378 J. CHEM. RESEARCH (S), 1997
J. Chem. Research (S),
1997, 378–379†
An Efficient Nucleophilic Cleavage of Oxiranes to 1,2-Azido
Alcohols†
Chintamani Sarangi,a Nalin B. Das,*a Bhagabat Nanda,a Amalendu Nayaka and
Ram P. Sharmab
aRegional Research Laboratory, Bhubaneswar-751013, India
bCentral Institute of Medicinal and Aromatic Plants, Lucknow-226015, India
.
Regioselective ring opening of oxiranes has been induced by the SnCl2 2H2O–Mg–THF/NaN3–H2O system to give the
corresponding 1,2-azido alcohols in good yields.
Epoxides are valuable intermediates in organic synthesis
because their nucleophilic cleavage leads to 1,2-difunction-
alized systems.1 Preparations of 1,2-azidoalcohols have been
reported2–8 regioselectively through nucleophilic cleavage of
oxirane rings. The present work has been undertaken in
order to determine the general applicability of the reaction
with epoxides, as well as to determine the direction of ring
opening for a number of representative symmetrical and
unsymmetrical epoxides. In continuation of our earlier
studies on applications of metal reagents,9,10 we have found
attacks exclusively at the secondary carbon atom of the epox-
ide ring. This interesting observation proves the structure of
the corresponding azido alcohol (Table 1, entry 5) from its
known reduction product, 2-amino-2-phenylethanol, with the
reducing agent LiAlH4. This has been further attributed to
the fact that an unsaturated group, viz. phenyl, helps to pro-
mote the positively charged secondary carbon atom of the
epoxide ring, in the presence of a nucleophilic reagent, owing
to its high degree of resonance stabilization. The increase in
electrophilicity of the oxirane carbon with this system pro-
motes the participation of the azide anion with trans ster-
eoselectivity, which is probably due to steric and electronic
effects.
.
that SnCl2 2H2O–Mg/NaN3–H2O/THF is a promising sys-
tem for regioselective ring opening of oxiranes to the corre-
sponding 1,2-azido alcohols.
The cleavage of oxirane rings has also been tried using
.
SnCl2 2H2O–NaN3–THF alone but the reaction did not
R1
N3
OH
R2
SnCl2•2H2O/Mg/THF
NaN3 H2O
O
R2
occur. However, the use of a stoichiometric amount of mag-
nesium facilitated the reaction. In addition, the possibility
exists of active zero-valent tin generated in principle by the
reduction of SnII to Sn0 in the presence of magnesium effect-
ively inducing nucleophilic attack. The reaction has also been
tried with MgCl2 instead of SnCl2 for a longer period but no
trace of the required reaction product was obtained.
R1
+
In the system SnCl2·2H2O–Mg/NaN3–H2O with cyclohex-
ene oxide, azide ion readily attacks the epoxide ring carbon
through a bimolecular nucleophilic displacement reaction
which proceeds with inversion, to give the azido alcohol. In
unsymmetrical epoxides (entries 2, 3, 4 and 7), the ring open-
ing appears preferably at the less substituted carbon, leading
to nucleophilic attack occurring predominantly at the ster-
ically less hindered site. In the case of styrene oxide, azide ion
Owing to the general interest in the smooth and selective
cleavage of these compounds, the mild reaction conditions,
good yields and some possible synthetic generalization, the
.
SnCl2 2H2O–Mg–THF/NaN3–H2O system will be a useful
addition to existing methods.
Table 1 Oxirane ring opening with SnCl2 ·2H2O/Mg/THF/NaN3–H2O
Entry Oxirane
Time (t/h)
Producta
Yield (%)b
85
Lit. ref.
6, 7, 8
OH
O
1
0.5
N3
O
OH
N3
2
0.75
83
11
O
N3
OH
3
0.5
0.75
0.5
1.5
2
88
70
95
82
92
6, 7
3
O
N3
4
OH
N3
O
5
6, 7
8
Ph CH CH2
Ph CH CH2 OH
OH
O
Ph CH CH Ph
N3
6
7
Ph CH CH Ph
OH
O
6, 7
Ph
O CH2 CH CH2
Ph
O CH2 CH CH2 N3
aAll the products were confirmed by spectral data. bTotal yield of the regioisomers.
*To receive any correspondence.
Experimental
1H NMR spectra were recorded in deuteriochloroform on a
JEOL FX-90 instrument. IR spectra were recorded on a JASCO
FT/IR-5300 instrument in chloroform. Mass spectra were recorded
†This is a Short Paper as defined in the Instructions for Authors,
Section 5.0 [see J. Chem. Research (S), 1997, Issue 1]; there is there-
fore no corresponding material in J. Chem. Research (M).
Sarangi, Chintamani
