Silylation of hydroxy groups with HMDS under microwave irradiation and solvent-free conditions

Article abstract of DOI:10.1080/10426500210255

Phenols and alcohols are silylated with hexamethyldisilazane (HMDS) under microwave irradiation in solvent-free condition in good to excellent yields.

Full text of DOI:10.1080/10426500210255

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Phosphorus, Sulfur, and Silicon and the Related
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Silylation of Hydroxy Groups with HMDS Under
Microwave Irradiation and Solvent-Free Conditions
M. M. Mojtahedi a , M. R. Saidi a , M. Bolourtchian b & M. M. Heravi b
a Department of Chemistry , Sharif University of Technology , Tehran, Iran
b Chemistry & Chemical Engineering Research Center of Iran , Tehran, Iran
Published online: 27 Oct 2010.
To cite this article: M. M. Mojtahedi , M. R. Saidi , M. Bolourtchian & M. M. Heravi (2002) Silylation of Hydroxy Groups with
HMDS Under Microwave Irradiation and Solvent-Free Conditions, Phosphorus, Sulfur, and Silicon and the Related Elements,
177:2, 289-292, DOI: 10.1080/10426500210255
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Phosphorus, Sulfur and Silicon, 2002, 177:289–292
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SILYLATION OF HYDROXY GROUPS WITH HMDS
UNDER MICROWAVE IRRADIATION AND
SOLVENT-FREE CONDITIONS
M. M. Mojtahedi,a M. R. Saidi,a M. Bolourtchian,b
and M. M. Heravib,
Department of Chemistry, Sharif University of Technology,
Tehran, Irana and Chemistry & Chemical Engineering Research
Center of Iran, Tehran, Iranb
(Received August 7 2001.)
Phenols and alcohols are silylated with hexamethyldisilazane (HMDS)
under microwave irradiation in solvent-free condition in good to excel-
lent yields.
Keywords: Phenols; silylation of alcohols
Many chemical conversions and multiple synthesis sequences often
require protection of hydroxy groups. The trimethylsilyl group is one
of the most widely used protecting groups in organic synthesis and
is often used to prepare silyl ethers as volatile derivatives of alcohols
5
and phenols.1 Several silylating reagents are available for this con-
version, including trimethylsilyl halides in the presence of a tertiary
amine6,7 or lithium sulfide,8 hexamethyldisilazane,9 hexamethyldis-
iloxane (HMDSO) in acidic media,10 allylsilazane,11,12 and so on.13,14
HMDS is an inexpensive and commercially available reagent; its han-
dling does not require special precautions and the work up of the reac-
tion mixture is easy and rapid. The major disadvantage and drawback
of this reagent is its poor silylating power, which needs special condi-
tions in most cases. Several catalysts such as trimethylchlorosilane,15
sulfuric acid, amines or trimethylsilyl amide,16 imidazole,17 zinc
chloride,18 metalloporphirins,19,20 and very recently iodine21 in CH2Cl2,
have been used for silylation with HMDS. Although these methods re-
sulted in improved reaction conditions in many cases, several hours are
still necessary for complete reaction.
Address correspondence to M. R. Saidi, Department of Chemistry, Sharif University
of Technology, Tehran, Iran.
289

290
M. M. Mojtahedi et al.
Microwave irradiation is a very useful technique in organic
27
synthesis,22
and microwave heating under solvent-free conditions
has attracted much attention in recent years.28
RESULTS AND DISCUSSION
In conjunction with our recent work on microwave-assisted reaction
under solvent-free condition,29,30 we now have found that phenols and
alcohols may be silylated by using HMDS under dry and nonpolluting
conditions. When a phenol or an alcohol is treated with neat HMDS
under microwave irradiation, the corresponding silyl ethers were ob-
tained. To establish the generality of this method, the reaction was
conducted with a variety of phenols and alcohols. Table I summarizes
the data for the preparation of silyl ethers, which were obtained in good
to excellent yields. In contrast, by the use of classical heating, silylation
of o-cresol with HMDS gave a low yield (ca. 20%) of silylated product
after 4 h. To examine relatively large scale synthesis, when 10 mmol
of 1-naphthol were irradiated in a conventional microwave oven for
8 min, 1-trimethylsiloxynaphalene was obtained in 90% isolated
yield.
SCHEME 1
In conclusion, domestic microwave irradiation under a solvent-free
condition provides a mild and excellent method for silylation of phe-
nols and alcohols in a short time and relatively large scale, using in-
expensive and easy to handle HMDS as silylating agent with high
yields.
EXPERIMENTAL
All chemicals were used as received without further purification.
All products were identified with their NMR and IR spectroscopic
data.

Silylation of Hydroxy-Compounds
291
TABLE I Silylation of Alcohols and Phenols with HMDS in Solvent-Free
Condition and Under Microwave Irraditiona
aReaction time: 5 min, except where stated;
bReaction time: 10 min.
General Procedure for the Preparation of Silylated
Phenols or Alcohols
The phenol or alcohol (2 mmol) and HMDS (2 mmol) were placed in a
10 mL beaker. The beaker was put into a 50 mL Teflon vessel and was
irradiated in a conventional microwave oven at 450 W; the reaction was
monitored by gas liquid chromatography (GLC). After the completion
of the reaction (Table I), the crude material was purified by distillation
with a bulb-to-bulb distillation unit to the corresponding silyl ether. The
yields shown in Table I are isolated yields. All products gave satisfactory
spectral data in accordance to the proposed structures.4,8,11,31 Spectral
data of the new compounds are: 2d, 1H NMR, , (CDCl3), 0.2 (s, 9H), 0.3
(s, 9H), 4.7 (s, 2H), 7.4 (m, 4H); 13C NMR, , (CDCl3), 0.5 (CH3), 0.4
(CH3), 59.6 (CH2), 118.4 (CH), 121.3 (CH), 127.5 (CH), 127.6 (CH), 131.6
(C), 152.1 (C); IR, (neat), 1250, 842 cm 1. 2m, 1H NMR, , (CDCl3), 0.2
1
(s, 9H), 3.8 (s, 3H), 7.3 (m, 4H); IR (CCl4), 1253, 849 cm
.

292
M. M. Mojtahedi et al.
ACKNOWLEDGMENT
We thank the Iranian Ministry of Science, Research and Technology for
its partial financial support of this work.
REFERENCES
[1] E. W. Colvin, Chem. Soc. Rev., 7, 15 (1978).
[2] T. W. Green and P. G. M. Wutz, Protective Groups in Organic Synthesis (Wiley: New
York, 1990), 2nd. ed.
[3] C. B. Reese, Protective Groups in Organic Chemistry (Plenum, London, 1973),
chap. 3.
[4] M. Lalonde and T. H. Chan, Synthesis, 817 (1985).
[5] G. A. Olah and D. A. Klumpp, Synthesis, 744 (1997).
[6] E. J. Corey and B. B. Snider, J. Am. Chem. Soc., 94, 2549 (1972).
[7] E. Haslam, Tetrahedron, 36, 2409 (1980).
[8] G. A. Olah, B. G. B. Gupta, S. C. Narang, and R. Molhotra, J. Org. Chem., 44, 4272
(1979).
[9] V. Montanari, S. Quici, and G. Resnati, Tetrahedron Lett., 35, 1941 (1979).
[10] H. W. Pennick, B. S. Bal, and N. H. Lazis, Tetrahedron, 34, 426 (1978).
[11] T. Morita, Y. Okamoto, and H. Sakurai, Tetrahedron, 36, 835 (1980).
[12] G. A. Olah, A. Husain, B. G. B. Gupta, G. F. Salem, and S. C. Narang, J. Org. Chem.,
46, 5212 (1981).
[13] D. A. Evans, J. M. Hoffman, and L. K. J. Truesdal, J. Am. Chem. Soc., 95, 5822
(1973).
[14] B. H. Lipshutz, J. Burgess-Henry, and G. P. Rath, Tetrahedron Lett., 34, 995 (1993).
[15] J. Cassy and P. Pale, Tetrahedron Lett., 28, 6039 (1987).
[16] C. A. Bruyness and T. K. Jurriens, J. Org. Chem., 47, 3966 (1982).
[17] C. Ainsworth and S. Torkelson, Synthesis, 722 (1976).
[18] H. Firouzabadi and B. Karimi, Synth. Commun., 23, 1633 (1993).
[19] H. Firouzabadi, Z. Khayat, A. R. Sardarian, and Sh. Tangestaninejad, Iran J. Chem.
& Chem. Eng., 15, 54 (1996).
[20] H. Firouzabadi, Z. Khayat, A. R. Sardarian, and Sh. Tangestaninejad, Chem. Abstr.,
127, 220704p.
[21] B. Karimi and B. Golshani, J. Org. Chem., 65, 7228 (2000).
[22] S. Caddick, Tetrahedron, 38, 10403 (1995).
[23] R. A. Abramovich, Org. Prep. Proced. Int., 23, 638 (1991).
[24] D. M. P. Mingos and D. R. Baghurst, Chem. Soc. Rev., 20, 1 (1990).
[25] M. Kidwai and P. Kumar, J. Chem. Res. (S), 245 (1996).
[26] R. L. E. Furlan, E. G. Mata, and O. A. Mascaretti, Tetrahedron Lett., 37, 5229 (1996).
[27] G. Bran, A. Loupy, D. Vellemin, and K. Smith, Solid Support and Catalyst in
Organic Synthesis (Ellis Harwood & Prentice Hall, New York), pp. 302–325.
[28] A. Loupy, A. Petit, Y. Ramadani, M. C. Vanaeff, M. Majdoub, B. Labiad, and
D. Villemin, Can. J. Chem., 71, 90 (1993).
[29] M. M. Heravi, K. Aghapoor, M. A. Nooshabadi, and M. M. Mojtahedi, Monatsch.
Chem., 128, 1143 (1997).
[30] K. Aghapoor, M. M. Heravi, and M. A. Nooshabadi, Indian J. Chem., 37B, 84 (1998).
[31] B. A. Keay, S. P. Maddaford, W. A. Cristofoli, N. G. Andersen, M. S. Passafaro, N. S.
Wilson, and J. A. Nieman, Can. J. Chem., 75, 1163 (1997).