Fan et al.
19
phase-transfer catalyst (quaternary ammonium salt) and a
strong acid catalyst (such as TsOH) have to be used to facili-
tate the cyclodehydration reaction. Even so, xanthenedione
derivatives 3 (Scheme 2) can only be obtained from para-
substituted aromatic aldehydes through a much longer reac-
tion period. In the case of ortho- and meta-substituted aro-
matic aldehydes, non-cyclodehydrated products 4 (Scheme 2)
instead of 3 were obtained. In contrast, the substrates are
well-dissolved in the [bmim][BF4]/In3+ system, no phase-
transfer catalyst is needed, and the reaction time is much
shorter in our situation. Moreover, aromatic aldehydes with
ortho- or meta-substituents can react smoothly with 2 to pro-
duce xanthenedione derivates 3 in good yields (Table 2,
entries 5 and 10). In another case, microwave irradiation
technique has also been successfully used in the condensa-
tion of aldehydes with 5,5-dimethyl-1,3-cyclohexanedione to
give xanthenedione (7b). However, its potential use for
larger scale preparation may be rather limited compared to
the method presented in this paper.
225~227). ν: IR (KBr, cm–1) ν: 3030, 2950, 2878, 1685,
1
1660, 1627, 1467, 1357, 1203. H NMR (CDCl3) δ: 1.04 (s,
6H, 2 × CH3), 1.11 (s, 6H, 2 × CH3), 2.14~2.46 (m, 8H, 4 ×
CH2), 4.77 (s, 1H, CH), 7.31(d, J = 8.4 Hz, 2H, ArH), 7.65
(d, J = 8.4 Hz, 2H, ArH). Anal. calcd. for C23H25FO3: C
74.98, H 6.84; found: C 74.88, H 6.75.
9-(2′-Bromophenyl)-3,3,6,6-tetramethyl-3,4,5,6,7,9-
hexahydro-1H-xanthene-1,8-(2H)-dione (3h)
Colorless needles, mp 226~228. IR (KBr, cm–1) ν: 2959,
2871, 1679, 1666, 1627, 1469, 1357, 1203. 1H NMR
(CDCl3) δ: 1.04 (s, 6H, 2 × CH3), 1.11 (s, 6H, 2 CH3),
2.14~2.46 (m, 8H, 4 CH2), 5.04 (s, 1H, CH), 6.98 (t, J =
8.0 Hz, 1H, ArH), 7.21 (t, J = 4.0 Hz, 1H, ArH), 7.45 (m,
1H, ArH), 7.47 (d,d, J = 8.0, 0.9 Hz, 1H, ArH). Anal. calcd.
for C23H25BrO3: C 64.39, H 5.87; found: C 64.25, H 5.77.
9-(4′-Bromophenyl)-3,3,6,6-tetramethyl-3,4,5,6,7,9-
hexahydro-1H-xanthene-1,8-(2H)-dione (3i)
Colorless needles, mp 234~236. IR (KBr, cm–1) ν: 2953,
2878, 1679, 1662, 1625, 1487, 1470, 1362. 1H NMR
(CDCl3) δ: 1.00 (s, 6H, 2 × CH3), 1.12 (s, 6H, 2 × CH3),
2.16~2.48 (m, 8H, 4 × CH2), 4.72 (s, 1H, CH), 7.18 (d, J =
8.4 Hz, 2H, ArH), 7.35 (d, J = 8.4 Hz, 2H, ArH). Anal.
calcd. for C23H25BrO3: C 64.39, H 5.87; found: C 64.30, H
5.82.
In conclusion, we have found a novel procedure for the
preparation of xanthenedione derivatives. The main advan-
tages of this procedure include high yields, simple experi-
mental procedure, and ease of recovering and reusing of the
catalyst and the reaction media. Therefore, the present
method is expected to serve as an alternative process for the
preparation of xanthenedione derivatives.
9-(3′-Nitrophenyl)-3,3,6,6-tetramethyl-3,4,5,6,7,9-
hexahydro-1H-xanthene-1,8-(2H)-dione (3j)
Experimental
Colorless crystals, mp 145~147. IR (KBr, cm–1) ν: 2958,
1677, 1655, 1622, 1525, 1475, 1363, 1202. 1H NMR
(CDCl3) δ: 1.02 (s, 6H, 2 × CH3), 1.14 (s, 6H, 2 × CH3),
2.17~2.53 (m, 8H, 4 CH2), 4.86 (s, 1H, CH), 7.43 (t, J =
8.0 Hz, 1H, ArH), 7.84 (d, J = 7.6 Hz, 1H, ArH), 7.99~8.04
(m, 2H, ArH). Anal. calcd. for C23H25NO5: C 69.86, H 6.37,
N 3.54; found: C 69.66, H 6.29, N 3.51.
Melting points were measured by a Kofler micromelting
point apparatus and the results were uncorrected. IR spectra
were recorded on a Bruker Vector 22 spectrometer in KBr
with absorption in cm–1. H NMR spectra were determined
1
on a Bruker AC 400 spectrometer as CDCl3 solutions.
Chemical shifts (δ) are expressed in ppm downfield from the
internal standard tetramethylsilane, and coupling constants
(J) are given in Hz. Elemental analyses were performed on
an EA-1110 instrument.
Acknowledgements
The ionic liquid [bmim][BF4] was prepared and purified
according to literature procedure (12). Other reagents were
of reagent grade and were used without further purification.
This work was financially supported by the National Nat-
ural Science Foundation of China (No. 20273019) and the
Science Foundation of Henan Normal University for Young
Scholars (No. 0307032).
General procedure for the preparation of
xanthenedione derivatives
References
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1
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© 2005 NRC Canada