Mo(CO)6-mediated synthesis of calix[4]arenes carrying β-hydroxy ketones or α,β-unsaturated-β-amino ketones

Article abstract of DOI:10.1016/j.tetlet.2006.10.082

Mo(CO)₆-mediated ring opening reactions of calix[4]arene isoxazolines/isoxazoles provide a new synthetic methodology for calix[4]arenes carrying bifunctional β-hydroxy ketones or α,β-unsaturated-β-amino ketones. Mo(CO)₆ is a highly s

Full text of DOI:10.1016/j.tetlet.2006.10.082

Tetrahedron Letters 47 (2006) 9077–9081
Mo(CO)6-mediated synthesis of calix[4]arenes carrying
b-hydroxy ketones or a,b-unsaturated-b-amino ketones
Annamalai Senthilvelan, Ming-Tsung Tsai, Kai-Chi Chang and Wen-Sheng Chung*
Department of Applied Chemistry, National Chiao-Tung University, Hsinchu 30050, Taiwan, ROC
Received 31 August 2006; revised 6 October 2006; accepted 17 October 2006
Available online 7 November 2006
Abstract—Mo(CO)6-mediated ring opening reactions of calix[4]arene isoxazolines/isoxazoles provide a new synthetic methodology
for calix[4]arenes carrying bifunctional b-hydroxy ketones or a,b-unsaturated-b-amino ketones. Mo(CO)6 is a highly selective and
convenient reagent for the ring opening process of these supramolecular isoxazolines/isoxazoles.
Ó 2006 Elsevier Ltd. All rights reserved.
The interest in calix[4]arene chemistry is rapidly increas-
ing because its derivatives can form inclusion complexes
with cations or neutral molecules.1 The introduction of
esters, ketones, amides or b-ketoimine groups to the
lower rim of calix[4]arenes have been known and they
act as efficient ligands2 for cationic bindings. In the
quest for new fluorogenic sensors for metal ions, we
have devised a strategy for attaching isoxazoline or iso-
xazole units onto the upper or lower rims of calix[4]-
arenes3 using 1,3-dipolar cycloadditions. Such a strategy
would provide arrays of calix[4]arenes possessing vari-
ous bifunctional groups if ring opening reactions on
the attached isoxazolines or isoxazoles could be exe-
cuted successfully. Traditionally, ring opening reactions
of such heterocycles have been performed using either
metal reducing agents4,5 or photochemical methods.6
ketones or a,b-unsaturated-b-amino ketones by the ring
opening reactions of calix[4]arene isoxazolines and iso-
xazoles. There are several methods known for achieving
N–O bond cleavage in an isoxazoline/isoxazole ring,
namely, reduction with Raney Ni,5,9 LiAlH4,10 H2/Pd–
C,11 TiCl3,12 SmI2,13 and Mo(CO)6.14 Among these
methods, the Mo(CO)6-mediated ring opening of isoxaz-
olines/isoxazoles appears to be the most efficient one. To
the best of our knowledge, the Mo(CO)6-mediated ring
opening reactions of calix[4]arene isoxazolines/isox-
azoles have not yet been reported previously.
Firstly, we studied the ring opening reactions of lower
rim calix[4]arene isoxazolines 1a–c, which were obtained
through 1,3-dipolar cycloaddition7 reaction of 25-allyl-
oxy-26,27,28-trihydroxycalix[4]arene15 with aryl hydr-
oximoyl chloride in THF using Et3N as a base. The
structures of 1a–c were confirmed spectroscopically.
The 13C NMR of 1a–c showing methylene bridge car-
bons between d 30 and 32 confirmed that calix[4]arenes
1a–c were in cone conformation. After refluxing a mix-
ture of 1a with Mo(CO)6 (4 mol equiv) in wet aceto-
nitrile for 48 h, we obtained the expected b-hydroxy
ketone 2a in a 38% yield. In addition to recovered
1a,16 we also obtained the cleaved product 3 in a 32%
yield. Likewise, Mo(CO)6-mediated ring opening reac-
tions of calix[4]arene isoxazolines 1b,c (Table 1) were
successfully carried out to the corresponding b-hydroxy
ketones 2b,c.
In an earlier publication,7 we reported the Raney Ni-
mediated ring opening reaction of a calix[4]arene isox-
azoline. Even though the reaction proceeded well, we
could not isolate the ring-opened product because it
formed a very strong complex with the Ni2+ ion, as con-
firmed by mass spectrometric and IR spectroscopic data.
In continuation of our interest on the Mo(CO)6-medi-
ated ring opening reactions of isoxazolines,8 we report
here the synthesis of calix[4]arenes carrying b-hydroxy
Keywords: Calix[4]arene isoxazolines/isoxazoles; Molybdenum hexa-
carbonyl; b-Hydroxy ketones; a,b-Unsaturated-b-amino ketones.
Corresponding author. Tel.: +886 35131517; fax: +886 35723764;
The structures of compounds 2a–c and 3 were confirmed
spectroscopically17 and compound 3 was compared
with the authentic sample. The cone conformation of
*
e-mail: wschung@cc.nctu.edu.tw
0040-4039/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2006.10.082

9078
A. Senthilvelan et al. / Tetrahedron Letters 47 (2006) 9077–9081
carbons at around d 31 in the 13C NMR spectra,
confirmed that structures of calix[4]arenes 4 and 5 were
in cone conformation.
Table 1. Ring opening reactions of lower rim calix[4]arene isoxazolines
1a–c
Mo(CO)6
Since, the ring opening reactions were successfully car-
ried out at lower and upper rim calix[4]arene isoxazo-
lines, we wondered whether the ring opening reaction
of the calix[4]arene isoxazolines would still work in the
presence of other functional groups at the lower rim.
Hence, we studied the ring opening reaction of amide-
substituted calix[4]arene isoxazoline 6, which was syn-
thesized by the reaction of 1a with bromoacetamide in
the presence of sodium methoxide (or K2CO3) using
THF/DMF as a solvent (Scheme 1). The structure of
compound 6 was confirmed by spectral data (see Supple-
mentary data). The cone conformation of calix[4]arene 6
was confirmed by 13C NMR spectrum, showing the
methylene bridge carbons at d 31.0, 31.4, and 31.7.
The reaction of 6 with Mo(CO)6 (3 mol equiv) in a wet
acetonitrile at 80 °C for 48 h, gave the expected b-hydr-
oxy ketone 7 (75%) and the recovered 6 (15%). Under
the reaction conditions, neither the amide linkage
nor the thienoisoxazoline group was cleaved (Scheme 1).
The structure of compound 7 was confirmed by spectral
data. The 13C NMR spectrum of 7 showing methylene
bridge carbons at d 31.0, 31.3, and 31.6, confirmed that
compound 7 was in cone conformation. The amide and
the b-hydroxy ketone carbonyls appeared at d 170.9 and
191.4, respectively (see Supplementary data). It is worth
noting that in the ring opening reactions of lower and
upper rim calix[4]arene isoxazolines, we did not observe
even a trace amount of metal complexation in the ring
opened products. This warrants that Mo(CO)6 is a suit-
able and selective reagent for the ring opening reactions
of calix[4]arene isoxazolines.19
HO
OH
OH
O
CH3CN/H2O
80 o
48 h
C
O
1a-c
N
R
+
HO
OH
OH
HO
O
OH
OH OH
OH
O
2a-c
3
R
Compound
R
2 Yielda (%) 3 Yielda (%)
1a
1b
1c
5-Methylthien-2-yl
5-Chlorothien-2-yl
38
31
32
17
15
5-Chlorofuran-2-yl 55
a Isolated yields based on recovered starting material.
calix[4]arenes 2a–c were confirmed by observing the
methylene bridge carbons between d 31 and 32 in 13C
NMR spectra. We also confirmed that the calix[4]arene
3 came from the direct cleavage of 1 but not from 2 be-
cause the reaction of isolated 2a with Mo(CO)6 under
the same reaction conditions did not lead to the forma-
tion of 3.
Next, we studied the ring opening reactions of upper rim
calix[4]arene isoxazolines 4a–c. Isoxazolines 4a–c were
synthesized by 1,3-dipolar cycloaddition reaction of 5-
allylcalix[4]arene15 with the aryl substituted hydrox-
imoyl chloride in THF by the known method.7
NH2
The structures of compounds 4a–c have been confirmed
by spectral data, where compound 4a has already been
reported previously.7 Table 2 summaries the results of
ring opening reactions of isoxazolines 4a–c in the pre-
sence of Mo(CO)6 (4 mol equiv) using CH3CN/H2O at
80 °C. The expected b-hydroxy ketones 5a–c, were
obtained in modest yields after 48–60 h of reaction.
The structures of compounds 5a–c were confirmed spec-
troscopically.18 The appearance of methylene bridge
Br
+
O
HO
OH
OH
O
O
OH
OH
O
CH3ONa
THF/DMF
Reflux, 13 h
O
O
N
O
NH2
1a
N
6
80%
S
S
CH3
CH3
80 o
48 h
C
Mo(CO)6
CH3CN/H2O
Table 2. Ring opening reactions of upper rim calix[4]arene isoxazo-
lines 4a–c
O
OH
O
N
R
R
O
OH
OH
O
Mo(CO)6
O
OH
CH3CN/H2O
NH2
(75%)a
80 o
C
HO
HO
OH
OH OH
OH
OH OH
7
O
48-60 h
4a-c
5a-c
S
Compound
R
5 Yield (%)
CH3
4a
4b
4c
Phenyl
5-Methylthien-2-yl
5-Chlorofuran-2-yl
30a
49
Scheme 1. Ring opening reaction of lower rim amide substituted
calix[4]arene isoxazoline 6. (a) Isolated yield based on recovered
starting material.
32
a Isolated yield based on recovered starting material.

A. Senthilvelan et al. / Tetrahedron Letters 47 (2006) 9077–9081
9079
Table 3. Ring opening reactions of calix[4]arene isoxazoles 12a,b
After successfully performing the ring opening reactions
on calix[4]arene isoxazolines, we extended this methodo-
logy to calix[4]arene isoxazoles. First, we optimized the
ring opening reaction condition for calix[4]arene isox-
azoles, by studying the ring opening reaction of isoxazole
8, obtained by the 1,3-dipolar cycloaddition of propar-
gyloxy benzene with phenyl nitrile oxide, using the
reported method.7 The reaction of isoxazole 8 with
Mo(CO)6 (3 mol equiv) in CH3CN/H2O for 36 h gave
the expected ring opened a,b-unsaturated-b-amino-
ketone 9 in a 63% yield (Scheme 2), in addition to
cleaved phenol 10 (15% yield). The structure of
compounds 8–10 were confirmed by spectral data (see
Supplementary data). Furthermore, compound 10 was
compared with the authentic sample.
Et3N
OH
R
HO
OH
OH
O
HO
+
OH
OH
N
O
Toluene
Reflux, 24 h
Cl
11
12a,b
60-66%
O
N
R
80 o
24-36 h
C
Mo(CO)6
CH3CN/H2O
HO
OH
OH
+
O
HO
OH
OH OH
O
Next, we studied the ring opening reaction of calix[4]-
arene isoxazoles, using the optimized reaction condition
mentioned above. Calix[4]arene isoxazoles 12a,b were
synthesized by 1,3-dipolar cycloaddition reaction of
25-propargyloxy-26,27,28-trihydroxycalix[4]arene 1120
with the aryl substituted hydroximoyl chloride in tolu-
ene using Et3N as a base (Table 3). The structures of
compounds 12a,b were consistent with the spectroscopic
data (see Supplementary data). Heating a solution of
12a with Mo(CO)6 (3 mol equiv) in wet acetonitrile at
80 °C for 36 h furnished the expected isoxazole ring-
opened b-amino-a,b-unsaturated ketone 13a in a 53%
yield. Likewise, calix[4]arene isoxazole 12b with
Mo(CO)6 under a similar reaction condition gave the ex-
pected b-amino ketone 13b in a 58% yield (Table 3).19 In
both cases calix[4]arene 3 was also observed, which was
confirmed by the authentic sample.
13a,b
3
NH2
R
Compound
R
13 Yield (%)
3 Yield (%)
12a
12b
5-Chlorothien-2-yl
5-Chlorofuran-2-yl
53
58
16
18
In summary, we have reported here a selective and
convenient method for the ring opening reactions of
calix[4]arene isoxazolines and isoxazoles. We have also
successfully demonstrated that the ring opening reaction
of calix[4]arene isoxazoline with amide substituent was
feasible. This 1,3-dipolar cycloaddition and ring opening
protocol provides an efficient method in attaching
bifunctional ligands onto the upper and/or lower rims
of calix[4]arenes. Further investigations on the ring
opening reactions of calix[4]arene bis-isoxazoles and
host–guest studies of the multifunctional calix[4]arenes
are ongoing in our laboratory.
The structures of 13a,b were confirmed by spectral
1
data.21 The H NMR spectra of compounds 12 and 13
showing AB quartets for methylene bridge protons with
coupling constant 13 Hz and the signals between d 31
and 32 in the 13C spectra were assigned to the methylene
bridge carbons, which confirmed the cone conformation
of calix[4]arenes 12a,b and 13a,b.
Acknowledgements
We thank the National Science Council (NSC) and
MOE ATU program of the Ministry of Education of
Taiwan, ROC for financial support.
In the ring opening reaction of calix[4]arene isoxazolines
or isoxazoles, molybdenum hexacarbonyl selectively
assisted the N–O bond cleavage to form a nitrene com-
plex, which underwent hydrolysis in the presence of
water to give b-hydroxy ketones or a,b-unsaturated-b-
amino ketones, respectively. The formation of nitrene
complex in the ring opening reactions of isoxazolines8,22
or isoxazoles23 has been already reported.
Supplementary data
Supplementary data associated with this article can
be found, in the online version, at doi:10.1016/j.tetlet.
2006.10.082.
References and notes
O
O
Mo(CO)6
CH3CN/H2O
1. (a) Gutsche, C. D. In Calixarenes Monographs in Supra-
molecular Chemistry; Stoddart, J. F., Ed.; The Royal
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148; (b) Gutsche, C. D. In Calixarenes Revisited Mono-
graphs in Supramolecular Chemistry; Stoddart, J. F., Ed.;
The Royal Society of Chemistry: Cambridge, 1998; Vol. 6,
pp 79–145.
O
N
O
NH2
+
80 o
36 h
C
OH
10
(15%)
(63%)
9
8
Scheme 2. Ring opening reaction of 5-(phenoxy methyl)-3-phenyl
isoxazole 8.
2. (a) Arduini, A.; Pochini, A.; Reverberi, S.; Ungaro, R.;
Andreetti, G. D.; Ugozzoli, F. Tetrahedron 1986, 42,

9080
A. Senthilvelan et al. / Tetrahedron Letters 47 (2006) 9077–9081
2089–2100; (b) Arduini, A.; Ghidini, E.; Pochini, A.;
605 (M++2, 3), 424 (100), 166 (90); HR MS (FAB) calcd
for C37H33NO5S 603.2079. Found 603.2075.
Ungaro, R.; Andreetti, G. D.; Calestani, G.; Ugozzoli, F.
J. Incl. Phenom. Macrocyl. Chem. 1988, 6, 119–134;
(c) Arnaud-Neu, F.; Collins, E. M.; Deasy, M.; Ferguson,
G.; Harris, S. J.; Kaitner, B.; Longh, A. J.; McKervey, M.
A.; Marques, E.; Ruhl, B. L.; Schwing-Weill, M. J.;
Sewand, E. M. J. Am. Chem. Soc. 1989, 111, 8681–8691;
(d) Halouani, H.; Dumazet-Bonnamour, I.; Perrin, M.;
Lamartine, R. J. Org. Chem. 2004, 69, 6521–6527.
Spectral data of 2a: Yellow solid; mp 140–142 °C; Rf = 0.4
(hexane/EtOAc = 3/1); 1H NMR (CDCl3, 300 MHz): d
2.54 (s, 3H, CH3), 3.44–3.62 (m, 6H), 4.11–4.53 (m, 6H),
4.85–4.87 (m, 1H), 5.02 (br s, 1H), 6.65–6.72 (m, 3H),
6.84–7.12 (m, 10H), 7.75 (d, J = 3.7 Hz, 1H), 9.47 (s, 1H),
9.50 (s, 1H), 9.85 (s, 1H); 13C NMR (CDCl3, 75.4 MHz): d
16.1 (CH3), 31.1 (CH2), 31.5 (CH2), 31.8 (CH2), 31.9
(CH2), 41.8 (CH2), 67.4 (CH), 80.5 (CH2), 121.1 (CH),
121.4 (CH), 122.0 (CH), 126.5 (CH), 127.1 (CH), 127.7
(Cq), 128.2 (Cq), 128.4 (Cq), 128.4 (Cq), 128.5 (CH), 128.6
(CH), 128.8 (CH), 128.9 (Cq), 129.0 (CH), 129.2 (CH),
129.7 (CH), 133.7 (CH), 133.8 (Cq), 134.5 (Cq), 141.8
(Cq), 148.9 (Cq), 150.0 (Cq), 150.5 (Cq), 150.7 (Cq), 150.9
(Cq), 191.0 (Cq); MS (EI) m/z 588 (M+ÀH2O, 6), 424
(100), 197 (40); HR MS (FAB) calcd for [M+ÀH2O]
C37H32O5S 588.1970; found 588.1993.
3. (a) Part of this work was presented previously; see Proc.
Int. Symp. Supramol. Chem., Notre Dame, USA, July 25–
30, 2004; Poster-1–31; (b) Shiao, Y.-J.; Chiang, P.-C.;
Senthilvelan, A.; Tsai, M.-T.; Lee, G.-H.; Chung, W.-S.
Tetrahedron Lett. 2006, 47, 8383–8386.
4. Kozikowski, A. P. Acc. Chem. Res. 1984, 17, 410–416.
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8. Senthilvelan, A.; Lee, G.-H.; Chung, W.-S. Tetrahedron
Lett. 2006, 47, 7179–7183.
9. Calvo, L. A.; Gonzalez-Nogal, A. M.; Gonzalez-Ortega,
A.; Sanudo, M. C. Tetrahedron Lett. 2001, 42, 8981–8984.
10. Ja¨ger, V.; Colinas, P. A. In The Chemistry of Heterocyclic
Compounds; John Wiley and Sons: New York, 2002; Vol.
59, Chapter 6.
11. (a) Asaoka, M.; Mukuta, T.; Takei, H. Tetrahedron Lett.
1981, 22, 735–738; (b) Fuentes, J. A.; Maestro, A.;
Testera, A. M.; Banez, J. M. Tetrahedron: Asymmetry
2000, 11, 2565–2577.
18. Procedure for the ring opening reaction of upper rim
calix[4]arene isoxazoline 4b: A mixture of 4b (0.20 mmol)
and molybdenum hexacarbonyl (0.802 mmol) in aceto-
nitrile (18 mL) containing water (three drops) was refluxed
at 80 °C for 48 h. After removing the solvent, the residue
was purified over silica gel column to give the expected
b-hydroxy ketone 5b (49%).
Spectral data of 4b: Yellow solid, mp 148–150 °C; Rf = 0.2
(hexane/EtOAc = 5/1); 1H NMR (CDCl3, 300 MHz): d
2.50 (s, 3H, CH3), 2.63–2.70 (m, 1H), 2.91–3.01 (m, 2H),
3.19–3.28 (m, 1H), 3.57 (br s, 4H), 4.27 (br s, 4H), 4.82–
4.88 (m, 1H), 6.70–6.79 (m, 4H, ArH), 6.93–6.96 (m, 3H,
ArH), 7.07–7.10 (m, 6H, ArH), 10.2 (s, 4H, OH); 13C
NMR (CDCl3, 75 MHz): d 15.4 (CH3), 31.6 (CH2), 39.9
(CH2), 40.0 (CH2), 81.8 (CH), 122.1 (CH), 122.2 (CH),
125.4 (CH), 128.1 (CH), 128.2 (Cq), 128.3 (Cq), 128.5
(Cq), 128.9 (CH), 128.9 (CH), 129.7 (CH), 129.8 (Cq),
130.5 (Cq), 143.3 (Cq), 147.5 (Cq), 148.7 (Cq), 148.7 (Cq),
152.3 (Cq); MS (EI) m/z (%): 604 (M++1, 10), 603 (M+,
40), 466 (45), 437 (100), 124 (50), 91 (50); HR MS (FAB)
m/z: calcd for [M+H+] C37H34NO5S 604.2157; found
604.2162.
Spectral data of 5b: Brownish yellow solid, mp 160–
162 °C; Rf = 0.22 (hexane/EtOAc = 3/1); 1H NMR
(CDCl3, 300 MHz): d 2.54 (s, 3H, CH3), 2.61–2.76 (m,
2H), 2.95–3.04 (m, 2H), 3.16 (br s, 1H, OH), 3.48–3.72 (br
m, 4H), 4.25–4.32 (br m, 5H), 6.72–6.82 (m, 4H, ArH),
6.95 (s, 2H, ArH), 7.06–7.14 (m, 6H, ArH), 7.47 (d,
J = 3.7 Hz, 1H, ArH), 10.21 (s, 4H, OH); 13C NMR
(CDCl3, 75.4 MHz): d 16.1 (CH3), 31.6 (CH2), 31.7 (CH2),
42.2 (CH2), 44.1 (CH2), 69.1 (CH), 122.3 (CH), 126.8
(CH), 128.2 (Cq), 128.2 (Cq), 128.3 (Cq), 128.9 (CH),
129.9 (CH), 131.5 (Cq), 133.2 (CH), 141.8 (Cq), 147.4
(Cq), 148.8 (Cq), 148.8 (Cq), 150.5 (Cq), 192.7 (Cq); MS
(EI) m/z (%): 589 (M+À17, 5), 588 (8), 466 (100), 125 (90),
91 (40); HR MS (FAB) m/z: calcd for [M+H+] C37H35O6S
607.2154; found 607.2127.
12. Andersen, S. H.; Sharma, K. K.; Torssell, K. B. G.
Tetrahedron 1983, 39, 2241–2245.
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4104; (b) Gelabert, L. I.; Fascio, M. L.; D’Accorso, N. B.
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16. The recovery of starting material is commonly observed in
the ring-opening reaction of isoxazolines using Mo(CO)6,
see: (a) Guarna, A.; Guidi, A.; Goti, A.; Brandi, A.; De
Sarlo, F. Synthesis 1989, 175–178; (b) Bode, J. W.;
Carreira, E. M. J. Org. Chem. 2001, 66, 6410–6424.
17. Procedure for the ring opening reaction of lower rim
calix[4]arene isoxazoline 1a: An acetonitrile (18 mL)
solution of 1a (0.247 mmol) and molybdenum hexacar-
bonyl (0.988 mmol) containing water (three drops) was
refluxed at 80 °C for 48 h. The solvent was removed under
reduced pressure and the residue was purified over silica
gel column to give 2a (38%), 3 (32%) and recovered 1a
(9%).
Spectral data of 1a: Yellow solid; mp 154–156 °C;
Rf = 0.47 (hexane/EtOAc = 3/1); 1H NMR (CDCl3,
300 MHz): d 2.49 (s, 3H, CH3), 3.36–3.70 (m, 5H), 4.06–
4.46 (m, 7H), 5.27–5.31 (m, 1H), 6.60–7.07 (m, 13H), 7.19
(d, J = 3.5 Hz, 1H), 8.68 (s, 1H), 9.03 (s, 1H), 9.26 (s, 1H);
13C NMR (CDCl3, 75.4 MHz): d 15.5 (CH3), 31.0 (CH2),
31.6 (CH2), 31.7 (CH2), 37.3 (CH2), 76.9 (CH2), 79.0
(CH), 120.4 (CH), 120.8 (CH), 121.7 (CH), 125.6 (CH),
126.3 (CH), 127.6 (Cq), 127.9 (Cq), 128.0 (Cq), 128.2
(CH), 128.2 (Cq), 128.3 (Cq), 128.3 (CH), 128.6 (CH),
128.6 (Cq), 128.7 (CH), 128.8 (CH), 129.0 (Cq), 129.3
(CH), 129.5 (CH), 129.6 (CH), 133.6 (Cq), 134.1 (Cq),
143.8 (Cq), 148.9 (Cq), 150.5 (Cq), 150.6 (Cq), 151.1 (Cq),
152.7 (Cq); MS (EI) m/z 603 (M+, 48), 604 (M++1, 10),
19. In addition to Mo(CO)6-mediated ring-cleavage, we also
attempted to cleave cycloadducts 1a and 12a using H2/Pd–
C. No reaction was observed in isoxazoline 1a. Whereas,
only complex mixtures of products were observed without
any major product in the ring opening reaction of
isoxazole 12a.
20. Compound 11 was synthesized by refluxing the mixture of
calix[4]arene (5 mmol), propargyl bromide (11.2 mmol)
and sodium methoxide (5.9 mmol) in acetonitrile (120 mL)
for 8 h. After completion of reaction, the solvent was
removed under reduced pressure and the residue was
purified by silica gel column to get 11 (60%). For the
synthesis of a similar p-tert-butylcalix[4]arene with prop-
´
argyloxyl group please see: Santoyo-Gonzalez, F.; Torres-

A. Senthilvelan et al. / Tetrahedron Letters 47 (2006) 9077–9081
9081
´
Pinedo, A.; Sanchez-Ortega, A. J. Org. Chem. 2000, 65,
4409–4414.
J = 4 Hz, 1H), 7.00–7.09 (m, 8H), 7.36 (d, J = 4 Hz, 1H),
9.40 (br s, 2H), 9.82 (br s, 1H); 13C NMR (CDCl3,
75.4 MHz): d 31.5 (CH2), 31.9 (CH2), 78.9 (CH2), 89.8
(CH), 120.9 (CH), 121.6 (CH), 125.9 (CH), 126.6 (CH),
127.4 (CH), 128.3 (Cq), 128.4 (CH), 128.4 (Cq), 128.6
(Cq), 128.7 (CH), 129.3 (CH), 133.9 (Cq), 134.2 (Cq),
137.1 (Cq), 149.6 (Cq), 150.6 (Cq), 152.6 (Cq), 154.5 (Cq),
193.2 (Cq); MS (EI) m/z 623 (M+, 5), 625 (M++2, 2), 607
(90), 424 (50), 150 (100); HRMS (FAB) calcd for
C36H3037ClNO5S 625.1504; found 625.1505.
21. Procedure for the ring opening reaction of calix[4]arene
isoxazole 12a: A mixture of 12a (0.169 mmol) and molyb-
denum hexacarbonyl (0.507 mmol) in acetonitrile 18 mL
containing water (three drops) was heated at 80 °C for
36 h. After completion of reaction, the expected a,b-
unsaturated-b-amino ketone 13a was obtained in a 53%
yield after column chromatography on silica gel.
Spectral data of 13a: Brown solid; mp 228–230 °C;
Rf = 0.4 (hexane/EtOAc = 3/1); 1H NMR (CDCl3,
300 MHz): d 3.44 and 4.52 (ABq, J = 13.0 Hz, 4H), 3.46
and 4.31 (ABq, J = 13.7 Hz, 4H), 4.85 (s, 2H), 5.91 (s,
1H), 6.64–6.71 (m, 3H), 6.86 (t, J = 7.5 Hz, 1H), 6.96 (d,
22. Baraldi, P. G.; Barco, A.; Benetti, S.; Manfredini, S.;
Simoni, D. Synthesis 1987, 276–278.
23. Nitta, M.; Kobayashi, T. J. Chem. Soc., Perkin Trans. 1
1985, 1401–1406.