Efficient conversion of tetrahydropyranyl (THP) ethers to their corresponding thiocyanates with in-situ-generated Ph3P(SCN) 2

Article abstract of DOI:10.1080/104265090917439

Immediate and efficient one-pot conversion of tetrahydropyranyl (THP) ethers to their corresponding thiocyanates by in-situ-generated Ph ₃P(SCN)₂ is described. Primary and secondary alkyls and also benzylic THP ethers are converted to their corresponding thiocyanates in excellent yields at room temperature by this method. Copyright Taylor & Francis Inc.

Full text of DOI:10.1080/104265090917439

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Efficient Conversion of
Tetrahydropyranyl (THP)
Ethers to Their Corresponding
Thiocyanates With in-
situ–Generated Ph3P(SCN)2
Nasser Iranpoor a , Habib Firouzabadi a & Hamid
Reza Shaterian a
a Chemistry Department , College of Sciences, Shiraz
University , Shiraz, Iran
Published online: 19 Aug 2006.
To cite this article: Nasser Iranpoor , Habib Firouzabadi & Hamid Reza Shaterian
(2005) Efficient Conversion of Tetrahydropyranyl (THP) Ethers to Their Corresponding
Thiocyanates With in-situ–Generated Ph3P(SCN)2 , Phosphorus, Sulfur, and Silicon and
the Related Elements, 180:9, 2093-2096, DOI: 10.1080/104265090917439
To link to this article: http://dx.doi.org/10.1080/104265090917439
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Phosphorus, Sulfur, and Silicon, 180:2093–2096, 2005
Copyright © Taylor & Francis Inc.
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/104265090917439
Efficient Conversion of Tetrahydropyranyl (THP) Ethers
to Their Corresponding Thiocyanates With
in-situ–Generated Ph3P(SCN)2
Nasser Iranpoor
Habib Firouzabadi
Hamid Reza Shaterian
Chemistry Department, College of Sciences, Shiraz University,
Shiraz, Iran
Immediate and efficient one-pot conversion of tetrahydropyranyl (THP) ethers to
their corresponding thiocyanates by in-situ–generated Ph3P(SCN)2 is described.
Primary and secondary alkyls and also benzylic THP ethers are converted to their
corresponding thiocyanates in excellent yields at room temperature by this method.
Keywords Ph3P(SCN)2; tetrahydropyranyl ethers; thiocyanates
INTRODUCTION
Tetrazoles are important aromatic heterocyclic compounds and their
use in medicinal chemistry is well established.1 Thiocyanates are con-
sidered important and valuable sulfur-containing compounds for the
synthesis of heterocycles such as tetrazoles and traditionally have been
used as pesticides.2
Tetrahydropyranylation is one of the most practical and popular
ways of protecting hydroxyl groups of alcohols and phenols, especially in
the synthesis of multifunctional organic molecules. THP ethers show
remarkable stability toward organometallic reagents, reduction with
hydrides, oxidation, oxidative alkylation, and so on. Transformation of
protected functional groups to other functionalities is of practical value
in organic synthesis.3,4 Literature research reveals that few reports
are available for direct conversion of THP ethers to other functional
Received March 20, 2001; accepted October 25, 2004.
The authors are grateful to the Shiraz University Research Council for their partial
support of this work.
Address correspondence to Nasser Iranpoor, Shiraz University, Chemistry Depart-
ment, College of Sciences, Shiraz 71454, Iran. E-mail: iranpoor@chem.susc.ac.ir
2093

2094
N. Iranpoor et al.
groups. The examples are conversion to bromides,5 sulfides,6 acetates7
into their esters.8 Recently, we have reported the conversion of a vari-
ety of silyl ethers9 and alcohols10 to their corresponding thiocyanates
by in-situ–generated Ph3P(SCN)2.
RESULTS AND DISCUSSION
In this article we wish to report the efficient conversion of THP ethers
into their corresponding thiocyanates at room temperature (Scheme 1).
Ph3P(SCN)2,CH3CN
ROTHP −−−−−−−−−−−→ RSCN
rt, immediately
R = prim., sec. alkyl and benzyl
SCHEME 1
The reaction has been performed in dry CH3CN with in-situ–
generated PPh3(SCN)2 obtained from the reaction of PPh3·Br2 and
NH4SCN. 31P-NMR confirms the in-situ generation of PPh3(SCN)2 that
is in agreement with the data reported in the literature.11 By the
presented method, benzyl and 4-substituted benzyltetrahydropyranyl
ethers with electron-withdrawing groups were transformed to their cor-
responding thiocyanates in excellent yields (92–95%) without the for-
mation of any isothiocyanate as a byproduct. A previous report indicates
that the preparation of benzylthiocyanate from benzyl alcohol that is
free from its isothiocyanate isomer is a difficult task due to the forma-
tion of a substantial amount of benzylisothiocyanate.12
4-Methoxybenzyltetrahydropyranyl ether was converted to its corre-
sponding thiocyanate in 88% that was accompanied with the formation
of isothiocyanate in only a 12% yield (Entry 4, Table I). Primary and
secondary saturated tetrahydropyranyl ethers (Entries 5–8, Table I)
were also transformed to their corresponding thiocyanates in excellent
yields (87–94%).
This method is not suitable for the preparation of thiocyanates from
highly hindered THP ethers. For example, the THP ether of diphenyl-
methanol was converted to its corresponding thiocyanate15c in a 12%
yield and isothiocyanate15d in a 73% yield.
In conclusion, in this article we have presented a new useful method
for the one-pot preparation of thiocyanates from THP ethers in high
yield under mild reaction conditions.

Efficient Conversion of THP Ethers
2095
TABLE I Conversion of THP Ethers to Thiocyanates
Entry
R-OTHP
% Total yielda
% RSCNb,c
% RNCSb
1
2
3
4
5
6
7
8
C6H5CH2OTHP
94
95
92
95
94
93
90
87
10011,13,15a
10011,13
10011,13
8811,13
10011
0
0
0
12
0
3
4-NO2C6H4CH2OTHP
4-ClC6H4CH2OTHP
4-MeOC6H4CH2OTHP
C6H5CH2CH2OTHP
CH3(CH2)6CH2OTHP
CH3(CH2)5CH(CH3)OTHP
PhCH(CH2CH3)OTHP
9711
9514
5
4
9615b
aThe products were identified by comparison of their physical data with those
reported for known samples.
bThe percentage of the products in the reaction mixture was determined by
1H-NMR and 13C-NMR.
cReference to the product.
EXPERIMENTAL
Products were characterized by comparison of their physical data with
those of a known sample. IR spectra were recorded on a Perkin Elmer
781 and Pye Unicam 8725 spectrometers. NMR spectra were recorded
on a Bruker DPX 250. The purity determination of the substrates and
reaction monitoring were accomplished by TLC on silica gel polygram
SILG/UV 254 plates or GLC on a Shimadzu GC-14A instrument.
GENERAL PROCEDURE FOR THE SYNTHESIS OF 1◦ AND 2◦
THIOCYANATES FROM THP ETHERS
A three-necked flask equipped with a dropping funnel, stirrer, drying
CaCl2 tube, and N2 gas inlet was charged with Ph3P (2.2 mmol) and
dry CH3CN (5 mL), then Br2 (2.2 mmol) was added dropwise to the so-
lution at room temperature under N2 atmosphere. When the addition
was completed, a solution of NH4SCN (4.4 mmol) in CH3CN (5 mL) was
added dropwise. Upon addition of THP ether (2 mmol) to the resulting
mixture, an spontaneous reaction occurred. To the resulting mixture,
silica gel was added and the solvent was evaporated on a rotary evapo-
rator. The resulting solid was applied on a silica gel column and washed
by petroleum ether 60–80◦C/EtOAc (9/1) to give the desired thiocyanate
(Table I).
REFERENCES
[1] B. W. Leblanc and B. S. Jursic, Synth. Comm., 28, 3591 (1998).
[2] A. A. Newman, Chemistry and Biochemistry of Thiocyanic Acid and Its Derivatives,
1st ed., Academic Press, 1975.

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N. Iranpoor et al.
[3] A. J. Pearson and W. J. Roush, HandBook of Reagents for Organic Synthesis Acti-
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[4] T. W. Greene and P. G. M. Wuts, Protective Groups in Organic Synthesis, 2nd ed.
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[10] N. Iranpoor, H. Firouzabadi, and H. R. Shaterian, J. Chem. Res.(S). 676 (1999).
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K. Saito, Chem. Pharm. Bull., 39, 784 (1991).
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4417 (1977).
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[15] Spectral data for (a) Benzyl thiocyanate: IR (KBr disc); ν(Cm−1): 3086, 3070, 3009,
2992, 2918, 2148, 1494, 1464, 1427, 1246, 1204, 1076, 769, 698, 645. 1H-NMR
(CDCl3, 250 MHz), δ(ppm): 4.2 (2H, s), 7.4 (5H, s); 13C-NMR (CDCl3, 63 MHz),
δ(ppm): 134.47, 129.05, 128.93, 128.80, 111.96, 38.20; MS (70 eV) m/z (% rela-
tive intensity): 149(M+, 3), 92(8), 91(100), 89(3), 65(12), 63(3), 51(3), 39(6). (b)
(1-thiocyanato-propyl)-benzene: IR (CCl4); ν(Cm−1): 3050, 3040, 2980, 2940, 2890,
2165, 1500, 1460, 1240, 1100, 1040, 750, 690. 1H-NMR(CDCl3, 250 MHz), δ(ppm):
0.96(3H,t), 2.1(2H,m), 4.6(1H,t), 7.2–7.4(5H,m). 13C-NMR(CDCl3, 63 MHz), δ(ppm):
137.1, 127.8, 127.7, 124.7, 111.9, 54.2, 31.3, 11.1. (c) 1-Thiocyanato-1,1-diphenyl
methane: IR(CCl4); ν(Cm−1): 3080, 3040, 2950, 2160, 1500, 1460, 1200, 1120, 1040,
1010, 750, 710. 1H-NMR(CDCl3, 250 MHz), δ(ppm): 5.3(1H,s), 7.2–7.5(10H,m).
13C-NMR(CDCl3, 63 MHz), δ(ppm): 131.5, 130.5, 130.4, 130.1, 112.2, 58.1. (d) 1-
Isothiocyanato-1,1-diphenyl methane: IR(CCl4); ν(Cm−1): 3060, 3050, 2950, 2060,
1490, 1450, 1180, 1030, 750, 700. 1H-NMR(CDCl3, 250 MHz), δ(ppm): 5.8(1H,s), 7.1–
7.3(10H,m). 13C-NMR(CDCl3, 63 MHz), δ(ppm): 142.9, 130.8, 129.8, 129.6, 128.2,
65.3.