Full text of DOI:10.1002/jccs.200100127

JournaloftheChineseChemicalSociety, 2001, 48, 877-878
877
Simple ProtocolforSynthesisandCleavageofTetrahydropyranylEthers
Using FeSO4 as an InexpensiveCatalyst
Babasaheb P. Bandgar* and Suhas P. Kasture
SchoolofChemicalSciences,OrganicChemistryResearchLab.,
Swami Ramanand Teerth Marathwada Uni ver sity, Nanded - 431 606, In dia
Protectionanddeprotectionofalcoholsandphenolsastetrahydropyranylethers(THPethers)usinganhy-
drous FeSO4 undermicrowaveirradiationwithoutsolventiscarriedout.
INTRODUCTION
Hydroxylgroupsarepresentinanumberofcompounds
primary,secondary,benzylic,allylicalcoholsandphenols.A
mix ture of al co hol or phe nol, 3,4-dihydro-2H-pyran and a
catalyticamountofanhydrousFeSO4 wasirradiatedwithmi-
cro waves. The re ac tion was com pleted in a few min utes to
givethecorrespondingTHPethersingoodyields.Theresults
are pre sented in the Ta ble 1. At tempts to carry out tetra-
hydropyranylation of hydroxyl groups using anhydrous
FeSO4 in di chloro methane un der mild con di tions (25 C)
failed. Tetrahydropyranylation of pri mary as well as sec ond-
ary al co holic groups of 1,2-octanediol took place si mul ta-
neouslyunderthesereactionconditions. Thisindicatesthat
the pres ent method is not se lec tive for tetra hydro pyranyla-
tion of pri mary al co hols in the pres ence of sec ond ary al co-
hols.
We next ex am ined deprotection of THP ethers us ing
FeSO4 and mi cro waves with a few drops of wa ter. Var i ous
THP ethers of pri mary, sec ond ary, benzylic and al lyl ic al co-
hols and phe nols un der went smooth clevage un der these re-
ac tion con di tions. The re sults are summerized in the Ta ble 1.
It is im por tant to note that other func tional groups such as
C C, C C, methoxy, methylenedioxy and epoxide re main
un al tered dur ing pro tec tion and deprotection of THP ethers
underthesereactionconditionswhichdepictstheapplicabil-
ityofthisprotocol.
ofbiologicalandsyntheticinterestincludingnucleosides,
car bo hy drates, ste roids and the side chain of some amino ac-
ids. Duringoxidation, acylation, halogenationanddehydra-
tion re ac tions of these com pounds a hydroxyl group must be
protected.1 THP ethers are one of the most widely used pro-
tectinggroupsemployedinchemicalsynthesisbecauseofits
low cost, the ease of in stal la tion, gen eral sta bil ity to most
non- acidic re agents and ease with which it can be re moved.1
Protic and Lewis ac ids,1 other re agents such as iodotri meth-
ylsilane,2 triphenylphosphinehydrobromide,3 montmorillo-
nite clay,4 envirocat EPZG,5 lithium perchlorate-diethyl
ether,6 ion ex change resin,7 zir co nium sulfophenyl phos-
phonate8 and alu mina im preg nated on zinc chlo ride9 have
been used to ef fect the tetrahydropyranylation of al co hols. In
spite of sev eral ef forts, the meth ods avail able for se lec tive
pro tec tion and deprotection of THP ether with out touch ing
epoxyfunctionalitypresentelsewhereinthemoleculeare
limited.10
We re port here use of FeSO4 asaninexpensivecatalyst
for pro tec tion and deprotection of al co hols and phe nols as
THP ethers under microwave irradiationwithout solvent
(Scheme I).
In con clu sion the pres ent re sults dem on strate the nov-
elty of FeSO4 whichshowssomeselectivityandconstitutesa
usefulalternativetothecommonlyacceptedproceduresof
pro tec tion and deprotection of THP ethers.
Scheme I
anhydrous
FeSO4, M.W.
+
ROH
FeSO4, 2 drops of HO, M.W.
2
O
RO
O
EXPERIMENTAL
1
2
General Procedure for Tetrahydropyranylation
Amixtureofalcoholorphenol(5mmol), 3,4-dihydro-
2H-pyran(5mmol)andanhydrousFeSO4 (1 mmol) was thor-
oughly mixed in a 25 mL glass beaker and ir ra di ated by mi-
cro waves (Kelvinator, In dia make, model T-37 at 2450 MHz
RESULTSANDDISCUSSION
Wefirstexaminedtetrahydropyranylationofaseriesof

878 J. Chin. Chem. Soc., Vol. 48, No. 5, 2001
Bandgar and Kasture
Table 1. Protection and Deprotection of THP Ethers Using FeSO4
and Microwave
General Procedure for Deprotection of Tetrahydro-
pyranyl Ethers
A mix ture of THP ether (5 mmol) andFeSO4 (1 mmol )
Sr.
Alcohols/Phenols Product Protection
Deprotection
Time Yielda,b Time Yielda,b
(min) (%) (min) (%)
withtwodropsofwaterwasirradiatedbymicrowavesforthe
time pe riod in di cated in the Ta ble 1. Af ter com ple tion of the
re ac tion (TLC) the prod uct was ex tracted with ethyl ac e tate
(2 10 mL) and dried over an hy drous Na2SO4. Re moval of
thesolventunderreducedpressuregaveaproductwhichwas
purifiedbycolumnchromatography(pet.ether:ethylacetate
= 9:1).
1m: I.R. (cm-1): 702, 740, 1011, 1025, 1203, 1450,
1510, 1605, 2975, 3041, 3410; 1H NMR (CDCl3, 300 MHz):
4.3 (d, 2H, CH2); 4.7 (s, 1H, OH); 4.9 (m, 1H); 5.5 (d, 1H);
7.2 (s, 5H, Ar-H).
No.
1a
1b
2a
2b
1.0
1.0
84
88
1.5
1.0
80
83
1c
2c
3.0
79
1.2
97
1d
1e
1f
2d
2e
2f
4.0
3.5
3.5
85
97
78
1.4
1.0
1.0
84
97
89
1g
2g
3.0
84
2.0
82
1h
1i
2h
2i
3.5
1.0
0.5
81
84
84
1.0
1.2
1.3
87
81
97
Received Feb ru ary 19, 2001.
1j
2j
Key Words
FeSO4; Catalyst; THP ethers; Alcohols.
1k
2k
0.5
81
1.5
83
1l
2l
0.5
3.0
84
82
1.3
1.0
87
87
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1m
2m
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1
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