Thermal rearrangement of 4-alkyl-4H-1,2,4-triazoles to 1-alkyl-1H-1,2,4-triazoles - A study of the mechanism by cross-over experiments

Article abstract of DOI:10.1002/1099-0690(200011)2000:22<3745::AID-EJOC3745>3.0.CO;2-K

The mechanism for the thermal rearrangement of 4-alkyl-1,2,4-triazoles to the corresponding 1-alkyl-1,2,4-triazoles, was studied by cross-over experiments with mixtures of 4-ethyl-3,5-diphenyl-4H-1,2,4-triazole and 3,5-bis(4-methylphenyl)-4-propyl-4H-1,2,

Full text of DOI:10.1002/1099-0690(200011)2000:22<3745::AID-EJOC3745>3.0.CO;2-K

FULL PAPER
Thermal Rearrangement of 4-Alkyl-4H-1,2,4-triazoles to 1-Alkyl-1H-1,2,4-
triazoles ؊ A Study of the Mechanism by Cross-over Experiments
Odd R. Gautun[a] and Per H. J. Carlsen*[a]
Keywords: Triazole / Rearrangements / Thermochemistry / Mechanism
The mechanism for the thermal rearrangement of 4-alkyl-
1,2,4-triazoles to the corresponding 1-alkyl-1,2,4-triazoles,
was studied by cross-over experiments with mixtures of 4-
zolium triazolate intermediate, and a subsequent nucleo-
philic attack of the triazolate anion at the 1- and 4-alkyl-
group positions to form the observed products. Further sup-
ethyl-3,5-diphenyl-4H-1,2,4-triazole and 3,5-bis(4-methyl- port was obtained by thermolysis of a mixture of 1-ethyl-3,5-
phenyl)-4-propyl-4H-1,2,4-triazole. This gave support to a
bis(4-methylphenyl)-4-propyl-1,2,4-triazolium
tetrafluoro-
proposed mechanism involving the formation of an ionic tria-
borate and potassium 3,5-diphenyl-1H-triazolate.
Introduction
(22%), 3,5-diphenyl-1-propyl-1H-1,2,4-triazole (4) (25%),
1-ethyl-3,5-bis(4-methylphenyl)-1H-1,2,4-triazole (5) (24%),
and 3,5-bis(4-methylphenyl)-1-propyl-1H-1,2,4-triazole (6)
(29%) (Scheme 1). The products were identified by co-chro-
matography with standard materials prepared by independ-
ent syntheses. IR spectroscopy with GC-FTIR, and com-
parison with authentic samples gave further proof of iden-
tity. The yields were determined by GC analysis and mass
spectrometric measurements.
We have studied the thermal rearrangement reactions of
neat 4-alkyl-substituted 4H-1,2,4-triazoles to the corres-
ponding 1-alkyl-1H-1,2,4-triazoles (see Figure 1), and dis-
cussed evidence for a consecutive nucleophilic displacement
reaction, and the formation of an ion-pair. The possibility
of a concerted [1,3]-migration has also been discussed, and
cannot be totally excluded.[1] It is essential to establish
whether the reactions are inter- or intramolecular, as evid-
ence for an intermolecular reaction would exclude a concer-
ted shift mechanism. One way to distinguish between inter-
or intramolecular mechanisms would be through cross-over
experiments. The rearrangements may proceed through a
dialkyltriazolium-triazolate ion-pair intermediate or by re-
actions between neutral molecules in a chain reaction.
Scheme 1. Cross-over experiment with 1 and 2
In the latter case the intensities of the molecular ion
peaks, 3 (249), 4 (263), 5 (277), and 6 (291) were measured
and compared with a mixture of known composition of in-
dependently prepared standard materials. Good agreement
was obtained in all cases. The products were obtained in
approximately equal amounts, and any deviations in yield
may be due to slight stereoelectronic substitution effects
and errors in the analytical techniques. It can be concluded
from these results, that the rearrangement of the triazoles
Figure 1. Thermolysis of 4H-1,2,4-triazoles
To elucidate the details of the mechanism we here de-
scribe a series of cross-over experiments.
Results and Discussion
Thermolysis of a 1:1 mixture of 4-ethyl-3,5-diphenyl-4H- is clearly bimolecular, and a concerted shift mechanism can
1,2,4-triazole (1) and 3,5-bis(4-methylphenyl)-4-propyl-4H- be excluded.
1,2,4-triazole (2) at 314Ϫ335 °C for 36 min. under a nitro-
The observations can be rationalized by a mechanism in
gen atmosphere in closed glass tubes yielded a series of which the N-1 atom in one triazole molecule participates
products which were readily separated by thin layer chro- in a nucleophilic displacement reaction and results in the
matography. The tolyl-substituted triazole 2 was chosen to formation of an ion-pair, and subsequent attack of the an-
minimize the electronic effects that may influence the out- ion on the alkyl groups in the triazolium cation, Scheme 2.
come of the reaction. The reaction mixture contained the The proposed mechanism resembles one reported by
four products 1-ethyl-3,5-diphenyl-1H-1,2,4-triazole (3) Bentley et al. for the rearrangement of 4-(β-hydroxyethyl)-
1,2,4-triazole[2] and finds further support in the work by
[a]
other groups.[3]
Department of Chemistry, Norwegian University of Science
and Technology
The mechanism outlined in Scheme 2 accounts for the
formation of the cross-over products 4 and 5. The re-
N-7491 Trondheim, Norway
E-mail: per.carlsen@chembio.ntnu.no
Eur. J. Org. Chem. 2000, 3745Ϫ3748
WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2000
1434Ϫ193X/00/1122Ϫ3745 $ 17.50ϩ.50/0
3745

O. R. Gautun, P. H. J. Carlsen
FULL PAPER
Scheme 2. Proposed mechanism for the formation of products 4 and 5
Scheme 3. Thermolysis of the ‘‘ion-pair’’ intermediate 7/8
maining products, 3 and 6, shown in Scheme 1 are the prod- ation of the ‘‘free’’ butyl group. However, as S-9 was reco-
ucts expected for pure 1 and 2. All products were formed vered unchanged, it must be the N-1 bonded butyl group
in essentially equal amounts.
that leaves, although from past experience this is predicted
To take this one step further, we decided to mimic the to be less likely as the N-4-position is the more reactive.
ionic step in the proposed reaction mechanism, by thermo- These data are rationalized as outlined in Scheme 4.
lysis of a mixture containing the dialkyltriazolium ion and
the triazole anion, and at the same time obtain cross-over
information. This was achieved by thermolysis of a well
blended 1:1 mixture of 1-ethyl-3,5-bis(4-methylphenyl)-4-
propyl-1,2,4-triazolium tetrafluoroborate, 8, and potassium
3,5-diphenyl-1H-triazolate, 7, under nitrogen in a sealed
glass tube at 329Ϫ335 °C for 30 minutes. The products
formed were 3 (9%), 4 (40%), 5 (38%) and 6 (13%),
Scheme 3. The product composition and yields were deter-
mined by GC-analysis using tetracosane, n-C24H50, as an
internal standard.
The products 4 and 5, derived from the direct reaction
between 7 and 8 predominate. However, small amounts of
products 3 and 6 were also formed, either owing to second-
Scheme 4. Partial thermolysis of S-9
ary reactions of the initial products formed or owing to
attack of 8 at the ethyl site of 7. From experience we de-
cided the latter to be less likely.[4,5] However, results from
the optically active 4-(S-2-butyl)-3,5-diphenyl-4H-1,2,4-tri-
azole (9) which was reported in a previous paper,[5] may
give new information. Partial thermolysis of the optically
active triazole 9 at 330 °C for 10 min and purification by
preparative TLC yielded 63% of recovered starting material,
which by CD-analysis showed that no or very little racemiz-
ation had taken place, (maximum 3Ϫ4% which may well be
within the experimental error). Similarly, the corresponding
triazole 1-(S-2-butyl)-3,5-diphenyl-1H-1,2,4-triazole (10)
did not undergo any noticeable racemization when thermo-
lyzed for 30 min. These results indicate that the racemiz-
This reaction scheme satisfies all the observed data. The
quantities of products 3 and 6 in Scheme 3, are in a reason-
able agreement with the degree of racemization indicated in
Scheme 4. Thus, approximately 85% of the reaction follows
route a and 15% route b. Alternative mechanisms, such as
cleavage of the 2-butyl group from the dialkyltriazolium
species shown in Scheme 4 and subsequent recombination
may actually also account for the formation of a partially
racemized product.
Conclusion
For the thermal rearrangement of 4-alkyl-1,2,4-triazoles
ation must take place during the rearrangement reaction. to the corresponding 1-alkyl-1,2,4-triazoles, cross-over ex-
We have shown previously, that thermolysis of S-9 pro- periments with a mixture of 4-ethyl-3,5-diphenyl-4H-1,2,4-
duced R-10 with approximately 70% ee, corresponding to triazole and 3,5-bis(4-methylphenyl)-4-propyl-4H-1,2,4-tri-
85% R and 15% of the S-enantiomer. This may take place azole give support to a mechanism which involves the
by cleavage of the N-2-butyl bond and subsequent racemiz- formation of an ionic triazolium triazolate intermediate,
3746
Eur. J. Org. Chem. 2000, 3745Ϫ3748

Thermal Rearrangement of 4-Alkyl-4H-1,2,4-triazoles to 1-Alkyl-1H-1,2,4-triazoles
FULL PAPER
Thermolysis of the ‘‘Ion-Pair Intermediate’’: The potassium salt of
3,5-diphenyl-1H-1,2,4-triazole (7) (21.2 mg, 0.0817 mmol) and
compound 8 (32.4 mg, 0.0834 mmol) were carefully mixed, placed
in a sealed glass tube under nitrogen and heated in an oven
(329Ϫ335 °C) for 30 min. Composition and product yields were
determined by GC measurements using tetracosane, n-C24H50, as
the internal standard. The products were identified by comparison
of their spectroscopic properties with those of authentic samples.
1-Ethyl-3,5-diphenyl-1H-1,2,4-triazole (3): 3.5 mg, 9%.
3,5-Diphenyl-1-propyl-1H-1,2,4-triazole (4): 17.6 mg, 40%.
1-Ethyl-3,5-bis(4-methylphenyl)-1H-1,2,4-triazole (5): 17.2 mg,
38%.
and subsequent nucleophilic attack of the triazolate com-
ponent at the 1- and 4-alkyl groups forms the observed
products.
Experimental Section
General: 1H and 13C NMR spectra were recorded on a JEOL JNM-
EX400 FT NMR spectrometer, with CDCl3 as the solvent and
tetramethylsilane (TMS) as the internal standard. IR and GC-IR
spectra were obtained on a Nicolet 20-SXC FT-IR (GC Carlo Reba
5160, 25 m, CP-Sil-5 CB). Mass spectra were recorded on a AEI
MS-902 spectrometer at 70 eV (IP) and 200 °C inlet temperature.
CD spectra were recorded at room temperature on a Jobin Yvon
Auto Dictograf Mark IV. GC measurements were performed on a
Varian 3700 gas chromatograph equipped with a BP-1 capillary
column (24 m).
3,5-Bis(4-methylphenyl)-1-propyl-1H-1,2,4-triazole (6): 6.1 mg,
13%.
The MS of the crude product mixture gave the following results:
MS: m/z (%) ϭ 292 (5), 291 (20) [Mϩ, (6)] 278 (22), 277 (100) [Mϩ,
(5)] 264 (15), 263 (77) [Mϩ, (4)], 250 (8), 249 (43) [Mϩ, (3)].
Potassium Salt of 3,5-diphenyl-1H-1,2,4-triazole (7): 1H NMR
(400 MHz, CD3OD): δ ϭ 7.29 (t, J ϭ 7.3 Hz, 2 H), 7.39 (t, J ϭ
7.5 Hz, 4 H), 8.06 (d, J ϭ 7.3 Hz, 4 H). Ϫ IR (KBr): ν˜ ϭ 3071,
4-Alkyl-4H-1,2,4-triazoles: The products were obtained by reacting
bis(α-chlorobenzylidene)hydrazine
[or
bis(α-chloro-4-methyl-
benzylidene)hydrazine] with the respective alkyl amines.[6]
3056, 1648, 1605, 1465, 1419, 1399, 1073, 991, 722, 709 cmϪ1
.
4-Ethyl-3,5-diphenyl-4H-1,2,4-triazole (1): This compound was ob-
tained as previously described in the literature.[1]
1-Ethyl-3,5-bis(4-methylphenyl)-4-propyl-1,2,4-triazolium
Tetra-
fluoroborate (8): Compound 8 was prepared as described in the
literature for similar compounds,[7] from triethyloxonium tetra-
fluoroborate and 3,5-bis(4-methylphenyl)-4-propyl-4H-1,2,4-tria-
zole (2). Ϫ 1H NMR (400 MHz): δ ϭ 0.63 (t, J ϭ 7.6 Hz, 3 H),
1.45 (q, J ϭ 7.7 Hz, 2 H), 1.56 (t, J ϭ 7.3 Hz, 3 H), 2.45 (s, 3 H),
2.51 (s, 3 H), 4.13 (t, J ϭ 7.8 Hz, 2 H), 4.24 (q, J ϭ 7.3 Hz, 2 H),
7.36 (d, J ϭ 8.3 Hz, 2 H), 7.50 (d, J ϭ 8.3 Hz, 2 H), 7.78 (d, J ϭ
8.3 Hz, 2 H), 7.86 (d, J ϭ 8.3 Hz, 2 H). Ϫ 13C NMR (25 MHz):
δ ϭ 10.7, 13.9, 21.6, 21.7, 22.2, 46.6, 48.3, 116.5, 120.7, 129.5,
129.9, 130.8, 142.2, 144.1, 151.5, 154.4. Ϫ IR (KBr): ν˜ ϭ 3037,
2968, 2936, 2877, 1619, 1508, 1084, 1061, 1038, 831 cmϪ1. Ϫ MS:
m/z (%) ϭ 340 (16), 339 (75) [Mϩ Ϫ BF3], 338 (34), 325 (20), 324
(81), 321 (24), 320 (100) [Mϩ Ϫ BF4], 319 (29), 318 (16), 292 (15),
291 (66), 290 (12), 278 (11), 227 (39), 276 (16), 250 (9), 249 (17),
145 (26), 132 (15), 131 (8), 118 (68), 117 (18), 116 (14), 103 (21),
91 (24), 77 (15).
3,5-Bis(4-methylphenyl)-4-propyl-4H-1,2,4-triazole
(2):
Bis(α-
chloro-4-methylbenzylidene)hydrazine (9.7 g, 0.032 mol) was re-
fluxed in propylamine (200 mL) for 99 h to yield, after crystalliza-
tion from toluene, compound 2 (6.84 g, 69%), m.p. 202Ϫ203.5 °C
of 99.7% purity (GC). Ϫ 1H NMR (100 MHz): δ ϭ 0.60 (t, J ϭ
7.3 Hz, 3 H), 1.39 (hex, J ϭ 7.3 Hz, 2 H), 2.43 (s, 6 H), 4.03 (t,
J ϭ 7.3 Hz, 2 H), 7.31 (d, J ϭ 7.8 Hz, 4 H), 7.55 (d, J ϭ 8.3 Hz,
4 H). Ϫ 13C NMR (25 MHz): δ ϭ 10.6, 21.4, 23.2, 46.3, 125.0,
128.7, 129.5, 140.0, 155.5. Ϫ IR (KBr): ν˜ ϭ 3068, 2976, 2958, 2944,
2921, 2876, 1479, 1474, 1465, 1449, 1417, 1383, 1347, 1339, 1021,
849, 822, 753 cmϪ1. Ϫ MS: m/z (%) ϭ 292 (23), 291 (100) [Mϩ],
290 (12), 276 (19), 249 (26), 132 (21), 118 (35), 103 (26), 91 (18),
77 (17). Ϫ HR-MS (C19H21N3): calcd. 291.1735; found 291.1737.
Ϫ C19H21N3 (291.39): C 78.32, H 7.26, N 14.42; found C 78.25, H
7.18, N 14.59.
Cross-over Experiments: A mixture of 4-ethyl-3,5-diphenyl-4H-
1,2,4-triazole (1) (23.2 mg, 0.093 mmol) and 3,5-bis(4-methyl-
Partial Thermolysis of Neat 4-(S-2-butyl)-3,5-diphenyl-4H-1,2,4-tri-
azole [(S)-(؉)-9]: This reaction was carried out as described above
phenyl)-4-propyl-4H-1,2,4-triazole (2) (26.6 mg, 0.091 mmol) was but for 10 min only (see also ref.[5]). Preparative TLC (silica/CHCl3)
carefully mixed and placed in a sealed glass tube under nitrogen
yielded two fractions:
and heated in an oven (314Ϫ335 °C) for 30 min. The reaction mix-
Fraction 1 (Rf ϭ 0Ϫ0.04) was dissolved in dichloromethane
ture was purified by preparative TLC (Silica, CHCl3). The fraction (15 mL) and extracted with NaOH (2 ). The solvent was then
Rf ϭ 0.19Ϫ0.66, yielded 40 mg of product which was analyzed by
MS and GC-IR. Product components were next isolated and iden-
tified by comparison with authentic samples.
evaporated under reduced pressure and dried under vacuum, to
yield (S)-(ϩ)-9 (11.7 mg, 63%), 99% pure by GC. CD analysis was
carried out and the CD spectrum was compared with that of an
authentic sample, indicating that up to 3Ϫ4% was racemized. This
number is near the error level of the measurements. 3,5-Diphenyl-
1,2,4-triazole (7) (2.4 mg, 14.5%) was isolated from the basic ex-
tract.
1-Ethyl-3,5-diphenyl-1H-1,2,4-triazole (3): 22% (by GC). Ϫ GC-IR:
ν˜ ϭ 3072, 2986, 2950, 1519, 1476, 1444, 1349, 1295, 1197, 1177,
1130, 1065, 1024, 974, 767, 730 cmϪ1
.
Fraction 2 (Rf ϭ 0.18Ϫ0.24) yielded 1.6 mg (8.6%) of 1-(R-2-bu-
tyl)-3,5-diphenyl-1H-1,2,4-triazole, (R-10), (95% pure by GC).
3,5-Diphenyl-1-propyl-1H-1,2,4-triazole (4): 25% (by GC). Ϫ GC-
IR: ν˜ ϭ 3073, 2979, 2947, 2889, 1558, 1515, 1474, 1444, 1402, 1378,
1348, 1296, 1179, 1130, 1064, 1023, 978, 917, 811, 784, 730 cmϪ1
.
1-Alkyl-3,5-diphenyl-1H- and 1-Alkyl-3,5-bis(4-methylphenyl)-1H-
1,2,4-triazoles. These compounds were prepared by alkylation of
3,5-diphenyl-1,2,4-triazole and 3,5-bis(4-methylphenyl)-1,2,4-tria-
zole, respectively, as described in the literature,[8] using a modifica-
tion described by Atkinson and Polya.[9] The following products
were prepared:
1-Ethyl-3,5-bis(4-methylphenyl)-1H-1,2,4-triazole (5): 24% (by GC).
Ϫ GC-IR: ν˜ ϭ 3072, 3029, 2989, 2935, 2888, 1619, 1475, 1421,
1345, 1296, 1183, 1129, 1019, 979, 825, 759, 702 cmϪ1
.
3,5-Bis(4-methylphenyl)-1-propyl-1H-1,2,4-triazole (6): 29% (by
GC). Ϫ GC-IR: ν˜ ϭ 3070, 3029, 2977, 2935, 2835, 1616, 1474,
1-Ethyl-3,5-diphenyl-1H-1,2,4-triazole (3): This compound has been
1420, 1342, 1297, 1182, 1128, 1017, 980, 825, 758 cmϪ1
.
described in the literature.[10]
Eur. J. Org. Chem. 2000, 3745Ϫ3748
3747

O. R. Gautun, P. H. J. Carlsen
FULL PAPER
3,5-Diphenyl-1-propyl-1H-1,2,4-triazole (4): Yield 102 mg (87%), as
125.5, 126.2, 128.4, 128.7, 129.2, 129.5, 138.8, 140.0, 155.5, 161.1.
an oil (94% pure by GC). Ϫ 1H NMR (100 MHz): δ ϭ 0.92 (t, J ϭ Ϫ IR (KBr): ν
˜ ϭ 2962, 2947, 2934, 2917, 2877, 1472, 1468, 1425,
7.3 Hz, 3 H), 1.97 (sextet, J ϭ 7.3 Hz, 2 H), 4.19 (t, J ϭ 7.3 Hz, 2
H), 7.31Ϫ7.60 (m, 6 H), 7.60Ϫ7.75 (m, 2 H), 8.10Ϫ8.24 (m, 2 H).
1352, 1182, 1129, 1018, 840, 826,759 cmϪ1. Ϫ MS: m/z (%) ϭ 292
(24), 291 (100) [Mϩ], 263 (12), 262 (58), 249 (48), 145 (48), 132
Ϫ
13C NMR (25 MHz): δ ϭ 11.0, 23.5, 50.8, 126.3, 126.9, 128.5, (13), 119 (21), 118 (76), 117 (28), 116 (17), 103 (28), 91 (21), 77
128.9, 129.0, 130.0, 131.1, 155.6, 161.3. Ϫ IR (neat): ν˜ ϭ 3067,
(21). Ϫ HR-MS (C19H21N3): calcd. 291.1736; found 291.1731. Ϫ
2966, 2935, 2876, 1477, 1464, 1443, 1409, 1385, 1355, 1291, 1249, C19H21N3 (291.39): C 78.32, H 7.26, N 14.42; found C 78.47, H
1132, 1071, 1017, 789, 772, 732 cmϪ1. Ϫ MS: m/z (%) ϭ 264 (11), 7.41, N 14.67.
263 (58) [Mϩ], 234 (32), 221 (28), 131 (32), 118 (18), 105 (100),
104 (76), 103 (17), 89 (33), 77 (60). Ϫ HR-MS (C17H17N3): calcd.
263.1423; found 263.1418. Ϫ C17H17N3 (263.34): C 77.54, H 6.51,
Acknowledgments
The authors wish to thank The Norwegian Research Council,
NFR, for financial support.
N 15.96; found C 77. 36, H 6.67, N 15.77.
1-Ethyl-3,5-bis(4-methylphenyl)-1H-1,2,4-triazole (5): Yield 70 mg
(63%), m.p. 95Ϫ96 °C (Ͼ 99% purity by GC). Ϫ 1H NMR
(100 MHz): δ ϭ 1.53 (t, J ϭ 7.3 Hz, 3 H), 2.39 (s, 3 H), 2.44 (s, 3
H), 4.27 (q, J ϭ 7.3 Hz, 2 H), 7.28 (t, J ϭ 7.5 Hz, 4 H), 7.57 (d,
J ϭ 7.8 Hz, 2 H), 8.04 (d, J ϭ 8.3 Hz, 2 H). Ϫ 13C NMR (25 MHz):
δ ϭ 15.2, 21.4, 44.2, 126.2, 128.6, 129.2, 129.5, 138.9, 140.1, 155.2,
161.4. Ϫ IR (KBr): ν˜ ϭ 2973, 2960, 2918, 1470, 1428, 1383, 1350,
1349, 1186, 1176, 1132, 1106, 1091, 1033, 1024, 1016, 830, 802,
754, 727 cmϪ1. Ϫ MS: m/z (%) ϭ 278 (19), 277 (100) [Mϩ], 249
(9), 145 (51), 118 (30), 84 (10). Ϫ HR-MS (C18H19N3): calcd.
277.1579; found 277.1576. Ϫ C18H19N3 (277.37): C 77.95, H 6.90,
N 15.15; found C 77.69, H 7.08, N 15.28.
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[3]
K. Smith, A. Small, M. G. Hutching, Chem. Lett. 1990, 347;
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[5]
[6]
P. H. J. Carlsen, O. R. Gautun, Acta Chem. Scand. 1990, 44,
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O. R. Gautun, P. H. J. Carlsen, Acta Chem. Scand. 1991, 45,
609.
3,5-Bis(4-methylphenyl)-1-propyl-1H-1,2,4-triazole (6): Yield 90 mg
(79%), m.p. 101Ϫ102.5 °C (recryst. from toluene, Ͼ 99% purity by
[7]
[8]
L. A. Lee, R. Evans, J. W. Wheeler, Org. Chem. 1972, 37, 343.
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M. R. Atkinson, J. B. Polya, J. Chem. Soc., 1954, 141.
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Received March 16, 2000
1
GC). Ϫ H NMR (100 MHz): δ ϭ 0.91 (t, J ϭ 7.3 Hz, 3 H),1.93
[9]
(sextet, J ϭ 7.3 Hz, 2 H), 2.38 (s, 3 H), 2.43 (s, 3 H), 4.16 (t, J ϭ
7.3 Hz, 3 H), 7.28 (t, 4 H), 7.55 (d, J ϭ 7.8 Hz, 2 H), 8.04 (d, J ϭ
8.2 Hz, 2 H). Ϫ 13C NMR (25 MHz): δ ϭ 11.0, 21.4, 23.5, 50.7,
[10]
[O00133]
3748
Eur. J. Org. Chem. 2000, 3745Ϫ3748