Preparation of oxetanes by silicon-directed 4-exo trig electrophilic cyclisations of homoallylic alcohols

Article abstract of DOI:10.1016/S0040-4039(01)00227-1

The reaction of homoallylic alcohols with bis(sym-collidine)bromine(I) hexafluoroantimonate led in good yields to the formation of oxetanes if a silyl group was fixed on the carbon-carbon double bond in terminal position. This reaction was stereospecific when no supplementary substituent was present on the double bond.

Full text of DOI:10.1016/S0040-4039(01)00227-1

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 42 (2001) 2481–2484
Preparation of oxetanes by silicon-directed 4-exo trig
electrophilic cyclisations of homoallylic alcohols
Mazin Rofoo, Marie-Claude Roux and Ge´rard Rousseau*
Laboratoire des Carbocycles (Associe´ au CNRS), Institut de Chimie Mole´culaire d’Orsay, Baˆt. 420, Universite´ de Paris-Sud,
91405 Orsay, France
Received 15 November 2000; accepted 2 February 2001
Abstract—The reaction of homoallylic alcohols with bis(sym-collidine)bromine(I) hexafluoroantimonate led in good yields to the
formation of oxetanes if a silyl group was fixed on the carbonꢀcarbon double bond in terminal position. This reaction was
stereospecific when no supplementary substituent was present on the double bond. © 2001 Elsevier Science Ltd. All rights
reserved.
We have reported in the preceding paper that oxetanes
could be obtained in good yields by electrophile driven
4-endo cyclisation of cinnamic alcohols.1 It was
expected that formation of oxetanes by 4-exo cyclisa-
tions of homoallylic alcohols could be a more easier
reaction pathway.2 In fact, the cyclisations of these
alcohols led mainly to the formation of tetrahydrofuran
ring system by 5-endo processes.3 However, some
results have already been reported concerning the for-
mation of oxetanes by this reaction. In general, mix-
tures of oxetanes and tetrahydrofurans were obtained,4
except when the structure of the alcohols did not
allow,5 or disfavoured6 the 5-endo process.
concerning such a possibility by reaction of a particular
alcohol with NBS.9 However, attempts of cyclisations
using a selenium reagent were unsuccessful.7c We
thought that bis(collidine)bromine(I) hexafluorophos-
phate could be an excellent electrophile for these cycli-
sations. Different alcohols possessing a carbonꢀcarbon
double bond of E-stereochemistry were prepared, as
outlined in Scheme 2, by reaction of the anions derived
from allylsilanes with carbonyl compounds.10
The starting allylsilanes were either commercially avail-
able (allyltrimethylsilane) or prepared by reaction of the
corresponding Grignard reagents in THF with the
chlorosilane in the presence of a catalytic amount of
CuCN (25°C, 24 h). The alcohol 1a possessing a car-
Intramolecular cyclisations of functionalised vinylsi-
lanes are recognised to favour the formation of hetero-
cycles by exo processes (Scheme 1). These reactions
were used for the formation of cyclic ethers,7 and
amines7c,8 using Lewis acids or NBS as reagents.
We decided to examine the preparation of oxetanes by
this process. There is already one report in the literature
Scheme 1.
Scheme 2.
* Corresponding author. Fax: 33 1.69.15.62.78; e-mail: grousseau@icmo.u-psud.fr
0040-4039/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(01)00227-1

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M. Rofoo et al. / Tetrahedron Letters 42 (2001) 2481–2484
bonꢀcarbon double bond of Z-stereochemistry was pre-
pared by DIBALH reduction11 of the corresponding
acetylenic compound12 (Scheme 3).
in methylene chloride at reflux.14 Our results are
reported in Table 1. The structures of the products 2
were established from their spectral data.15 In the case
of tertiary alcohols unsubstituted on the carbonꢀcarbon
double bond only one diastereoisomer was isolated
(entries a–c, e). Their stereochemistries were deduced
from their NMR spectra supposing the anti addition of
the alcohol function and the bromonium on the CC
double bonds. This means that vinylsilane 1a of Z
stereochemistry led to the oxetane 2a, while the vinyl
silane 1b of E stereochemistry led to the oxetane 2b
In a preliminary study, we found that reaction of
vinylsilanes with bis(collidine)bromine(I) nitrate or hexa-
fluorophosphate led to oxetanes in modest to low
yields. Numerous unidentified products were generally
formed. However, clean reactions were observed using
bis(collidine)bromine(I) hexafluoroantimonate.13 Best
yields were obtained when the reactions were conducted
Scheme 3.
Table 1. Reaction of vinylsilanes with biscollidinebromine(I) hexafluoroantimonate

M. Rofoo et al. / Tetrahedron Letters 42 (2001) 2481–2484
2483
Scheme 4.
diastereoisomer of 2a. When a methyl group was fixed
on the carbonꢀcarbon double bond a mixture of two di-
astereoisomers was obtained (entries f, g) whose stereo-
chemistries were not determined. However, we can con-
clude from these results, that the formation of oxetanes
occurred by intervention of a bromonium (vinylsilanes
1a–e), or a carbocation (vinylsilanes 1f–h) depending of
the substitution of the carbonꢀcarbon double bond.
With the secondary alcohol 1d, we could expect that the
cyclisation was also diastereospecific. In fact we
obtained a mixture of two isomers, due to the low facial
diastereoselection induced by the cyclohexyl group. The
stereochemistry of these two diastereomers was deter-
mined by a NOESY experiment. In the case of alcohol
1h, we isolated only two diastereoisomers, instead of
the four possible, whose stereochemistries were not
established.
Rheingold, A. L.; Concolino, T. Tetrahedron Lett. 1999,
40, 7051–7053.
7. (a) Miura, K.; Hondo, T.; Saito, H.; Ito, H.; Hosomi, A.
J. Org. Chem. 1997, 62, 8292–8293 and references cited
therein; (b) Adiwidjaja, G.; Floerke, H.; Kirschning, A.;
Schaumann, E. Liebigs Ann. Org. Bioorg. Chem. 1995,
501–508; (c) Fragale, G.; Wirth, T. Eur. J. Org. Chem.
1998, 1361–1369.
8. Miura, K.; Hondo, T.; Nakagawa, T.; Takahashi, T.;
Hosomi, A. Org. Lett. 2000, 2, 385–388.
9. Ehlinger, E.; Magnus, P. J. Am. Chem. Soc. 1980, 102,
5004–5011.
10. Semeyn, C.; Blaauw, R. H.; Hiemstra, H.; Speckamp, W.
H. J. Org. Chem. 1997, 62, 3426–3427.
11. Marko´, I. E.; Bayston, D. J. Tetrahedron 1994, 50, 7141–
7156.
12. Compain, P.; Gore´, J.; Vate`le, J.-M. Tetrahedron 1996,
52, 10405–10416.
We examined also the reactivity of bis(col-
lidine)iodine(I) hexafluoroantimonate with the vinylsi-
lane 1b. We obtained the oxetane 3 in 35% yield
(Scheme 4). This reagent appears thus less interesting
that the bromo reagent for the preparation of oxetanes.
13. This reagent was prepared in two steps (70% overall
yield) by reaction of silver hexafluoroantimonate with
collidine in water, followed by reaction of the silver salt
with bromine as reported for the preparation of the
hexafluorophosphate salt. See: Homsi, F.; Robin, S.;
Rousseau, G. Org. Synth. 2000, 77, 206–211.
14. Representative procedure: To a solution of alcohol (2
mmol) in methylene chloride (10 mL) heated at reflux was
added over 6 h a methylene chloride solution (40 mL) of
bis(collidine)bromine(I) hexafluoroantimonate (5 mmol).
After complexion of the addition and cooling, the solvent
was removed under vacuum and the residue purified by
liquid chromatography over silica gel (hexanes–ether).
In conclusion, we report that formation of oxetanes by
4-exo electrophilic cyclisation of homoallylic alcohols
using bis(collidine)bromine hexafluoroantimonate is an
efficient process, if a silicon atom is fixed in terminal
position on the carbonꢀcarbon double bond. These
cyclisations are diastereospecific when the carbon of the
double bond in b of the silicon atom is non substituted.
1
15. Selected data: Oxetane 2a: H NMR (CDCl3, 250 MHz)
l 4.72 (q, J=8 Hz, 1H), 3.38 (d, J=10 Hz, 1H), 2.35 (dd,
J=6 and 11 Hz, 1H), 2.08 (dd, J=6 and 11 Hz, 1H),
2.00–1.20 (m, 10H). Oxetane 2b: H NMR 4.75 (q, J=7
References
1
Hz, 1H), 3.45 (d, J=7 Hz, 1H), 2.42–2.20 (m, 2H),
2.00–1.00 (m, 10H). 13C NMR 81.7, 74.7, 47.5, 39.1, 38.2,
37.9, 25.1, 22.8, 22.2, −2.3. Oxetane 2c: 1H NMR 4.65 (q,
J=7 Hz, 1H), 3.40 (d, J=8 Hz, 1H), 2.45–2.20 (m, 2H),
1.80–1.10 (m, 8H), 1.05–0.80 (m, 6H), 0.15 (s, 9H). 13C
NMR 83.7, 76.4, 47.1, 42.3, 41.0, 37.5, 29.7, 16.6, 16.4,
14.5, −2.3. Oxetane 2d (major diastereomer): 1H NMR
4.75 (d, J=7 Hz, 1H), 4.26 (q, J=7 Hz, 1H), 3.35 (d,
J=8 Hz, 1H), 2.75–2.55 (m, 1H), 2.35–2.15 (m, 1H),
2.00–1.05 (m, 11H), 0.15 (s, 9H). 13C NMR 81.3, 77.3,
46.8, 44.5, 32.4, 27.7, 26.4, 26.0, 25.5, 25.3, −2.3. Oxetane
2d (minor diastereomer): 1H NMR 4.83–4.72 (m, 1H),
4.32 (q, J=7 Hz, 1H), 3.55 (d, J=5 Hz, 1H), 2.70–2.55
(m, 1H), 2.45–2.28 (m, 1H), 1.80–1.05 (m, 11H), 0.15 (s,
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1
9H). Oxetane 2e: H NMR 4.78 (q, J=8 Hz, 1H), 3.62
(d, J=8 Hz, 1H), 2.40–2.15 (m, 2H), 2.00–1.10 (m, 10H),
0.95 (s, 9H), 0.15 (s, 3H), 0.05 (s, 3H). 13C NMR 81.4,
74.7, 46.0, 38.6, 38.2, 37.5, 27.0, 25.2, 22.9, 22.3, 17.3,
−5.4, −6.5. Oxetane 2f (major diastereomer): 1H NMR
3.81 (s, 1H), 2.25 (d, J=9 Hz, 1H), 2.08 (d, J=9 Hz,

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M. Rofoo et al. / Tetrahedron Letters 42 (2001) 2481–2484
1H), 1.55 (s, 3H), 1.50–1.10 (m, 10H), 1.00 (s, 9H), 0.25
(s, 3H), 0.05 (s, 3H). Minor diastereomer: H NMR 3.60
(s, 1H), 2.35 (d, J=9 Hz, 1H), 2.15 (d, J=9 Hz, 1H),
diastereomer: 1H NMR 3.65 (s, 1H), 2.25 (q, 2H, AB
1
system), 1.55 (s, 3H), 1.50–1.10 (m, 10H), 1.05 (s, 3H),
0.97 (s, 9H), 0.19 (s, 3H), 0.18 (s, 3H). Oxetane 3: 1H
NMR 4.42 (q, J=7 Hz, 1H), 3.35 (d, J=9 Hz, 1H), 2.40
(dd, J=8 and 10 Hz, AB system (part A), 2.08 (dd, J=8
and 10 Hz, AB system (part B)), 1.90–1.50 (m, 10H), 0.10
(s, 9H).
1.54 (s, 3H), 1.50–1.10 (m, 10H), 1.00 (s, 9H), 0.20 (s,
1
6H). Oxetane 2g (major diastereomer): H NMR 3.89 (s,
1H), 2.20 (q, 2H, AB system), 1.50 (s, 3H), 1.50–1.10 (m,
10H), 0.97 (s, 9H), 0.20 (s, 3H), 0.03 (s, 3H). Minor
.
.