Triphenylphosphine/2,3-dichloro-5,6-dicyanobenzoquinone (DDQ)/[n-Bu4N]OCN as a useful system for the efficient conversion of tetrahydropyranyl (THP) ethers to the corresponding alkyl isocyanates

Article abstract of DOI:10.1080/10426500802508212

Triphenylphosphine/2,3-dichloro-5,6-dicyanobenzoquinone/tetrabutylammonium cyanate was used as an efficient system for the conversion of tetrahydropyranyl ethers to the corresponding alkyl isocyanates. Taylor & Francis Group, LLC.

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Triphenylphosphine/2,3-
Dichloro-5,6-
dicyanobenzoquinone
(DDQ)/[n-Bu4N]OCN as
a Useful System for the
Efficient Conversion of
Tetrahydropyranyl (THP) Ethers
to the Corresponding Alkyl
Isocyanates
Batool Akhlaghinia a b & Sima Samiei b
a Department of Chemistry, Faculty of Sciences ,
Ferdowsi University of Mashhad , Mashhad, Iran
b Department of Chemistry , Damghan University of
Basic Sciences , Damghan, Iran
Published online: 21 Sep 2009.
To cite this article: Batool Akhlaghinia & Sima Samiei (2009) Triphenylphosphine/2,3-
Dichloro-5,6-dicyanobenzoquinone (DDQ)/[n-Bu4N]OCN as a Useful System for the
Efficient Conversion of Tetrahydropyranyl (THP) Ethers to the Corresponding Alkyl
Isocyanates, Phosphorus, Sulfur, and Silicon and the Related Elements, 184:10,
2525-2529, DOI: 10.1080/10426500802508212
To link to this article: http://dx.doi.org/10.1080/10426500802508212
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Phosphorus, Sulfur, and Silicon, 184:2525–2529, 2009
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500802508212
Triphenylphosphine/2,3-Dichloro-5,6-
dicyanobenzoquinone (DDQ)/[n-Bu4N]OCN as a Useful
System for the Efficient Conversion of Tetrahydropyranyl
(THP) Ethers to the Corresponding Alkyl Isocyanates
Batool Akhlaghinia1,2 and Sima Samiei2
1Department of Chemistry, Faculty of Sciences, Ferdowsi University of
Mashhad, Mashhad, Iran
2Department of Chemistry, Damghan University of Basic Sciences,
Damghan, Iran
Triphenylphosphine/2,3-dichloro-5,6-dicyanobenzoquinone/tetrabutylammonium
cyanate was used as an efficient system for the conversion of tetrahydropyranyl
ethers to the corresponding alkyl isocyanates.
Keywords Alkyl isocyanate; 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ); tetrahy-
dropyranyl ether (ROTHP); triphenylphosphine (TPP)
INTRODUCTION
Isocyanates are useful compounds capable of participating in a variety
of reactions including nucleophilic addition reactions with alcohols
and amines to produce carbamates and ureas, cycloaddition reactions
to generate heterocycles, and polymerization reactions to produce
commodities such as polyurethanes.1 The high yields and the lack
of byproducts associated with isocyanate chemistry have led to their
widespread application in the pharmaceutical, agrochemical, and
polymer industries.
Typically, aliphatic and aromatic isocyanates are generated from
amines in the reaction with phosgene2 or phosgene equivalents,
such as diphosgene (trichloromethyl chloroformate)3 or triphosgene
[bis(trichloromethyl) carbonate],4 or via thermal dissociation of
Received 5 September 2008; accepted 24 September 2008.
We gratefully acknowledge the partial support of this study by Damghan University
Research Council.
Address correspondence to Batool Akhlaghinia, Department of Chemistry, Fer-
dowsi University of Mashhad, Mashhad, Iran. E-mail: akhlaghinia@um.ac.ir or
b akhlaghinia@dubs.ac.ir
2525

2526
B. Akhlaghinia and S. Samiei
carbamic acid derivatives using chloroformates,5 diphenylcarbonate,6
or N,Nꢀ-carbonyldiimidazole.7 Aryl isocyanates can also be generated
from non-amine precursors via the rearrangements of acyl azides (Cur-
tius rearrangement)8 and hydroxamic acids (Lossen rearrangement).9
Tetrahydropyranylation is one of the most practical and popular
ways of protecting hydroxy groups of alcohols and phenols, especially
in the synthesis of multifunctional organic molecules. THP ethers show
remarkable stability towards some reagents such as organometallic
reagents and hydrides, as well as reducing and oxidizing agents. Chem-
ical transformation of protected functional groups to other functional
groups is an important step in organic synthesis.10 Literature search
reveals that only a few reports are available for the direct conversion
of THP ethers to other functional groups. The known examples in-
clude conversion of THP ethers to bromides,11,12 iodides,13 sulfides,14
acetates,15 and esters.16
In this study, a novel and simple method for the efficient conversion
of tetrahydropyranyl ethers to alkyl isocyanates is reported.
RESUTS AND DISCUSSION
Recently, we have reported the application of Ph3P/DDQ/R4NX (X
= Cl, Br, I, CN, N3, NO2, OCN) and 2,4,6-trichloro[1,3,5]triazine
(TT)/R4NX (X = CN, NO2) systems for the conversion of alcohols, thi-
ols, selenols, trimethylsilyl ethers, N3, OCN, and tetrahydropyranyl
ethers to the corresponding alkyl halides, cyanides, azides, nitrites,
and isocyanates.17 Due to the wide applicability of tetrahydropyranyl
ethers in multistep syntheses and in continuation of the study on
the conversion of tetrahydropyranyl ethers to alkyl cyanides17d and
azides,17e the transformation of THP ethers to alkyl isocyanates using
the Ph3P/DDQ/[n-Bu4N]OCN system under neutral and mild reaction
condition was investigated (Scheme 1).
In order to optimize the reaction conditions, at first the effects
of different ratios of ROTHP/PPh3/DDQ/[n-Bu4N]OCN, solvent, and
temperature for the conversion of PhCH2OTHP to PhCH2NCO were
SCHEME 1

Conversion of Tetrahydropyranyl Ethers to Isocyanates
2527
TABLE I Conversion of Tetrahydropyranyl Ethers to Alkyl Iso-
cyanates in Dry Acetonitrile Under Reflux Conditions
ROTHP
Time (h)
Conversion (%)a
Isolated yield (%)
8
11
100
100
95
90
11.5
30
100
100
94
89
9
8.5
7
100
100
100
100
97
96
98
98
5
9
100
100
93
90
11
34
100
97
aGC yield using internal standard.
examined. Employing the ratio of 1:2:2:2 in refluxing CH3CN gave
the best result and produced benzyl isocyanate after 7 h in 98%
yield. These optimized conditions were applied for the conversion of
structurally different tetrahydropyranyl ethers to the corresponding
alkyl isocyanates. The results are shown in Table I.
As shown in Table I, this method is very suitable for the conversion
of primary, secondary, and tertiary tetrahydropyranyl ethers to alkyl
isocyanates in excellent yields.
A 13C NMR signal at 127 ppm is assigned to the quaternary carbon
atom of the N C O group. A strong and sharp absorption band at
2280–2230 cm−1 and a weak absorption band at 1450–1380 cm−1 are
typical for the isocyanate moiety.
In conclusion, the present investigation has demonstrated that the
use of Ph3P/DDQ/[n-Bu4N]OCN offers a simple, novel, and convenient
method for the conversion of a wide variety of tetrahydropyranyl ethers
to the corresponding alkyl isocyanates.

2528
B. Akhlaghinia and S. Samiei
EXPERIMENTAL
Chemicals were obtained from Merck and Fluka. FT-IR spectra were
recorded on a Perkin Elmer RXI spectrophotometer. NMR spectra were
recorded with a Bruker Avance DPX 250 MHz instrument. The prod-
ucts were purified by column chromatography, and the purity of the
products was determined by GC on a Shimadzu model GC 10-A instru-
ment using n-octane as internal standard or by thin layer chromatog-
raphy on silica gel polygram on SIL G/UV 254 plates.
Typical Procedure for Conversion of Tetrahydropyranyl Ethers
to Alkyl Isocyanate
To a flask containing a mixture of DDQ (2 mmol, 0.454 g) and Ph3P
(2 mmol, 0.524 g) in dry CH3CN (5 mL), while stirring Bu4N[OCN]
(2 mmol, 0.568 g) was added. Tetrahydropyranyl ether (1 mmol) was
then added to this mixture. The reaction mixture was refluxed. GC
analysis showed the completion of the reaction. The solvent was evap-
orated under reduced pressure. Column chromatography of the crude
product on silica-gel using n-hexane as eluent gave alkyl isocyanates.
The product was identified by comparison of its physical constants and
spectral data with those of an authentic sample.
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2529
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