Regioselective opening of epoxides catalyzed by Sn (IV). A new method for the synthesis of halohydrins?

Article abstract of DOI:10.3390/50300468

The regioselective opening of epoxides with organotin oxides 1 and 2, in presence of halogenated alcohols was developed, yielding the halohydrin derivatives.

Full text of DOI:10.3390/50300468

468
Molecules 2000, 5
Regioselective Opening of Epoxides Catalyzed by Sn (IV).
A New Method for the Synthesis of Halohydrins?
Claudio J. Salomon
Facultad de Cs. Bioquímicas y Farmacéuticas. IQUIOS-CONICET, Universidad Nacional de Rosario.
Suipacha 531, 2000 Rosario, Argentina
E-mail: salomon@citynet.net.ar
Abstract: The regioselective opening of epoxides with organotin oxides 1 and 2, in pres-
ence of halogenated alcohols was developed, yielding the halohydrin derivatives.
Introduction
Epoxides are among the most versatile intermediates in organic chemistry due to the particular po-
larity and strength of their three member ring. Those characteristics make them in a very suitable sub-
strate to the attack or many nucleophilic and electrophilic reagents [1].
The regioselective opening of oxiranes has been the subject of interest for many years, since these
heterocyclics are frequently used as starting material for the preparation of natural products and bio-
logical active compounds [2].
Many different organotin reagents have been employed to effect the regio- and stereoselective
cleavage of oxiranes in the presence of nucleophiles affording 1,2-alcoxialcohols, 1,2-aminoalcohols,
1, 2-azidoalcohols, etc [3].
Results and Discussion
As a part of our ongoing research work concerning the development of organotin reagents for the
opening of epoxides [4], the bis(tributyltin) oxide (1) and bis(chlorodibutyltin) oxide (2) were sub-
jected to act as Lewis acids assisting the opening of epoxides in the presence of halogenated alcohols.
When styrene oxide was reacted with t-BuOH and 1, the starting material was recovered unchanged
after 5 days, probably due to steric hindrances. However, when the same reaction was carried out using
the oxide 2, after 3 days a compound was isolated and identified as the chlorohydrin. In this case,
bis(chlorodibutyltin) oxide would act as a Lewis acid and, moreover, as a chloride donor.
In view of the result described above, we decided to extend the study using a series of halogenated
alcohols as a nucleophiles in the presence of the organotin oxides 1 or 2.
These results outlined in Scheme 1, shows the formation of the halohydrin derivatives in very good

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Molecules 2000, 5
yield by the highly regioselective opening of styrene oxide.
Cl
H
OH
Ph
2
t-BuOH
O
1
N. R.
Ph
t-BuOH
1 o 2
X
O
X
OH
H
OH
Ph
X=F, Cl, Br
However, when the same methodology was applied to other monosubstituted epoxides, the results
obtained were different. While the oxide 1, showed a low reactivity towards aliphatic oxiranes, the
oxide 2 was able to assist the cleavage of those heterocycles by the nucleophilic attack of the alcohol,
or by the chloride anion originated from (ClBu2Sn)2O.
The unusual formation of the chlorohydrin compounds would be due to the reaction of the nucleo-
phile with the reagent 2, and the subsequent nucleophilic attack of the chloride over the epoxide.
In summary, (ClBu2Sn)2O emerge as a new reagent for the regioselective opening of epoxides
yielding the chlorohydrin derivatives, in mild and non-hydrolytic conditions.
Acknowledgements: I wish to thanks to Dr. O.A.Mascaretti for his interest and to the Agencia Nacional
de Promoción Científica y Tecnológica (SECYT) and Universidad Nacional de Rosario for their finan-
cial support.
References and Notes
1. Smith, G. J. Synthesis 1984, 629.
2. Schanen, V.; Cherrier, M.; Melo, S.; Quirion, J.; Husson, H. P. Synthesis 1996, 833.
3. Hwang, G.; Chung, J.; Lee, W. J. Org. Chem. 1996, 61, 6183.
4. Salomon, C.J.; Laborde, M.A; Gonzalez Sierra, M.; Mascaretti, O.A. Main Group Metal Chemis-
try 1998, 21, 617.