94
J . Org. Chem. 2001, 66, 94-98
A “Gr een ” Rou te to P er ylen e Dyes: Dir ect Cou p lin g Rea ction s of
1,8-Na p h th a lim id e a n d Rela ted Com p ou n d s u n d er Mild Con d ition s
Usin g a “New ” Ba se Com p lex Rea gen t, t-Bu OK/DBN
Takaaki Sakamoto and Chyongjin Pac*
Kawamura Institute of Chemical Research, 631 Sakado, Sakura, Chiba 285-0078, J apan
chyongjin-pac@ma.dic.co.jp
Received J uly 17, 2000
The direct coupling reactions of 1,8-naphthalimide compounds efficiently occurred at 130 or 170
°C without the intervention of the leuco form dyes in the presence of base complex reagent, t-BuOK/
1,5-diazabicyclo[4.3.0]non-5-ene (DBN), to give the corresponding perylene dyes in good yields with
>95% purities. A possible mechanistic speculation for these oxidative coupling reactions is briefly
discussed.
In tr od u ction
perylene dyes in high purities without tedious proce-
dures. In this paper, we wish to report that the t-BuOK/
1,5-diazabicyclo[4.3.0]non-5-ene (DBN) reagent efficiently
promotes the direct coupling reactions of 1,8-naphthal-
imide (1a ) and related compounds (1b-p ) to the corre-
sponding perylene dyes (2a -p ) at 130 or 170 °C without
the intervention of the leuco form dyes (Chart 1).
Base-promoted condensation reactions of organic com-
pounds are of synthetic importance as a general class of
organic reactions, in which the activation of acidic CH,
OH, or NH by base reagents is generally involved as an
essential rate-determing process.1 In the case of low
acidic CH, therefore, base-promoted reactions of relevant
compounds require severe reaction conditions, e.g., the
use of a large excess of base reagents and high reaction
temperatures. A typical example is the production of
perylene dyes that has been carried out, not only in
commercial scale but also in laboratory scale, by the
coupling reactions of 1,8-naphthalimide compounds in
molten alkaline salts at very high temperatures (>200
°C).2-4 This alkaline-fusion method is simple but has
some crucial problems as follows: (1) Molten alkaline
salts very often cause extensive corrosion of the reaction
vessel. (2) Isolation of the final products requires multi-
step procedures such as dissolution of the excess alkaline
salts with a plentiful amount of water, isolation of the
leuco form dyes, and their air oxidation to the final
perylene products. (3) The applicability of the alkaline-
fusion reaction is rather limited because attempted
reactions often fail in production of the desired products
or result in only poor yields and/or low purities of the
perylene dyes. (4) Environmental pollution may occur by
formation of alkaline mists during the reactions as well
as upon dissolution of the alkaline salts and also by
massive alkaline waste. Moreover, such severe reaction
conditions might limit applications of the coupling reac-
tions to attempted synthesis of “modern” functional dyes
having extended π-conjugations,5 even though outstand-
ing chemical and optical functionalities are expected.2,4,6
As an extension of our research project on the develop-
ment of simple synthetic methods for the production of
pure functional compounds,7 we attempted to find new
base reagents with which the aryl-coupling reactions can
be successfully achieved under mild conditions to produce
Resu lts a n d Discu ssion
Dir ect Cou p lin g Rea ction of Na p h th a lim id e 1a to
P er ylen e Dye 2a . As already mentioned, the coupling
reaction of 1,8-naphthalimide (1a ) in the presence of
alkaline salts occurs only at high temperatures (>200 °C),
presumably because of low basicity of the inorganic bases.
It can therefore be easily predicted that highly basic
reagents might promote the coupling reaction at lower
temperatures, while the reagents are required to be
stable at those reaction temperatures. From this view-
point, we initially used various combinations of MOH (M
) Li, Na, and K) and organic bases for the coupling
reaction of 1a because base combinations may often
generate stronger base reagents, like BuLi/t-BuOK8 and
BuLi/Me2N(CH2)2OLi,1,9 than the component bases. In
fact, it was found that heating of a 1:3:5 mixture of 1a ,
KOH, and DBN at 170 °C under N2 gave directly
perylene-3,4,9,10-tetracarboxylic bisimide (2a ) in a 13%
(5) (a) Langhals, H.; J aschke, H.; Ring, U.; von Unold, P. Angew.
Chem., Int. Ed. Engl. 1999, 38, 201. (b) Zhao, Y.; Wasielewski, M. R.
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Chem., Int. Ed. Engl. 1998, 37, 952. (d) Rohr, U.; Schlichting, P.; Bo¨hm,
A.; Gross, M.; Meerholz, K.; Bra¨uchle, C.; Mu¨llen, K. Angew. Chem.,
Int. Ed. Engl. 1998, 37, 1434. (e) Quante, H.; Geerts, Y.; Mu¨llen, K.
Chem. Mater. 1997, 9, 495. (f) Holtrup, F. O.; Mu¨ller, G. R. J .; Uebe,
J .; Mu¨llen, K. Tetrahedron 1997, 53, 6847. (g) Quante, H.; Mu¨llen, K.
Angew. Chem., Int. Ed. Engl. 1995, 34, 1323. (h) Langhals, H.;
Scho¨nmann, G.; Feiler, L. Tetrahedron Lett. 1995, 36, 6423. (i) Law,
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(6) De´silets, D.; Kazmaier, P. M.; Burt, R. A. Can. J . Chem. 1995,
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(7) (a) Sakamoto, T.; Yonehara, H.; Pac, C. J . Org. Chem. 1997, 62,
3194. (b) Yao, J .; Yonehara, Y.; Pac, C. Bull. Chem. Soc. J pn. 1995,
68, 1001. (c) Sakamoto, T.; Yonehara, H.; Pac, C. J . Org. Chem. 1994,
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(2) Desilets, D.; Kazmaier, P. M.; Burt, R. A.; Hamer, G. K. Can. J .
Chem. 1995, 73, 325.
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10.1021/jo0010835 CCC: $20.00 © 2001 American Chemical Society
Published on Web 12/12/2000