New method for the synthesis of N-tert-alkoxyarylaminyl radicals

Article abstract of DOI:10.1021/jo0600959

The reactions of 2,4-diaryl-6-tert-butylnitrosobenzenes with 2,2′-azobis[2-(methoxycarbonyl)propane] (5a), 2,2′-azobis(2-cyano-4- methylpentane) (5b), and 2,2′-azobis(2-cyano-4-methyl-4-methoxypentane) (5c) in refluxing benzene gave stable N-tert-alkoxy-2

Full text of DOI:10.1021/jo0600959

New Method for the Synthesis of N-tert-Alkoxyarylaminyl Radicals1
,†
†
‡
Yozo Miura,* Yoshikazu Muranaka, and Yoshio Teki
Department of Applied Chemistry, Graduate School of Engineering, Osaka City UniVersity, Sumiyoshi-ku,
Osaka 558-8585, Japan, and Department of Material Science, Graduate School of Science, Osaka City
UniVersity, Sumiyoshi-ku, Osaka 558-8585, Japan
miura@a-chem.eng.osaka-cu.ac.jp
ReceiVed January 17, 2006
The reactions of 2,4-diaryl-6-tert-butylnitrosobenzenes with 2,2′-azobis[2-(methoxycarbonyl)propane] (5a),
2,2′-azobis(2-cyano-4-methylpentane) (5b), and 2,2′-azobis(2-cyano-4-methyl-4-methoxypentane) (5c)
in refluxing benzene gave stable N-tert-alkoxy-2,4-diaryl-6-tert-butylphenylaminyls, which were suc-
cessfully isolated as radical crystals in 13-52% yields after column chromatography. The radical yields
depended on the reaction time and the molar ratio of azo compounds to nitroso compounds. In the same
manner, acetyl- and cyano-group-carrying N-tert-alkoxyarylaminyls were generated by the reaction of
2-phenyl-4-(4-acetylphenyl)-6-tert-butylnitrosobenzene and 2-phenyl-4-(4-cyanophenyl)-6-tert-butylni-
trosobenzene with 5a and 5b, and they were isolated as radical crystals. X-ray crystallographic analyses
were performed for two radicals, and their molecular structures were discussed in detail. The magnetic
properties were measured for the two isolated radicals with SQUID in the temperature range 1.8-300 K.
One radical showed a weak ferromagnetic interaction (θ ) 0.2 K) between the radicals, and the other
showed a weak antiferromagnetic interaction (θ ) -3.8 K). The ferromagnetic interaction was analyzed
based on the X-ray crystallographic structure.
Introduction
attention as the spin source and building blocks in the study on
8
-10
organic magnetism.
Radicals 1-3 were generated by the
Although a variety of N-alkoxyalkylaminyls (R N4 OR′) and
N-alkoxyarylaminyls (R N4 OAr) have widely been investigated
by ESR spectroscopy, their isolation has been unsuccessful for
2
a long time. This has been in contrast to the chemistry of
thioaminyl (R N4 SR′). Thioaminyls are the sulfur analogues of
N-alkoxyaminyls, and a variety of thioaminyls have been
3
isolated as radical crystals. However, quite recently we found
that N-alkoxyarylaminyls 1-3 can be successfully isolated as
4
radical crystals. This was the first isolation of N-alkoxyaryl-
reaction of the lithium salts of the corresponding 2,4,6-
aminyls. Interestingly, the N-tert-alkoxyarylaminyls are ther-
mally very stable and do not react with oxygen.1
,4-7
In recent
(2) Danen, W. C.; Neugebauer, F. A. Angew. Chem., Int. Ed. Engl. 1975,
years, the isolable, stable, free radicals have attracted much
14, 783. Danen, W. C.; West, C. T.; Kensler, T. T. J. Am. Chem. Soc.
1973, 95, 5716. Kaba, R. A.; Ingold, K. U. J. Am. Chem. Soc. 1976, 98,
7
375. Woynar, H.; Ingold, K. U. J. Am. Chem. Soc. 1980, 102, 3813. Ahrens,
*
To whom correspondence should be addressed. Phone: +81-6-6605-2798.
Fax: +81-6-6605-2769.
W.; Wieser, K.; Berndt, A. Tetrahedron Lett. 1973, 3141. Balaban, A. T.;
Frangopol, P. T.; Frangopol, M.; Negoitå, N. Tetrahedron 1967, 23, 4661.
Negoita, N.; Baican, R.; Balaban, A. T. Tetrahedron Lett. 1973, 1877.
Ahrens, W.; Berndt, A. Tetrahedron Lett. 1973, 4281. Negareche, M.; Boyer,
M.; Tordo, P. Tetrahedron Lett. 1981, 22, 2879.
†
Graduate School of Engineering.
Graduate School of Science.
‡
(1) ESR Studies of Nitrogen-Centered Free Radicals. 60. For part 59,
see: Miura, Y.; Nishi, T. Y. J. Org. Chem. 2005, 70, 4177.
10.1021/jo0600959 CCC: $33.50 © 2006 American Chemical Society
4
786
J. Org. Chem. 2006, 71, 4786-4794
Published on Web 05/23/2006

Synthesis of N-tert-Alkoxyarylaminyl Radicals
trisubstituted anilines with tert-alkylperoxybenzoates in THF
SCHEME 1
at -78 °C.1
,4-7
Although the above method is convenient, there
are some problems. For example, the isolated radical yields are
1
,4-7
low,
(12-27%) and the use of butyllithium in the radical
syntheses refuses the presence of functional groups. To over-
come these problems, much effort has been paid, and we have
now established a new convenient method for the synthesis of
N-tert-alkoxyarylaminyls.11 The method involves the addition
of a tert-alkyl radical to 2,4-diaryl-6-tert-butylnitrosobenzenes.
Because tert-alkyl radicals can be conveniently generated by
thermolysis of azo compounds, the procedure for the synthesis
of N-tert-alkoxyarylaminyls is only to heat solutions of ni-
trosobenzenes and azo compounds. This method has widely been
used as the spin-trapping technique to identify the transient
radicals in the fields of biochemistry, photochemistry, and
Results and Discussion
The azo compounds used in this study were 5a-c, and their
half-life times (τ1/2) in toluene are 80 min at 80 °C (5a), 10
min at 80 °C (5b), and about 3.5 min at 70 °C (5c),14
respectively. The reactions of nitrosobenzenes with azo com-
pounds were carried out in refluxing benzene under a nitrogen
atmosphere.
12
polymer chemistry. However, it should be noted that the
reactions of alkyl radicals with nitroso compounds give ami-
noxyls (nitroxides) alone as the spin adducts. However, Konaka
and Terabe found that, when 2,4,6-tri-tert-butylnitrosobenzene
was used as a spin trapping agent, N-alkoxy-2,4,6-tri-tert-
butylphenylaminyls were generated as the spin adducts, together
with N-alkyl-2,4,6-tri-tert-butylphenylaminoxyls. They also
found that the ratios of N-alkoxyaminyls to aminoxyls depended
Reactions of 2,4,6-Triphenylnitrosobenzene (4a) with Azo
Compounds. The reactions of 4a with 5a-c were initially
investigated (Scheme 1). When solutions of 4a and 0.65-1.0
equiv of 5a were heated in refluxing benzene for 0.5-4 h, the
color of the solutions changed from light greenish blue to light
yellow. The light blue color is due to the nitrosobenzene. After
the mixtures were heated for a given time, the ESR signals from
the mixtures were measured at room temperature. The observed
spectrum was a 1:1:1 triplet and its aN and g values were 1.274
mT and 2.0059, respectively. The aN and g values are similar
to those for aminoxyls 9a and 9b (aN ) 1.322-1.340 mT, g )
13
on the bulkiness of the attacking radicals. N-Alkoxy-2,4,6-
tri-tert-butylphenylaminyls react with oxygen, different from
1
-3, and nobody has succeeded in the isolation of them.
Standing on this background, we investigated the reaction of
,4,6-triphenylnitrosobenzene (4a), 2,4-diphenyl-6-tert-butylni-
2
15-17
trosobenzene (4b), and 2,4-bis(4-chlorophenyl)-6-tert-butylni-
trosobenzene (4c) with azo compounds 5a-c in refluxing
benzene. Although the reaction of 4a with 5a-c gave the
corresponding aminoxyls alone as the spin adducts, the reaction
of 4b and 4c with 5a-c gave predominantly N-alkoxy-2,4-
diaryl-6-tert-butylphenylaminyls, which were isolated as radical
crystals. Herein, we wish to report a new methodology for the
preparation of N-tert-alkoxyphenylaminyls and their isolation,
ESR spectroscopic study, and magnetic properties.
2.0062),
demonstrating that the observed radical is aminoxyl
6
a. In the same manner, the reactions of 4a with 5b and 5c
were carried out, and the ESR signals observed from the reaction
mixtures showed that they were due to aminoxyls 6b and 6c.
On the basis of the above ESR results, it is concluded that the
reactions of 4a with 5a-c yield aminoxyls 6a-c alone.
Reactions of 2,4-Diaryl-6-tert-butylnitrosobenzene (4b)
with 5a-c. When the mixtures of 4b and 5a-c were heated in
refluxing benzene for 0.5-4.0 h (Scheme 2), the color of the
mixtures changed from light greenish blue to deep red. This
color change is different from those observed in the reactions
of 4a with 5a-c. After cooling, the ESR spectra were measured.
When a mixture of 4b with 0.65 equiv of 5a was heated for 1.0
h, two kinds of 1:1:1 triplet ESR signals were observed from
the mixture, as shown in Figure 1. The aN and g values for the
triplet signal shown by a are 1.294 mT and 2.0061, respectively,
(
3) Miura, Y. Trends Org. Chem. 1997, 6, 197-217; Recent Res. DeV.
Org. Chem. 1998, 2, 251-268.
(
4) Miura, Y.; Tomimura, T. Chem. Commun. 2001, 627.
(5) Miura, Y.; Tomimura, T.; Matsuba, N.; Tanaka, R.; Nakatsuji, M.;
Teki, Y. J. Org. Chem. 2001, 66, 7456.
6) Miura, Y.; Matsuba, N.; Tanaka, R.; Teki, Y.; Takui, T. J. Org. Chem.
002, 67, 8764.
(
2
(
7) Miura, Y.; Nishi, T.; Teki, Y. J. Org. Chem. 2003, 68, 10158.
(14) Dixon, K. W. In Polymer Handbook, 4th ed.; Brandrup, J.,
Immergut, E. H., Grulke, E. A., Eds.; John Wiley & Sons: New York,
1999; pp II/1-II/76.
(8) Morita, Y.; Kawai, J.; Fukui, K.; Nakazawa, S.; Sato, K.; Shiomi,
D.; Takui, T.; Nakasuji, K. Org. Lett. 2003, 5, 3289 and references therein.
9) Zienkiewicz, J.; Kaszynski, P.; Young, V. G., Jr. J. Org. Chem. 2004,
9, 7525.
10) Magnetic Properties of Organic Materials; Lahti, P. M., Ed.; Marcel
Dekker: New York, Basel, 1999.
11) A preliminary communication of the present work: Miura, Y.;
Muranaka, Y. Chem. Lett. 2005, 34, 480.
(
(15) Rozantsev, E. G. Free Nitroxyl Radicals; Plenum Press: New York
and London, 1970. Forrester, A. R.; Hay, J. M.; Thomson, H. R. In Organic
Chemistry of Stable Free Radicals; Academic Press: London and New York,
1968; Chapter 5. Volodarsky, L. B.; Reznikov, V. A.; Ovcharenko, V. I.
Synthetic Chemistry of Stable Nitroxides; CRC Press: Boca Raton, 1994.
(16) Calder, A.; Forrester, A. R. Chem. Commun. 1967, 682.
(17) Hoffmann, A. K.; Feldman, A. M.; Gelblum, E. J. Am. Chem. Soc.
1964, 86, 646.
6
(
(
(
12) Janzen, E. G. Acc. Chem. Res. 1971, 4, 31,
(13) Terabe, S.; Konaka, R. J. Chem. Soc., Perkin Tran. 2 1973, 369.
J. Org. Chem, Vol. 71, No. 13, 2006 4787

Miura et al.
TABLE 1. Results of the Reactions of 4b, 4c, 13a, and 13b with
a-ca
5
azo
compoundb
(mmol)
nitroso
molar ratio time isolated yieldd
run
compoundc
of 5 to 4
(h)
radical
(%)
1
2
3
4
5
6
7
8
9
5a (0.515)
5a (0.515)
5a (0.515)
5a (0.793)
5a (0.793)
5a (1.59)
5b (0.515)
5b (0.515)
5b (0.793)
4b
4b
4b
4b
4b
4b
4b
4b
4b
4b
4b
4b
4b
4c
0.65
0.65
0.65
1.0
1.0
2.0
0.65
0.65
1.0
1.0
2.0
0.65
1.0
0.65
1.0
1.0
1.0
1.0
2.0
4.0
4.0
6.0
4.0
1.0
2.0
0.5
1.0
1.0
0.5
0.5
1.0
1.0
2.0
4.0
4.0
1.0
7a
7a
7a
7a
7a
7a
7b
7b
7b
7b
7b
7c
20
32
37
38
45
13
27
44
49
46
18
33
49
33
52
50
36
33
49
FIGURE 1. ESR spectrum recorded at room temperature after a
mixture of 4b and 0.65 equiv of 5a in benzene was heated at 80 °C for
10 5b (0.793)
11 5b (1.59)
1
h. The observed 7a and 8a are shown by b and a, respectively.
12
5c (0.515)
SCHEME 2
13 5c (0.793)
7c
1
1
1
1
1
1
4
5
6
7
8
9
5b (0.793)
5b (0.793)
5b (0.793)
5a (0.793)
5a (0.793)
5b (0.793)
7d
7d
7d
11
12a
12b
4c
4c
13a
13b
13b
1.0
1.0
a
Benzene, 30 mL; temperature, 80 °C. b The τ1/2 of 5a and 5b in toluene
at 80 °C are 80 and 10 min, respectively, and that of 5c in toluene at 70 °C
is about 3.5 min. c 0.793 mmol. d Isolated yields based on the nitrosoben-
zene.
when the ratio for 5b/4b is 2.0, the yield of 7b decreases to
1
8% (run 11), again indicating that the use of a large excess of
azo compound drastically reduces the yield of 7b.
Because the half-life time of 5c is very short (>10 min at 80
°C), the mixtures of 4b and 5c were heated for only 0.5 h. The
radicals detected from the reaction mixtures were 7c alone. Table
1 shows that the reaction of 4b with 0.65 equiv of 5c gives 7c
in 33% yield (run 12), and the reaction of 4b with 1.0 equiv of
5c gives 7c in 49% yield (run 13). Consequently, the yields of
radicals are not different from those in the reactions of 4b with
5a or 5b. The only difference is the shorter reaction time.
Influence of the Reaction Time on the Yields of 7a. To
elucidate the influence of the reaction time on the yields of 7a
in more detail, the mixtures of 4b and 5a in tert-butylbenzene
were heated to 80 °C in a degassed ESR tube set in an ESR
cavity, and the concentrations of 7a were plotted against time.
The concentrations of 7a were determined by the double
integration of the ESR signals using tetramethylpiperidynyl-N-
oxyl (TEMPO) as the reference. The results are shown in Figure
2. When 4b was allowed to react with 1.0 equiv of 5a (Figure
2a), the concentrations of 7a increased with time and reached
which indicate that it is aminoxyl 8a. On the other hand, the aN
and g values for the triplet signal shown by b are 0.993 mT
and 2.0039, respectively, which are very similar to those for
1-3 (aN ) 0.984-1.05 mT, g ) 2.0041-2.0043). On the basis
of the analogous ESR parameters, it is concluded that the later
radical is the desired N-alkoxyphenylaminyl 7a. The relative
intensity of 7a to 8a determined by the double integration of
the ESR signals is 3.7, which shows that 7a is predominantly
formed in the reaction of 4b with 5a. When a mixture of 4b
and 0.65 equiv of 5a was heated for a longer time (2.0 and 4.0
h), the relative intensities of 7a to 8a increased to 5.4 and 9.5,
respectively.
The above results prompted us to isolate 7a. Because 7a was
inert to oxygen, similar to 1-3 and their analogues,1
,4-7
isolation
of 7a was quite easy; the red-colored reaction mixture was
concentrated under reduced pressure, and the red zone was
separated by column chromatography. Recrystallization from
MeOH gave red needles. The results are summarized in Table
-
1
an almost constant concentration of 12.9 mmol L at 7 h. The
ESR yield of 7a calculated from the radical concentration is
48%, which agrees with the isolated yield of 45% for the
corresponding reaction (run 5) shown in Table 1. On the other
hand, the yield of aminoxyl 8a always remains below 4.3%,
which suggests that the formed 8a further reacts during the
reaction. A plausible secondary reaction of 8a may be the
reversible reaction to nitrosobenzene 4b and 2-(methoxycarbo-
nyl)-2-propyl radical or the coupling reaction between of 8a
and 2-(methoxycarbonyl)-2-propyl radical. Unfortunately, TLC
analysis of the reaction mixture gave no information about this
point. When 4b was allowed to react with 2.0 equiv of 5a
(Figure 2b), the concentration of 7a increased with time and
showed a maximum at 3 h. However, after that, it drastically
1. Table 1 shows that when the ratio for 5a/4b is 0.65, the yields
of 7a are in the range from 20 to 37% (runs 1-3), and when
the ratio is 1.0, the reaction mixtures give 7a in 38-45% yield
(runs 4 and 5). On the other hand, when the ratio is increased
to 2.0, the yield decreases to 13% (run 6). Therefore, the use of
a large excess of the azo compounds leads to a drastic reduction
in the yield of 7a.
The reactions of 4b with 5b were carried out in the same
manner as above. Because the half-life time of 5b is only 10
min (at 80 °C), the reaction time was shortened to 2 h or less.
Upon heating, the reaction mixtures showed a strong ESR signal
due to 7b, while the signal due to 8b was very weak or not
observed. When the ratio for 5b/4b is 0.65, the yields of 7b are
-
1
2
7-44% (runs 7 and 8), and when the ratio for 5b/4b is 1.0,
decreased to 0.69 mol L . The maximum ESR yield is 25%,
and the yield at 4 h is only 14%. This yield agrees with the
the yields are increased to 46-49% (runs 9 and 10). However,
4788 J. Org. Chem., Vol. 71, No. 13, 2006

Synthesis of N-tert-Alkoxyarylaminyl Radicals
SCHEME 3
FIGURE 2. Plots of the ESR yields of 7a and 8a in the reaction of
4
b with 5a at 80 °C against time. The yields of 7a and 8a are shown
in solid and broken lines, respectively. (a) The 5a/4b ratio is 1.0. (b)
The 5a/4b ratio is 2.0.
isolated yield of 13% for the corresponding reaction (run 6)
shown in Table 1. Consequently, Figure 2b clearly shows that
the use of a large excess of azo compounds leads to a drastic
decrease in the yield of 7a, in agreement with the results of
runs 6 and 11 in Table 1. A possible reaction to reduce the
yields of 7a is the secondary reactions of 7 with tert-alkyl
radicals as mentioned above. After a mixture of 4b and 2.0 equiv
of 5a was heated for 6.0 h, the resultant mixture was analyzed
with TLC. The TLC analysis showed the formation of many
products. Although effort was made to identify possible products
including 10 from the secondary reaction of 7a with 2-meth-
oxycarbonyl-2-propyl radical, no products were identified.
was heated for 4 h, 12a was obtained in 33% yield, and when
a mixture of 13b and 1.0 equiv of 5b was heated for 1 h, the
reaction mixture gave 12b in 49% yield. As found in Table 1,
the yields of 11 and 12 are almost similar to those in the
reactions of 4b with 5a-c, demonstrating that the present
method can be applicable to the syntheses of functional-group-
carrying radicals.
X-ray Crystallographic Analyses. Fortunately, because two
radicals, 7c and 7d, gave good single crystals suitable for X-ray
crystallographic analysis, the analyses were successfully per-
formed for the two radicals. The molecular structures of 7c and
Generation and Isolation of Functional-Group-Carrying
N-tert-Alkoxy-2,4-diaryl-6-tert-butylphenylaminyls. Because
the present methodology does not use agents to react with
functional groups, functional-group-carrying N-tert-alkoxy-2,4-
diaryl-6-tert-butylphenylaminyls can be prepared by using the
present method. We selected acetyl and cyano groups as
functional groups, and acetyl-group-carrying N-tert-alkoxyaryl-
aminyl 11 and cyano-group-carrying N-tert-alkoxyarylaminyls
7d are illustrated in Figures 3 and 4. In the case of 7c, the torsion
angle for O1-N1-C1-C2 is -18.5(6)° (for O1-N1-C1-
C6, 160.6(3)°), indicating that ring A defined by C1-C6 is fairly
twisted from the NO radical center π system. This is in contrast
to the X-ray results of 1 (Ar ) Ph). The corresponding torsion
angle of 1 is only -175.4(2)°, showing that N1, O1, and ring
A are almost in the same plane. This difference may be ascribed
to the difference in the bulkiness of the tert-alkoxy groups of
7c and 1. The dihedral angle between ring A and ring B defined
by C7-C12 is 69.7°, suggesting that there is a large congestion
around the NO radical center. On the other hand, the dihedral
1
2 were prepared using this method. The corresponding ni-
trosobenzenes 13a and 13b were prepared according to Scheme
. When a mixture of 13a and 1.0 equiv of 5a was heated in
3
refluxing benzene for 4 h, 11 was obtained in 36% yield. In
the same manner, when a mixture of 13b and 1.0 equiv of 5a
J. Org. Chem, Vol. 71, No. 13, 2006 4789

Miura et al.
FIGURE 5. ESR spectrum of 7a in benzene at room temperature.
FIGURE 3. ORTEP drawing of 7c at 50% probability. The selected
bond lengths (Å), bond angles (°), and torsion angles (°) are as
follows: N(1)-O(1), 1.382(4); O(1)-N(1)-C(1), 110.8(3); N(1)-
O(1)-C(23), 111.0(3); O(1)-N(1)-C(1)-C(2), -18.5(6); O(1)-
N(1)-C(1)-C(6), 160.6(3).
FIGURE 6. ESR spectrum of 7a-d10 in benzene at room temperature.
FIGURE 4. ORTEP drawing of 7d at 50% probability. The selected
bond lengths (Å), bond angles (°), and torsion angles (°) are as
follows: N(1)-O(1), 1.386(3); O(1)-N(1)-C(1), 112.22 (19); N(1)-
O(1)-C(23), 109.98 (19); O(1)-N(1)-C(1)-C(2), 13.9(3); O(1)-
N(1)-C(1)-C(6), -164.20 (18).
N H
The a and a are determined by computer simulation.
ESR spectra, the 2- and 4-phenyl groups of 7a were deuterated.
The deuterated radical, 7a-d10, was prepared according to the
angle between ring A and ring C defined by C13-C18 is 19.5°,
suggesting that the unpaired electron spin can be delocal-
ized onto the ring C to some extent. In the case of 7d, the tor-
sion angle between for O1-N1-C1-C2 is 13.9(3)° (for O1-
N1-C1-C6, -164.20(18)°), which is smaller than that in 7c,
but indicates that ring A defined C1-C6 is fairly twisted
from the NO radical center π system. On the other hand, the
dihedral angles between ring A and ring B defined by C7-
C12 and that between ring A and ring C defined by C13-C18
are 62.7 and 49.5°, respectively, suggesting that the delocal-
ization of the unpaired electron spin onto rings B and C is a
very small.
same procedure as that for the nondeuterated radical. As found
in Figure 6, the ESR spectrum is split into 1:2:1 triplets of a
1:1:1 triplet, from which a and a were determined to be 0.993
N
H
and 0.165 mT, respectively, by computer simulation. The hfc
constants and g values for 7, 11, and 12 are summarized in
Table 2, together with UV-vis spectral data. The aN values
are in the range of 0.965-1.01 mT, which are close to those
for 1-3 (0.984-1.05 mT). The somewhat smaller aNs observed
for 11 and 12 can be accounted for in terms of an increase in
the relative importance of canonical form B as a result of the
presence of an electron-withdrawing acetyl or cyano group
(Scheme 4). The proton hyperfine splittings observed for 7a-
d10 are assigned to the aniline meta protons (2H).
ESR Spectroscopy. ESR spectra of 7, 11, and 12 were
measured at room temperature using benzene as the solvent.
All the radicals measured (other than the deuterated radical)
showed a broad 1:1:1 triplet, as illustrated in Figure 5. No
resolution or quite poor resolution due to aromatic protons can
be ascribed to the presence of numerous protons with unresolved
small hyperfine coupling (hfc) constants. To obtain well-resolved
4790 J. Org. Chem., Vol. 71, No. 13, 2006

Synthesis of N-tert-Alkoxyarylaminyl Radicals
TABLE 2. ESR and UV-Vis Data for 7, 11, and 12a
TABLE 3. Calculated Hyperfine Coupling Constants for 7d
hfc constant,
mT
λmax, nm
1
(ꢀ, L mol cm-1
)
-
radical
g
7
7
7
7
7
1
a
0.993b
2.0039 334 (30 800), 541 (1660)
c
0.993, 0.165 (2H)d 2.0039 334 (29 400), 540.5 (1620)
b
a-d10
b
c
b
0.988
1.01
2.0038 334 (27 300), 540 (1570)
2.0041 342 (25 800), 546 (1470)
2.0038 334 (26 200), 539 (1490)
2.0041 359.5 (23 300), 534 (750)
2.0040 349 (32 600), 539 (900)
2.0039 352 (28 200), 544 (920)
b
b
b
b
b
d
0.998
0.985
0.965
0.973
1
1
1
2a
2b
calcd hfc consta,b
obsd hfc consta,b,c
position
Nd
O
H3
H5
1.081
-0.290
0.223
0.998
a
b
Solvent, benzene; room temperature (∼25 °C). The hfc constant for
c
the NO nitrogen. The hfc constants are determined by computer simulation.
The hfc constant for the aniline meta protons.
e
d
0.165
0.165
e
0.234
a
The hfc constants are given in mT. b The MO calculations are performed
SCHEME 4
c
d
by the UB3LYP/6-31G(d) method. Shown in the absolute values. The
NO nitrogen. e The proton hfc constants for 7d-d10 are shown.
Spin Density Calculations. To discuss the spin density
distribution in detail, the DFT calculations for 7d were
performed by the UB3LYP/6-31G(d) method using the geometry
determined by X-ray crystallography.18 The total atomic spin
densities are illustrated in Figure 7, and some calculated hfc
FIGURE 8. Plots of øT vs T for 7d. The theoretical curve is drawn
using the values calculated by the Curie-Weiss law.
crystalline samples of 7c and 7d in the temperature range 1.8-
3
00 K with SQUID. The diamagnetic components were
subtracted by the estimation based on Pascal’s sum rule. The
ømol (molar magnetic susceptibility) versus the ømolT plots for
FIGURE 7. Total atomic spin densities of 7d calculated by the
UB3LYP/6-31G(d) method, using the geometry determined by X-ray
crystallography.
7
d are depicted in Figure 8. The ømolT value at 300 K is 0.345
-
1
emu K mol , from which the spin concentration is calculated
to be 92% based on the theoretical value of 0.375 emu K mol
-1
constants are compared with the observed ones in Table 3. Table
for the paramagnetic S ) 1/2 spin system. The ømolT value is
constant in the temperature range 300-12 K, and below 12 K,
it increases slightly. This indicates that a weak ferromagnetic
interaction operates between the neighboring radical molecules.
The ømolT versus T plots were analyzed with the Curie-Weiss
law (eq 1), and the Weiss temperature (θ) was determined to
be +0.2 K.
3
shows that the calculated hfc constants are in good agreement
with the observed ones. Relatively large spin densities are found
on NO and the aniline benzene ring (ring A). While small spin
densities are found on the 4-phenyl group (ring C), those on
the 2-phenyl group (ring B) are negligibly small. This is due to
a large twisting of ring B from the aniline benzene ring.
Magnetic Susceptibility Measurements. The magnetic
susceptibility measurements were carried out using the poly-
C
T - θ
ø )
(1)
(
18) All DFT calculations were carried out using the following: Frisch,
M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.;
Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A., Jr.; Stratmann,
R. E.; Burant, J. C.; Dapprich, S.; Millam, J. M.; Daniels, A. D.; Kudin, K.
N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone, V.; Cossi, M.; Cammi,
R.; Mennucci, B.; Pomelli, C.; Adamo, C.; Clifford, S.; Ochterski, J.;
Petersson, G. A.; Ayala, P. Y.; Cui, Q.; Morokuma, K.; Malick, D. K.;
Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Cioslowski, J.; Ortiz, J.
V.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.;
Gomperts, R.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng,
C. Y.; Nanayakkara, A.; Gonzalez, C.; Challacombe, M.; Gill, P. M. W.;
Johnson, B. G.; Chen, W.; Wong, M. W.; Andres, J. L.; Head-Gordon, M.;
Replogle, E. S.; Pople, J. A. Gaussian 98, revision A.9; Gaussian, Inc.:
Pittsburgh, PA, 1998.
The crystal structure of 7d shows that the radical molecules
are stacked along the b axis. Because the magnetic interaction
is very weak, there may be some possible explanations for the
weak ferromagnetic interaction. However, we found a plausible
mechanism by the careful examination of the crystal structure
of 7d, as described below. The radicals interact through C16- - -
C17′ and C17- - -C16′, with an intermolecular distance of 3.573
Å between the neighboring radicals, as shown in Figure 9. The
J. Org. Chem, Vol. 71, No. 13, 2006 4791

Miura et al.
Experimental Section
,2′-Azobis[2-(methoxycarbonyl)propane] (5a), 2,2′-azobis(2-
2
cyano-4-methylpentane) (5b), and 2,2′-azobis(2-cyano-4-methyl-
-methoxypentane) (5c) were commercially available. 2,4,6-
Triphenylnitrosobenzene (4a), 2,4-diphenyl-6-tert-butylnitrosobenzene
4b), and 2,4-di(phenyl-d )-6-tert-butylnitrosobenzene (4b-d10) were
4
(
5
5
prepared according to the reported methods. Silica gel column
chromatography was performed on silica gel 60 N (purchased from
a commercial supplier), while alumina column chromatography was
carried out on aluminum oxide 90 (purchased from a commercial
supplier).
ESR Study. ESR spectra were measured with a Bruker ESP 300.
Hyperfine splitting constants and g values were determined by the
comparison with Fremy’s salt in dilute K
) 1.309 mT, g ) 2.0055).
In the kinetic ESR study, the relative concentrations of N-
2 3
CO aqueous solution
(a
N
alkoxyaminyls and aminoxyls during the reactions were determined
by the double integration of one peak in the lowest magnetic field
of the corresponding 1:1:1 triplets ESR signals. After the measure-
ments were finished, the ESR cells were immediately cooled to
room temperature, and the individual concentrations of N-alkoxyami-
nyls and aminoxyls were determined using the calibration curves
drawn by using the known concentration tert-butylbenzene solutions
of TEMPO.
Magnetic Susceptibility Measurements. Magnetic susceptibility
measurements were carried out using polycrystalline samples in
the temperature range 1.8-300 K. The diamagnetic components
were subtracted by the estimation based on Pascal’s sum rule.
FIGURE 9. Stacking mode of 7d. The dotted lines show the
ferromagnetic interactions between two radical molecules. The distance
between C16- - -C17′ (and C17- - -C16′) is 3.573 Å.
spin densities on C16 and C17 predicted by the DFT calculations
are +0.0255 and -0.0139, respectively. According to the
McConnell rule,1 the magnetic interaction between the two
radical molecules is ferromagnetic, which is in agreement the
observed result. However, because the spin densities on C16
and C17 are very low, the ferromagnetic interaction is very
weak.
2
-tert-Butyl-4-(4-acetylphenyl)aniline (15a). A mixture of 3.96
g (17.4 mmol) of 2-tert-butyl-4-bromoaniline, 4.80 g (29.3 mmol)
of 4-acetylphenylboronic acid, 1.20 g (1.04 mmol) of Pd(PPh
and 7.37 g of Na CO in 112 mL of benzene, 32 mL of EtOH, and
9
3 4
) ,
2
3
44 mL of water was refluxed for 24 h with stirring under N . After
2
cooling to room temperature, the mixture was extracted with
benzene, and the combined benzene extracts were washed with
brine, dried over anhydrous MgSO , and evaporated. The residue
4
On the other hand, the ømolT versus T plots of 7c showed a
weak antiferromagnetic behavior. The ømolT value was constant
above ∼80 K, and below ∼80 K, it gradually decreased.
Analysis of the ømolT versus T plots with the Curie-Weiss law
showed -3.8 K as θ, indicating that the antiferromagnetic
interaction was weak. To clarify the mechanism for the
antiferromagnetic interaction, the crystal structure of 7c was
investigated in detail. Because many weak antiferromagnetic
and weak ferromagnetic interactions were found between the
neighboring radicals, it was difficult to determine the mechanism
for the observed weak antiferromagnetic interaction between
the neighboring radicals.
was then chromatographed on silica gel with 2:3 EtOAc-hexane
to give 15a in 65% yield (3.01 g, 11.3 mmol). Recrystallization
1
from EtOH gave light yellow needles with mp 151-153 °C. H
NMR (CDCl
3
) δ 1.48 (s, 9H), 2.62 (s, 3H), 4.00 (br s, 2H), 6.77
(
)
d, J ) 8.0 Hz, 1H), 7.35 (dd, J ) 8.0 and 2.4 Hz, 1H), 7.54 (d, J
2.4 Hz, 1H), 7.63 (d, J ) 8.2 Hz, 2H), 7.99 (d, J ) 8.2 Hz, 2H).
Anal. Calcd for C H NO: C, 80.86; H, 7.92; N, 5.24. Found: C,
18
21
80.95; H, 7.99; N, 5.24.
2-Bromo-4-(4-acetylphenyl)-6-tert-butylaniline (16a). A mix-
ture of 3.00 g (11.2 mmol) of 15a, 5.24 g (13.4 mmol) of
benzyltrimethylammonium tribromide (BTMABr
CaCO in 100 mL of CH Cl and 35 mL of MeOH was stirred for
h at room temperature. After filtration, the CH Cl layer was
washed with aqueous NaHSO and then brine, dried over anhydrous
MgSO , and evaporated. The residue was then chromatographed
3
), and 1.46 g of
3
2
2
4
2
2
3
Conclusions
4
on silica gel with benzene. Recrystallization from EtOH gave 16a
The reactions of 2,4,6-triphenyl- and 2,6-diaryl-6-tert-bu-
tylnitrosobenzenes with three kinds of azo compounds 5a-c
were carried out with a purpose to establish a new methodology
for the synthesis of isolable stable N-alkoxyphenylaminyls.
Although the reactions of 2,4,6-triphenylnitrosobenzene with
as colorless needles in 96% yield (3.72 g, 10.7 mmol). Mp 116-
1
1
2
17 °C; H NMR (CDCl
3
) δ 1.48 (s, 9H), 2.63 (s, 3H), 4.57 (br s,
H), 7.47 (d, J ) 2.0 Hz, 1H), 7.60 (d, J ) 8.4 Hz, 2H), 7.66 (d,
J ) 2.0 Hz, 1H), 7.99 (d, J ) 8.4 Hz, 2H). Anal. Calcd for C H -
18
20
BrNO: C, 62.44; H, 5.82; N, 4.05. Found: C, 62.43; H, 5.81; N,
3.87.
5
a-c in refluxing benzene gave aminoxyls alone, the reactions
of 2,4-diaryl-6-tert-butylnitrosobenzenes with 5a-c gave the
desired N-alkoxyphenylaminyls 7, which were isolated as the
radical crystals in 18-52% yields. When the same procedure
was used, functional-group-carrying N-alkoxyphenylaminyls
were prepared and isolated as radical crystals. In conclusion,
this method will serve as a useful procedure for the synthesis
of stable N-alkoxyphenylaminyls.
2-Phenyl-4-(4-acetylphenyl)-6-tert-butylaniline (17a). A mix-
ture of 3.41 g (9.84 mmol) of 16a, 1.56 g (12.8 mmol) of
phenylboronic acid, 0.683 g (0.591 mmol) of Pd(PPh
g of K CO in 100 mL of benzene, 45 mL of water, and 20 mL of
EtOH was refluxed for 24 h with stirring under N . After cooling,
3 4
) , and 5.44
2
3
2
water was added, and the mixture was extracted with benzene. After
the combined benzene extracts were washed with brine and dried
over anhydrous MgSO , the solvent was evaporated under reduced
4
pressure and the residue was chromatographed on silica gel with
(19) McConnell, H. M. J. Chem. Phys. 1963, 39, 1910.
1:8 EtOAc-hexane. Recrystallization from EtOH gave 17a as
4792 J. Org. Chem., Vol. 71, No. 13, 2006

Synthesis of N-tert-Alkoxyarylaminyl Radicals
colorless needles in 83% yield (2.81 g, 8.18 mmol). Mp 168-170
pressure and the residue was chromatographed on silica gel with
1
°
C; H NMR (CDCl
3
) δ 1.53 (s, 9H), 2.62 (s, 3H), 4.13 (br s, 2H),
1:4 EtOAc-hexane. Recrystallization from hexanes-EtOAc gave
7
4
.32 (d, J ) 2.4 Hz, 1H), 7.38-7.41 (m, 1H), 7.48 (d, J ) 4.4 Hz,
H), 7.58 (d, J ) 2.4 Hz, 1H), 7.66 (d, J ) 8.4 Hz, 2H), 7.98 (d,
25NO: C, 83.93; H, 7.34;
N, 4.08. Found: C, 83.72; H, 7.22; N, 4.00.
-Phenyl-4-(4-acetylphenyl)-6-tert-butylnitrosobenzene (13a).
A solution of 1.96 g (5.71 mmol) of 17a in 25 mL of CH Cl was
cooled to 0 °C with stirring, and a solution of 2.76 g (16.0 mmol)
of m-chloroperbenzoic acid in 30 mL of CH Cl was added
17b as light yellow needles in 69% yield (0.972 g, 2.98 mmol).
1
Mp 141-143 °C; H NMR (CDCl
3
) δ 1.52 (s, 9H), 4.16 (br s,
J ) 8.4 Hz, 2H). Anal. Calcd for C24
H
2H), 7.27 (d, J ) 2.0 Hz, 1H), 7.36-7.50 (m, 5H), 7.53 (d, J )
2.0 Hz, 1H), 7.65 (s, 4H). Anal. Calcd for C23 : C, 84.63; H,
6.79; N, 8.58. Found: C, 84.59; H, 6.80; N, 8.58.
2-Phenyl-4-(4-cyanophenyl)-6-tert-butylnitrosobenzene (13b).
A solution of 0.688 g (2.11 mmol) of 17b in 10 mL of CH Cl
was cooled to 0 °C with stirring, and a solution of 1.02 g (5.90
mmol) of m-chloroperbenzoic acid in 10 mL of CH Cl was added
22 2
H N
2
2
2
2
2
2
2
dropwise for 15 min. After the completion of the addition, the
mixture was raised to room temperature with stirring and 100 mL
2
2
dropwise for 15 min. After the completion of the addition, the
mixture was raised to room temperature with stirring and 50 mL
of water was added. The CH
over anhydrous MgSO , and evaporated under reduced pressure.
2 2
Cl layer was washed with brine, dried
4
of water was added. The CH
on anhydrous MgSO , and evaporated under reduced pressure. The
2 2
Cl layer was washed with brine, dried
The residue was then chromatographed on silica gel with 1:8
benzene-EtOAc to give 13a as green microneedles containing
small amounts of impurities. Accordingly, the compound was
further purified with a recycling preparative HPLC instrument with
4
residue was then chromatographed on silica gel with 1:8 benzene-
EtOAc, and crystallization from EtOH gave 13b as green needles
1
in 92% yield (0.664 mg, 1.95 mmol). Mp 128-130 °C; H NMR
CHCl
08 °C; H NMR (CDCl
m, 2H), 7.24 (d, J ) 2.0 Hz, 1H), 7.32-7.34 (m, 3H), 7.74 (d, J
8.4 Hz, 2H), 7.89 (d, J ) 2.0 Hz, 1H), 8.06 (d, J ) 8.4 Hz, 2H).
Anal. Calcd for C24 : C, 80.64; H, 6.49; N, 3.92. Found:
C, 80.78; H, 6.34; N, 3.83.
3
as the eluent. Yield 70% (1.42 g, 3.97 mmol); mp 106-
3
(CDCl ) δ 1.70 (s, 9H), 6.81-6.84 (m, 2H), 7.21 (d, J ) 2.0 Hz,
1
1
(
3
) δ 1.72 (s, 9H), 2.66 (s, 3H), 6.83-6.86
1H), 7.34-7.34 (m, 3H), 7.73 (d, J ) 8.5 Hz, 2H), 7.76 (d, J )
8.8 Hz, 2H), 7.84 (d, J ) 2.0 Hz, 1H). Anal. Calcd for
)
23 20 2
C H N O: C, 81.15; H, 5.92; N, 8.23. Found: C, 80.79; H, 5.90;
H23NO
2
N, 8.21.
N-[2-(Methoxycarbonyl)-2-propoxy]-2-phenyl-4-(4-cyanophe-
nyl)-6-tert-butylphenylaminyl (12a). A solution of 250 mg (0.734
mmol) of 13b and 169 mg (0.743 mmol) of 5a in 30 mL of benzene
N-[2-(Methoxycarbonyl)-2-propoxy]-2-phenyl-4-(4-acetylphe-
nyl)-6-tert-butylphenylaminyl (11). A solution of 200 mg (0.56
mmol) of 13a and 129 mg (0.56 mmol) of 5a in 30 mL of benzene
2
was refluxed for 4 h under a N atmosphere. The red mixture was
was refluxed for 4 h under a N
2
atmosphere. The red mixture was
evaporated under reduced pressure, and the residue was chromato-
graphed on silica gel with 1:4 ethyl acetate-hexane to give 12a in
33% yield (102 mg, 0.231 mmol). Recrystallization from MeOH
gave red needles with mp 154-156 °C. Anal. Calcd for
evaporated under reduced pressure, and the residue was chromato-
graphed on silica gel with 1:4 EtOAc-hexane to give 11 in 36%
yield (131 mg, 0.286 mmol). Recrystallization from MeOH gave
red needles with mp 125-127 °C. Anal. Calcd for C29
5.96; H, 7.03; N, 3.05. Found: C, 75.84; H, 6.96; N, 2.79.
-tert-Butyl-4-(4-cyanophenyl)aniline (15b). A mixture of 3.80
g (16.5 mmol) of 2-tert-butyl-4-bromoaniline, 4.41 g (30.0 mmol)
of 4-cyanophenylboronic acid, 0.577 g (0.50 mmol) of Pd(PPh
and 7.1 g of Na CO in 112 mL of benzene, 32 mL of EtOH, and
4 mL of water was refluxed for 24 h with stirring under N . After
4
H32NO : C,
28 29 2 3
C H N O : C, 76.16; H, 6.62; N, 6.34. Found: C, 76.10; H, 6.62;
7
N, 6.33.
2
N-(2-Cyano-4-methyl-2-pentoxy)-2-phenyl-4-(4-cyanophenyl)-
6-tert-butylphenylaminyl (12b). A solution of 270 mg (0.793
mmol) of 13b and 128 mg (0.793 mmol) of 5b in 30 mL of benzene
3 4
) ,
2
was refluxed for 1 h under a N atmosphere. The red mixture was
2
3
4
2
evaporated under reduced pressure, and the residue was chromato-
graphed on alumina with 1:16 ethyl acetate-hexane to give 12b
in 49% yield (175 mg, 0.388 mmol). Recrystallization from MeOH
gave red needles with mp 131-133 °C. Anal. Calcd for
C H N O: C, 79.97; H, 7.16; N, 9.34. Found: C, 79.97; H, 7.17;
30 32 3
N, 9.30.
cooling to room temperature, the mixture was extracted with
benzene and the combined benzene extracts were washed with brine,
dried over anhydrous MgSO , and evaporated. The residue was then
4
chromatographed on silica gel with 1:6 EtOAc-hexane to give 15b
in 49% yield (2.01 g, 8.03 mmol). Recrystallization from EtOH
1
gave colorless plates with mp 112-114 °C. H NMR (CDCl
3
) δ
X-ray Crystallography. All measurements were made on a
Rigaku/MSC Mercury CCD diffractometer with graphite mono-
chromated MoKR (λ ) 0.710 70 Å) radiation, and the X-ray
crystallographic data were collected at -50 °C. The structure of
7c was solved by direct methods (SRI92).20 The methoxy group
showed disorders over two sites with an occupancy of 0.5. The
ORTEP drawing shown in Figure 3 is one of them. Refinement of
1
.47 (s, 9H), 4.02 (br s, 2H), 6.73 (d, J ) 8.3 Hz, 1H), 7.30 (dd,
J ) 8.3 and 2.2 Hz, 1H), 7.48 (d, J ) 2.2 Hz, 1H), 7.62 (d, J )
.3 Hz, 2H), 7.66 (d, J ) 8.3 Hz, 2H). Anal. Calcd for C17
C, 81.56; H, 7.25, N, 11.19. Found: C, 81.47; H, 7.14; N, 11.28.
-Bromo-4-(4-cyanophenyl)-6-tert-butylaniline (16b). A mix-
ture of 0.944 g (3.77 mmol) of 15b, 1.76 g (4.52 mmol) of
BTMABr , and 0.49 g of CaCO in 32 mL of CH Cl and 10 mL
of MeOH was stirred for 2 h at room temperature. After filtration,
the CH Cl layer was washed with aqueous NaHSO and then brine,
dried over anhydrous MgSO , and evaporated. The residue was then
8
18 2
H N :
2
2
the structure was carried out on F by full-matrix, least-squares
3
3
2
2
method. The non-hydrogen atoms were refined anisotropically, and
the hydrogen atoms were placed in the fixed position and not
refined. All calculations were performed using the teXsan crystal-
lographic software package.21 On the other hand, the structure of
7d was solved by direct methods using the SHELX 97 software
2
2
3
4
chromatographed on silica gel with 1:4 EtOAc-hexane and
recrystallization from EtOH gave 16b as colorless needles in 86%
yield (1.07 g, 3.25 mmol). Mp 148-150 °C; H NMR (CDCl
1
22
) δ
package. In 7d, the C30-C32 group and the cyano group
3
1
)
.48 (s, 9H), 4.60 (br s, 2H), 7.43 (d, J ) 2.0 Hz, 1H), 7.60 (d, J
exhibited disorder over two sites with an occupancy of 0.5. The
ORTEP drawing shown in Figure 4 is one of them. Refinement of
8.2 Hz, 2H), 7.62 (d, J ) 2.0 Hz, 1H), 7.68 (d, J ) 8.2 Hz, 2H).
: C, 62.02; H, 5.20; N, 8.51. Found:
2
Anal. Calcd for C17
H17BrN
2
the structure was carried out on F by full-matrix, least-squares
method using the SHELX 97 software package.23 The nonhydrogen
C, 61.98; H, 5.15; N, 8.44.
-Phenyl-4-(4-cyanophenyl)-6-tert-butylaniline (17b). A mix-
ture of 1.42 g (4.31 mmol) of 16b, 0.684 g (5.61 mmol) of
phenylboronic acid, 0.299 g (0.259 mmol) of Pd(PPh , and 2.4 g
of K CO in 43 mL of benzene, 19 mL of water, and 9 mL of
EtOH was refluxed for 24 h with stirring under N . After cooling,
2
(20) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, M.; Giaco-
vazzo, C.; Guagliardi, A.; Polidori, G. J. Appl. Crystallogr. 1994, 27, 435.
3
)
4
(
21) TeXsan; Crystal Structure Analysis Package; Molecular Structure
Corporation: The Woodlands, TX, 1985 and 1999.
22) Sheldrick, G. M. SHELXS97; Program for Crystal Structure Solution;
University of G o¨ ttingen: G o¨ ttingen, Germany, 1997.
23) Sheldrick, G. M. SHELXL97; Program for Crystal Structure Refine-
ment; University of G o¨ ttingen, G o¨ ttingen, Germany, 1997.
2
3
2
(
water was added and the mixture was extracted with benzene. After
the combined benzene extracts were washed with brine and dried
over anhydrous MgSO , the solvent was evaporated under reduced
4
(
J. Org. Chem, Vol. 71, No. 13, 2006 4793

Miura et al.
atoms were refined anisotropically, and the hydrogen atoms were
placed in ideal positions and refined as riding atoms. R1) Σ||F
7d: C29
H
31Cl
2
N
2
O; formula weight, 494.46; monoclinic, space
o
|
group C2/c(#15); a ) 49.366(5), b ) 9.5302(9), c ) 11.4601(11)
2
o
2 2
2 2 1/2 24
3
-
|F
Crystal Data. 7c: C30
clinic, space group P2 /n(#14); a ) 10.470(2), b ) 36.980(6), c )
c
||/Σ|F
o
|, wR2 ) [(Σw(F - F ) /Σw(F ) )]
.
Å; â ) 98.786(5)°; V ) 5412.0(9) Å ; Z ) 8; Dcalc ) 1.214 g
c
o
-
3
-1
H
35
N
2
2
O ; formula weight, 455.62; mono-
cm ; F(000) ) 2088.00; µ ) 2.63 cm ; crystal size 0.25 × 0.48
0.07 mm; 2θmax ) 55.0°; reflections collected, 20 023; unique,
086 (Rint ) 0.0456); parameter, 332; R1 ) 0.0750 (for I > 2.0σ-
1
×
3
6
1
0
2
.8100(8) Å; â ) 97.120(7)°; V ) 2616.4(7) Å ; Z ) 4; Dcalcd )
6
-
3
-1
.157 g cm ; F(000) ) 980.00; µ ) 0.72 cm ; crystal size )
.06 × 0.05 × 0.35 mm; 2θmax ) 55.0°; reflections collected,
0 344; unique, 5929 (Rint ) 0.071); parameter, 317; R1 ) 0.0996
(
I)); wR2 ) 0.1646 (all data); GOF ) 1.183.
Supporting Information Available: The synthetic procedures
(
for I > 2.30σ(I)); wR2 ) 0.179; GOF ) 1.68.
of 4c and 7a-d and their analytical data. The CIF files containing
X-ray structural data of 7c and 7d. This material is available free
of charge via the Internet at http://pubs.acs.org.
(24) The crystal structure data for radicals 6c and 6d have been deposited
at the Cambridge Database: CCDC numbers 261609 and 294749, respec-
tively. Copies of the data can be obtained free of charge via www.ccdc-
.cam.ac.uk/retrieving.html.
JO0600959
4794 J. Org. Chem., Vol. 71, No. 13, 2006