Ring closing and opening reactions leading to aza-polycyclic aromatic compounds

Article abstract of DOI:10.1016/j.tet.2012.02.047

A series of functionalized aza-polycyclic aromatic compounds were prepared by a superacid-promoted ring closing and opening reaction cascade. A reaction mechanism is proposed, which involves reactive dicationic intermediates. A key step in the conversions involves ipso protonation of an aryl group and elimination of an alkyl phenyl group.

Full text of DOI:10.1016/j.tet.2012.02.047

Tetrahedron 68 (2012) 3357e3360
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Tetrahedron
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Ring closing and opening reactions leading to aza-polycyclic aromatic compounds
*
Anila Kethe, Ang Li, Douglas A. Klumpp
Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, IL 60115, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of functionalized aza-polycyclic aromatic compounds were prepared by a superacid-promoted
ring closing and opening reaction cascade. A reaction mechanism is proposed, which involves reactive
dicationic intermediates. A key step in the conversions involves ipso protonation of an aryl group and
elimination of an alkyl phenyl group.
Received 23 January 2012
Received in revised form 17 February 2012
Accepted 20 February 2012
Available online 3 March 2012
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Heterocycle
Superacid
Dication
Aza-polycyclic aromatic compounds
Condensation
1. Introduction
intermediate 3. While interesting from a mechanistic standpoint,
the benzene elimination step only serves as a means of generating
Aza-polycyclic aromatic compounds are substances useful in
material science applications as they can have interesting optical
properties.1 The substances can also have a variety of biological
activities.2 As such, the aza-polycyclic aromatic compounds have
been the frequent targets of synthetic methods.3 Our own
superacid-promoted reactions gave aza-polycyclic aromatic com-
pounds by reactions involving dicationic intermediates (Eq. 1).4 For
example, compound 1 is diprotonated to give ion 2 which cyclizes
to compound 4. The reaction involves cyclization of 2 followed by
an unusual benzene elimination step. This reaction step is envi-
sioned to occur by an ipso-protonation of the phenyl group on
the new p-bond. Other than the aromatic ring, no functionality is
produced on the arene by this reaction step. In this manuscript, we
describe chemistry leading to aza-polycyclic aromatic compounds
with additional aryl-alkyl groups. The products are formed by
a ring-closure, ring-opening cascade.
2. Results
We reasoned that indane and tetraline-type substituent groups
could lead to phenethyl-substituted aza-polycyclic aromatic com-
pounds by a ring-closure and ring-opening sequence. To test this
hypothesis, a series of heterocyclic alcohols were prepared and
reacted with superacidic CF3SO3H (Table 1). The alcohol substrates
were prepared from the reactions of organolithium reagents with
tetralones and other ketones (Eq. 2).
For example, 3-hydroxy-2-methylpyridine is converted to
compound 5 by standard Suzuki coupling methods.5 Methyl
deprotonation is readily accomplished with 2-methylpyridines (2-
* Corresponding author. E-mail address: dklumpp@niu.edu (D.A. Klumpp).
0040-4020/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2012.02.047

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A. Kethe et al. / Tetrahedron 68 (2012) 3357e3360
Table 1
migration, ring closure, and then ring opening reaction steps
Benzo[f]quinolone products from the reactions of alcohols 6e10
(Scheme 2). Thus, compound 18 was prepared from 2,5-
diphenyloxazole and 2-tetralone. Reaction of substrate 18 with
CF3SO3H gave the phenethyl-substituted product 19 in good yield.
Initial ionization gives the 1,3-dication (20) and charge migration
provides the 1,4-dication (21). Previous studies have shown that
such isomerizations occur by deprotonationereprotonation steps,4a
rather than by direct hydride shift. The charge migration is driven by
chargeecharge repulsive effects and formation of the stabilized
benzylic carbocation. Ring-closure and ring-opening steps then lead
to product 19. Thus, the entire transformation occurs in 11 reaction
steps (protonationedeprotonation steps included). Interestingly,
compound 22 provides the expected product 23 but a rearranged
product (24) is also formed in an almost equal amount. The scram-
bling of the methyl and phenethyl groups is somewhat unexpected
but it may occur by arene protonationealkyl shiftedeprotonation
mechanisms.9 This may also account for product 24.
Starting material
Product
Yielda (%)
98
99
96
89
Scheme 1.
99
a
Isolated yield.
picolines),6 so compound 5 provides substrate 6 from 1-tetralone.
When compound 6 is reacted in superacid, the benzo[f]quinolone
derivative (11) is formed in quantitative yield (Table 1). As expec-
ted, the tetraline ring system provided the 3-phenylpropyl sub-
stituent group. With the 1,4-benzodioxan derivative, cyclization
occurs at the 5-position to give product 12.7 Product 12 is likewise
formed in nearly quantitative yield with the 3-phenylpropyl sub-
stituent group. Utilization of a methoxy-substituted tetralone gives
alcohol 8 and reaction with superacid yields the benzo[f]quinolone
derivative (13) having the 3-(4-methoxyphenyl)propyl group. Re-
action of the indan-derivative (9) forms the phenethyl-substituted
benzo[f]quinolone (14) in good yield. Reaction of compound 10
leads to formation of a 2-phenethylphenyl-substituted benzo[f]
quinolone (15).
The conversions to aza-polycyclic aromatic compounds are
thought to occur by a series of reaction steps involving dicationic
intermediates (Scheme 1). Initial ionization of the pyridyl and hy-
droxyl groups leads to dication 16, which forms the spirocyclic in-
termediate. The superacidic media leads to protonation of arene
carbons8 so dication 17 is formed. This leads to ring opening and
product formation. Previously, we described chemistry leading to
aza-polycyclic aromatic compounds and a key step involved charge
migration.4a We have found that substrates may undergo charge
Scheme 2.
Although compound 9 does provide the desired phenethyl-
substituted arene (14), we have observed that ring-opening re-
actions with five-membered rings are very sluggish. Compound 9

A. Kethe et al. / Tetrahedron 68 (2012) 3357e3360
3359
produces the spirocyclic intermediate (25) quantitatively but for-
mation of the final product (14) requires an extended reaction
period. When compound 26 is reacted in CF3SO3H, product 27 is
formed but no ring-opened product could be isolated (even with
extended forcing conditions).
7.01e7.04 (m, 1H), 7.11e7.20 (m, 2H), 7.23e7.27 (m, 1H), 7.41 (br s,
1H), 7.51e7.55 (m, 2H), 8.56 (dd, J¼4.8, 1.78 Hz, 1H). 13C NMR
(75 MHz, CDCl3)
d (ppm): 20.0, 29.4, 36.2, 43.7, 64.3, 73.3, 117.2,
117.9, 121.3, 122.1, 126.0, 126.7, 127.1, 128.5, 132.2, 136.5, 138.0, 138.2,
142.7, 143.24, 143.26, 146.8, 157.4.
4.2.3. 6-Methoxy-1-((3-phenylpyridin-2-yl)methyl)-1,2,3,4-
tetrahydronaphthalen-1-ol (8). 1H NMR (300 MHz, CDCl3)
d (ppm):
1.28e1.36 (m, 1H), 1.64e1.79 (m, 3H), 2.49e2.78 (m, 2H), 3.18 (dd,
J¼40.1, 14.9 Hz, 2H), 3.76 (s, 3H), 6.52 (s, 1H), 6.72 (dd, J¼8.6, 2.5 Hz,
1H), 7.05e7.08 (m, 2H), 7.27e7.42 (m, 6H), 7.57 (dd, J¼7.7, 1.7 Hz,
1H), 8.52e8.60 (m, 1H). 13C NMR (75 MHz, CDCl3)
d (ppm): 20.1,
29.7, 36.4, 44.0, 55.2, 73.0, 112.2, 112.7, 121.4, 127.6, 128.3, 128.4,
129.0, 135.3, 137.9, 138.2, 138.5, 139.0, 147.1, 157.2, 158.2. Low-
resolution mass spectrum (EI): 327 (Mꢀ18), 326, 312, 282, 168.
High-resolution mass spectrum (EI), calcd for C23H21NO (Mꢀ18)
327.16232, found 327.16115.
3. Conclusion
In summary, we have observed the formation of functionalized
aza-polycyclic aromatic compounds from cyclization/ring-opening
reaction cascades. These reactions produce arenes with phenethyl
and 3-(aryl)propyl groups. The proposed mechanism involves
a series of dicationic intermediates.
4.2.4. 1-((3-Phenylpyridin-2-yl)methyl)-2,3-dihydro-1H-inden-1-ol
(9). 1H NMR (300 MHz, CDCl3)
d (ppm): 2.01e2.22 (m, 2H),
2.47e2.57 (m, 1H), 2.91 (ddd, J¼15.9, 8.40, 2.91 Hz, 1H), 3.1 (dd,
J¼39.3, 14.7 Hz, 2H), 6.75e6.78 (m, 2H), 6.84 (d, J¼7.5 Hz, 1H),
7.04e7.10 (m, 1H), 7.17e7.19 (m, 2H), 7.24e7.32 (m, 4H), 7.35 (br s,
1H), 7.74 (dd, J¼7.7, 1.8 Hz, 1H), 8.61 (dd, J¼4.9, 1.8 Hz, 1H). 13C NMR
4. Experimental section
(75 MHz, CDCl3)
d (ppm): 29.0, 40.7, 41.8, 83.4, 121.5, 123.1, 124.7,
126.3, 127.5, 127.7, 128.3, 128.8, 138.0, 138.3, 138.8, 142.2, 147.0,
4.1. Materials and methods
147.8, 157.1. Low-resolution mass spectrum (EI): 283 (Mꢀ18), 282,
267, 167, 154. High-resolution mass spectrum (EI), calcd for C21H17
N
Unless otherwise indicated, all reagents and chemical were
obtained from commercial suppliers. The trifluoromethanesulfonic
acid was distilled from an argon atmosphere prior to its use. All
reactions were done in oven-dried glassware with an inert atmo-
sphere (Ar). High-resolution mass spectral analyses were done by
an off-site analytical laboratory, while low-resolution mass spectra
were obtained directly from a gas chromatography instrument
equipped with a mass-selective detector.
(Mꢀ18) 283.13610, found 283.13673.
4.2.5. 1-((3-Phenylpyridin-2-yl)methyl)-dibenzosuberol
NMR (300 MHz, CDCl3) (ppm): 2.58e2.82 (m, 4H), 3.74 (s, 2H),
(10). 1H
d
6.84e6.87 (m, 2H), 6.96e6.99 (m, 2H), 7.09e7.18(m, 5H), 7.34e7.43
(m, 4H), 7.96e7.99 (m, 2H), 8.54 (dd, J¼4.8, 1.7 Hz, 1H). 13C NMR
(75 MHz, CDCl3)
d (ppm): 34.4, 46.4, 78.8, 121.5, 125.9, 126.9, 127.7,
128.0, 128.2, 129.5, 130.1, 137.9, 138.2, 138.6, 138.8, 144.1, 146.6,
156.2. Low-resolution mass spectrum (EI): 359 (Mꢀ18), 358, 208,
4.2. General synthetic method to prepare alcohol substrates
180,169,168. High-resolution mass spectrum (EI), calcd for C27H21N
(6e10, 20, 22)
(Mꢀ18) 359.16740, found 359.16550.
2-Methyl-3-phenylpyridine or 2,5-diphenyloxazole (2.3 mmol)
is dissolved in anhydrous Et2O (10 mL) and the solution is cooled to
ꢀ78 ꢁC. n-BuLi solution (2.5 mmol) is then added and the mixture is
stirred for 2 h. The ketone substrate (2.5 mmol, dissolved in 10 mL
of Et2O) is added and the mixture is stirred 16 h, during which time
the solution warms to 25 ꢁC. The mixture is then quenched with
H2O, diluted with Et2O, washed with brine, and dried over Na2SO4.
Concentration in vacuo provides a product, which is further puri-
fied by flash chromatography (hexane/ether).
4.3. General synthetic method to prepare functionalized
arenes (11e15, 19, 23, 24, 27)
The alcohol precursor (2 mmol) is dissolved in 2 mL of CHCl3, and
4 mL of CF3SO3H is added. After stirring overnight, the mixture is
poured over ice and the solution is made basic with 10 M NaOH. The
solution is then extracted with CHCl3 (3ꢂ30 mL) and the combined
organic extracts are washed with H2O (1ꢂ) and brine (2ꢂ). The
resulting solution is then dried with anhydrous Na2SO4. If necessary,
the product is purified by chromatography (hexane/ether).
4 . 2 . 1. 1 - ( ( 3 - P h e n y l p y r i d i n - 2 - y l ) m e t h y l ) - 1, 2 , 3 , 4 -
tetrahydronaphthalen-1-ol (6). 1H NMR (300 MHz, CDCl3)
d
(ppm):
4.3.1. 6-(3-Phenylpropyl)benzo[f]quinolone (11). 1H NMR (300 MHz,
1.29e1.38 (m, 1H), 1.67e1.83 (m, 3H), 2.5e2.6 (m, 1H), 2.7e2.8 (m,
1H), 3.19 (dd, J¼37, 15 Hz, 2H), 6.98e7.04 (m, 3H), 7.11e7.14 (m, 2H),
7.28e7.36 (m, 4H), 7.46e7.49 (m, 1H), 7.57 (dd, J¼7.7, 1.8 Hz, 1H), 8.6
CDCl3)
d
(ppm): 2.00e2.11 (m, 2H), 2.72 (t, J¼7.5 Hz, 2H), 3.09 (t,
J¼15.7 Hz, 2H), 7.10e7.23 (m, 5H), 7.64e7.69 (m, 3H), 7.93e7.97 (m,
1H), 8.11 (s, 1H), 8.55e8.58 (m, 1H), 8.84 (dd, J¼5.0, 1.3 Hz, 1H), 9.13
(dd, J¼4.9, 1.8 Hz, 1H). 13C NMR (75 MHz, CDCl3)
d
(ppm): 20.0, 29.3,
(d, J¼8.3 Hz, 1H). 13C NMR (75 MHz, CDCl3)
d (ppm): 31.5, 33.0, 35.8,
36.3, 43.8, 73.3,121.4,125.9,126.7, 127.0, 127.6,128.39,128.44,129.0,
136.4, 138.2, 138.5, 138.9, 142.7, 147.1, 157.2. Low-resolution mass
spectrum (EI): 297 (Mꢀ17), 296, 168, 167, 128. High-resolution mass
spectrum (EI), calcd for C22H19N (Mꢀ18) 297.15175, found 297.15028.
120.9, 121.5, 123.3, 125.1, 125.9, 126.0, 128.2, 128.5, 128.5, 128.7,
128.8, 131.1, 135.5, 141.5, 143.0, 144.1, 146.3. Low-resolution mass
spectrum (EI): 297 (Mþ), 204, 193, 91. High-resolution mass spec-
trum (EI), C22H19N calcd 297.15175, found 297.15220.
4.2.2. 1-((3-(2,3-Dihydrobenzo[b][1,4]dioxin-6-yl)pyridin-2-yl)
4.3.2. 6-(3-Phenylpropyl)-2,3-dihydrobenzo[b][1,4]dioxin[2,3-f]quin-
methyl)-1,2,3,4-tetrahydronaphthalen-1-ol (7). 1H NMR (300 MHz,
oline (12). 1H NMR (300 MHz, CDCl3)
d (ppm): 2.06 (m, 2H), 2.76 (t,
CDCl3)
d
(ppm): 1.20e1.52 (m, 1H), 1.67e1.82 (m, 3H), 2.56e2.84
J¼7.4 Hz, 2H), 2.99 (t, J¼7.5 Hz, 2H), 4.41 (s, 4H), 7.16e7.30 (m, 5H),
(m, 2H), 3.21 (dd, J¼31.2, 14.9 Hz, 2H), 4.27 (s, 4H), 6.50 (dd, J¼8.2,
7.38 (s, 1H), 7.97 (d, J¼8.37 Hz, 3H), 8.89 (s, 1H), 9.23 (d, J¼7.5 Hz,
2.07 Hz, 1H), 6.58 (d, J¼2.04 Hz, 1H), 6.83 (d, J¼21.6 Hz, 1H),
1H). 13C NMR (75 MHz, CDCl3)
d (ppm): 31.1, 33.3, 35.7, 64.6, 110.6,

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A. Kethe et al. / Tetrahedron 68 (2012) 3357e3360
112.0, 115.1, 121.0, 123.0, 126.1, 126.3, 126.6, 128.4, 128.4, 138.8, 139.1,
139.9, 141.2, 146.0, 146.3, 149.0. Low-resolution mass spectrum (EI):
355 (Mþ), 340, 326, 270, 254. High-resolution mass spectrum (EI),
C24H21NO2 calcd 355.15723, found 355.15859.
(m, 1H), 8.34e8.36 (m, 1H), 8.38e8.40 (m, 1H). 13C NMR (CDCl3,
125 MHz) (ppm): 13.8, 30.9, 36.5, 119.6, 120.9, 124.6, 125.4, 125.7,
126.2, 126.8, 127.3, 127.8, 128.4, 128.6, 128.9, 130.3, 130.9, 131.9,
139.1, 142.0, 143.6, 144.8, 161.8. Low-resolution mass spectrum (EI):
363 (Mþ), 272, 141, 115, 91. High-resolution mass spectrum (EI),
C26H21NO calcd 363.16232, found 363.16340.
d
4.3.3. 6-(3-(3-Methoxyphenyl)propyl)benzo[f]quinolone
NMR (300 MHz, CDCl3) (ppm): 2.00e2.11 (m, 2H), 2.72 (t,
(13). 1H
d
J¼7.44 Hz, 2H), 3.01 (t, J¼7.5 Hz, 2H), 3.72 (s, 3H), 6.66e6.70 (m,
2H), 6.76 (d, J¼7.6 Hz, 1H), 7.15 (t, J¼7.8 Hz, 1H), 7.68e7.79 (m, 2H),
7.91 (dd, J¼8.4, 5.3 Hz, 1H), 7.96e7.99(m, 1H), 8.18(s, 1H),
8.62e8.66(m, 1H), 9.01 (dd, J¼223.0, 8.78 Hz, 1H), 8.93 (dd, J¼5.2,
4.3.9. 20,30-Dihydro-5H-spiro[benzo[f]quinoline-6,10-indene]
(25). 1H NMR (300 MHz, CDCl)
d (ppm): 1.93e2.27 (m, 2H),
2.85e3.07 (m, 2H), 3.36 (dd, J¼122.5, 15.6 Hz, 2H), 6.81 (dd, J¼7.7,
1.0 Hz, 1H), 7.19e7.37 (m, 7H), 7.81 (d, J¼7.0 Hz, 1H), 8.08 (dd, J¼7.9,
2.3 Hz, 1H), 8.50 (dd, J¼4.8, 1.4 Hz, 1H). 13C NMR (75 MHz, CDCl3)
1 Hz, 1H). 13C NMR (75 MHz, CDCl3)
d (ppm): 31.3, 33.0, 35.8, 55.1,
111.4, 114.1, 118.7, 120.9, 121.3, 123.6, 125.2, 126.4, 128.0, 128.9, 129.4,
129.5, 130.9, 138.1, 140.6, 142.0, 142.9, 148.2, 159.6. Low-resolution
mass spectrum (EI): 327 (Mþ), 326, 298, 206, 193, 122. High-
resolution mass spectrum (EI), C23H21NO calcd 327.16232, found
327.16126.
d (ppm): 29.9, 39.3, 43.9, 52.7, 122.5, 124.1, 124.3, 124.8, 126.6, 126.8,
127.1, 127.4, 128.7, 129.7, 130.5, 132.0, 143.7, 144.7, 147.8, 148.1, 156.1.
Low-resolution mass spectrum (EI): 283 (Mþ), 282, 268, 254, 154.
High-resolution mass spectrum (EI), C21H17N calcd 283.13610,
found 283.13579.
4.3.4. 6-Phenethylbenzo[f]quinoline (14). 1H NMR (300 MHz, CDCl)
4.3.10. Compound 27. Yellow solid, mp: 225e227 ꢁC. 1H NMR
d
(ppm): 3.16e3.22 (m, 2H), 3.46e3.52 (m, 2H), 7.21e7.29 (m, 1H),
(CDCl3, 500 MHz)
d
(ppm): 3.51e3.56(q, J1¼15.7 Hz, J2¼7.2 Hz, 1H),
7.31e7.35 (m, 4H), 7.52e7.56 (m, 1H), 7.71e7.75 (m, 2H), 7.9 (s, 1H),
3.78 (d, J¼15.7 Hz, 1H), 4.15e4.18 (t, J¼7.4 Hz, 1H), 4.62 (d, J¼7.5 Hz,
1H), 6.94 (d, J¼7.5 Hz, 1H), 7.09e7.12 (t, J¼7.5 Hz, 1H), 7.16e7.19 (t,
J¼7.3 Hz, 1H), 7.29e7.51 (m, 7H), 7.57e7.58 (m, 1H), 8.08e8.10 (m,
8.20e8.24 (m, 1H), 8.69e8.72 (m, 1H), 8.93e8.96 (m, 2H). 13C NMR
(75 MHz, CDCl3) d (ppm): 35.3, 36.2, 120.9, 123.2, 124.4,124.7, 126.2,
126.8, 127.2, 127.4, 128.4, 128.5, 130.1, 130.4, 130.9, 140.5, 141.7, 148.1,
149.8. Low-resolution mass spectrum (EI): 283 (Mþ), 192, 191, 166,
91. High-resolution mass spectrum (EI), C21H17N calcd 283.13610,
found 283.13524.
2H). 13C NMR (CDCl3, 125 MHz)
d (ppm): 120.4, 123.9, 124.7, 125.1,
126.3,126.4,127.2,127.3,127.5,128.7,129.4,130.2,135.0,138.1,141.6,
144.0, 145.7, 161.0. Low-resolution mass spectrum (EI): 355 (Mþ),
231, 202, 166. High-resolution mass spectrum (EI), C24H17NO calcd
335.13102, found 335.13152.
4.3.5. 6-(2-Phenethylphenyl)benzo[f]quinoline
(15). 1H
NMR
(300 MHz, CDCl) (ppm): 2.67e2.85 (m, 4H), 6.82e6.85 (m, 2H),
d
Acknowledgements
7.08e7.11 (m, 3H), 7.35e7.49 (m, 4H), 7.54e7.63 (m, 3H), 7.69e7.75
(m, 1H), 7.75 (s, 1H), 8.73 (d, J¼8.3 Hz, 1H), 9.01e9.05 (m, 2H). 13C
We gratefully acknowledge the support of the National Science
Foundation (CHE-0749907) and the NIH-National Institute of
General Medical Sciences (GM085736-01A1).
NMR (75 MHz, CDCl3) d (ppm): 35.5, 37.5, 121.4, 122.9, 125.2, 125.8,
126.1, 127.1, 127.3, 127.4, 128.2, 128.2, 128.3, 128.7, 129.3, 129.8,
130.5, 130.6, 131.6, 139.2, 140.3, 141.6, 142.1, 147.7, 150.1. Low-
resolution mass spectrum (EI): 359 (Mþ), 268, 267, 254, 91. High-
resolution mass spectrum (EI), C27H21N calcd 359.16740, found
359.16616.
Supplementary data
Characterization data for compounds 6e10, 1H and 13C NMR
spectra for compounds 11e15, 23e25, and 27. Supplementary data
associated with this article can be found in the online version, at
doi:10.1016/j.tet.2012.02.047.
4.3.6. 2-Phenyl-4-(2-phenylethyl)naphtho[2,1-d]oxazole
(19). Yellow solid, mp: 145e147 ꢁC. 1H NMR (CDCl3, 500 MHz)
d
(ppm): 3.27e3.20 (t, J¼8.1 Hz, 2H), 3.49e3.52 (t, J¼8.1 Hz, 2H),
7.24e7.26 (m, 1H), 7.32e7.36 (m, 4H), 7.52e7.63 (m, 6H), 7.91 (d,
J¼8.1 Hz, 1H), 8.30 (d, J¼8.1 Hz, 1H), 8.40e8.41 (m, 2H). 13C NMR
References and notes
(CDCl3, 125 MHz)
d (ppm): 33.6, 36.3, 119.3, 120.1, 123.4, 125.6,
126.0, 127.4, 127.8, 128.2, 128.4, 128.6, 128.9, 131.0, 131.8, 132.8,
138.7, 142.1, 143.6, 146.3, 162.0. Low-resolution mass spectrum (EI):
349 (Mþ), 259, 258, 127, 91. High-resolution mass spectrum (EI),
C25H19NO calcd 349.14667, found 349.14608.
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4.3.7. 5-Methyl-2-phenyl-4-(2-phenylethyl)naphtho[2,1-d]oxazole
(23). Yellow solid, mp: 165e167 ꢁC. 1H NMR (CDCl3, 500 MHz)
d
(ppm): 2.65 (s, 3H), 3.09e3.12 (m, 2H), 3.58e3.61 (m, 2H),
3. (a) Cai, Q.; Li, Z.; Wei, J.; Fu, L.; Ha, C.; Pei, D.; Din, K. Org. Lett. 2010, 12, 1500; (b)
Bandini, M.; Eichholzer, A.; Monari, M.; Piccinelli, F.; Umani-Ronchi, A. Eur. J. Org.
Chem. 2007, 2917; (c) Pratap, R.; Ram, V. J. Tetrahedron Lett. 2007, 48, 5039; (d)
Hewlins, M. J. E.; Salter, R. Synthesis 2007, 2164.
4. (a) Li, A.; Gilbert, T. M.; Klumpp, D. A. J. Org. Chem. 2008, 73, 3654; (b) Li, A.;
Kindelin, P. J.; Klumpp, D. A. Org. Lett. 2006, 8, 1233.
7.26e7.27 (m, 1H), 7.33e7.37 (m, 4H), 7.57e7.64 (m, 5H), 8.14 (d,
J¼8.4 Hz, 1H), 8.34 (d, J¼8.7 Hz, 1H), 8.39e8.41 (m, 2H). NOE en-
hancement observed between d 2.65 (CH3) and d
8.14 (CH). 13C NMR
(CDCl3, 125 MHz) d (ppm): 14.4, 30.8, 36.6, 119.5, 120.6, 125.2, 125.5,
125.6, 125.9, 127.4, 128.3, 128.6, 128.8, 130.4, 130.8, 131.3, 138.7,
142.2, 144.9, 161.7. Low-resolution mass spectrum (EI): 363 (Mþ),
272, 141, 115, 91. High-resolution mass spectrum (EI), C26H21NO
calcd 363.16232, found 363.16305.
5. (a) Suzuki, A. Chem. Commun. 2005, 4759; (b) Pasquinet, E.; Rocca, P.; Richalot, S.;
ꢀ
ꢀ
ꢀ
Gueritte, F.; Guenard, D.; Godard, A.; Marsais, F.; Queguiner, G. J. Org. Chem. 2001,
66, 2654.
6. Kim, Y. H.; Kim, T. H.; Kim, N. Y.; Cho, E. S.; Lee, B. Y.; Shin, D. M.; Chung, Y. K.
Organometallics 2003, 22, 1503.
7. The structural assignment for compound 14 was aided by comparison to
a closely related system prepared recently in our research group (see Ref. 4a).
8. Olah, G. A.; Prakash, G. K. S.; Molnar, A.; Sommer, J. Superacid Chemistry, 2nd ed.;
Wiley & Sons: New York, NY, 2009.
9. Li, A.; DeSchepper, D.; Klumpp, D. A. Tetrahedron Lett. 2009, 50, 1924; See also:
Xu, D.; Penning, T. M.; Blair, I. A.; Harvey, R. G. J. Org. Chem. 2009, 74, 597.
4.3.8. 4-Methyl-2-phenyl-5-(2-phenylethyl)naphtho[2,1-d]oxazole
(24). Yellow solid, mp: 126e128 ꢁC. 1H NMR (CDCl3, 500 MHz)
d
(ppm): 2.76 (s, 3H), 3.00e3.03 (m, 2H), 3.47e3.50 (m, 2H),
7.31e7.35 (m, 3H), 7.38e7.41 (m, 2H), 7.58e7.64 (m, 5H), 8.22e8.23