Generation of biradicals and subsequent formation of quinolines and 5H- benzo[b]carbazoles from N-[2-(1-Alkynyl)phenyl]ketamines

Full text of DOI:10.1021/jo9804285

J . Org. Chem. 1998, 63, 3517-3520
3517
Sch em e 1
Gen er a tion of Bir a d ica ls a n d Su bsequ en t
F or m a tion of Qu in olin es a n d
5H-Ben zo[b]ca r ba zoles fr om
N-[2-(1-Alk yn yl)p h en yl]k eten im in es
Chongsheng Shi and Kung K. Wang*
Department of Chemistry, West Virginia University,
Morgantown, West Virginia 26506-6045
Sch em e 2
Received March 9, 1998
In tr od u ction
The biradical-forming cycloaromatization reactions
have attracted considerable attention in recent years.1,2
This is due mainly to the discovery of several very potent
antitumor antibiotics which cleave DNA via generation
of biradicals under mild conditions.3 Among the ther-
mally induced biradical-forming reactions, the Bergman
cyclization of (Z)-3-hexene-1,5-diynes (enediynes) to 1,4-
didehydrobenzenes and the Myers cyclization of (Z)-1,2,4-
heptatrien-6-ynes (enyne-allenes) to R,3-didehydrotolu-
enes have been investigated extensively. The Moore
cyclization of enyne-ketenes provides easy access to
biradicals having an aryl and a phenoxy radical center.4
While several synthetic pathways to enyne-ketenes and
their versatility as reactive intermediates have been
reported, the biradical-forming reactions involving other
heteroatoms in the conjugated system remained virtually
unexplored. Attempts to generate biradical 2 and sub-
sequently 2-isopropylpyridine by thermolysis of 1 in C6D6
containing an excess of 1,4-cyclohexadiene (1,4-CHD) as
a hydrogen-atom donor were unsuccessful (Scheme 1).5a
A similar attempt to involve the nitrile group in a
biradical-forming reaction also failed.5b Interestingly,
when C,N-dialkynyl imines 3 were heated in refluxing
benzene, enynyl nitriles 5 were produced in excellent
yields presumably through the putative 2,5-didehydro-
pyridines 4, which could not be captured by 1,4-CHD or,
in the case of 4b, by the carbon-carbon double bond
intramolecularly (Scheme 2).6a Recently, it was observed
that a very small amount of 4a could be captured to
produce 2-methyl-4,5-diphenylpyridine when the reaction
was conducted in the presence of moderate amounts of a
protic acid.6b We now report successful examples of
generating and trapping the biradicals produced from
cycloaromatization of N-[2-(1-alkynyl)phenyl]ketenimines
having a nitrogen atom in the conjugated system.
Sch em e 3
titative yields.7 Treatment of 6 with Ph3PBr2 gave the
iminophosphoranes 7 (Scheme 3).8a The aza-Wittig
reaction8b between 7a (R ) H) and diphenylketene9 was
carried out in benzene containing a large excess of 1,4-
CHD at 0 °C followed by reflux for 2 h to furnish the
quinoline 10a (R ) H) in 49% yield. Apparently, the
reaction proceeded through an initial formation of the
ketenimine 8a followed by cycloaromatization to produce
the biradical 9a and subsequently 10a .
Attempts to isolate 8a resulted in its decomposition
after the solvent was removed. However, the IR spec-
trum taken immediately after 7a was treated with
diphenylketene in C6D6 containing an excess of 1,4-CHD
exhibited an intense absorption at 2002 cm-1, attribut-
Resu lts a n d Discu ssion
The Pd-catalyzed cross-coupling reactions between
2-iodoaniline and 1-alkynes furnished 6 in nearly quan-
1
able to 8a . The H NMR spectrum of the same solution
(1) (a) Wang, K. K. Chem. Rev. 1996, 96, 207-222. (b) Grissom, J .
W.; Gunawardena, G. U.; Klingberg, D.; Huang, D. Tetrahedron 1996,
52, 6453-6518. (c) Wang, K. K.; Wang, Z.; Tarli, A.; Gannett, P. J .
Am. Chem. Soc. 1996, 118, 10783-10791.
also showed the disappearance of the acetylenic C-H
signal of 7a at δ 3.26 and the appearance of a new signal
at δ 2.86, attributable to the acetylenic C-H of 8a . The
rate of disappearance of 8a and appearance of 10a was
(2) (a) Wang, Y.; Finn, M. G. J . Am. Chem. Soc. 1995, 117, 8045-
8046. (b) Miyawaki, K.; Suzuki, R.; Kawano, T.; Ueda, I. Tetrahedron
Lett. 1997, 38, 3943-3946.
(3) Maier, M. E. Synlett 1995, 13-26.
(7) (a) Villemin, D.; Goussu, D. Heterocycles 1989, 29, 1255-1261.
(b) Arcadi, A.; Cacchi, S.; Marinelli, F. Tetrahedron Lett. 1989, 30,
2581-2584. (c) Iritani, K.; Matsubara, S.; Utimoto. K. Tetrahedron Lett.
1988, 29, 1799-1802.
(8) (a) Molina, P.; Alajarin, M.; Vidal, A. J . Chem. Soc., Chem.
Commun. 1990, 1277-1279. (b) Molina, P.; Alajarin, M.; Vidal, A.;
Sanchez-Andrada, P. J . Org. Chem. 1992, 57, 929-939.
(9) Taylor, E. C.; McKillop, A.; Hawks, G, H. Org. Synth. 1972, 52,
36-38.
(4) (a) Moore, H. W.; Yerxa, B. R. Chemtracts 1992, 273-313. (b)
Tarli, A.; Wang, K. K. J . Org. Chem. 1997, 62, 8841-8847.
(5) (a) Wang, K. K.; Wang, Z.; Sattsangi, P. D. J . Org. Chem. 1996,
61, 1516-1518. (b) Gillmann, T.; Heckhoff, S. Tetrahedron Lett. 1996,
37, 839-840.
(6) (a) David, W. M.; Kerwin, S. M. J . Am. Chem. Soc. 1997, 119,
1464-1465. (b) Hoffner, J .; Schottelius, M. J .; Feichtinger, D.; Chen,
P. J . Am. Chem. Soc. 1998, 120, 376-385.
S0022-3263(98)00428-9 CCC: $15.00 © 1998 American Chemical Society
Published on Web 04/23/1998

3518 J . Org. Chem., Vol. 63, No. 10, 1998
Notes
Sch em e 4
Sch em e 5
0.186 ( 0.004 h-1, t1/2 ) 3.73 h at 72 °C). With the
absence of an apparent proton source, it is also unlikely
that the reaction could proceed through a cationic reac-
tion mechanism involving an initial protonation of the
nitrogen atom in 8b.
When 8c (R ) SiMe3) was heated under refluxing
benzene, the benzocarbazole 13c was produced (k ) 0.78
( 0.06 h-1, t1/2 ) 0.89 h at 72 °C). Again the ability of
the trimethylsilyl group in stabilizing the adjacent radical
site in 11c13 along with the arising of nonbonded interac-
tions in 9c direct the reaction toward 13c. Thermolysis
of 8d (R ) Pr) in refluxing 1,4-CHD furnished the
quinoline 10d (58%) and the benzocarbazole 13d (33%)
1
monitored with IR and H NMR. The reaction exhibited
clean first-order behavior over three half-lives with k )
1.87 ( 0.04 h-1 (t1/2 ) 0.37 h) at 22 °C.
Treatment of 7b with diphenylketene furnished 8b ,
which was isolated in 71% yield. Interestingly, thermoly-
sis of 8b in refluxing benzene gave the benzocarbazole
13b in 98% yield. The cascade sequence outlined in
Scheme 3 with an initial formation of a five-membered
ring to produce biradical 11b followed by an intramo-
lecular radical-radical combination to form 12b and a
subsequent tautomerization could account for the forma-
tion of 13b. The greater stability of the vinyl radical site
in 11b because of the presence of a tert-butyl substituent
along with the emergence of severe nonbonded steric
interactions between the tert-butyl group at the C-3
position and the substituent at the C-2 position of the
quinoline biradical 9b (R ) tert-butyl) are probably
responsible for directing the reaction toward 11b. Such
a preference resembles the formation of the five-mem-
bered ring biradicals in several analogous cases of ring
closures of enyne-ketenes10 and enyne-allenes.11
(k of the disappearance of 8d ) 1.01 ( 0.11 h-1, t1/2
)
0.69 h at 52 °C). Apparently, the reaction could proceed
through biradicals 9d and 11d with comparable ef-
ficiency. If one compares the rate of formation of 13d (k
) 0.36 h-1, t1/2 ) 1.93 h at 52 °C) with that of 13b, the
steric factors do not appear to affect the rate of reaction
dramatically, again contrary to what would be expected
of a concerted Diels-Alder mechanism. When 7e (R )
Ph) was treated with diphenylketene at room tempera-
ture for 1 h, the benzocarbazole 13e (93%) was produced
exclusively. Presumably because the phenyl substituent
can further stabilize the vinyl radical site in 11e, the
ketenimine 8e was thermally labile and was readily
converted to 13e.
Alternatively, the ketenimines 8 could also be produced
in situ by dehydration of 18 with P2O5 in refluxing
pyridine,14 leading to 10a (34%), 10d (35%), 13d (31%),
and 13e (70%) (Scheme 5). In the case of 18c (R )
SiMe3), the resulting benzocarbazole 13c is prone to
protodesilylation under the reaction condition, and a
significant amount of the desilylated adduct 13a (R )
H) was produced. Treatment of the reaction mixture
with 1 N HCl at 40 °C for 1 h completely converted 13c
to 13a , which was isolated in an overall yield of 81% from
18c. It is interesting to note that 13a could not be
prepared directly from 18a or 7a , which leads to the
quinoline 10a . By starting from 19, derived from acyla-
tion of 6d with phenylacetyl chloride (97% yield), the
benzocarbazole 20 was produced in 27% isolated yield (eq
1).
Alternatively, a one-step intramolecular Diels-Alder
reaction of 8b could also produce 12b8b,12 as reported
previously by Differding and Ghosez in an elegant
synthesis of carbazoles 17 by using 14 to generate in situ
the acetylenic vinylketenimines 15 (Scheme 4).12a How-
ever, unlike 15, a sterically demanding tert-butyl group
is at the acetylenic terminus of 8b. Examination of the
molecular model for the transformation from 8b to 12b
via the Diels-Alder mechanism reveals the emergence
of severe nonbonded steric interactions in the transition
state between the tert-butyl group and the phenyl groups
at the ketenimine terminus, making the concerted pro-
cess highly unlikely. On the other hand, the two-step
biradical mechanism permits the sterically demanding
tert-butyl group to bend away in the first step, greatly
reducing the steric interactions and allowing the reaction
to occur under relatively mild thermal conditions (k )
(10) Foland, L. D.; Karlsson, J . O.; Perri, S. T.; Schwabe, R.; Xu, S.
L.; Patil, S.; Moore, H. W. J . Am. Chem. Soc. 1989, 111, 975-989.
(11) (a) Schmittel, M.; Strittmatter, M.; Kiau, S. Angew. Chem., Int.
Ed. Engl. 1996, 35, 1843-1845. (b) Schmittel, M.; Kiau, S.; Siebert,
T.; Strittmatter, M. Tetrahedron Lett. 1996, 37, 7691-7694. (c)
Schmittel, M.; Strittmatter, M.; Vollmann, K.; Kiau, S. Tetrahedron
Lett. 1996, 37, 999-1002. (d) Schmittel, M.; Maywald, M.; Strittmatter,
M. Synlett 1997, 165-166. (e) Schmittel, M.; Strittmatter, M.; Kiau,
S. Tetrahedron Lett. 1995, 36, 4975-4978. (f) Gillmann, T.; Hulsen,
T.; Massa, W.; Wocadlo, S. Synlett 1995, 1257-1259. (g) Garcia, J . G.;
Ramos, B.; Pratt, L. M.; Rodriguez, A. Tetrahedron Lett. 1995, 36,
7391-7394.
Con clu sion s
In summary, ketenimines 8 having a nitrogen atom
in the conjugated system could serve as excellent precur-
(12) (a) Differding, E.; Ghosez, L. Tetrahedron Lett. 1985, 26, 1647-
1650. (b) Molina, P.; Lopez-Leonardo, C.; Alcantara, J . Tetrahedron
1994, 50, 5027-5036.
(13) Wilt, J . W.; Aznavoorian, P. M. J . Org. Chem. 1978, 43, 1285-
1286.
(14) Stevens, C. L.; Singhal, G. H. J . Org. Chem. 1964, 29, 34-37.

Notes
J . Org. Chem., Vol. 63, No. 10, 1998 3519
solution of 0.097 g of diphenylketene (0.50 mmol) in 2.0 mL of
C6D6 and 1.5 mL of 1,4-CHD at 22 °C. The rate of disappearance
of 8a and appearance 10a was monitored with IR (cell thickness
) 0.11 mm) and 1H NMR.
sors for generation of biradicals. Because of prevalence
of the amide functionality in biological systems, struc-
tures similar to those of 18 are particularly attractive
for the development of new DNA-cleaving agents. The
cascade sequences outlined in Schemes 3 and 5 also
provide alternative pathways to quinolines and 5H-
benzo[b]carbazoles.8b,15
Preparation of 10a by the dehydration method was carried
out in a 100-mL flask containing 0.400 g of 18a (1.29 mmol), 2
g of Florisil, 1.10 g of P2O5 (7.72 mmol), 30 mL of pyridine, and
1.66 mL of γ-terpinene (10.3 mmol), and the reaction flask was
flushed with nitrogen. The mixture was stirred vigorously and
heated under reflux (oil bath temperature 135 °C) for 16 h before
it was allowed to cool to room temperature. The liquid phase
was filtered through a short Florisil column using dry pyridine
as eluent. The residue in the flask was extracted with dry
pyridine (3 × 15 mL), and the combined pyridine extracts were
passed through the same Florisil column. The combined pyri-
dine solutions were concentrated in vacuo. The residue was
purified by column chromatography (silica gel/5-20% of diethyl
ether in hexanes). The eluent was allowed to evaporate slowly
to furnish 0.128 g of 10a (0.434 mmol, 34%) as yellow crystals:
Exp er im en ta l Section
Gen er a l. The 2-(1-alkynyl)anilines 6 (83-98% yield) were
prepared according to the reported procedures.7 Diphenylketene
was prepared by dehydrochlorination of diphenylacetyl chloride
as
reported
previously.9
2-Iodo-
aniline was purchased from Oakwood Products, Inc. and was
used as received. 1-Alkynes were obtained from Farchan
Laboratories, Inc. and were used without further purification.
Dibromotriphenylphosphorane (Ph3PBr2), phenylacetyl chloride,
diphenylacetyl chloride, Pd(PPh3)2Cl2, 1,4-CHD, and γ-terpinene
were purchased from Aldrich. Pyridine and triethylamine were
distilled over CaH2 prior to use. The kinetic studies were carried
out in a constant-temperature bath ((0.5 °C). Melting points
are uncorrected. 1H (270 MHz) and 13C (67.9 MHz) NMR spectra
mp 104-105 °C; IR (KBr) 1594, 1495, 824, 756, 719, 698 cm-1
;
1H δ 8.09 (1 H, d, J ) 8.3 Hz), 8.07 (1 H, d, J ) 8.3 Hz), 7.79 (1
H, dd, J ) 8.2 and 1.1 Hz), 7.70 (1 H, tm, J ) 7.7 and 1.6 Hz),
7.51 (1 H, tm, J ) 7.5 and 1.1 Hz), 7.35-7.20 (11 H, m), 5.94 (1
H, s); 13C δ 163.07, 147.85, 142.59 (2 carbons), 136.29, 129.41,
129.34, 128.40, 127.44, 126.78, 126.55, 126.20, 121.91, 60.08; MS
m/z 295 (M+), 294, 218, 217, 216, 165. Anal. Calcd for
were recorded in CDCl3 using CHCl3 (1H δ 7.26) or CDCl3
δ 77.00) as the internal standard.
(
13C
C
22H17N: C, 89.46; H, 5.80; N, 4.74. Found: C, 89.26; H, 5.79;
N, 4.73.
6-P h en yl-5H-ben zo[b]ca r ba zole (13a ). Preparation of 13a
2 -E t h y n y l -N -(t r i p h e n y l p h o s p h o r a n y l i d e n e )b e n -
zen a m in e (7a ).8b Iminophosphorane 7a was prepared accord-
ing to the reported procedure.8a To 3.798 g of Ph3PBr2 (9.00
mmol) was added a mixture of 1.053 g of 2-ethynylaniline (6a ,
9.00 mmol) and 2.5 mL of anhydrous triethylamine in 100 mL
of anhydrous benzene via cannula under a nitrogen atmosphere.
The reaction mixture was heated under reflux for 4 h. The white
triethylammonium bromide precipitate was removed by filtra-
tion, and the filtrate was concentrated in vacuo. The residue
was purified through a short column (silica gel/40-60% diethyl
ether in hexanes) to furnish 2.239 g (5.94 mmol, 66%) of 7a as
colorless crystals: mp 142-143 °C (lit.8b 141 °C); IR (KBr) 3279,
by the dehydration method was carried out by using the same
procedure described for 10a except that a mixture of 0.766 g of
18c (2.00 mmol), 4 g of Florisil, 1.70 g of P2O5 (12.0 mmol), 50
mL of pyridine, and 0.80 mL of 1,4-CHD (8.5 mmol) was used.
A mixture of 13c and 13a was isolated by column chromatog-
raphy (silica gel/5-20% diethyl ether in hexanes). Treatment
of the mixture of 13c and 13a in 5 mL of dichloromethane with
3.0 mL of 1 N HCl at 40 °C for 1 h converted all of 13c to the
corresponding desilylated adduct 13a . Purification by column
chromatography (silica gel/20% diethyl ether in hexanes) fol-
lowed by recrystallization from 10% of diethyl ether in hexanes
furnished 0.475 g of 13a (1.62 mmol, 81%) as pale yellow
crystals: IR (KBr) 3400, 751, 693 cm-1; 1H δ 8.60 (1 H, s), 8.24
(1 H, d, J ) 7.7 Hz), 8.15-8.10 (1 H, m), 7.87-7.84 (1 H, m),
7.82 (1 H, br s, NH), 7.68-7.52 (5 H, m), 7.50-7.41 (3 H, m),
7.34-7.25 (2 H, m); 13C δ 141.84, 137.64, 136.76, 130.74, 130.64,
129.22, 128.75, 128.61, 127.81, 127.34, 125.16, 124.96, 124.44,
123.35, 122.63, 121.15, 119.44, 118.32, 118.10, 110.22; MS m/z
293 (M+), 146.
1
2094, 1584, 1479, 1436, 1368, 1110, 750, 715 cm-1; H δ 7.88-
7.80 (6 H, m), 7.56-7.39 (10 H, m), 6.87 (1 H, td, J ) 7.7 and
1.6 Hz), 6.59 (1 H, t, J ) 7.4 Hz), 6.47 (1 H, d, J ) 8.1 Hz), 3.34
(1 H, s); 13C δ 153.57, 133.57, 132.61 (d, J ) 9.8 Hz), 131.63 (d,
J ) 2.6 Hz), 130.92 (d, J ) 99.7 Hz), 128.82, 128.49 (d, J ) 11.9
Hz), 121.19 (d, J ) 9.8 Hz), 117.23 (d, J ) 23.2 Hz), 116.80,
85.12, 79.22.
Keten im in e 8b. To a solution of 0.433 g of 7b (1.00 mmol)
in 30 mL of anhydrous diethyl ether was introduced 0.194 g of
diphenylketene (1.00 mmol) in 5 mL of anhydrous diethyl ether
via cannula at 0 °C under a nitrogen atmosphere. The reaction
mixture was stirred for 10 min before it was allowed to warm
to room temperature. After 1 h, the reaction mixture was
concentrated in vacuo. The residue was purified by column
chromatography (silica gel/5-10% diethyl ether in hexanes) to
furnish 0.248 g (0.71 mmol, 71%) of 8b as a yellow oil: IR (neat)
2000, 1594, 1491, 758, 693 cm-1; 1H δ 7.49-7.16 (14 H, m), 1.25
(9 H, s); 13C δ 188.80, 141.29, 134.16, 133.73, 128.74, 128.42,
127.89, 126.91, 126.21, 123.43, 119.68, 105.25, 76.47, 75.70,
30.78, 28.19; MS m/z 349 (M+).
2-(Dip h en ylm eth yl)qu in olin e (10a ). To 0.189 g of 7a (0.50
mmol) was added a mixture of 0.097 g of diphenylketene (0.50
mmol) and 2.9 mL of 1,4-CHD in 4 mL of anhydrous benzene
via cannula at 0 °C under a nitrogen atmosphere. After 10 min,
the reaction mixture was allowed to warm to room temperature
for 1 h and then was heated under reflux for 2 h. The reaction
mixture was concentrated in vacuo, and the residue was purified
by column chromatography (silica gel/5-20% of diethyl ether
in hexanes). The eluent was allowed to evaporate slowly to
furnish 0.072 g of 10a (0.244 mmol, 49%) as yellow crystals.
The rate of reaction was determined by using a solution
obtained from treatment of 0.189 g of 7a (0.50 mmol) with a
11-ter t-Bu t yl-6-p h en yl-5H -b en zo[b]ca r b a zole (13b ).
A
solution of 0.150 g of 8b (0.43 mmol) in 3 mL of anhydrous
benzene was heated under reflux for 24 h. Benzene was allowed
to evaporate slowly to afford 0.147 g of 13b (0.42 mmol, 98%) as
yellow crystals: mp 132-133 °C; IR (KBr) 3410, 1601, 1462, 747,
1
699 cm-1; H δ 8.81 (1 H, dd, J ) 8.0 and 2.2 Hz), 8.43 (1 H, d,
J ) 8.1 Hz), 7.78 (1 H, br, NH), 7.75-7.71 (1 H, m), 7.67-7.54
(5 H, m), 7.44-7.20 (5 H, m), 2.06 (9 H, s); 13C δ 143.17, 141.79,
138.44, 137.08, 131.46, 131.00, 129.27, 128.68, 127.77, 127.32,
127.07, 126.33, 124.60, 124.12, 124.06, 123.66, 120.07, 118.31,
116.93, 109.93, 38.55, 33.63; MS m/z 349 (M+), 334, 293, 241,
146, 57; HRMS calcd for C26H23N 349.1831, found 349.1827. The
rate of reaction was determined by conducting the reaction in
C6D6 and using 1H NMR to monitor the disappearance of 8b
and the appearance of 13b at 72 °C.
6-P h en yl-11-(tr im eth ylsilyl)-5H-ben zo[b]ca r ba zole (13c).
A mixture of 0.183 g of 8c (0.50 mmol) in 3 mL of anhydrous
benzene was heated under reflux for 24 h. The reaction mixture
was then concentrated in vacuo, and the residue was purified
by column chromatography (silica gel/5-20% diethyl ether in
hexanes). The eluent was allowed to evaporate slowly to afford
0.163 g of 13c (0.447 mmol, 89%) as pale yellow crystals: mp
1
153-154 °C; IR (KBr) 3403, 1260, 847, 769, 748, 702 cm-1; H
δ 8.60-8.53 (1 H, m), 8.33 (1 H, d, J ) 7.9 Hz), 7.83 (1 H, br s,
NH), 7.82-7.77 (1 H, m), 7.67-7.52 (5 H, m), 7.47-7.36 (3 H,
m), 7.32 (1 H, d, J ) 7.9 Hz), 7.23 (1 H, tm, J ) 7.9 and 1.1 Hz),
0.78 (9 H, s); 13C δ 142.27, 137.01, 136.82, 133.31, 132.29. 131.40,
130.77, 130.20, 129.53, 129.27, 127.92, 126.92, 126.53, 124.89,
124.53, 123.81, 121.67, 119.73, 118.33, 110.06, 3.47; MS m/z 365
(15) (a) Pindur, U.; Haber, M.; Erfanian-Abdoust, H. Heterocycles
1992, 34, 781-790. (b) Pindur, U.; Erfanian-Abdoust, H. Chem. Rev.
1989, 89, 1681-1689. (c) Gribble, G. W.; Saulnier, M. G.; Obaza-
Nutaitis, J . A.; Ketcha, D. M. J . Org. Chem. 1992, 57, 5891-5899. (d)
Sha, C.-K.; Chuang, K.-S.; Wey, S.-J . J . Chem. Soc., Perkin Trans. 1
1987, 977-980.

3520 J . Org. Chem., Vol. 63, No. 10, 1998
Notes
(M+), 350. Anal. Calcd for C25H23NSi: C, 82.14; H, 6.34; N, 3.83.
Found: C, 82.26; H, 6.42; N, 3.80. The rate of reaction was
determined by conducting the reaction in C6D6 and using 1H
NMR to monitor the disappearance of 8c and the appearance of
13c at 72 °C.
N-[2-(P h en yleth yn yl)p h en yl]p h en yla ceta m id e (19). The
same procedure was repeated as described for 18a except that
a mixture of 0.965 g of 2-(phenylethynyl)aniline (6e, 5.00 mmol),
0.70 mL of phenylacetyl chloride (0.82 g, 5.3 mmol), and 1.4 mL
of triethylamine in 20 mL of diethyl ether was stirred at room
temperature for 3 h to afford 1.512 g (4.86 mmol, 97%) of 19 as
colorless crystals: IR (KBr) 3300, 1664, 756, 688 cm-1; 1H δ 8.45
(1 H, d, J ) 8.3 Hz), 7.96 (1 H, br s), 7.44-7.29 (9 H, m), 7.15 (2
H, tm, J ) 7.2 and 1.0 Hz), 7.09-7.01 (2 H, m), 3.80 (2 H, s);
13C δ 169.21, 138.67, 133.86, 131.87, 131.79, 129.64, 129.50,
129.18, 128.85, 128.28, 127.65, 123.52, 122.19, 119.29, 112.00,
95.92, 83.60, 45.39; MS m/z 311 (M+), 220, 193, 165, 91.
6,11-Dip h en yl-5H-ben zo[b]ca r ba zole (13e). To a solution
of 0.453 g of 7e (1.00 mmol) in 30 mL of anhydrous diethyl ether
was introduced 0.194 g of diphenylketene (1.00 mmol) in 5 mL
of anhydrous diethyl ether at 0 °C. The reaction mixture was
allowed to warm to room temperature and was stirred for 1 h.
At this point, the benzocarbazole 13e had already formed. The
reaction mixture was concentrated in vacuo, and the residue was
purified by column chromatography (silica gel/5-20% diethyl
ether in hexanes). The eluent was allowed to evaporate slowly
to afford 0.343 g of 13e (0.93 mmol, 93%) as pale yellow crystals.
Preparation of 13e by the dehydration method was carried
out by using the same procedure described for 10a except that
a mixture of 0.724 g of 18e (1.87 mmol), 3 g of Florisil, 1.59 g of
P2O5 (11.2 mmol), 40 mL of pyridine, and 0.71 mL of 1,4-CHD
(7.5 mmol) was used. Purification by column chromatography
afforded 0.483 g of 13e (1.31 mmol, 70%) as pale yellow
11-P h en yl-5H-ben zo[b]ca r ba zole (20). The same dehydra-
tion procedure was repeated as described for 10a except that a
mixture of 0.622 g of 19 (2.00 mmol), 3 g of Florisil, 1.42 g of
P2O5 (10.0 mmol), 30 mL of triethylamine, and 0.57 mL of 1,4-
CHD (6.0 mmol) was used. The reaction mixture was heated
under reflux for 40 h. Purification by column chromatography
followed by recrystallization afforded 0.157 g of 20 (0.54 mmol,
27%) as pale yellow crystals: IR (KBr) 3408, 748, 704 cm-1; 1H
δ 8.00 (1 H, br s, NH), 7.97 (1 H, d, J ) 8.3 Hz), 7.79 (1 H, s),
7.73 (1 H, d, J ) 8.5 Hz), 7.68-7.60 (3 H, m), 7.55-7.45 (3 H,
m), 7.39-7.36 (2 H, m), 7.31 (1 H, tm, J ) 7.6 and 1.2 Hz), 6.96-
6.87 (2 H, m); 13C δ 142.15, 138.92 (2 carbons), 133.87, 132.55,
130.13, 128.90, 127.78, 127.51, 126.97, 126.90, 126.34, 125.00,
123.60, 123.29, 123.11, 122.68, 119.15, 109.87, 104.73; MS m/z
293 (M+), 146.
1
crystals: mp 241-242 °C; IR (KBr) 3451, 754, 702 cm-1; H δ
7.88 (1 H, d, J ) 8.7 Hz), 7.85 (1 H, br s, NH), 7.80 (1 H, d, J )
8.5 Hz), 7.70-7.53 (10 H, m), 7.42 (1 H, tm, J ) 7.5 and 1.3
Hz), 7.37-7.27 (3 H, m), 6.92-6.90 (2 H, m); 13C δ 141.99, 139.06,
137.11, 136.83, 133.42, 130.89, 130.53, 130.23, 129.29, 128.95,
127.86, 127.81, 127.65, 126.99, 126.56, 125.01, 124.41, 123.45,
123.20, 122.94, 122.50, 119.14, 117.57, 109.87; MS m/z 369 (M+),
291, 183, 146. Anal. Calcd for C28H19N: C, 91.03; H, 5.18; N,
3.79. Found: C, 90.75; H, 5.27; N, 3.71.
N-(2-Eth yn ylp h en yl)d ip h en yla ceta m id e (18a ). To 0.351
g of 2-ethynylaniline (6a , 3.00 mmol) in a 50-mL flask were
added 0.762 g of diphenylacetyl chloride (3.30 mmol), 5 mL of
anhydrous diethyl ether, and 0.8 mL of anhydrous triethylamine
under a nitrogen atmosphere. The reaction mixture was heated
under reflux for 2 h and then was concentrated in vacuo. The
residue was purified by column chromatography (silica gel/10-
20% diethyl ether in hexanes) to furnish 0.803 g (2.58 mmol,
86%) of 18a as yellow crystalline needles: IR (KBr) 3290, 3219,
Ack n ow led gm en t. We thank the National Science
Foundation (CHE-9618676) for financial support.
Su p p or tin g In for m a tion Ava ila ble: Experimental pro-
cedures, spectroscopic and analytical data for 7b-e, 8c,d , 10d ,
1
13d , and 18c-e, and H and 13C NMR spectra for compounds
7b-e, 8b-d , 10a , 10d , 13a -e, 18a , 18c-e, 19, and 20 (46
pages). This material is contained in libraries on microfiche,
immediately follows this article in the microfilm version of the
journal, and can be ordered from the ACS; see any current
masthead page for ordering information.
1
2107, 1665, 755, 701, 656 cm-1; H δ 8.55 (1 H, d, J ) 8.1 Hz),
8.24 (1 H, br s), 7.43-7.29 (12 H, m), 7.03 (1 H, td, J ) 7.6 and
1.1 Hz), 5.21 (1 H, s), 3.01 (1 H, s); 13C δ 170.25, 139.45, 138.83,
131.81, 130.13, 129.19, 128.96, 127.45, 123.48, 118.98, 110.84,
84.18, 78.25, 60.63; MS m/z 311 (M+), 194, 168, 167, 165, 152,
116.
J O9804285