F12O2P
530.25
C23H19F12O2Sb
677.13
C34H28F9O2Sb
761.31
monoclinic
18.148(3)
9.737(2)
36.418(7)
90
98.600(8)
90
3176.6(17)
C2/c
triclinic
13.246(8)
14.373(8)
22.504(10)
74.13(2)
82.51(2)
87.62(2)
4086(4)
P1h
triclinic
10.691(3)
12.257(4)
19.324(7)
102.894(6)
90.004(5)
91.278(5)
2468(2)
P1h
common structural feature of hypervalent compounds containing
a four-membered ring.9,12,14 The C1-Sb1-C4 bond angle of
14c [120.4(3)°] is somewhat wider than that of 14a [115.7(1)°]
because of the steric repulsion between the phenyl group at the
3-position of the 1,2-oxastibetane ring and the 4-tert-butylphenyl
group on the antimony atom of 14c. Judging from the torsion
angles of Sb1-C1-C2-O1 [8.6(3)° for 14a and 1.1(5)° for
14c] and the sum of the interior angles of the 1,2-oxastibetane
ring [359.0° for 14a and 360.0° for 14c], the 1,2-oxastibetane
ring of 14c is almost planar, while that of 14a slightly deviates
from planarity.
space group
Z
8
4
8
D
calcd/gcm-1
1.724
1.823
1.590
R1 (I > 2σ(I))
wR2 (all data)
GOF
0.0820
0.1489
1.069
0.0619
0.0672
1.097
0.1016
0.1799
1.427
The C1-Sb1-O1 [68.2(1)°] angle of 14a is smaller than the
corresponding angles [76.5(1)°] of 3, indicating that the structure
of 14a is more distorted from the ideal TBP structure than that
of 3. The large distortion of 14a results from the longer
pnictogen Pn-O and Pn-C bond lengths of 14a (Pn ) Sb)
than those of 3 (Pn ) P) corresponding to the atomic radius of
the central atom (P:1.10 Å, Sb:1.41 Å).18
triflate gave benzylstibonium triflate 17 (Scheme 6). Addition
of LiTMP (2.0 equiv) to benzylstibonium triflate 17 at -78 °C
in THF followed by bubbling of HFA (excess) afforded
3-phenyl-1,2-oxastibetane 14e in 2% yield. The crude material
contained mainly the benzylbutylstiborane and butyl(2-hydroxy-
alkyl)stiborane that were formed by the attack of n-BuLi, which
was used to prepare LiTMP, on 17 or stibonium ylide 18 and
14e, respectively.
X-ray Crystallographic Analyses. Single crystals of 1,2-
oxaphosphetane 3 and 1,2-oxastibetanes 14a and 14c were
obtained by recrystallization from hexane. X-ray crystallographic
analyses of 3, 14a, and 14c were performed to clarify the crystal
structures and the relative configurations. The unit cell of 3
contains four independent molecules, which have similar
conformations around the phosphorus atom, and that of 14a
contains two independent molecules. ORTEP drawings of 3 (one
of four molecules), 14a (one of two molecules), and 14c are
shown in Figure 1. Their crystallographic data, selected bond
lengths, and angles are summarized in Tables 1 and 2.
The X-ray crystallographic analyses of 14a and 14c, similarly
to that of 3, showed their distorted trigonal bipyramidal (TBP)
structures with two oxygen atoms at the apical positions and
three carbon atoms at the equatorial positions in the crystalline
state. The relative configuration of the phenyl group at the
3-position of 14c is cis to both the 4-tert-butylphenyl group
and the phenyl group at the 4-position of the 1,2-oxastibetane
ring.
1
NMR Studies. In the H NMR spectra of 1,2-oxastibetanes
14a-d, signals due to the ortho protons of the Martin ligand
relative to the antimony atom were observed at a lower field
(δH 8.02-8.21) than those of other aryl protons, as observed
with other hypervalent compounds with a TBP structure bearing
the Martin ligand.9,12,14 In the 19F NMR spectra, 14a-d showed
a pair of quartets due to the CF3 groups of the Martin ligand.
These spectral features of 14a-d are consistent with the TBP
structures in the crystalline state.
When the single crystals of 3-phenyl-1,2-oxastibetane 14c
were dissolved in CDCl3, the solution initially showed only one
set of signals, at δ -79.3 (s, 3F), -76.8 (q, 4JFF ) 8.2 Hz, 3F),
and -74.3 (q, 4JFF ) 8.2 Hz, 3F) in the 19F NMR spectra. After
the sample was allowed to stand at room temperature for 1 h,
4
a new set of signals at δ -78.0 (s, 3F), -75.5 (q, JFF ) 9.4
4
Hz, 3F), and -74.4 (q, JFF ) 9.4 Hz, 3F) together with the
original signals were observed in the 19F NMR spectra. The
integral ratio (the new peaks:the original peaks ) 1:4) subse-
1
quently remained unchanged at room temperature. In the H
(17) Chen, X.; Ohdoi, K.; Yamamoto, Y.; Akiba, K.-y. Organometallics
1993, 12, 1857.
(18) Emsley, J. In The Elements, 3rd ed.; Oxford University Press: New
York, 1998; pp 22-23, 152-153.
The O1-Sb1-O2 bond angles of both 14a [166.2(1)°] and
14c [165.4(2)°] deviated from linearity. Such a deviation is a
662 J. Org. Chem., Vol. 71, No. 2, 2006

Pentacoordinate 1,2-Oxastibetanes
a
SCHEME 7
SCHEME 8
CHART 2. Examples of the Compounds that Epimerize:
1,2-Oxagermetanide 19 (left) and 1,2-Oxathietane 20 (right)
a FVP condition: 500 °C, 1 × 10-1 Torr, N2 flow.
TABLE 3. Results of FVP of 1,2-Oxaphosphetane 3 and
1,2-Oxastibetane 14a
yields (%)
recovery
21
22
23
24
25
26
15a
NMR spectra, the chemical shift due to the ortho proton of the
Martin ligand (δH 8.41) of the newly generated compound was
observed at a lower field than that of 14c (δH 8.19). The large
inequality of the two quartets in the 19F NMR spectra and the
3 (Pn ) P)
0
45
55
4
85
0
5
0
0
15
0
13
0
1
0
6
14a (Pn ) Sb)
SCHEME 9. Formation Mechanisms of Oxirane 24 by FVP
of 14a
1
downfield shift of the ortho proton in the H NMR spectra of
the new compound are consistent with the epimer 14c′ without
a change of configuration at the 3- and 4-positions of the 1,2-
oxastibetane ring, which is in equilibrium with 14c in solution
(Scheme 7). Another candidate for the newly generated com-
pound is the pseudorotamer bearing a carbon atom of the four-
membered ring at the apical position, which was observed in
pentacoordinate 1,2-azaphosphetidines and some pentacoordi-
nate 1,2-oxaphosphetanes,19,20 though it is excluded by incon-
1
sistency with the downfield shift of the ortho proton in the H
NMR spectra. Pentacoordinate 1,2-oxagermetanide 1921 and
tetracoordinate 1,2-oxathietane 209a also showed such an
equilibrium with the epimers under thermal conditions (Chart
2). These epimerization reactions are considered to proceed via
pseudorotation.
Flash Vacuum Pyrolysis (FVP) of 1,2-Oxastibetane 14a
and Its Reaction Mechanism. Thermolyses of 1,2-oxastibet-
anes were attempted to obtain some experimental information
about the mechanism of the reactions of a stibonium ylide with
a carbonyl compound because the pentacoordinate 1,2-oxasti-
betanes were expected to be intermediates in the olefin formation
reaction. However, neither 14a nor 14b decomposed in o-
xylene-d10 upon heating, even at 220 °C. Their thermal stability
contrasted with the thermolysis of 1,2-oxaphosphetane 3 in
toluene-d8 at 200 °C for 11 h giving olefin 21 (65%) and cyclic
phosphinate 22 (65%) with recovery of 3 (35%).12 Flash vacuum
pyrolyses22 of 14a and 3 were carried out at a much higher
temperature. All products were detected by 1H NMR, 19F NMR,
and GC-MS and their yields were determined by 19F NMR
spectroscopy. Upon heating at 500 °C with nitrogen flow for 6
h, 3 decomposed entirely (Scheme 8 and Table 3). The
decomposition products of 3 were olefin 21 (55%), cyclic
phosphinate 22 (85%), and hexafluoroacetone 23 (5%). In
contrast, 1,2-oxastibetane 14a was recovered in 45% yield in
its FVP under similar conditions. The products of the FVP of
14a were olefin 21 (4%), oxirane 24 (15%), cyclic stibinite 25
(13%), hexafluorocumyl alcohol 26 (1%), and hydroxystiborane
15a (6%). It is interesting that the FVP of 1,2-oxastibetane 14a
gave oxirane 24 and cyclic stibinite 25, whereas that of 1,2-
oxaphosphetane 3 gave neither oxirane 24 nor the corresponding
cyclic phosphinite at all. Hydroxystiborane 15a was probably
obtained by hydrolysis of 14a.
There are three possibilities for the formation mechanism of
oxirane 24: the ligand coupling reaction through the formal
apical-equatorial coupling (mechanism A), the radical mecha-
nism (mechanism B), and the intramolecular attack of the oxide
anion of an anti-betaine intermediate on the carbon atom
attached to the antimony atom (mechanism C) (Scheme 9). The
Sb-O (314 kJ/mol) and Sb-C (215 kJ/mol) bond energies are
smaller than the P-O (407 kJ/mol) and P-C (264 kJ/mol) bond
energies,18 respectively, and homolytic cleavage could occur
easily. But, if the reaction proceeded through the radical pathway
as in the case of 1,2-oxatelluretane,9e the corresponding alcohol
27 should be obtained by hydrogen abstraction. The absence
of the formation of 27 suggests that 24 is unlikely to be formed
(19) Kawashima, T.; Soda, T.; Okazaki, R. Angew. Chem., Int. Ed. Engl.
1996, 35, 1096.
(20) Kojima, S.; Sugino, M.; Matsukawa, S.; Nakamoto, M.; Akiba, K.-
y. J. Am. Chem. Soc. 2002, 124, 7674.
(21) Kawashima, T.; Nishiwaki, Y.; Okazaki, R. J. Organomet. Chem.
1995, 499, 143.
(22) (a) Yamamoto, Y.; Akiba, K.-y. In Chemistry of HyperValent
Compounds; Akiba, K.-y., Ed.; Wiley: New York, 1998; Chapter 9, pp
279-294. (b) Akiba, K.-y. Pure Appl. Chem. 1996, 68, 837.
J. Org. Chem, Vol. 71, No. 2, 2006 663

Uchiyama et al.
TABLE 4. Thermolyses of 3-Phenyl-1,2-oxastibetane 14c under Various Conditions
conditions
yields (%)
entry
solvent
temp/°C
time/h
additive
none
none
none
none
none
LiBr
LiI
14c
25
28
29
30
31
32
1
2
3
4
5
6
7
8
9
o-xylene-d10
o-xylene-d10
CD3CN
CD3CN
CD3CN
CD3CN
CD3CN
CD3CN
CD3CN
220
140
140
140
140
140
140
140
140
140
17
48
9
48
112.5
10
10
43
43
10
5
98
98
52
19
12
56
68
61
10
89
2
2
48
80
88
44
32
39
<1
90
2
2
46
80
10
18
13
33
<1
0
0
0
0
0
71
19
18
<1
<1
0
0
0
0
0
0
0
2
5
0
0
0
1
0
0
0
0
0
5
0
0
0
1
0
0
0
0
0
(n-Bu)4NBr
(n-Bu)4NI
LiBPh4‚3DME
<1
85
10
CD3CN
SCHEME 10
SCHEME 11
of 29 than that of tetrabutylammonium salts despite the short
reaction time. In contrast, the thermolysis of 14c alone gave no
29 (entry 5). These results indicate that both lithium cation and
bromide anion are important for the formation of oxirane 29
with inversion of configuration in the thermolyses of 14c.
The thermolysis of 14c in the presence of (n-Bu)4NBr or (n-
Bu)4NI provided a trace amount of olefin 30, which was not
obtained at all in the reactions with LiBr and LiI (entries 6-9).
Interestingly, olefin 30 was obtained in good yield (85%) in
the thermolysis of 14c in the presence of LiBPh4‚3DME
complex (entry 10). The counterpart of 30, compounds bearing
both antimony and the Martin ligand such as 25, could not be
obtained as compounds identified by NMR spectroscopy and
mass spectrometry.
Plausible Mechanism for the Formation of Oxiranes 28
and 29. The formation of oxirane 28 with retention of
configuration is explained by the formal apical-equatorial
ligand coupling on the antimony atom because the stereochem-
istry was retained in the formation of 28 from 14c alone (Scheme
11). The apical-equatorial ligand coupling is symmetry forbid-
den and the apical-apical or equatorial-equatorial coupling is
symmetry allowed, according to the Woodward-Hoffmann
rule.23 In a theoretical calculation on the reaction pathway of
the H2 elimination of a series of PnH5 (Pn ) P, As, Sb, and Bi)
species, PnH5 (Pn ) P, As, and Sb) undergo the equatorial-
equatorial ligand coupling, whereas pentahydrobismuthane
undergoes polar apical-equatorial ligand coupling.23 Although
the apical-equatorial ligand coupling reactions of stiboranes
14c in thermal conditions are considered to be unfavorable, such
a ligand coupling may occur if the reaction proceeds via a polar
transition state similar to that expected by the theoretical
calculation on the reaction pathway of pentahydrobismuthane.23
In the thermolyses of 14c, the transition state to give 28 should
be more stabilized by the polar Sb-O bond, which is much
more polar than the Sb-H bond of the pentahydrostiborane.
The clearly observed solvent effect in the thermolysis of 14c
supports that the reaction proceeded via a polar transition state
(Scheme 11).
by the radical reaction though mechanism B cannot be ruled
out completely due to the low total yields of identified products.
Furthermore, the reaction is unlikely to proceed via an anti-
betaine (mechanism C), because the polar state is highly unstable
in the gas phase even though the Sb-O bond of 14a is more
polar than the P-O bond of 3. Thus, we think that the oxirane
is formed via mechanism A, although it cannot be determined
unambiguously.
Thermolyses of 1,2-oxastibetane 14c. Thermolyses of 1,2-
oxastibetane 14c bearing a phenyl group on the 3-position of
the 1,2-oxastibetane ring were investigated to determine the
stereochemistry of the oxirane formation reactions of a penta-
coordinate 1,2-oxastibetane and to get some information about
the reaction mechanism. The results are summarized in Scheme
10 and Table 4. Thermolysis of 14c in o-xylene-d10 at 220 °C
for 17 h gave the corresponding oxirane 28 (90%) with retention
of relative configuration and stibine 25 (89%) in high yields
(entry 1). Neither oxirane 29 with inversion of configuration
nor olefin 30 were formed at all, whereas trace amounts of
rearranged ketone 31 and tert-butylbenzene 32 were formed.
Relative thermal instability of 14c and the simple results of the
thermolysis are in contrast to the FVP of 1,2-oxastibetane 14a.
Furthermore, the reaction rates for the thermolysis of 14c depend
on the solvents used. Upon heating at 140 °C for 48 h, 48% of
14c was converted in CD3CN to give 28 (46%), whereas only
2% of 14c was converted in o-xylene-d10 to give 28 (2%)
(entries 2 and 4). These results show that a polar solvent
accelerates the thermolysis of 14c and that 28 forms faster in
CD3CN than in o-xylene-d10.
Thermolyses of 14c in the presence of LiBr and LiI as the
additive in CD3CN at 140 °C for 10 h provided 28 in 10% and
18% yields, respectively (entries 6 and 7), which are better yields
than that in the absence of any additives (2%) (entry 3). These
results suggested that the counteranions of lithium salts affect
the yields of 28 in the thermolyses of 14c.
Use of LiBr and (n-Bu)4NBr as the additive in the thermolysis
of 14c gave better yields of 29 than that of LiI and (n-Bu)4NI
(entries 6-9). The use of lithium salts gave much better yields
The plausible mechanisms for the formation of oxiranes 28
and 29 in the thermolyses of 14c in the presence of additives
(23) Moc, J.; Morokuma, K. J. Am. Chem. Soc. 1995, 117, 11790.
664 J. Org. Chem., Vol. 71, No. 2, 2006

Pentacoordinate 1,2-Oxastibetanes
SCHEME 12
SCHEME 13
SCHEME 14
are summarized in Scheme 12. A Lewis acid, such as the lithium
cation, coordinates to the oxygen of the Sb-O bond of 14c to
give a polar transition state A, which easily gives oxirane 28
by ligand coupling at antimony. A nucleophile such as the
bromide ion attacks the antimony atom of A, and the Sb-O
bond cleaves to afford B. Both the cation-oxygen interaction
and the attack on antimony by the nucleophile promote cleavage
of the Sb-O bond. After the C-C bond rotation to form
intermediate C, attack of the oxide anion of C on the carbon
atom next to the antimony and elimination of stiborate D gives
oxirane 29. Elimination of the salt, NuE, from D yields stibine
25. Therefore, the thermolysis of 14c to give oxirane 28 was
accelerated in the presence of LiBr or LiI compared with that
without salts under similar conditions. In contrast, the yields of
oxirane 28 decreased in the thermolyses of 14c in the presence
of ammonium salts and LiBPh4‚3DME, because the interaction
between the antimony and the counteranion is more predominant
than the E+‚‚‚O interaction and the polar transition state A,
which leads to B, is destabilized. Both the E+‚‚‚O interaction
and the nucleophilic attack of the nucleophile on the antimony
atom are important for the formation of oxirane 29. The ratio
of 29 to 28 is higher in the presence of a lithium salt than an
ammonium salt as the additive. Furthermore, the ratio is higher
in the thermolysis with LiBr than with LiI. The former fact is
explained by noting that Sb-O bond cleavage proceeds more
easily because there is the Li+‚‚‚O interaction. The latter fact
is explained by noting that the reverse reaction of B to A is
retarded because of the poor leaving ability of the bromide anion
compared with the iodide anion. Thus, both lithium cation and
bromide anion play important roles in the formation of oxirane
29 with inversion of configuration.
Plausible Mechanism for the Formation of Olefin 30.
Formation of olefin 30 in the thermolyses of 14c with (n-
Bu)4NBr and (n-Bu)4NI and the lack of formation in thermolyses
with LiBr and LiI indicate the importance of the character of
the cation of the additives for the formation of 30. Because the
tetrabutylammonium ion is inert toward oxygen compared with
lithium ion, the olefin formation is independent of both the
cation-oxygen interaction and the Sb-O bond cleavage.
Moreover, the high yield of 30 in the thermolysis of 14c with
LiBPh4‚3DME should be mentioned. In this case, the Li+‚‚‚Ã
interaction is not effective for the formation of 30 because the
lithium cation should interact with DME, which is included in
commercially available LiBPh4. As mentioned above, other
products containing antimony and the Martin ligand were
obtained as a complex mixture and could not be identified by
1H and 19F NMR spectroscopy. The FAB-MS of the reaction
mixture showed a peak at m/z 573, which is attributable to a
fragment ion of the antimony compound (RFSbPhAr: RF ) the
Martin ligand, Ar ) 4-t-BuC6H4). This result strongly suggests
that a phenyl group was transferred from tetraphenylborate onto
the antimony atom of 14c to generate the corresponding
hexacoordinate phenyl-1,2-oxastibetanide 33, which gave olefin
30 (Scheme 13). The formation of olefin 30 would proceed via
cleavage of the Sb-C and C-O bonds of the 1,2-oxastibetane
ring. Transformation of the equatorial (sp2) bonds of 14c to the
weaker hypervalent bonds of a hexacoordinate compound 33
would enable the olefin formation reaction. A similar hexaco-
ordinate antimony intermediate has been postulated in the
formation of an olefin bearing an electron-withdrawing group
from an R-stiboranylcarbanion and benzaldehyde, while hexa-
coordinate species bearing a 1,2-oxastibetane ring have never
been observed.24,25
Formation of Hexacoordinate 1,2-Oxastibetanides and
Their Reactivity. To clarify whether the hexacoordinate species
gives the corresponding olefin or not, hexacoordinate 1,2-
oxastibetanides were synthesized by other methods. The 2-hy-
droxyalkylstiborane 7c was heated with 1.5 equiv of LiH at
140 °C for 6 h to give olefin 30 (87%) together with
hydroxystiborane 34 (30%) and bis(stiboranyl)oxide 35 (58%)
(Scheme 14). Therefore, we considered that olefin 30 and
hydroxystiborane 34 were obtained by decomposition of hexa-
coordinate 1,2-oxastibetanide 36 that was generated from 7c-
Li (Scheme 14). Formation of only one isomer of 36 was
detected by 19F NMR spectroscopy of the reaction solution at
4
δ -73.6 (s, 3F), -76.4 (q, JFF ) 8.5 Hz, 3F), and -77.0 (q,
4JFF ) 8.5 Hz, 3F), showing that there was only one isomer,
(24) Kojima, S.; Takagi, R.; Akiba, K.-y. J. Am. Chem. Soc. 1997, 119,
5970.
(25) (a) Matsukawa, S.; Kojima, S.; Kajiyama, K.; Yamamoto, Y.; Akiba,
K.-y.; Re, S.; Nagase, S. J. Am. Chem. Soc. 2002, 124, 13154. (b)
Kawashima, T.; Watanabe, K.; Okazaki, R. Tetrahedron Lett. 1997, 38,
551. (c) Kojima, S.; Akiba, K.-y. Tetrahedron Lett. 1997, 38, 547. (d)
Kojima, S.; Kawaguchi, K.; Akiba, K.-y. Tetrahedron Lett. 1997, 38, 7753.
(e) Bojin, M. L.; Barkallah, S.; Evans, S. A., Jr. J. Am. Chem. Soc. 1996,
118, 1549.
J. Org. Chem, Vol. 71, No. 2, 2006 665

Uchiyama et al.
SCHEME 15
decreases the thermal stability of the 1,2-oxastibetanes. When
the oxirane is formed, either the apical-equatorial ligand
coupling of the 1,2-oxastibetane or the decomposition of an anti-
betaine intermediate would take place. The X-ray analyses
revealed that the endocyclic C-Sb-O angles around the
antimony atoms of 1,2-oxastibetanes 14a and 14c are smaller
than the endocyclic C-P-O angle of 3, resulting in the easier
ligand coupling reaction around the antimony atoms than the
1,2-oxaphosphetanes, giving the oxirane with retention of
configuration. In contrast, when the olefin is obtained, the
reaction must proceed via the hexacoordinate 1,2-oxastibetanide.
Taking into consideration the results of the thermolyses of the
pentacoordinate 1,2-oxastibetanes, they can be regarded as
potential intermediates in the reaction of a stibonium ylide with
a carbonyl compound.
though the stereochemistry is not clear. Considering that the
oxygen atom of the four-membered ring is located at the
opposite side of the oxygen atom of the Martin ligand in the
most stable isomer of hexacoordinate 1,2-oxaphosphetanides,25c
the oxygen atoms of 36 are presumed to be located similarly.
Elimination of olefin 30 from 36 and successive hydrolysis of
the counterpart should give hydroxystiborane 34, and its
dehydrative dimerization should give 35. Compounds 34 and
35 are in equilibrium, and attempted separation of 34 and 35
by gel permeation chromatography was unsuccessful.
Moreover, the reaction of pentacoordinate 1,2-oxastibetane
14c with PhLi in THF at 0 °C provided the mixture (3:1) of
two diastereomers of 33, which were detected by 19F NMR
spectroscopy (Scheme 15). Exchange of the solvent of the
reaction mixture from THF to PhCN and successive thermolysis
gave olefin 30 and lithium stibonyloxide 37, which was
protonated and dimerized with dehydration to give 38. The FAB-
MS of the reaction mixture showed peaks at m/z 1163 and 573,
which are attributable to [38 + H]+ and the fragment ion of
RFSbPhAr, respectively. Hydrolysis of 33 provided 2-hydroxy-
alkylstiborane 39 in good yield and the reaction of 39 with LiH
gave 33, which was detected by 19F NMR spectroscopy,
quantitatively. These results suggest the intermediacy of a
hexacoordinate 1,2-oxastibetanide, though the stereochemistry
except at the 3- and 4-positions of the oxastibetane ring is not
clear (Scheme 15).
Experimental Section
1,1-Bis[4-(tert-butyl)phenyl]-3,3-bis(trifluoromethyl)-1-(2-tri-
fluoromethyl-2-hydroxy-3,3,3-trifluoropropyl)-3H-2,1-benzox-
astibole (7a). To a solution of 1,1-bis[4-(tert-butyl)phenyl]-1-
chloro-3,3-bis(trifluoromethyl)-3H-2,1-benzoxastibole (6) (381 mg,
0.573 mmol) in THF (10 mL) was added at -78 °C a THF solution
(5 mL) of lithium butyltelluromethylide, which was prepared from
bis(butyltelluro)methane (269 mg, 0.701 mmol) and n-BuLi (0.50
mL, 0.77 mmol) at -78 °C for 10 min. After the reaction mixture
was stirred for 10 min, n-BuLi (0.50 mL, 0.77 mmol) was added
to it at -78 °C and the reaction mixture was further stirred for 10
min. HFA gas, which was generated by dehydration of HFA‚3H2O
(2.0 mL, 14 mmol), was bubbled to the reaction solution at -78
°C for 2 h, and the solution was warmed slowly to room
temperature. The mixture was treated with aqueous NH4Cl and
extracted with Et2O. The extracts were washed with H2O and brine
and dried with MgSO4. After removal of the solvent, the residue
was separated by wet column chromatography (WCC) (SiO2,
hexane/CH2Cl2 ) 4/1) and HPLC (CHCl3) to give 7a (60 mg, 0.074
mmol, 13%), 1,1-bis[4-(tert-butylphenyl)]-1-methyl-3,3-bis(trifluo-
romethyl)-3H-2,1-benzoxastibole (8) (36 mg, 0.056 mmol, 10%),
and bis{1,1-bis[4-(tert-butyl)phenyl]-3,3-bis(trifluoromethyl)-3H-
2,1-benzoxastibolyl}methane (9) (175 mg, 0.136 mmol, 24%).27
7a: colorless crystals (EtOH), mp 200-201 °C dec; 1H NMR (500
3
MHz, CDCl3) δ 1.34 (s, 18H), 2.90 (s, 2H), 7.44 (d, JHH ) 7.3
Hz, 1H), 7.48-7.50 (m, 5H), 7.56 (d, 3JHH ) 8.3 Hz, 4H), 7.63 (t,
3JHH ) 7.3 Hz, 1H), 7.91 (br d, 3JHH ) 7.3 Hz, 1H), 8.59 (br s, 1H,
OH); 13C{1H} NMR (126 MHz, CDCl3) δ 29.4 (s, CH2), 31.1 (s,
2
2
CH3), 34.9 (s), 74.8 (sept, JCF ) 30 Hz), 78.3 (sept, JCF ) 29
Conclusion
1
1
Hz), 123.4 (q, JCF ) 289 Hz), 123.6 (q, JCF ) 291 Hz), 126.4
(s), 126.9 (s), 128.3 (br s), 129.7 (s), 130.4 (s), 132.2 (s), 134.5
(s), 134.8 (s), 137.3 (s), 154.4 (s); 19F NMR (254 Hz, CDCl3) δ
-78.4 (s, 6F), -75.0 (s, 6F); MS (FAB) m/z 811 (M + H+, 50),
57 (100%); IR (KBr, cm-1) 3081 (w), 2968 (w), 2871 (w), 1699
(s), 1590 (w), 1558 (w), 1507 (w), 1493 (w), 1464 (w), 1388 (w),
1364 (s), 1271 (vs), 1189 (vs), 1144 (s), 1120 (s), 1064 (w), 1011
(m); IR (CHCl3, cm-1) 3073 (w), 2966 (w), 2906 (w), 2871 (w),
1589 (s), 1493 (w), 1464 (w), 1387 (w), 1303 (w), 1275 (m), 1236
(w), 1216 (vs), 1207 (m), 1193 (m), 1167 (w), 1144 (w), 1119
(w), 1060 (w), 1010 (w). Anal. Calcd for C33H33F12O2Sb: C, 48.85;
H, 4.10. Found: C, 48.92; H, 4.19.
We have described the syntheses, structures, and thermolyses
of the pentacoordinate 1,2-oxastibetanes with and without a
phenyl group at the 3-position on the 1,2-oxastibetane ring,
which are considered as formal [2 + 2]-cycloadducts of the
reaction of a stibonium ylide and a carbonyl compound. In fact,
the reaction of the stibonium benzylide with HFA gave the
corresponding pentacoordinate 1,2-oxastibetane. The 1,2-oxa-
stibetane without a phenyl group at the 3-position did not
decompose even at 220 °C in o-xylene-d10, whereas the
3-phenyl-1,2-oxastibetane decomposed under similar conditions
to give the corresponding oxirane with retention of configuration
as the sole product, in sharp contrast to the result of the
thermolysis of the 1,2-oxaphosphetane bearing the Martin ligand.
Thermolysis of the 3-phenyl-1,2-oxastibetane in the presence
of LiBr and LiBPh4‚3DME gave selectively the oxirane with
inversion of configuration and the corresponding olefin as the
main product, respectively. These results showed that 3-phenyl-
1,2-oxastibetanes thermally decompose to give both the oxirane
and the olefin and that the phenyl group at the 3-position
1,1-Bis[4-(tert-butyl)phenyl]-1-(2-hydroxy-2-phenyl-3,3,3-tri-
fluoropropyl)-3,3-bis(trifluoromethyl)-3H-2,1-benzoxastibole (7b).
7b: colorless crystals (EtOH), mp 201-202 °C dec; 1H NMR (500
2
MHz, CDCl3) δ 1.27 (s, 9H), 1.39 (s, 9H), 3.27 (d, JHH ) 12.5
Hz, 1H), 3.36 (d, 2JHH ) 12.5 Hz, 1H), 6.97-7.00 (m, 3H), 7.06-
(26) Marvel, C. S.; Johnston, H. W.; Meier, J. W.; Mastin, T. W.;
Whitson, J.; Himel, C. M. J. Am. Chem. Soc. 1944, 66, 914.
(27) The yields of 7a, 8, and 9 were calculated assuming that 1 mol of
6 gives 1 mol of 7a and 8, and 0.5 mol of 9, respectively.
666 J. Org. Chem., Vol. 71, No. 2, 2006

Pentacoordinate 1,2-Oxastibetanes
7.10 (m, 3H), 7.14 (dt, 3JHH ) 8.6 Hz, 4JHH ) 1.9 Hz, 2H), 7.34-
(m, 3F), -74.6 (q, 4JFF ) 9.4 Hz, 3F), -73.6 (m, 3F); MS (FAB)
m/z 895 (M + H+, 6), 629 (M+ - CH2C(CF3)OH, 100%); IR (KBr,
cm-1) 3145 (w, OH), 3072 (m), 2965 (w), 2905 (w), 2870 (w),
1589 (w), 1552 (w), 1493 (w), 1455 (w), 1396 (w), 1386 (w), 1364
(w), 1300 (w), 1266 (vs), 1226 (m), 1201 (m), 1183 (vs), 1166
(m), 1134 (w), 1114 (m), 1078 (w). Anal. Calcd for
C44H42F9O2Sb: C, 59.01; H, 4.73. Found: C, 58.75; H, 4.84. 7d:
7.39 (m, 3H), 7.40-7.50 (m, 4H), 7.57 (td, 3JHH ) 8.3 Hz, 4JHH
)
1.1 Hz, 1H), 7.71 (br s, 1H, OH), 7.92 (br d, 3JHH ) 7.7 Hz, 1H);
13C{1H} NMR (126 MHz, CDCl3) δ 31.1 (s), 31.2 (s), 32.0 (s,
CH2), 34.7 (s), 34.9 (s), 74.9 (q, 2JCF ) 29 Hz), 78.3 (sept, 2JCF
)
29 Hz), 123.4 (q, 1JCF ) 290 Hz), 124.0 (q, 1JCF ) 290 Hz), 125.6
(s), 125.6 (q, 1JCF ) 287 Hz), 125.9 (s), 126.2 (s), 126.7 (s), 127.6
(s), 127.9 (s), 128.0 (s), 128.4 (s), 129.0 (s), 130.3 (s), 131.9 (s),
133.1 (s), 134.6 (s), 134.7 (s), 135.4 (s), 137.4 (s), 138.5 (s), 153.6
(s), 153.8 (s); 19F NMR (254 Hz, CDCl3) δ -81.5 (s, 3F), -74.8
1
colorless crystals (EtOH), mp 174-175 °C dec; H NMR (500
MHz, CDCl3) δ 1.23 (s, 9H), 1.34 (s, 9H), 4.54 (s, 1H), 6.58 (m,
2
3H), 6.96-7.01 (m, 6H), 7.12 (t, JHH ) 7.3 Hz, 1H), 7.28-7.36
2
2
(q, JFF ) 9.0 Hz, 3F), -74.1 (q, JFF ) 9.0 Hz, 3F); MS (FAB)
m/z 819 (M + H+, 45), 629 (M+ - CH2C(CF3)OH, 100%); IR
(KBr, cm-1) 3068 (w), 2971 (m), 2907 (w), 2871 (w), 2832 (w),
1589 (w), 1552 (w), 1492 (w), 1465 (w), 1449 (w), 1388 (w), 1364
(s), 1269 (s), 1223 (m), 1202 (m), 1176 (s), 1159 (vs), 1142 (m),
1122 (w), 1105 (w), 1054 (m). Anal. Calcd for C38H38F9O2Sb: C,
55.70; H, 4.67. Found: C, 55.62; H, 4.68.
(m, 7H), 7.50 (t, 3JHH ) 7.9 Hz, 1H), 7.79-7.83 (m, 4H), 7.97 (s,
1H, OH); 13C{1H} NMR (126 MHz, CDCl3) δ 31.0 (s), 31.2 (s),
34.6 (s), 34.8 (s), 62.9 (s), 77.8 (sept, 2JCF ) 29 Hz), 79.5 (q, 2JCF
1
1
) 27 Hz), 123.5 (q, JCF ) 291 Hz), 124.3 (q, JCF ) 290 Hz),
1
125.2 (q, JCF ) 289 Hz), 125.3 (s), 125.4 (s), 125.48 (s), 125.55
(s), 127.1 (s), 127.6 (s), 127.8 (s), 128.7 (s), 129.3 (s), 130.1 (s),
131.3 (s), 133.1 (s), 134.4 (s), 134.6 (s), 134.95 (s), 135.01 (s),
135.2 (s), 135.3 (s), 136.7 (s), 140.1 (s), 153.0 (s), 153.1 (s); 19F
NMR (470 Hz, CDCl3) δ -74.1 (q, 4JFF ) 9.4 Hz, 3F), -73.5 (s,
1-Benzyl-1,1-bis[4-(tert-butyl)phenyl]-3,3-bis(trifluoromethyl)-
3H-2,1-benzoxastibole (12). To magnesium turnings (70 mg, 2.9
mmol) in Et2O (5 mL) was added dropwise an ethereal solution (5
mL) of benzyl chloride (0.31 mL, 2.7 mmol) over 1 h under reflux
and the mixture was stirred at room temperature for 1 h. To the
reaction mixture was added an ethereal solution (15 mL) of
chlorostiborane 6 (1.62 g, 2.44 mmol). After the reaction mixture
was stirred at room temperature overnight, it was treated with
aqueous NH4Cl and extracted with Et2O. The extracts were washed
with H2O, aqueous Na2CO3, and brine and dried with MgSO4. After
removal of the solvent, the residue was washed with hexane to
give 12 (1.37 g, 78%) as a white solid. 12: colorless crystals
4
3F), -73.1 (q, JFF ) 9.4 Hz, 3F); MS (FAB) m/z 895 (M + H+,
6), 629 (M+ - CH2C(CF3)OH, 100%); IR (KBr, cm-1) 3429 (w,
OH), 3218 (w), 3069 (w), 3030 (w), 2965 (w), 2906 (w), 2871
(w), 1631 (w), 1590 (w), 1495 (w), 1464 (w), 1444 (w), 1387 (w),
1363 (w), 1264 (w), 1239 (m), 1223 (m), 1203 (m), 1184 (m), 1141
(m), 1114 (m), 1061 (w), 1032 (w), 1010 (w). Anal. Calcd for
C44H42F9O2Sb: C, 59.01; H, 4.73. Found: C, 58.84; H, 4.84.
1-Bromo-1-[4-(tert-butyl)phenyl]-3,3-bis(trifluoromethyl)-1-
(2-trifluoromethyl-2-hydroxy-3,3,3-trifluoropropyl)-3H-2,1-ben-
zoxastibole (13a). To a solution of 2-hydroxyalkylstiborane 7a (127
mg, 0.156 mmol) in CHCl3 (5 mL) was added dropwise a solution
of bromine (0.04 mL, 0.8 mmol) in CHCl3 (1 mL) at 0 °C for 10
min in the dark, and the mixture was stirred at room temperature
for 0.5 h. After removal of the solvent, the residue was washed
with hexane to give 13a (118 mg, 100%) as a white solid. 13a:
1
(hexane), mp 142-143 °C dec; H NMR (500 MHz, CDCl3) δ
3
1.30 (s, 18H), 3.98 (s, 2H), 7.00 (br s, 5H), 7.08 (d, JHH ) 7.6
Hz, 1H), 7.26 (d, 3JHH ) 8.4 Hz, 4H), 7.31 (d, 3JHH ) 8.4 Hz, 4H),
3
3
7.39 (t, JHH ) 7.6 Hz, 1H), 7.57 (t, JHH ) 7.6 Hz, 1H), 7.94 (br
d, JHH ) 7.6 Hz, 1H); 13C{1H} NMR (126 MHz, CDCl3) δ 31.2
(s), 34.7 (s), 35.2 (s), 78.6 (sept, JCF ) 29 Hz), 125.5 (q, JCF
3
2
1
1
)
colorless crystals (hexane), mp 141-145 °C dec; H NMR (500
2
283 Hz), 125.6 (s), 126.0 (s), 127.7 (s), 128.2 (s), 129.0 (s), 129.8
(s), 130.0 (s), 131.2 (s), 131.4 (s), 134.67 (s), 134.70 (s), 135.4 (s),
138.6 (s), 153.2 (s); 19F NMR (470 MHz, CDCl3) δ -74.9 (s, 6F);
MS (FAB) m/z 721 (M + H+, 18), 629 (M+ - PhCH2, 100%).
Anal. Calcd for C36H37F6OSb: C, 59.93; H, 5.17. Found C, 59.66;
H, 5.23.
MHz, CDCl3) δ 1.31 (s, 9H), 3.20 (d, JHH ) 13.7 Hz, 1H), 3.66
3
(m, 1H), 6.48 (br s, 1H, OH), 7.56 (d, JHH ) 8.6 Hz, 2H), 7.73
3
4
3
(td, JHH ) 7.6 Hz, JHH ) 1.0 Hz, 1H), 7.78 (td, JHH ) 7.6 Hz,
4JHH ) 1.0 Hz, 1H), 7.86 (br d, 3JHH ) 7.6 Hz, 1H), 8.07 (d, 3JHH
3
4
) 8.6 Hz, 2H), 8.45 (dd, JHH ) 7.6 Hz, JHH ) 1.0 Hz, 1H);
13C{1H} NMR (126 MHz, CDCl3) δ 31.0 (s, CH3), 35.0 (s), 43.0
2
2
(s, CH2), 74.9 (sept, JCF ) 31 Hz), 80.8 (sept, JCF ) 30 Hz),
1,1-Bis[4-(tert-butyl)phenyl]-1-(2-hydroxy-1,2-diphenyl-3,3,3-
trifluoropropyl)-3,3-bis(trifluoromethyl)-3H-2,1-benzoxasti-
boles (7c and 7d). To a solution of tetramethylpiperidine (0.39
mL, 2.20 mmol) in benzene (5 mL) was added n-BuLi (1.50 mL,
2.10 mmol) at room temperature and the mixture was stirred at
room temperature for 0.5 h. To the reaction mixture was added a
benzene solution (15 mL) of benzylstiborane 12 (720 mg, 1.00
mmol) at room temperature. After the reaction mixture was stirred
at room temperature for 12 h, a benzene solution (1 mL) of
trifluoroacetophenone (390 mg, 2.24 mmol) was added to the
reaction solution and the solution was stirred at room temperature
for 0.5 h. The mixture was treated with aqueous NH4Cl and
extracted with CHCl3. The organic layer was washed with H2O
and brine and dried with MgSO4. After removal of the solvent, the
residue was separated by WCC (hexane/CHCl3 ) 1/1) to give 7c
(360 mg, 40%) and 7d (248 mg, 28%). 7c: colorless crystals (EtOH/
CHCl3 ) 4/1), mp 251-252 °C dec; 1H NMR (500 MHz, CDCl3)
δ 1.16 (s, 9H), 1.42 (s, 9H), 4.37 (s, 1H), 6.50 (d, 2JHH ) 8.5 Hz,
2H), 6.99-7.12 (m, 9H), 7.44 (br d, 2JHH ) 7.3 Hz, 2H), 7.53 (dt,
3JHH ) 7.3 Hz, 1H), 7.57-7.60 (m, 6H), 7.66 (dd, 3JHH ) 7.5 Hz,
1
1
122.7 (q, JCF ) 288 Hz), 122.8 (q, JCF ) 288 Hz), 123.2 (br q,
1JCF ) 288 Hz), 127.0 (s), 127.7 (s), 127.8 (s), 128.6 (s), 131.7 (s),
133.5 (s), 133.8 (s), 135.0 (s), 135.8 (s), 156.4 (s); 19F NMR (254
4
4
Hz, CDCl3) δ -79.0 (br q, JFF ) 9.4 Hz, 3F), -77.9 (q, JFF
)
9.4 Hz, 3F), -75.5 (br q, 4JFF ) 9.4 Hz, 3F), -74.7 (q, 4JFF ) 9.4
Hz, 3F); MS (FAB) m/z 757 (M + H+, 4), 677 (M+ - Ar, 100%);
IR (KBr, cm-1) 3224 (w), 3077 (w), 2967 (w), 2872 (w), 1699 (s),
1652 (w), 1558 (w), 1490 (w), 1463 (w), 1447 (w), 1397 (s), 1305
(m), 1272 (vs), 1242 (s), 1195 (vs), 1148 (s), 1117 (m), 1059 (w),
1050(w), 1007 (m); IR (CHCl3, cm-1) 3274 (w), 3074 (w), 2968
(w), 1653 (w), 1558 (w), 1489 (w), 1463 (w), 1444 (w), 1396 (w),
1364 (w), 1304 (m), 1277 (m), 1237 (m), 1223 (s), 1215 (s), 1200
(s), 1147 (m), 1117 (w), 1050 (w), 1008 (w). Anal. Calcd for
C23H20BrF12O2Sb: C, 36.44; H, 2.66. Found: C, 36.66; H, 2.93.
1-Bromo-1-[4-(tert-butyl)phenyl]-1-(2-hydroxy-2-phenyl-3,3,3-
trifluoropropyl)-3,3-bis(trifluoromethyl)-3H-2,1-benzoxasti-
bole (13b). 13b: colorless crystals (hexane), mp 143-145 °C dec;
2
1H NMR (500 MHz, CDCl3) δ 1.27 (s, 9H), 3.69 (d, JHH ) 12.7
Hz, 1H), 3.82 (d, 2JHH ) 12.7 Hz, 1H), 5.52 (br s, 1H, OH), 7.03-
3
3
4JHH ) 1.0 Hz, 1H), 7.88 (br d, JHH ) 7.5 Hz, 1H), 8.59 (s, 1H,
7.05 (m, 3H), 7.24 (d, JHH ) 8.5 Hz, 2H), 7.46-7.48 (m, 2H),
OH); 13C{1H} NMR (126 MHz, CDCl3) δ 31.0 (s), 31.3 (s), 34.6
7.57 (d, JHH ) 8.5 Hz, 2H), 7.69 (td, JHH ) 7.6 Hz, JHH ) 1.2
Hz, 1H), 7.73 (td, 3JHH ) 7.6 Hz, 4JHH ) 1.2 Hz, 1H), 7.84 (br d,
3JHH ) 7.6 Hz, 1H), 8.43 (dd, 3JHH ) 7.6 Hz, 4JHH ) 1.2 Hz, 1H);
13C{1H} NMR (126 MHz, CDCl3) δ 31.0 (s, CH3), 34.8 (s), 49.3
(s, CH2), 75.8 (q, 2JCF ) 30 Hz), 80.8 (sept, 2JCF ) 30 Hz), 122.9
(q, 1JCF ) 289 Hz), 123.4 (q, 1JCF ) 288 Hz), 124.9 (q, 1JCF ) 287
Hz), 126.5 (s), 126.6 (s), 126.9 (s), 127.5 (s), 128.1 (s), 129.0 (s),
3
3
4
2
(s), 34.9 (s), 64.9 (s), 77.6 (m), 78.1 (q, JCF ) 27 Hz), 123.4 (q,
1JCF ) 291 Hz), 124.0 (q, 1JCF ) 290 Hz), 125.1 (s), 126.5 (q, 1JCF
) 289 Hz), 126.3 (s), 127.4 (s), 127.5 (s), 127.76 (s), 127.83 (s),
128.1 (s), 130.3 (s), 130.6 (s), 130.8 (s), 131.4 (s), 133.8 (s), 134.3
(s), 134.5 (s), 134.8 (s), 135.3 (s), 135.4 (s), 136.1 (s), 136.6 (s),
137.3 (s), 153.18 (s), 153.24 (s); 19F NMR (470 Hz, CDCl3) δ -77.0
J. Org. Chem, Vol. 71, No. 2, 2006 667

Uchiyama et al.
129.1 (s), 131.5 (s), 133.2 (s), 133.8 (s), 135.2 (s), 136.0 (s), 136.2
(126 MHz, CDCl3) δ 31.0 (s, CH3), 35.2 (s), 50.0 (s, CH2), 76.0
2
2
1
(s), 155.2 (s): 19F NMR (254 MHz, CDCl3) δ -81.6 (s, 3F), -75.3
(sept, JCF ) 31 Hz), 82.1 (sept, JCF ) 30 Hz), 123.2 (q, JCF )
4
4
(q, JFF ) 9.1 Hz, 3F), -74.5 (br q, JFF ) 9.1 Hz, 3F); IR (KBr,
cm-1) 3411 (m), 3073 (w), 2964 (m), 2906 (w), 2870 (w), 1634
(w), 1587 (w), 1490 (w), 1463 (w), 1451 (w), 1396 (s), 1365 (w),
1305 (m), 1272 (vs), 1232 (s), 1214 (vs), 1192 (vs), 1166 (s), 1147
(s), 1120 (m), 1102 (w), 1074 (w), 1059 (w), 1050 (w), 1007 (w);
MS (FAB) m/z 765 (M + H+, 10), 513 (100%). Anal. Calcd for
C28H25F12O2Sb: C, 43.89; H, 3.29. Found C, 43.81; H, 3.32.
1-Bromo-1-[4-(tert-butyl)phenyl]-1-(2-hydroxy-1,2-diphenyl-
3,3,3-trifluoropropyl)-3,3-bis(trifluoromethyl)-3H-2,1-benzoxas-
tibole (13c). Major isomer of 13c: colorless crystals (hexane/CHCl3
) 1/1), mp 199-200 °C dec; 1H NMR (500 MHz, CDCl3) δ 1.17
(s, 9H), 5.47 (s, 1H), 6.47 (br s, 1H), 6.84-6.91 (m, 2H), 7.07-
7.24 (m, 8H), 7.54 (br d, 2JHH ) 7.1 Hz, 2H), 7.66-7.69 (m, 2H),
288 Hz), 123.3 (q, 1JCF ) 288 Hz), 123.8 (q, 1JCF ) 286 Hz), 124.0
(q, 1JCF ) 286 Hz), 125.1 (s), 127.3 (s), 127.4 (s), 128.1 (s), 131.4
(s), 132.9 (s), 133.5 (s), 134.0 (s), 136.9 (s), 157.2 (s); 19F NMR
(470 MHz, CDCl3) δ -78.4 (q, 4JFF ) 8.8 Hz, 3F), -77.5 (q, 4JFF
) 8.8 Hz, 3F), -76.8 (q, 4JFF ) 8.5 Hz, 3F), -74.4 (q, 4JFF ) 8.5
Hz, 3F); MS (FAB) m/z 677 (M + H+, 89), 57 (100%). Anal. Calcd
for C23H19F12O2Sb: C, 40.80; H, 2.83. Found C, 40.82; H, 2.97.
1-[4-(tert-Butyl)phenyl]-4-phenyl-3,3,4′-tris(trifluoromethyl)-
spiro{2,1-benzoxastibole-1(3H),2′λ5-[1,2]oxastibetane} (14b).
14b: 1H NMR (270 MHz, CDCl3) δ 1.27 (s, 9H), 4.58 (d, 2JHH
)
13.0 Hz, 1H), 4.41 (d, 2JHH ) 13.0 Hz, 1H), 7.29-8.00 (m, 12H),
8.12-8.14 (m, 1H); 19F NMR (254 MHz, CDCl3) δ -81.0 (s, 3F),
4
4
-76.9 (q, JFF ) 8.1 Hz, 3F), -74.2 (q, JFF ) 8.1 Hz, 3F); MS
(FAB) m/z 685 (M + H+, 11), 513 (100%). 15b: 1H NMR (270
2
7.77-7.82 (m, 3H), 8.62 (d, JHH ) 7.8 Hz, 1H); 13C{1H} NMR
2
(126 MHz, CDCl3) δ 30.9 (s), 34.6 (s), 74.1 (s), 79.9 (q, 2JCF ) 28
Hz), 80.5 (sept, 2JCF ) 31 Hz), 122.7 (q, 1JCF ) 289 Hz), 123.0 (q,
MHz, CDCl3) δ 1.34 (s, 9H), 4.18 (d, JHH ) 13.2 Hz, 1H), 4.46
(d, 2JHH ) 13.2 Hz, 1H), 7.29-8.00 (m, 12H), 8.03-8.10 (m, 1H);
19F NMR (254 MHz, CDCl3) δ -79.9 (q, 4JFF ) 8.8 Hz, 3F), -76.7
1
1JCF ) 289 Hz), 123.4 (q, JCF ) 286 Hz), 125.5 (s), 125.8 (s),
4
4
(q, JFF ) 8.4 Hz, 3F), -74.3 (q, JFF ) 8.4 Hz, 3F).
126.4 (s), 127.0 (s), 127.4 (s), 127.9 (s), 128.2 (s), 128.3 (s), 128.5
(s), 131.6 (s), 132.1 (s), 132.6 (s), 133.9 (s), 134.3 (s), 134.6 (s),
134.8 (s), 135.8 (s), 154.6 (s); 19F NMR (470 Hz, CDCl3) δ -77.69
1-[4-(tert-Butyl)phenyl]-3′,4′-diphenyl-3,3,4′-tris(trifluoro-
methyl)spiro{2,1-benzoxastibole-1(3H),2′λ5-[1,2]oxastibetane}
4
1
to -77.68 (m, 3F), -74.08 (q, JFF ) 9.9 Hz, 3F), -73.63 to
(14c). 14c: colorless crystals (hexane); mp 189-190 °C dec; H
-73.60 (m, 3F); MS (FAB) m/z 842 (C34H3981BrF6O2Sb+, 2), 186
(100%); IR (KBr, cm-1) 3398 (s), 3352 (m), 3071 (m), 3028 (w),
2963 (w), 2906 (w), 2869 (w), 1635 (w), 1587 (w), 1493 (m), 1454
(w), 1441 (w), 1424 (w), 1397 (m), 1364 (m), 1350 (m), 1301 (m),
1286 (s), 1267 (vs), 1236 (vs), 1187 (vs), 1157 (vs), 1144 (vs),
1103 (vs), 1078 (m), 1061 (m). Anal. Calcd for C34H29BrF9O2Sb:
C, 48.49; H, 3.47. Found: C, 48.28; H, 3.64. Minor isomer of
13c: 1H NMR (500 MHz, CDCl3) δ 1.22 (s, 9H), 5.13 (s, 1H),
NMR (500 MHz, CDCl3) δ 1.30 (s, 9H), 6.09 (s, 1H), 6.65 (d,
3JHH ) 7.5 Hz, 2H), 6.94 (t, JHH ) 7.4 Hz, 2H), 7.04 (t, JHH
)
3
3
3
7.5 Hz, 1H), 7.16-7.19 (m, 5H), 7.30 (br d, JHH ) 6.4 Hz, 2H),
3
3
7.55 (d, JHH ) 8.4 Hz, 2H), 7.68 (t, JHH ) 7.9 Hz, 1H), 7.74 (t,
3JHH ) 7.1 Hz, 1H), 7.87 (br d, 3JHH ) 7.3 Hz, 1H), 8.19 (d, 3JHH
) 7.4 Hz, 1H); 13C{1H} NMR (126 MHz, CDCl3) δ 31.1 (s, CH3),
2
2
35.1 (s), 78.7 (s, CH), 81.7 (q, JCF ) 28 Hz), 82.1 (sept, JCF
)
1
1
30 Hz), 123.38 (q, JCF ) 288 Hz), 123.41 (q, JCF ) 288 Hz),
124.5 (q, 1JCF ) 288 Hz), 126.2 (s), 126.4 (s), 127.1 (s), 127.3 (s),
127.4 (s), 127.8 (s), 128.2 (s), 128.3 (s), 128.5 (s), 130.1 (s), 131.3
(s), 132.3 (s), 132.4 (s), 133.5 (s), 134.1 (s), 136.5 (s), 137.2 (s),
156.4 (s); 19F NMR (470 MHz, CDCl3) δ -79.3 (s, 3F), -76.8 (q,
2
6.84-6.91 (m, 3H), 7.07-7.24 (m, 8H), 7.40 (br d, JHH ) 7.6
Hz, 1H), 7.54 (br d, 2JHH ) 7.1 Hz, 1H), 7.66-7.69 (m, 2H), 7.77-
2
7.82 (m, 3H), 8.62 (d, JHH ) 7.8 Hz, 1H); 19F NMR (470 Hz,
CDCl3) δ -76.26 to -76.25 (m, 3F), -74.64 (br s, 3F), -74.11 to
-74.05 (m, 3F).
4JFF ) 8.2 Hz, 3F), -74.3 (q, JFF ) 8.2 Hz, 3F); MS (FAB) m/z
4
761 (M + H+, 8), 187 (100%). Anal. Calcd for C34H28F9O2Sb: C,
53.64; H, 3.71. Found C, 53.68; H, 3.89. X-ray crystallographic
analysis of 14c revealed that 4-(tert-butyl)phenyl and two phenyl
groups of the 1,2-oxastibetane ring are cis to each other. 14c′: 1H
NMR (500 MHz, CDCl3) δ 1.34 (s, 9H), 6.34 (s, 1H), 6.55 (d,
1-Bromo-1-[4-(tert-butyl)phenyl]-1-(2-hydroxy-1,2-diphenyl-
3,3,3-trifluoropropyl)-3,3-bis(trifluoromethyl)-3H-2,1-benzoxas-
tibole (13d). Major isomer of 13d: colorless crystals (hexane/CHCl3
1
) 5/1), mp 160-161.5 °C dec; H NMR (500 MHz, CDCl3) δ
1.24 (s, 9H), 5.35 (s, 1H), 5.67 (br s, 1H), 6.91 (br, 1H), 7.10-
3JHH ) 7.2 Hz, 2H), 6.85 (t, JHH ) 7.4 Hz, 2H), 6.93-7.20 (m,
3
2
7.13 (m, 5H), 7.19 (t, JHH ) 7.4 Hz, 1H), 7.31-7.39 (m, 3H),
3
7.43-7.46 (m, 1H), 7.47-7.64 (m, 3H), 7.64-7.79 (m, 4H); 19F
NMR (470 Hz, CDCl3) δ -75.1 (br s, 3F), -74.6 (br s, 3F), -73.3
(br s, 3F); MS (FAB) m/z 842 (C34H3981BrF6O2Sb+, 1), 186 (100%);
IR (KBr, cm-1) 3324 (w), 3065 (w), 3039 (w), 2965 (w), 2871
(w), 1633 (w), 1585 (w), 1491 (w), 1449 (w), 1396 (w), 1302 (w),
1270 (m), 1241 (m), 1226 (m), 1184 (vs), 1142 (m), 1108 (m),
1076 (m), 1050 (m). Anal. Calcd for C34H29BrF9O2Sb: C, 48.49;
H, 3.47. Found: C, 48.58; H, 3.48. Minor isomer of 13d: 1H NMR
(500 MHz, CDCl3) δ 1.21 (s, 9H), 5.55 (s, 1H), 5.67 (br s, 1H),
6.91 (br, 1H), 7.10-7.13 (m, 5H), 7.19-7.39 (m, 4H), 7.43-7.46
(m, 1H), 7.47-7.64 (m, 3H), 7.64-7.79 (m, 4H); 19F NMR (470
Hz, CDCl3) δ -74.4 (s, 3F), -74.1 (q, 4JFF ) 9.9 Hz, 3F), -72.34
to -72.35 (m, 3F).
3H), 7.30-7.31 (m, 4H), 7.58-7.66 (m, 3H), 7.73 (t, JHH ) 7.4
Hz, 1H), 8.01 (d, 3JHH ) 7.3 Hz, 2H), 8.41 (d, 3JHH ) 8.4 Hz, 1H);
19F NMR (470 MHz, CDCl3) δ -78.0 (s, 3F), -75.5 (q, JHH
)
4
4
9.4 Hz, 3F), -74.4 (q, JHH ) 9.4 Hz, 3F).
1-[4-(tert-Butyl)phenyl]-3′,4′-diphenyl-3,3,4′-tris(trifluoro-
methyl)spiro{2,1-benzoxastibole-1(3H),2′λ5-[1,2]oxastibetane}
1
(14d). 14d: colorless solids; H NMR (270 MHz, CDCl3) δ 1.37
(s, 9H), 5.89 (s, 1H), 6.93-7.39 (m, 6H), 7.48-7.76 (m, 9H), 8.08
(d, JHH ) 8.4 Hz, 2H), 8.21 (d, JHH ) 7.5 Hz, 1H); 19F NMR
(254 MHz, CDCl3) δ -76.8 (q, 4JFF ) 7.9 Hz, 3F), -74.3 (q, 4JFF
) 7.9 Hz, 3F), -72.5 (s, 3F); MS (FAB) m/z 761 (M + H+, 8),
187 (100%). 15d: 1H NMR (270 MHz, CDCl3) δ 1.29 (s, 9H),
5.95 (s, 1H), 6.85-7.30 (m, 6H), 7.34-7.57 (m, 9H), 7.95 (d, 3JHH
) 8.1 Hz, 2H), 8.29 (d, 3JHH ) 7.5 Hz, 1H); 19F NMR (470 MHz,
3
3
1-[4-(tert-Butyl)phenyl]-3,3,4′,4′-tetrakis(trifluoromethyl)-
spiro{2,1-benzoxastibole-1(3H),2′λ5-[1,2]oxastibetane} (14a). To
a suspension of NaH (48 mg, 1.2 mmol) in THF (1 mL) was added
a solution of bromo(2-hydroxyalkyl)stiborane 13a (250 mg, 0.33
mmol) in THF (6 mL) at room temperature and the mixture was
stirred for 2 h. After the reaction mixture was filtered through Celite,
THF was removed in vacuo, and the residue was separated by
preparative gel permeation liquid chromatography (GPLC) (CHCl3)
to give 1,2-oxastibetane 14a (86%) as a colorless solid. 14a:
4
4
CDCl3) δ -76.8 (q, JFF ) 8.2 Hz, 3F), -74.6 (q, JFF ) 8.2 Hz,
3F), -73.2 (s, 3F).
1-Benzyl-1-bromo-1-[4-(tert-butyl)phenyl]-3,3-bis(trifluoro-
methyl)-3H-2,1-benzoxastibole (16). To a solution of benzylstibo-
rane 12 (73 mg, 0.10 mmol) in CCl4 (4 mL) was added dropwise
a solution of bromine (12 mL, 0.20 mmol) in CCl4 (1 mL) at 0 °C
in the dark. After the mixture was stirred at room temperature for
30 min, the solvent was removed and the residue was washed with
hexane to give 16 (65 mg, 98%) as a colorless solid. 16: colorless
1
colorless crystals (hexane); mp 148-150 °C dec; H NMR (500
2
1
MHz, CDCl3) δ 1.32 (s, 9H), 4.09 (d, JHH ) 14.1 Hz, 1H), 4.41
crystals (hexane), mp 132-133.5 °C dec; H NMR (500 MHz,
2
3
(d, JHH ) 14.1 Hz, 1H), 7.62 (d, JHH ) 8.3 Hz, 2H), 7.71-7.74
CDCl3) δ 1.27 (s, 9H), 4.13 (d, 2JHH ) 11.3 Hz, 1H), 4.28 (d, 2JHH
) 11.3 Hz, 1H), 7.18-7.20 (m, 3H), 7.25-7.27 (m, 2H), 7.37 (d,
3
3
(m, 2H), 7.89 (br d, JHH ) 7.0 Hz, 1H), 7.92 (d, JHH ) 8.3 Hz,
2H), 8.02 (dd, 3JHH ) 7.0 Hz, 4JHH ) 1.8 Hz, 1H); 13C{1H} NMR
3
3JHH ) 8.5 Hz, 2H), 7.68-7.76 (m, 4H), 7.85 (br d, JHH ) 7.5
668 J. Org. Chem., Vol. 71, No. 2, 2006

Pentacoordinate 1,2-Oxastibetanes
3
4
Hz, 1H), 8.55 (dd, JHH ) 7.5 Hz, JHH ) 1.5 Hz, 1H); 13C{1H}
(FAB) m/z 839 (M + H+, 3), 573 (100%); HRMS (FAB) m/z calcd
for C40H35F9O2Sb [M + H+] 839.1532, found 839.1582. Minor
isomer of 39: 1H NMR (500 MHz, CDCl3) δ 1.16 (s, 9H), 4.34 (s,
NMR (126 MHz, CDCl3) δ 31.0 (s), 34.8 (s), 47.8 (s, CH2), 80.6
2
1
1
(sept, JCF ) 30 Hz), 123.4 (q, JCF ) 289 Hz), 123.6 (q, JCF
)
3
289 Hz), 126.0 (s), 127.4 (s), 127.5 (s), 128.5 (s), 130.0 (s), 130.1
(s), 131.0 (s), 131.3 (s), 132.1 (s), 132.7 (s), 134.5 (s), 135.5 (s),
1H), 6.50 (d, JHH ) 8.6 Hz, 1H), 6.98-7.12 (m, 8H), 7.15-7.18
(m, 2H), 7.51-7.61 (m, 7H), 7.65-7.68 (m, 3H), 7.68-7.70 (m,
1H), 7.86-7.88 (m, 1H), 8.46 (s, 1H, OH); 19F NMR (470 MHz,
CDCl3) δ -77.0 to -76.9 (m, 3F), -74.3 to -74.5 (m, 3F), -73.6
to -73.5 (m, 3F).
137.4 (s), 155.3 (s); 19F NMR (254 Hz, CDCl3) δ -75.7 (q, 2JFF
)
8.9 Hz, 3F), -74.7 (q, 2JFF ) 8.9 Hz, 3F); MS (FAB) m/z 668 (M
+ H+, 5), 91 (100%). Anal. Calcd for C26H24BrF6OSb: C, 46.74;
H, 3.62. Found: C, 46.64; H, 3.77.
Thermolysis of (2-Hydroxyalkyl)stiborane 7c in the Presence
of LiH. To a solution of 7c (89 mg, 0.10 mmol) in PhCN (1.0 mL)
was added LiH (2.3 mg, 0.29 mmol) at room temperature and the
reaction mixture was stirred at room temperature for 0.5 h. The
mixture was stirred at 140 °C for 6 h. The solvent was removed
under reduced pressure and the residue was separated by GPLC
(CHCl3) to give olefin 30 (56 mg, 87%) and a mixture (21 mg) of
34 (30%) and 35 (58%) as a white solid.31 A 1:2 mixture of 34
and 35: 1H NMR (500 MHz, CDCl3) δ 1.26 (s, 72H), 1.30 (s,
18H), 1.47 (s, 1H, OH), 7.23 (d, J ) 8.4 Hz, 16H), 7.34-7.39 (m,
1-Benzyl-1-[4-(tert-butyl)phenyl]-3,3-bis(trifluoromethyl)-3H-
2,1-benzoxastibonium Trifluoromethanesulfonate (17). A mix-
ture of benzylbromostiborane 16 (410 mg, 0.615 mmol) and AgOTf
(210 mg, 0.734 mmol) in THF (10 mL) was stirred at room
temperature for 2 h, and filtered through Celite. Removal of the
solvent gave 17 (452 mg, 100%) as a colorless oil. 17: colorless
1
2
oil; H NMR (500 MHz, CDCl3) δ 1.26 (s, 9H), 4.26 (d, JHH
)
2
14.9 Hz, 1H), 4.54 (d, JHH ) 14.9 Hz, 1H), 7.23-7.27 (m, 3H),
3
3
7.33 (d, JHH ) 6.2 Hz, 2H), 7.44 (s, 4H), 7.79 (t, JHH ) 7.2 Hz,
3
3
3
3
5H), 7.51 (d, JHH ) 8.4 Hz, 4H), 7.58 (t, JHH ) 8.1 Hz, 4H),
7.62-7.66 (m, 18H), 7.88 (d, 3JHH ) 7.7 Hz, 4H), 8.01 (d, 3JHH
1H), 7.83 (t, JHH ) 7.2 Hz, 1H), 7.91 (d, JHH ) 7.2 Hz, 1H),
8.35 (d, 3JHH ) 7.2 Hz, 1H); 13C{1H} NMR (126 MHz, CDCl3) δ
)
8.4 Hz, 4H), 8.20 (d, 3JHH ) 7.2 Hz, 4H), 8.31 (d, 3JHH ) 7.1 Hz,
1H); 13C{1H} NMR (126 MHz, CDCl3) δ 31.1 (s), 34.5 (s), 34.9
(s), 79.5 (sept, 2JCF ) 29 Hz), 123.9 (q, 1JCF ) 290 Hz), 126.0 (s),
126.5 (s), 127.4 (s), 127.5 (s), 130.1 (s), 130.5 (s), 130.8 (s), 131.3
(s), 131.7 (s), 131.8 (s), 132.1 (s), 133.9 (s), 134.1 (s), 134.3 (s),
134.4 (s), 134.7 (s), 137.8 (s), 138.4 (s), 154.1 (s), 155.1 (s). An
aliphatic carbon of the t-Bu group, two quaternary carbons of CF3
group, and two aromatic carbons were not observed; 19F NMR (254
Hz, CDCl3) δ -75.0 (s, 24F), -74.9 (s, 6F); FAB-MS m/z 1275
(M + H+ for 35), 646 (M+ for 34).
2
30.9 (s), 35.0 (s), 41.7 (s, CH2), 82.2 (sept, JCF ) 29 Hz), 119.3
(q, 1JCF ) 319 Hz, Tf), 123.0 (q, 1JCF ) 288 Hz), 125.4 (s), 127.2
(s), 127.8 (s), 127.9 (s), 128.3 (s), 129.0 (s), 129.6 (s), 130.1 (s),
132.7 (s), 133.5 (s), 133.8 (s), 134.8 (s), 138.3 (s), 156.8 (s); 19F
NMR (254 Hz, CDCl3) δ -77.2 (s, 3F), -75.6 (q, 2JFF ) 8.0 Hz,
3F), -75.2 (q, JFF ) 8.0 Hz, 3F); MS (FAB) m/z 587 (M+
-
2
TfO, 21), 91 (100%).
1-[4-(tert-Butyl)phenyl]-3′-phenyl-3,3,4′,4′-tris(trifluorometh-
yl)spiro{2,1-benzoxastibole-1(3H),2′λ5-[1,2]oxastibetane} (14e).
To a solution of stibonium triflate 17 (196 mg, 0.270 mmol) in
THF (5 mL) was added at -78 °C a THF solution (3 mL) of
LiTMP, which was prepared from tetramethylpiperidine (0.18 mL,
1.00 mmol) and n-BuLi (0.65 mL, 1.0 mmol) at -78 °C for 10
min. After the reaction mixture was further stirred for 10 min, HFA
gas, which was generated by dehydration of HFA‚3H2O (1.5 mL,
11 mmol), was bubbled to the reaction solution at -78 °C for 2 h,
and the solution was warmed slowly to room temperature. The
mixture was treated with aqueous NH4Cl and extracted with Et2O.
The extracts were washed with H2O and brine and dried with
MgSO4. After removal of the solvent, the residue was separated
by GPLC (CHCl3) and preparative thin-layer chromatography
(PTLC) (SiO2, hexane/CH2Cl2 ) 1/1) to give a mixture containing
14e (4.2 mg, 2%). 14e: 1H NMR (270 MHz, CDCl3) δ 6.06 (s,
1H), other aliphatic and aromatic signals could not be assigned;
19F NMR (254 Hz, CDCl3) δ -71.9 (q, 2JFF ) 9.1 Hz, 3F), -74.3
The Flash Vacuum Pyrolyses (FVP) of 3 and 14a. A quartz
tube containing the starting materials (16 mg of 3 or 14a) was
evacuated and the pressure was kept in 1 × 10-1 Torr under a
gentle and constant stream of nitrogen gas throughout the pyrolysis.
To assist sublimation of the starting materials, 3 and 14a, the head
of the quartz tube was preheated with a ribbon heater at 47-50
and 105-107 °C, respectively, and the sublimed starting materials
were pyrolyzed by passing through the quartz tube filled with quartz
fillings heated at 500 °C in the oven. The decomposed products
were accumulated in a trap cooled with liquid nitrogen. Heating
was continued for 6 h and the products in a trap were analyzed by
GC-MS and 19F NMR spectroscopy. The yields of the products
were summarized in Table 3.
A Typical Procedure of the Thermolysis of 3-Phenyl-1,2-
oxastibetane (14c). In an NMR tube was placed an o-xylene-d10
(0.55 mL) solution of 1,2-oxastibetane 14c (10 mg, 0.013 mmol).
After several freeze-pump-thaw cycles, the tube was evacuated
and sealed. The solution was heated at 220 °C for 17 h while being
monitored by 1H and 19F NMR spectroscopy. The reaction
conditions and the yields are summarized in Table 4. The products
of the thermolysis, oxirane 28 with retention of configuration,28
1,3-dihydro-3,3-bis(trifluoromethyl)-1-(4-tert-butylphenyl)-1,2-ben-
zoxastibole 25, olefin 30,29 and oxirane 29 with inversion of relative
configuration,30 were identified with authentic samples. 25: color-
2
2
(q, JFF ) 8.1 Hz, 3F), -76.8 (q, JFF ) 8.9 Hz, 3F), -77.0 (q,
2JFF ) 8.6 Hz, 3F); MS (FAB) m/z 753 (M + H).
1-[4-(tert-Butyl)phenyl]-1-(2-hydroxy-1,2-diphenyl-3,3,3-tri-
fluoropropyl)-1-phenyl-3,3-bis(trifluoromethyl)-3H-2,1-benzox-
astibole (39). To a solution of 14c (11 mg, 0.014 mmol) in THF
(0.5 mL) was added PhLi (2.28 M, 7.0 µL, 0.016 mmol) at room
temperature and the mixture was stirred at room temperature for 1
h. The mixture was treated with aqueous NH4Cl and extracted with
Et2O. The organic layer was washed with brine and dried with
MgSO4. After removal of the solvent, the residue was separated
by PTLC (hexane/CHCl3 ) 1/1) to give a mixture of diastereomers
(20:1) of 39 (11 mg, 94%). Major isomer of 39: 1H NMR (500
MHz, CDCl3) δ 1.42 (s, 9H), 4.38 (s, 1H), 6.59 (d, 3JHH ) 7.5 Hz,
2H), 6.98-7.12 (m, 8H), 7.15-7.18 (m, 2H), 7.42-7.44 (m, 2H),
1
less solid (hexane/CHCl3 ) 1/1), mp 138-139 °C dec; H NMR
(270 MHz, CDCl3) δ 1.27 (s, 9H), 7.39 (s, 4H), 7.52-7.64 (m,
3
3H), 7.80 (d, JHH ) 7.3 Hz, 1H); 19F NMR (254 Hz, CDCl3) δ
2
2
-77.2 (q, JFF ) 8.9 Hz, 3F), -74.9 (q, JFF ) 8.9 Hz, 3F); MS
(FAB) m/z 496 (M+). Anal. Calcd for C19H17F6OSb: C, 45.91; H,
3.45. Found: C, 45.78; H, 3.55.
3
3
7.51-7.61 (m, 7H), 7.69 (d, JHH ) 7.5 Hz, 1H), 7.88 (br d, JHH
) 7.4 Hz, 1H), 8.53 (s, 1H, OH); 13C{1H} NMR (126 MHz, CDCl3)
δ 31.3 (s), 34.5 (s), 65.4 (s), 78.1 (q, 2JCF ) 27 Hz), 123.4 (q, 1JCF
Thermolysis of 1,2-Oxastibetane 14c in the Presence of PhLi.
To a solution of 14c (11 mg, 0.014 mmol) in THF (0.5 mL) was
1
1
) 291 Hz), 123.6 (q, JCF ) 289 Hz), 124.0 (q, JCF ) 290 Hz),
126.4 (s), 127.4 (s), 127.5 (s), 127.6 (s), 127.8 (s), 128.1 (s), 130.0
(s), 130.1 (s), 130.3 (s), 130.8 (s), 131.5 (s), 131.7 (s), 133.6 (s),
133.7 (s), 134.3 (s), 134.5 (s), 134.6 (s), 134.8 (s), 136.1 (s), 136.6
(s), 137.4 (s), 153.3 (s). A quaternary carbon due to C(CF3)2 was
not observed.; 19F NMR (470 Hz, CDCl3) δ -77.1 to -77.0 (m,
(28) Shanklin, J. R.; Johnson, C. R.; Ollinger, J.; Coates, R. M. J. Am.
Chem. Soc. 1973, 95, 3429.
(29) Nader, B. S.; Cordova, J. A.; Reese, K. E.; Powell, C. L. J. Org.
Chem. 1994, 59, 2898.
(30) House, H. O. J. Am. Chem. Soc. 1955, 77, 3070.
(31) The yields of 30, 34, and 35 were calculated assuming that 1 mol
of 7c gives 1 mol of 30 and 34, and 0.5 mol of 35, respectively.
4
3F), -74.6 (q, JFF ) 9.4 Hz, 3F), -73.6 to -73.5 (m, 3F); MS
J. Org. Chem, Vol. 71, No. 2, 2006 669

Uchiyama et al.
added PhLi (2.28 M, 7.0 µL, 0.016 mmol) at room temperature
and the mixture was stirred for 1 h. After the solvent was exchanged
from THF to PhCN (0.5 mL), the reaction mixture was heated at
140 °C for 6 h to give olefin 30 (72%) and bis(stiboranyl)oxide
38, which was assigned by FAB-MS spectra.
data and selected bond lengths and angles for 3, 14a, and 14c are
summarized in Tables 1 and 2.
Acknowledgment. This work was supported by Grants-in-
Aid for The 21st Century COE Program for Frontiers in
Fundamental Chemistry (T.K.) and for Scientific Research
(T.K.) from the Ministry of Education, Culture, Sports, Science
and Technology of Japan. We thank Central Glass and Tosoh
Finechem Corporation for the gifts of organofluorine compounds
and organolithium reagents, respectively.
X-ray Crystallographic Analyses of 3, 14a, and 14c. Single
crystals of 3, 14a, and 14c were grown by the slow evaporation of
the saturated hexane solution at room temperature. A colorless block
crystal of 3, 14a, and 14c having approximate dimensions of 0.60
× 0.40 × 0.25 mm3, 0.20 × 0.20 × 0.15 mm3, and 0.15 × 0.10 ×
0.05 mm3, respectively, was mounted on a glass fiber. All
measurements were made on a Rigaku Mercury-CCD with graphite
monochromated Mo KR radiation (λ ) 0.71070 Å). The structure
was solved by direct methods and expanded by using Fourier
techniques. All non-hydrogen atoms were refined anisotropically,
while hydrogen atoms were refined isotropically. There are four
and two independent molecules of 3 and 14a, which have slightly
different structures in the unit cell, respectively. Crystallographic
Supporting Information Available: Experimental procedures
of 6, 7b, 13b-d, 14b-d, 15b, and 15d, physical and spectral data
of 6, 8, and 9, and data for the X-ray crystallographic analyses of
3, 14a, and 14c (CIF). This material is available free of charge via
the Internet at http://pubs.acs.org.
JO0520700
670 J. Org. Chem., Vol. 71, No. 2, 2006