Polynucleating open-chain systems with imidazole and proton-ionizable 1,2,4-triazole structural motifs

Article abstract of DOI:10.1021/jo0056794

A multistep route for obtaining the polynucleating open-chain systems 3-5 is reported. These advanced intermediates required elaborate processes that proceeded for the pentanuclear protophanes 3 in seven steps, whereas the trinuclear compounds 4 and 5 were obtained in six steps.

Full text of DOI:10.1021/jo0056794

J . Org. Chem. 2001, 66, 2291-2295
2291
P olyn u clea tin g Op en -Ch a in System s w ith Im id a zole a n d
P r oton -Ion iza ble 1,2,4-Tr ia zole Str u ctu r a l Motifs
Ermitas Alcalde,* Carlos Ayala, Immaculada Dinare`s, and Neus Mesquida
Laboratori de Quı´mica Orga`nica, Facultat de Farma`cia, Universitat de Barcelona,
08028-Barcelona, Spain
betaines@farmacia.far.ub.es
Received October 11, 2000
A multistep route for obtaining the polynucleating open-chain systems 3-5 is reported. These
advanced intermediates required elaborate processes that proceeded for the pentanuclear proto-
phanes 3 in seven steps, whereas the trinuclear compounds 4 and 5 were obtained in six steps
Acyclic polydentate building blocks containing hetero-
aromatic subunits are of interest for the construction of
a broad array of molecules from crown ethers1,2 and
macrocycles1,3 to a variety of multitopic metal-binding
molecules and supramolecular entities, e.g., metallo-
supramolecular systems.1,4 Accordingly, the proton-ioniz-
able molecules of generalized structure 1 and 2 could
allow access to novel molecular architectures, e.g., within
polyazamacrocycles, the [1n]heterophanes with a bis-
betaine nature.5 On the other hand, the building blocks
of either simple or complex chemical targets are difficult
to synthesize.6 Therefore, we set out to develop a multi-
step route for obtaining the chemical building blocks 1
and 2. The advanced intermediates 3-5 required elabo-
rate processes which proceeded for the pentanuclear
protophanes 3 in seven steps, whereas the trinuclear
compounds 4 and 5 were obtained in six steps.
Among the general routes to simple 1,2,4-triazoles,1b,c
hydrazine-induced cyclization to specific 3,5-bis-(substi-
tuted)-1,2,4-triazoles appears to be the most appropriate2b,c
and it has been conveniently applied for the synthesis of
nonclassical [14]-meta-heterophanes containing betaine
subunits7a,b as well as for protophane 3a .7c According to
the retrosynthetic analysis of Figure 1, the cyanomethyl
compounds 6 and 7 could react with hydrazine to form
the targeted symmetrical 3,5-disubstituted-1H-1,2,4-tri-
azoles 3b,c, 4, and 5.
(1) (a) Atwood, J . L., Davis, J . E. D., Macnicol, D. D., Vo¨gtle, F.,
Eds. Comprehensive Supramolecular Chemistry; Elsevier: Oxford,
1996; Vol. 9. (b) Progress in Heterocyclic Chemistry; Gribble, G. M.,
F igu r e 1.
Gilchrist, T. L., Eds.; Pergamon: Elsevier Science Ltd.: Oxford, 1998;
Vol. 10; (c) 1999; Vol. 11.
By a two-step sequence shown in Scheme 1, the
pentanuclear building blocks 3b and 3c were formed from
the corresponding cyanomethyl derivatives 6b and 6c.
Similarly, 3-cyanomethylbenzylic alcohol 7 was trans-
formed to the trinuclear bis-hydroxymethyl derivative 10,
and subsequent halogenation gave the 3,5-bis[3-(halo-
methyl)benzyl]-1H-1,2,4-triazoles 4 and 5. Due to their
reactivity, the targeted bis-halomethyl trinuclear sub-
units 4 and 5 have a limited stability and they should
be stored, but for no more than 24 h.
(2) (a) Bradshaw, J . S.; Izatt, R. M. Acc. Chem. Res. 1997, 30, 338-
345. (b) McDaniel, C. W.; Bradshaw, J . S.; Izatt, R. M. Heterocycles
1990, 30, 665-706. (c) Bradshaw, J . S.; Nielsen, R. B.; Tse, P.-K.;
Arena, G.; Wilson, B. E.; Dalley, J . D.; Lamb, J . D.; Christensen, J . J .;
Izatt, R. M. J . Heterocycl. Chem. 1986, 23, 361-368.
(3) Vo¨gtle, F. Cyclophane Chemistry; J ohn Wiley & Sons: Chiches-
ter, 1993.
(4) (a) Constable, E. C.; Smith, D. Chem. Britain 1995, 33-37. (b)
Piguet, C.; Bernardelli, G.; Hopfgartner, G. Chem. Rev. 1997, 97, 2005-
2062. (c) Cuccia, L. A.; Lehn, J .-M.; Homo, J .-C.; Schmutz, M. Angew.
Chem., Int. Ed. 2000, 39, 233-237 and references therein.
(5) Alcalde, E.; Ayala, C.; Dinare`s, I.; Mesquida, N.; Sanchez-
Ferrando, F. J . Org. Chem. 2001, 66, 2281-2290.
(6) Sierra, M. A.; Torre, M. C. Angew. Chem., Int. Ed. 2000, 39,
1538-1559.
(7) (a) Alcalde, E.; Alemany, M.; Pe´rez-Garc´ıa, L.; Rodriguez, M. L.
J . Chem. Soc., Chem. Commun. 1995, 1239-1240. (b) Alcalde, E.;
Alemany, M.; Gisbert, M. Tetrahedron 1996, 15171-17188 and refer-
ences therein. (c) Alcalde, E.; Gisbert M. Synlett 1996 285-288.
The structures of the new protophanes were character-
ized on the basis of spectroscopic data, and all gave
satisfactory elemental analysis. Table 1 shows the most
1
relevant H and 13C NMR chemical shifts, and individual
assignments were made using NMR experiments.
10.1021/jo0056794 CCC: $20.00 © 2001 American Chemical Society
Published on Web 03/07/2001

2292 J . Org. Chem., Vol. 66, No. 7, 2001
Alcalde et al.
Sch em e 1a
a
Reagents: (a) NH2-NH2•H2O; (b) NaNO2/HCl; (c) SOCl2; (d); SOBr2.
Ta ble 1. Selected 1H NMR a n d 13C NMR Da ta in CDCl3 of Com p ou n d s 3b,c, 8b,c, 4, 5, 9, a n d 10
a
b
Unambiguous assignments were made by NOESY. Unambiguous assignments were made by HMBC, HMQC. c Signal not observed.
d
CD3OD.
The “3 + 5” convergent stepwise synthesis of [18]-meta-
with thionyl bromide produced only alteration and de-
composition products.8
heterophanes was improved using the bis-bromomethyl
trinuclear protophane 5 instead of the bis-chloromethyl
counterpart 4 due to its greater reactivity.5 The simple
mononuclear building block is 3,5-bis(bromomethyl)-1H-
1,2,4-triazole, and its preparation was then explored.
Bromination of bis(hydroxymethyl)-1H-1,2,4-triazole2c
The synthesis of the cyanomethyl key compounds 6b,c
and 7 started with 3-bromomethyl-5-tert-butylbenzylic
alcohol 16, which was obtained in 79% by a two-step
sequence from commercially available 5-tert-butyliso-
phthalic acid 139 (Scheme 2). 3-Chloromethyl-5-tert-

Proton-Ionizable Protoheterophanes
J . Org. Chem., Vol. 66, No. 7, 2001 2293
Sch em e 2a
a
Reagents: (a) PhCO2H/NaOH/TBABr; (b) NaOH; (c) BH3•THF (ref 11b); (d) SOCl2; (e) HBr concentrated; (f) imidazole/KOH; (g) 4,5-
dibutylimidazole•HCl/KOH; (h) NaCN/DMF; (i) NaCN/TBABr, H2O/CH2Cl2
butylbenzylic alcohol 15 was also prepared. Comparison
of the reaction between the compound pair 15 or 1610a
and the appropriate imidazole revealed that the bromo-
methyl counterpart 16 is the best key intermediate,
which provided significantly higher yield (84%) of 17c
and purity of compounds 17b and 17c.
The conversion of the benzylic alcohols 17b and 17c
to the benzylic halides 18b,c and 19b10b was the critical
step toward the synthesis of the multitopic molecules 3.
The use of thionyl chloride gave good yet variable yields
of 18b due to its troublesome isolation and purifi-
cation, whereas the chloromethyl derivative 18c was
obtained in high yield and purity (Scheme 2). Reaction
with HBr concd was similarly capricious within “b” and
“c” series, and it was possible to obtain the desired
intermediate of “b” series (19b ). Further, standard
transformation of 19b and 18c provided the key aryl-
acetonitriles 6b,c (Scheme 2). Similarly, 3-bromomethyl-
5-tert-butylbenzylic alcohol 16 was transformed to 3-
cyanomethylbenzylic alcohol 7.
In summary, we report the synthesis of polynuclear
acyclic systems which constitute a reservoir of structural
building blocks based on π-excessive heteroaromatic and
aromatic structural motifs for the construction of new
molecular architectures and materials, such as macro-
cyclic systems and multitopic scaffolds with metal-ion
binding capabilities.
(8) The 3, 5-bis(chloromethyl)-1H-1,2,4-triazole was prepared ac-
cording to Bradshaw et al.2c from 3, 5-bis(hydroxymethyl)-1H-1,2,4-
triazole and it is the mononuclear building block for producing both
the dicationic [14]-meta-heterophanes7a, b and [16]-meta-heterophanes,5a
through the convergent “3 + 1” and “5 + 1” approaches. As shown in
eq 1, attempts were made to prepare the bis-bromomethyl counter-
part. Using thionyl bromide, bis-hydroxymethyl compound gave prod-
ucts of alteration and decomposition, whereas using HBr concd the
starting material was recovered unaltered (see the Experimental
Section).
Exp er im en ta l Section
Gen er a l Meth od s. Melting point: CTP-MP 300 hot-plate
apparatus with ASTM 2C thermometer (see Table 2, Support-
ing Information). IR (NaCl or KBr disks): Nicolet 205 FT
spectrophotometer. 1H NMR: Varian Gemini 200 and Varian
Gemini 300 spectrometers (200 and 300 MHz) at 298 K.
Chemical shifts were referenced and expressed in ppm (δ)
relative to the central peak of methanol-d4 (3.40 ppm) and TMS
for chloroform-d. 13C NMR: Varian Gemini 200 and Varian
Gemini 300 spectrometers (50.3 and 75.4 MHz) at 298 K.
Chemical shifts were referenced and expressed in ppm (δ)
relative to the central peak of methanol-d4 (49.0 ppm) and
chloroform-d (77.0 ppm). HMQC, HMBC and NOESY experi-
ments: Varian VXR-500 spectrometer (500 MHz). TLC: Merck
precoated silica gel 60 F254 plates or Panreac aluminum oxide
60-200 UV254 Polyester CCM plates using UV light (254 nm)
as visualizing agent and/or H2PtCl2 3% aq/KI 10% aq (1:1) or
(9) An alternative and less efficient three-step procedure was,
however, studied starting from the bis-bromomethyl compound 11
(Scheme 2).
(10) (a) The benzylic halide pair 15 and 16 are unstable and they
should not be left to stand for more than 24h. (b) The benzylic halides
18b,c and 19b were fairly stable.

2294 J . Org. Chem., Vol. 66, No. 7, 2001
Alcalde et al.
KMnO4 ethanolic solution. Column chromatography was per-
formed on neutral aluminum oxide 90 activity II-III (Merck).
Ma ter ia ls. Solvents were distilled prior to use and dried.
Imidazole and compound 13 are commercially available.
Compounds 1111a and 1411b together with 4,5-dibutylimidazole
hydrochloride11c were prepared as described in the literature.
Ca u tion : bis-h a lom eth yl tr in u clea r com p ou n d s (4) and
(5) are severe skin irritants and should be handled with care.
3,5-Bis[[3-t er t -b u t yl-5-(im id a zolylm e t h yl)p h e n yl]-
m et h yl]-1,2,4-t r ia zole 3b a n d 3,5-Bis[[[3-ter t-b u t yl-5-
(4,5-d ibu tylim id a zolyl)m eth yl]p h en yl]m eth yl]-1,2,4-tr i-
a zole 3c. To a cold solution (0-10 °C) of 1.18 mmol of
compound 8b or 8c (0.63 or 0.90 g) in 40 mL of aqueous 3 M
HCl (for 8c, additional 15 mL ethanol was added) was added
dropwise a solution of NaNO2 (0.20 g, 2.90 mmol) in 15 mL of
water. The mixture was then warmed to room temperature
for 4 or 5 h, respectively. The mixture was adjusted to pH 8
with Na2CO3 (for 8c, an additional 100 mL of water was
added). The suspension was extracted with CH2Cl2 (3 × 100
mL), the combined organic layers were dried (anhydrous
Na2SO4), and the solvent was eliminated in a rotary evaporator
to afford compound 3b or 3c (0.47 or 0.78 g) as a foamy solid.
3,5-Bis[[3-ter t-bu tyl-5-(ch lor om eth yl)p h en yl]m eth yl]-
1,2,4-tr ia zole 4. To a suspension of diol 10 (0.21 g, 0.51 mmol)
in 10 mL of dry CH2Cl2 at 0 °C was added dropwise a solution
of SOCl2 (0.4 mL, d ) 1.635, 5.50 mmol) in dry CH2Cl2 (3 mL).
The reaction mixture was stirred at room temperature for 5
h, and the solvent was then removed to dryness under reduced
pressure to give compound 4 as a white foamy hygroscopic
solid.
3,5-Bis[[3-(br om om eth yl)-5-ter t-bu tylp h en yl]m eth yl]-
1,2,4-tr ia zole 5. To a suspension of 0.15 g (0.36 mmol) of diol
10 in 10 mL of dry CH2Cl2 at 0 °C was added dropwise a
solution of SOBr2 (0.27 mL, d ) 2.683, 3.60 mmol) in dry
CH2Cl2 (10 mL). The reaction mixture was stirred at room
temperature for 1.5 h, and then the solvent was removed to
dryness under reduced pressure. The crude residue was
dissolved in 25 mL of CH2Cl2, washed in a saturated aqueous
solution of Na2CO3 (2 × 25 mL) and water (2 × 25 mL), the
organic layer was dried (anhydrous Na2SO4), and the solvent
was removed under reduced pressure to afford 0.15 g of
compound 5 as a pale yellow foamy hygroscopic solid.
[3-t er t -B u t y l-5-(im id a z o ly lm e t h y l)p h e n y l]a c e t o -
n itr ile 6b a n d [3-ter t-Bu tyl-5-[(4,5-d ibu tylim id a zolyl)-
m eth yl]p h en yl]a ceton itr ile 6c. To a suspension of NaCN
(0.30 g, 6.12 mmol) in DMF (15 mL) was added 1.29 mmol of
19b or 18c (0.50 or 0.53 g, respectively) in DMF (40 mL). The
reaction mixture was heated to 80 °C (5 or 24 h, respectively),
a saturated aqueous solution of Na2CO3 (100 mL) was added,
and the solvent was removed in a rotary evaporator. The
residue was dissolved in water (200 mL) and extracted with 3
× 100 mL portions of CH2Cl2. The combined extracts were
dried (anhydrous Na2SO4), and the solvent was removed in
vacuo to afford compound 6b or 6c as an oil.
residue was triturated in ethyl acetate (100 mL), and the
yellow solid obtained was filtered and dried to afford 1.90 g of
8b.
4-Am in o-3,5-bis[[[3-ter t-bu tyl-5-(4,5-dibu tylim idazolyl)-
m eth yl]p h en yl]m eth yl]-1,2,4-tr ia zole 8c. A stirred solution
of 1.30 g of 6c (3.56 mmol) and hydrazine hydrate (2.0 mL, d
) 1.032, 41.23 mmol) was maintained in a bath at 100 °C for
1 h, and then the bath temperature was raised to 140 °C for
16 h. The excess of hydrazine and water was distilled off for
1h at 170 °C. The residue was dissolved in ethyl acetate (100
mL), and washed in aqueous saturated solution of NaCl (50
mL) and water (2 × 50 mL). The organic layer was dried
(anhydrous Na2SO4) and the solvent was eliminated in rotary
evaporator to give 0.99 g of 8c as a yellow foamy solid.
4-Am in o-3,5-bis[[3-ter t-bu tyl-5-(h ydr oxym eth yl)ph en yl]-
m eth yl]-1,2,4-tr ia zole 9. A stirred solution of 1.60 g (7.88
mmol) of compound 7 in hydrazine hydrate (2.0 mL, d) 1.032,
41.23 mmol) was maintained in a bath at 100 °C for 48 h, and
then the bath temperature was raised to 170 °C for 2 h to
distill off the excess of hydrazine and water. The residue was
triturated in ethyl acetate (50 mL), and the white solid
obtained was filtered and dried to afford 1.32 g of pure
aminotriazole 9.
3,5-bis[[3-ter t-bu tyl-5-(h yd r oxym eth yl)p h en yl]m eth yl]-
1,2,4-tr ia zole 10. To a cold solution (0-10 °C) of compound 9
(0.91 g, 2.09 mmol) in 50 mL of HCl (3 M in methanol) was
added dropwise a solution of NaNO2 (0.19 g, 2.75 mmol) in 10
mL of water. The mixture was warmed to room temperature
for 24 h and treated with Na2CO3 to pH 8, and the solvent
was removed in rotary evaporator. The residue was crushed
with absolute ethanol (20 mL, 1 h) and filtered, and the
ethanolic solution was evaporated to dryness to give a yellow
solid that was purified by triturating in ethyl acetate (10 mL)
to afford 0.67 g of triazole 10 as a white solid.
[3-(Ben zoyloxym eth yl)-5-ter t-bu tylp h en yl]m eth yl ben -
zoa te 12. A 15 g (46 mmol)portion of 11 in chloroform (100
mL) was added to a solution of benzoic acid (14.3 g, 117 mmol)
in NaOH 4 M (150 mL) and tetrabutylammonium bromide (4.5
g, 14.11 mmol). The reaction mixture was refluxed for 12 h,
and the layers were then separated. The aqueous layer was
washed in chloroform (2 × 100 mL), the combined organic
layers were dried over anhydrous Na2SO4, and the solvent was
eliminated in rotary evaporator. The crude residue was
purified by column chromatography (silica gel; hexane/ethyl
acetate, 95:5) to yield 12.5 g of diester 12 as a white solid.
[3-ter t-Bu tyl-5-(ch lor om eth yl)p h en yl]m eth a n ol 15. To
a suspension of diol 14 (2 g, 10.3 mmol) in 1.2 mL (d ) 0.983,
14.91 mmol) of pyridine and 60 mL of dry distilled toluene at
-40 °C was added dropwise a solution of SOCl2 (1.2 mL, d )
1.635, 16.49 mmol) in dry distilled toluene (10 mL). The
reaction mixture remained at room temperature for 18 h and
was then poured over water (50 mL) and extracted with diethyl
ether (3 × 100 mL). The organic layer was washed in an
aqueous solution of Na2CO3 5% (3 × 200 mL) and dried
(anhydrous Na2SO4), and the solvent was eliminated in a
rotary evaporator. The residue was purified by chromatogra-
phy (silica gel, CH2Cl2) giving 0.83 g of colorless oil 15.
[3-(Br om om eth yl)-5-ter t-bu tylp h en yl]m eth a n ol 16. To
0.50 g (2.57 mmol) of diol 14 stirred at 0 °C, 3.5 mL (30.9 mmol)
of HBr concentrated (48% v/v, aq) was added dropwise, and
the reaction mixture remained at room temperature for 5 h.
50 mL of water was added and extracted with CH2Cl2 (2 × 50
mL). The organic layer was dried (anhydrous Na2SO4) and the
solvent was evaporated under reduced pressure. The crude
residue was purified by chromatography (silica gel; diethyl
ether/hexane, 9:1) to give 0.54 g of colorless oil 16.
[3-ter t-Bu tyl-5-(h yd r oxym eth yl)p h en yl]a ceton itr ile 7.
To a solution of NaCN (3.4 g, 70 mmol) and tetrabutylammo-
nium bromide (0.2 g, 0.68 mmol) in water (20 mL) was added
3.6 g (14.08 mmol) of 16 in CH2Cl2 (200 mL). The reaction
mixture was stirred at room temperature for 48 h, and the
layers were then separated. The aqueous layer was washed
in CH2Cl2 (2 × 50 mL), the combined organic layers were dried
(anhydrous Na2SO4), and the solvent was eliminated in rotary
evaporator to give 2.47 g of pale yellow oil 7.
4-Am in o-3,5-b is[[3-t er t -b u t yl-5-(im id a zolylm e t h yl)-
p h en yl]m eth yl]-1,2,4-tr ia zole 8b. A stirred solution of 2.19
g (8.69 mmol) of compound 6b in hydrazine hydrate (4.0 mL,
d ) 1.032, 82.46 mmol) was maintained in a bath at 100 °C
for 72 h, and then the bath temperature was raised to 170 °C
for 3 h to distill off the excess of hydrazine and water. The
[3-ter t-Bu tyl-5-(im idazolylm eth yl)ph en yl]m eth an ol 17b.
A stirred suspension of 1H-imidazole (0.2 g, 2.74 mmol) and
finely powered KOH 85% (0.24 g, 3.56 mmol) in dry acetonitrile
(60 mL) was maintained at room temperature for 2 h. To the
yellow suspension, a solution of compound 15 or 16 (2.74 mmol)
in dry acetonitrile (25 mL) was added dropwise, and the
reaction mixture was refluxed for 24 h. The solvent was
evaporated to dryness, and the solid residue was dissolved in
water (200 mL) and extracted with CH2Cl2 (3 × 100 mL). The
(11) (a) Moore, S. S.; Tarnowski, T. L.; Newcomb, M.; Cram, D. J .,
J . Am. Chem. Soc. 1977, 99, 5. (b) Bennani, Y. L.; Marron, K. S.; Mais,
D. E.; Flatten, K.; Nadzan, A. M.; Boehm, M. F., J . Org. Chem. 1998,
543, 3-550. (c) Stetter, H.; Ra¨msch, R. Y.; Kuhlmann, H., Synthesis
1976, 733-735.

Proton-Ionizable Protoheterophanes
J . Org. Chem., Vol. 66, No. 7, 2001 2295
organic layer was dried (anhydrous Na2SO4) and the solvent
was eliminated in rotary evaporator to yield compound 17b
as a dark yellow oil.
[[3-(Br om om et h yl)-5-ter t-b u t ylp h en yl]m et h yl]im id -
a zoliu m Br om id e 19b. To 1.82 g (7.46 mmol) of alcohol 17b
stirred at 0 °C, 10 mL (89.5 mmol) of HBr concentrated (48%
v/v, aq) was added dropwise, and the reaction mixture re-
mained at room temperature for 18 h. The suspension was
filtered, and the solid was washed in water (5 × 20 mL) and
dried in a vacuum oven (80 °C, 3 h) to give 2.28 g of 19b as a
white solid.
[3-ter t-Bu tyl-5-[(4,5-d ibu tylim id a zolyl)m eth yl]p h en yl]-
m eth a n ol 17c. A suspension of 4,5-dibutyl-1H-imidazole (0.45
g, 2.08 mmol) and finely powered KOH 85% (0.40 g, 5.41 mmol)
in a mixture of dry dioxane (50 mL) and dry acetonitrile (10
mL) was vigorously stirred at room temperature for 4 h. To
the brown suspension, a solution of compound 15 or 16 (2.08
mmol) in dry acetonitrile (12 mL) was added dropwise and the
reaction mixture was refluxed for 17 h. The solvent was
evaporated to dryness, and the solid residue was dissolved in
water (150 mL) and extracted with CH2Cl2 (3 × 100 mL). The
organic layer was dried (anhydrous Na2SO4), and the solvent
was eliminated in rotary evaporator to yield compound 17c
as a dark yellow oil.
[[3-ter t-Bu t yl-5-(ch lor om et h yl)p h en yl]m et h yl]im id -
a zoliu m ch lor id e 18b a n d 4,5-Dibu tyl-1-[[3-ter t-bu tyl-5-
(ch lor om eth yl)p h en yl]m eth yl]im id a zoliu m ch lor id e 18c.
To a solution of 1.75 mmol alcohol 17b or 17c (0.68 or 0.62 g
respectively) in 25 mL of dry CH2Cl2 at 0 °C, a solution of
SOCl2 (0.9 mL, d ) 1.635, 12.25 mmol) in dry CH2Cl2 (10 mL)
was added dropwise. The reaction mixture was stirred at room
temperature for 5 h and the solvent was then removed to
dryness under reduced pressure. The brown residue was
triturated with dry hexane (25 mL) and filtered to give
compound 18b or 18c as a beige solid.
The physical data of compounds 3-10, 12, and 15-19 are
listed in Table 2 (see the Supporting Information).
Ack n ow led gm en t . We thank DGESICYT (MEC,
Spain) for financial supports through grant PB 98-1164.
Thanks are also due to the Comissionat per a Univer-
sitats i Recerca de la Generalitat de Catalunya for
grants 1999SGR-77. C.A. thanks the Departament
d’Ensenyament de la Generalitat de Catalunya for a
F.P.I. fellowship.
Su p p or tin g In for m a tion Ava ila ble: Physical data of
1
compounds 3-10, 12, and 15-19 (Table 2). H and 13C NMR
data for all compounds discussed therein (Tables 3 and 4) and
1H NMR spectra for all compounds lacking CHN analyses. This
material is available free of charge via the Internet at
htpp://pubs.acs.org.
J O0056794