Asian Journal of Chemistry; Vol. 29, No. 3 (2017), 614-616
A
SIAN
J
OURNAL OF HEMISTRY
C
Synthesis of 4-Chloro-5,6-dihydro-2H-pyran Derivatives by NbCl5
Mediated Cyclization of Epoxides with Homopropargylic Alcohols
1,2
3,*
1
2
N. MARUTHI RAJU , K. RAJASEKHAR , J. MOSES BABU and B. VENKATESWARA RAO
1Custom Pharmaceutical Services, Dr. Reddy’s Laboratories Limited, Bollaram Road, Miyapur, Hyderabad-500 049, India
2Department of Organic Chemistry, Foods, Drugs and Water, Andhra University, Visakhapatnam-530 003, India
3Ragas Pharmaceuticals Private Limited (OPC), IDA Cherlapally, Hyderabad-500 051, India
*Corresponding author: E-mail: koorella.rajasekhar@gmail.com
Received: 31 August 2016;
Accepted: 8 November 2016;
Published online: 30 December 2016;
AJC-18212
Epoxides undergoes cyclization with homopropargylic alcohols in the presence of niobium pentachloride under mild condition to afford
the corresponding dihydropyran derivatives in good yield.
Keywords: Epoxides, Homopropargylic alcohols, Dihydropyrans, Niobium pentachloride.
was added niobium pentachloride (540 mg, 2 mmol) at room
temperature. The mixture was stirred under a nitrogen atmos-
phere for 45 min.After completion byTLC, the reaction mixture
was quenched with water and extracted with methylene chloride
(2 × 25 mL). The organic extracts were combined, dried over
anhydrous Na2SO4, filtered and concentrated under reduced
pressure. The crude product was purified by column chromato-
graphy over silica gel (ethyl acetate-hexane, 3-7) to afford 3a
in 76 % yield.
INTRODUCTION
The dihydro and tetrahydropyran ring present in many
natural products represent an important class of six member
ring heterocycles of oxygen [1,2]. Especially the dihydropyrans
are much useful intermediates due to the presence of olefin
functionality, which allows further fictionalization to obtain
poly substituted tetrahydropyrans [3-6].
Among existing methods, the Prins cyclization is the most
common and successful method and has been emerged as a
powerful tool in the synthesis of pyran ring system. Although
other methods are available [7-11], their numerous applications
and increasing demand have prompted us to develop methods,
which give access to this structure. Furthermore, the develop-
ment of efficient and simple methods would be more useful.
Epoxides are the most convenient starting materials for the
preparation of various compounds due to the strained ring
system [12-17]. In recent years, niobium pentachloride has
emerged as an efficient Lewis acid in promoting various organic
transformations [18,19]. Herein, we report the formation of
dihydropyran derivatives by the reaction of epoxides and
homopropargylic alcohols using niobium pentachloride.
RESULTS AND DISCUSSION
We initiated our investigation by treating the mixture of
styrene oxide and 3-buten-1-ol with niobium pentachloride in
anhydrous methylene chloride at room temperature under
nitrogen atmosphere. The mixture was stirred at room tempe-
rature for 45 min. to achieve the quantitative yield.After work-
up, the crude product was subjected to column chromato-
graphy on silica gel allowed the isolation of pure product with
good isolated yields. By the spectroscopic data, confirmed
the product as 3a and compared with the literature data [11]
(Scheme-I).
Cl
EXPERIMENTAL
O
R
NbCl
5
1H NMR, 13C NMR spectra were recorded on Bruker 300
NMR spectrometer and Mass spectra were recorded at 70 eV.
General procedure: To a stirred solution of styrene oxide
(500 mg, 4.16 mmol) and 3-butyn-1-ol (291 mg, 4.16 mmol)
in dry methylene chloride (25 mL) under nitrogen atmosphere,
+
OH
Ph
DCM, r.t.
O
3
1
2a
R
R = H or Aryl
Scheme-I
Maruthi Raju
