Efficient regio- and stereoselective conversions of oxiranes and aziridines into β-(nitrooxy)-substituted alcohols and amines by using bismuth nitrate

Article abstract of DOI:10.1002/hlca.200790002

Oxiranes and aziridines efficiently undergo ring opening with bismuth nitrate at room temperature to furnish the corresponding β-(nitrooxy)- substituted alcohols and amines respectively. The conversions are highly regio- and stereoselective and afford the

Full text of DOI:10.1002/hlca.200790002

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Helvetica Chimica Acta – Vol. 90 (2007)
Efficient Regio- and Stereoselective Conversions of Oxiranes and Aziridines
into b-(Nitrooxy)-Substituted Alcohols and Amines by Using Bismuth
Nitrate1)
by Biswanath Das*, Maddeboina Krishnaiah, Katta Venkateswarlu, and Vtukuri Saidi Reddy
Organic Chemistry Division-I, Indian Institute of Chemical Technology, Hyderabad-500 007, India
(phone: +91-40-7193434; fax: +91-40-7160512; e-mail: biswanathdas@yahoo.com)
Oxiranes and aziridines efficiently undergo ring opening with bismuth nitrate at room temperature
to furnish the corresponding b-(nitrooxy)-substituted alcohols and amines respectively. The conversions
are highly regio- and stereoselective and afford the nitrooxy-compounds in excellent yields within a short
period of time.
Introduction. – Oxiranes [1] and aziridines [2] are important precursors in organic
synthesis. They can easily be cleaved with nucleophiles forming regio- and stereoselec-
tive ring-opened products. The ring-opening reactions of these compounds have been
studied with various nucleophiles [3]. However, the applications of nitrate ions as
nucleophiles for these reactions are limited. b-(Nitrooxy)-substituted alcohols and
amines are functionalized alkyl nitrates which can be employed as intermediates in
organic synthesis [4]. Oxiranes were previously converted into b-(nitrooxy) alcohols
by ring opening with concentrated HNO3 [5a], ceric ammonium nitrate (CAN) [5b],
or NO in air [5c]. All of these methods are associated with several drawbacks. The
first method afforded the products in low yields under strongly acidic conditions.
CAN converted ꢀstyrene oxideꢁ into benzaldehyde as major product. The reactions
of oxiranes with this reagent were generally conducted at high temperature (808),
and regioselectivity for opening of some oxiranes are weak. The conversion of oxiranes
[5c] and aziridines [4] with NO required long reaction times (12–32 h). Recently, we
have also reported [6] the ring opening of these compounds using zirconyl nitrate to
prepare b-(nitrooxy)-substituted alcohols and amines. However, this method was
unsuitable for the conversion of 2-aryl-1-tosylaziridines as significant amounts of the
corresponding b-amino alcohols were also formed. Moreover, the conversion times
with 2-alkylaziridines and bicyclic aziridines were high (4.5–8 h). Thus, we searched
for an alternative better method for ring opening of both oxiranes and aziridines
with nitrate ions. As a result of our continuous efforts for the synthesis of b-
(nitrooxy)-substituted alcohols and amines we discovered that these compounds can
efficiently be prepared from oxiranes and aziridines by using bismuth nitrate at room
temperature.
1
)
Part 106 in the series, ꢀStudies on novel synthetic methodologiesꢁ; IICT Communication No. 061215.
ꢂ 2007 Verlag Helvetica Chimica Acta AG, Zürich

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Results and Discussion. – Various oxiranes and N-tosylaziridines were treated with
bismuth nitrate in MeCN to form the nitrooxy compounds in excellent yields (Scheme
and Table). They were also treated with other, different metal nitrates such as lantha-
num nitrate and silver nitrate under similar reaction conditions, but no nitrooxy prod-
ucts could be detected. Bismuth nitrate acted here both as a reagent and as a catalyst.
The time required to cleave 2-aryloxiranes and 2-aryl-1-tosylaziridines was only 15–20
min. Bicyclic oxiranes also underwent cleavage within similar times. However, in the
case of 2-alkyloxiranes as well as 2-alkyl-1-tosylaziridines, somewhat longer times
(1.5–2 h) were required. Contrary to our previous observation [6], no b-amino alcohols
were obtained by ring opening of 2-arylaziridines with bismuth nitrate. Thus, the pres-
ent method represents an improved protocol for the synthesis of b-(nitrooxy) alcohols
and amines.
Scheme 1
The conversions of both oxiranes and aziridines took place with high regio- and ster-
eoselectivity. The 2-aryloxiranes and 2-aryl-1-tosylaziridines yielded the products
formed by opening at the benzylic ring position, while 2-alkyloxiranes and 2-alkyl-1-
tosylaziridines furnished the products formed by cleavage at the unsubstituted ring
position. Bicyclic oxiranes and aziridines underwent stereoselective ring cleavage in
anti manner forming the products with trans-configuration. The structures and config-
1
urations of the products were confirmed by comparison of their spectral (IR, H- and
13C-NMR, and MS) values with those reported earlier [6].
In conclusion, we reported an improved and advantageous method for the ring
opening of oxiranes and aziridines by using bismuth nitrate at room temperature to
form the corresponding b-(nitrooxy)-substituted alcohols and amines, respectively, in
high yields and with impressive regio- and stereoselectivity. The method is equally
applicable for the conversion of 2-aryl- and 2-alkyloxiranes and -aziranes and of bicy-
clic oxiranes and aziridines.
The authors thank UGC, New Delhi, for financial assistance.
Experimental Part
General Procedure. To a soln. of an oxirane or 1-tosylaziridine (1 mmol) in MeCN (5 ml), bismuth
nitrate (1.2 mmol) was added. The mixture was stirred at r.t., and the reaction was followed by TLC.

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Helvetica Chimica Acta – Vol. 90 (2007)
Table. Bismuth Nitrate Mediated Ring Opening of Oxiranes and Aziridinesa)
Oxirane or aziridine
Product
Time [min] Isolated yield [%]b)
8090
9089
9091
9088
45
94
98
4092
15
2085
2096
2098
c
c
12090
12083
15
)
)
98

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Table (cont.)
Oxirane or aziridine
Product
Time [min] Isolated yield [%]b)
15
95
9094
9095
1
a) The structures of the products were established from their spectral (IR, H- and 13C-NMR, and MS)
and analytical data and by comparision of the values with those reported earlier for the known com-
c
pounds [6]. b) With respect to isolated material. ) The other regioisomer (ca. 5%) was also obtained.
After completion, the reaction was quenched with H2O (10ml), and the mixture was extracted with
AcOEt (3”5 ml). The extract was concentrated and subjected to column chromatography (silica gel, hex-
ane/AcOEt 9 :1): pure b-(nitrooxy) alcohol or amine.
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Received September 7, 2006