Acta Chini. Slov. 2001, 48, 427-430.
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SELECTIVE DEALKYLATION OF TETRA-0-PROPYL-/>-tert-BUTYL CALIX[4]ARENE AT THE LOWER RIM BY AICI3
Saeed Taghvaei-Ganjali*, Atoussa Modjallal
Department of Environmental Engineering, Faculty of Environment, University of Tehran, Tehran, Iran, Fax: +98-21-658111, e-mail: taqvaee(a)khavam.ut.ac.ir
Received 08-01-2001
Abstract
As a result of experimental studies on the dealkylation of tetra-0-propyl-p-?ert-butyl calix[4]arene 1, we have found that by treating 1 with the stoichiometric amount of AICI3, the tri, di and mono-0-propyl-£>-?ert-butyl calix[4]arene are obtained in good yield. In these reactions fert-butyl groups at the upper rim are uchanged.
Introduction
The extensive use of calixarenes and in particular calix[4]arenas, in supramolecular
chemistry justifies the efforts of several research groups to find synthetic methodologies for their selective functionalization both at the upper and lower rim. Several useful synthetic methodologies have been reported which allow the synthesis of tetra substituted calix [4] arenas at the lower rim. Apart from one example by Gutsche who reported the synthesis of monoallyloxy calix [4] arene, no general methodology is available for the synthesis of calix[4]arene mono alkyl ethers. Several attempts to obtain these compounds by direct alkylation of p-tert calix [4] arene failed, this reaction giving tetra and dialkylated " products or mixture of compounds.
Results and discussion
An alternative to direct alkylation for generating partially alkylated calix [4] arenas
involves selective dealkylation of the readily available tetra-O- propyl-p-te/t-butyl calix[4]arene by means of stiochiometric amounts of AICI3. By this procedure, 75-83% yields of tri, di and mono-0-propyl-/?-ter£-butyl calix [4] arene have been obtained.
S. Taghvaei-Ganjali, A. Modjallal: Selective dealkylation oftetra-O-propyl-p-tert-butyl-...
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Acta Chini. Slov. 2001, 48, 427-430.
t-Bu
t-Bu
t-Bu
n eg A1C1 Toluene RT
t-Bu-
t-Bu
t-Bu
2a: n=l Rl=OH, R2=R3=R4=OPr 2b: n=2 Rl=R3=OH, R2=R4=OPr 2c: n=3 Rl=OPr, R2=R3=R4=OH
Scheme
The cavity of the upper rim can be modified by introducing substituents at the para positions of the phenol rings of calix[4]arene. Gutsche et al. have described the modification via a Claisen rearrangement. They prepared calix[4]arene by aluminium chloride-catalyzed debutylation of p-tert-butyl calix[4]arene at the upper rim. The comparison between this two reaction show that the dealkylation of O-Pr groups at the lower rim take place before dealkylation of tert-butyl at the upper rim.
The calix[4]arene tetrapropylether 1 is produced in quantitative yield by simple
o
alkylation procedure.   The compound 1 is used for dealkylation step (Scheme) and tri, di, and mono propylethers are obtained in 83, 79 and 75% yield, respectively.
All products show a cone conformation. In compounds 2a and 2c the H NMR spectra show a typical pattern represent by two doublets for the equatorial and two doublets for the axial protons of the bridging methylene (ArCH^Ar). Compound 2c interestingly shows two sharp signals for the three OH groups, one at 10.15 ppm (2H) and one at 9.57 ppm (IH). The high chemical shift for two OH groups indicates that these two H bonds are weaker than the other one and are those probably formed by the two opposite phenolic OH groups with the neighbour alkoxy oxygen atom with according to molecular mechanics calculations, bears less negative charge than a hydroxyl oxygen atom.9 (Scheme 2)
S. Taghvaei-Ganjali, A. Modjallal: Selective dealkylation oftetra-0-propyl-p-tert-buty\-...
Acta Chini. Slov. 2001, 48, 427-430.
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Experimental
Melting points are taken on a Buchi SMP-20 apparatus and are uncorrected.   H-
NMR spectra were recorded on  a  Bruker AM-400 MHz in CDCI3 with  Me4Si as an internal standard.  IR spectra were recorded on Bruker IFS 25  spectrophotometer. Compounds 2a-2c have bee reported, for microanalytical and spectral data, see ref. 8. General Procedure for the preparation of 2a-2c:
Calix[4]arene tetrapropylether 1 (1.0 mmol) and AICI3 (1.04 mmol for preparation of 2a, 2.08 mmol for 2b and 3.12 mmol for 2c) in 50 ml of dried and distilled toluene, were stirred for 6 h at room temperature. The reaction mixture was diluted with 10% HCl solution (100 ml). The organic layer was separated and dried over MgSCU. After filtration, the filtrate was concentrated to dryness. The residue was recrystalized from CH2CI2-CH3OH.
2a: mp 191-193 °C yield 83%; IR (KBr/crn"1) v0H 3530; JH NMR (400 MHz; CDCI3) G 0.81 (s, 18H, t-Bu), 0.96 (t, 3H, CH3), 1.10 (t, 3H, CH3), 1.30 (s, 9H, t-Bu), 1.32 (s, 9H, t-Bu), 1.82-2.00 (m, 2H, CH2), 2.28-2.38 (m, 4H, CH2), 3.15, 4.29 (2d, 4H, ArCH2Ar), 3.22, 4.33 (2d, 4H, ArCH2Ar), 5.54 (s, IH, OH), 6.47 (d, 2H, ArH), 6.48 (d, 2H, ArH), 7.03 (s, 2H, ArH), 6.94 (s, 2H, ArH).
2b: mp 246-249 °C yield 79%; IR (KBr/crn1) v0H 3375; JH NMR (400 MHz; CDCI3) G 0.94 (s, 18H, t-Bu), 1.26 (t, 6H, CH3), 1.29 (s, 18H, t-Bu), 1.96-2.05 (m, 4H, CH2), 3.29, 4.25 (2d, 8H, ArCH2Ar), 3.93 (t, 4H, CH2), 6.75 (s, 4H, ArH), 7.04 (s, 4H, ArH), 7.75 (s, 2H, OH).
2c: mp 236-238 °C yield 75%; IR (KBr/ cm"1) v0H 3180, 3300; lR NMR (400 MHz; CDCI3) G 1.18 (s, 9H, t-Bu), 1.20 (s, 18H, t-Bu), 1.21 (s, 9H, t-Bu), 1.24 (t, 3H, CH3), 2.13-2.22 (m, 2H, CH2), 3.41, 4.27 (2d, 4H, ArCH2Ar), 3.43, 4.36 (2d, 4H, ArCH2Ar), 4.10 (t, 2H, OCH2), 6.99 (d, 2H, ArH), 7.04 (s, 2H, ArH), 7.06 (d, 2H, ArH), 7.09 (s, 2H, ArH), 9.57 (s, IH, OH), 10.15 (s, 2H, OH).
Acknowledgments
Saeed Taghvaei-Ganjali is grateful to the Research Council of Tehran University.
Generous support from Prof. Dr. J. Ipaktschi, Institute of Organic Chemistry, Giessen University is highly acknowledged.
S. Taghvaei-Ganjali, A. Modjallal: Selective dealkylation oftetra-O-propyl-p-tert-butyl-...
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Acta Chini. Slov. 2001, 48, 427-430.
References
1.     Clixarenes a versatile class of macrocyclic compounds, Vicenc, J. and Böhmer, V. Eds., Kluwer Academic publishers, Dordrecht, the Netherlands, 1990.
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Povzetek
Opazili smo, da z obdelavo tetra-0-propil-p-ter?-butilkaliks[4]arena s stehiometricno množino A1C13 lahko pripravimo tri, di in mono-tetra-0-propil-/?-ter?-butilkaliks[4]arene. Pri the pretvorbah ostanejo ferc-butilne skupine na gornejm robu nedotaknjene.
S. Taghvaei-Ganjali, A. Modjallal: Selective dealkylatìon oftetra-O-propyl-p-tert-butyl-...