S. Takekuma et al.
Bull. Chem. Soc. Jpn. Vol. 87, No. 4 (2014)
521
as below: namely, 11E was obtained as dark-yellow plates.
Similar to 4, the characteristic UV-vis absorption bands from
guaiazulene (3) (Figure 1A) were not observed, while the
characteristic absorption wavelengths of 11E appeared at -max
240, 287, 337, 455, and 621 nm, suggesting the formation of an
extended π-electron system with a 3-guaiazulenyl group. The
IR spectrum showed a specific absorption band arising from
the C=O bond at ¯max 1686 cm¹1, the specific band, which
coincided with that of 4. The molecular formula C24H24O was
determined by exact EI-MS, whose spectrum showed M+ ion
shifts upfield (152.2 and 128.6) of 6; however, other carbon
signals of 5 revealed shifts downfield of 6: namely, the order
of larger downfield shift was HC-α (¦ ¤ 112.9) > C-7¤¤
(32.4) > C-3a¤,3a¤¤ (25.2) > C-5¤¤ (24.4) > C-7¤ (24.3) > C-8a¤
(23.4) > C-3¤ (22.0) > C-5¤ (19.5) > C-2,6, C-1¤¤ (14.8) >
C-8a¤¤ (12.4) > C-1¤ (11.7) > C-6¤¤ (10.6) > C-6¤ (9.4) > C-4¤
(9.2) > C-4¤¤ (8.7) > C-8¤¤ (7.8) > C-4 (5.7) > C-8¤ (5.3) >
C-3¤¤ (4.1) > C-2¤¤ (1.6) > C-2¤ (0.5) (Tables 3, 4, and 6). In
previous papers,1-8,10-21 we reported that in the case of the 3-
1
guaiazulenylmethylium ion unit, the H and 13C NMR signals
1
peak. Along with the above spectroscopic data, the H and
13C NMR spectral analyses (Tables 1-4) for 11E led to the
molecular structure illustrated in Scheme 2.
of the C-5 position are downfield of the C-6 position; however,
with the 3-guaiazulenylmethyl group, the 1H and 13C NMR
signals of the C-6 position are downfield of the C-5 position.
1
The target monocarbenium ion compound 12 (83% isolated
yield) was obtained as a green powder. The UV-vis spectrum of
12 showed that the longest absorption wavelength (¯max 724 nm,
log ¾ = 4.41) of 12 revealed a larger bathochromic shift (¦
109 nm) and a larger hypochromic effect (¦ log ¾ = 0.48) than
5 (Figure 1C), owing to the difference between the (E)-N=
N- linkage of 5 and the (E)-CH=CH- linkage of 12. The IR
spectrum showed two specific absorption bands resulting from
In conclusion, the H and 13C NMR chemical shifts of 5, com-
pared with those of 6, apparently suggested the formation of the
3¤¤-(guaiazulenyl)methylium ion compound 5 with the two
representative resonance structures of the 3¤¤-guaiazulenylium
ion form 5¤ and the 3¤-guaiazulenylium ion form 5¤¤ (Chart 2).
1H and 13C NMR Spectral Parameters of 12 and 13.
1
From comparative studies of chemical shifts (¤) for H NMR
signals of 12 (Chart 2) and 13 (Scheme 2), it was found that the
H-2¤¤, CH3-4¤¤, (CH3)2CH-7¤¤, (CH3)2CH-7¤¤, H-8¤¤, CH3-1¤¤¤,
and (CH3)2CH-7¤¤¤ proton signals of 12 coincided with those of
13; however, other proton signals of 12 showed shifts downfield
of 13: namely, the order of larger downfield shift was HC-α (¦ ¤
4.02) > H-5¤¤¤ (1.47) > H-6¤¤¤ (0.99) > H-2¤,6¤ (0.80) > H-2¤¤¤
(0.66) > H-8¤¤¤ (0.47) > (CH3)2CH-7¤¤¤ (0.42) > CH3-4¤¤¤
(0.39) > H-3¤,5¤, H-2 (0.27) > H-5¤¤ (0.16) > H-1 (0.15) >
CH3-1¤¤, H-6¤¤ (0.10) (Tables 1, 2, and 5). Along with the
above results, from comparative studies of chemical shifts (¤)
for 13C NMR signals of 12 and 13, it was found that the C-1 and
C-2¤¤¤ carbon signals of 12 coincided with those of 13; however,
the C-1¤ (¤ 135.1) and C-4¤¤ (134.3) carbon signals of 12 were
upfield (141.6 and 145.6) of 13, while other carbon signals
of 12 appeared downfield of 13: namely, the order of larger
downfield shift was HC-α (¦ ¤ 114.0) > C-7¤¤¤ (28.4) > C-3a¤¤¤
(27.5) > C-5¤¤¤ (23.2) > C-8a¤¤¤ (21.9) > C-3¤¤¤ (18.9) > C-4¤¤¤
(11.9) > C-6¤¤¤ (9.8) > C-4¤ (9.4) > C-7¤¤ (9.1) > C-2¤,6¤
(7.2) > C-1¤¤¤ (6.2) > C-2 (6.1) > C-8¤¤¤ (6.0) > C-3a¤¤ (4.8) >
C-5¤¤ (3.4) > C-8a¤¤ (2.8) > C-8¤¤, C-3¤,5¤ (2.3) > C-6¤¤ (2.2) >
C-1¤¤ (1.7) > C-2¤¤, C-3¤¤ (1.1) (Tables 3, 4, and 6). In
¹
counter anion (PF6 ) at 841 and 556 cm¹1, the bands coincided
with those of 5 (Figure 2C). Elemental analysis confirmed the
formula C195H206F36P6 (i.e., 5C39H41 + 5PF6 + HPF6) and
further, the formula C39H41 based on the monocarbenium ion
[M ¹ PF6]+ was determined by exact FAB-MS, whose spec-
trum showed the corresponding monocation peak. Along with
the above elemental analysis and spectroscopic data, the 1H and
13C NMR spectral analyses (Tables 1-6) for 12 led to the target
monocarbenium ion compound illustrated in Scheme 2. Similar
to 5 and 6, the detailed studies on the 1H and 13C NMR spectral
parameters (¤) of the new products 12 and 13, for comparative
study, are described below.
The reduction of 12 with NaBH4 in a mixed solvent of
ethanol and acetonitrile at room temperature for 30 min gave
13, in 96% isolated yield, which was obtained as green needles.
The molecular ion peak (M+) was observed by FAB-MS
spectrum. Along with the MS spectroscopic datum, the 1H
and 13C NMR spectral analyses (Tables 1-6) for 13 led to the
molecular structure {4-[(E)-2-(3-guaiazulenyl)ethenyl]phen-
yl}(3-guaiazulenyl)methane (Scheme 2), in which a hydride
ion attached to the HC+-α carbon atom of 12 selectively, the
1
conclusion, the above H and 13C NMR chemical shifts of 12,
¹
result, of which coincided with the H -reduction of 5.
compared with those of 13, suggest the formation of the 3¤¤¤-
(guaiazulenyl)methylium ion compound 12 with a resonance
structure of the 3¤¤¤-guaiazulenylium ion form 12¤; however,
from the C-5¤¤ and C-6¤¤ chemical shifts of the 3¤¤-guaiazulenyl
group of 12, it is suggested that 12 does not form a resonance
structure of the 3¤¤-guaiazulenylium ion form 12¤¤ (Chart 2).
Thus, the great difference between the resonance structures of
5 and those of 12 is suspected.
1H and 13C NMR Spectral Parameters of 5 and 6. From
1
comparative studies of chemical shifts (¤) for H NMR signals
of 5 (Chart 2) and 6 (Scheme 1), it was found that the CH3-1¤,
(CH3)2CH-7¤, H-3,5, and CH3-1¤¤ proton signals of 5 coincided
with those of 6; however, the H-2¤-(CH3)2CH-7¤, H-8¤, H-2,6,
CH-α, CH3-4¤¤-H-8¤¤ proton signals of 5 showed downfield
shifts in comparison with those of 6: namely, the order of
larger downfield shift was HC-α (¦ ¤ 4.07) > H-5¤¤ (1.68) >
H-5¤ (1.22) > H-6¤¤ (1.12) > H-6¤ (0.92) > H-2,6 (0.86) >
H-2¤ (0.62) > CH3-4¤¤ (0.51) > H-8¤¤ (0.50) > (CH3)2CH-7¤¤
(0.45) > H-8¤ (0.42) > (CH3)2CH-7¤ (0.41) > CH3-4¤ (0.14) >
(CH3)2CH-7¤¤ (0.11), while the H-2¤¤ (7.89) proton signal of 5
revealed a shift upfield (8.07) of 6 (Tables 1, 2, and 5). Along
with the above results, from comparative studies of chemical
shifts (¤) for 13C NMR signals of 5 and 6, it was found that the
C-1 (¤ 133.9) and C-3,5 (126.4) carbon signals of 5 showed
Variable-Temperature 1H NMR Spectra of 5.
In a
previous paper,13 the variable-temperature 500 MHz H NMR
studies of 16 in CD3CN at 70, 40, 25, 0, and ¹40 °C were
reported, suggesting the formation of the rotational stereo-
isomers of the generated resonance structure 16¤¤ (Chart 1)
under the measurement conditions. Similar to 16, the variable-
1
1
temperature 700 MHz H NMR spectra of 5 in CD3CN at 60,
40, 25, 0, ¹20, and ¹40 °C were measured, no spectrum
showed a proton from the protonated diazene unit, because of