C. K. BRADSHER AND T. W. G. SOLOMONS
1808
[CONTRIBUTION FROM
THE
Vol. 82
DEPARTMENT OF CHEMISTRY, DUKEUNIVERSITY ]
Aromatic Cyc1odehydration.l XLIV. The Benz [b IAcridizinium System2 BY C. K. BRADSHER AND T. W , G. SOLONONS~ RECEIVED JULY 13, 1959 The usual hydrobromic acid cyclization of the crude quaternary salts formed by the reaction of isoquinoline-3-carboxaldehyde with either benzyl bromide or a-bromo-p-xylene did not lead t o the expected benz[b]acridizinium salts I X and X , b u t gave instead what are believed t o be the dimers V and VI. The oxime derivatives VI1 and VI11 were found to cyclize more rapidly and thus allowed isolation of the benz [b lacridizinium salts before appreciable dimerization had occurred. T h e benz [blacridizinium bromides were found to be dimerized by boiling hydrobromic acid or by light.
I n earlier communications4 it was demonstrated that acridizinium salts (I) could be obtained by the hydrobromic acid-catalyzed cyclization of the crude quaternary salts formed from pyridine-2carboxaldehyde and various benzyl halides. It seemed likely, therefore, that the pyridine-2-carbox-
the basis of spectral evidence and certain analogies with the acridizinium photodimer,8 they are believed to be the dimers V and VI. Although no dimerization such as this had been observed in the synthesis of other acridizinium salts, i t had been shown that acridizinium salts photodimerize under the influence of ultraviolet light. T h a t light was not necessary for the formation of V was indicated by the fact that a similar cyclization carried out in total darkness also gave ba \ m R the dimerized product. It appeared, therefore, that the benz [blacridizinium system was formed, I but was so reactive that it dimerized under the usual aldehyde could be replaced by isoquinoline-3-car- cyclization conditions. This consideration led to boxaldehyde in the same general scheme and thus the search for an intermediate that would cyclize provide a route to benz [blacridizinium salts. Al- more rapidly and thus allow isolation of the benzthough partially hydrogenated derivatives of the [blacridizinium salts. benz [blacridizinium system have been known for I t was gratifying to find that the quaternary some time,5,6the fully aromatic system has not, salts VI1 and VIII, obtained by the reaction of isountil now, been synthesized. quinoline-3-aldoxime7 with either I11 or IV, met The aldehyde I1 was prepared readily by the se- this requirement.9 The cyclization of VI1 in boillenium dioxide oxidation of 3-methylis~quinoline~ ing hydrobromic acid for only ten minuteslo gave a 23% yield of benz [b]acridizinium bromide ( I X ) BrCH2 accompanied by a 35% yield of the dimer IT. In a 1, quaternize similar way, cyclization of VI11 for four minutes 2, HBr, 8 hours gave a 71y0 yield of 2-methylbenz [blacridiziniun~ CHO R bromide (X). The salts I X and X are red-orange I1 111, R = H II', R = CH3 crystalline solids and in solution show a yellowgreen fluorescence. 2 Br-
-
/
-
R' 1 2
V, R = H VI, R = CH3
and in separate experiments was quaternized with either benzyl bromide (111) or a-bromo-p-xylene (IV). Treatment of these crude salts with boiling hydrobromic acid for eight hours gave faintly orange solids which on recrystallization yielded colorless nonfluorescent products, obviously not the highly conjugated benz [blacridizinium salts. On (1) For t h e preceding communication of this series see C. K . Brad, 1146 (1960). sher a n d S . L. D u t t a . THISJ O U R N A L82, (2) This investigation was supported b y a research g r a n t (XSFG2364) of t h e National Science Foundation. (3) Abstracted from p a r t of a dissertation s u b m i t t e d by T. W. G. Solomons in partial fulfillment of t h e requirements for t h e degree of Doctor of Philosophy a t Duke University. (4) C. K . Bradsher a n d I,. E. Beavers, THISJ O U R N A 77. L . 4S3, 481% (1953).
( 5 ) R. Campbell, R . D. I l a w o r t h a n d W. 11. Perkins, J r . , J . Chein. Soc., 129, 32 (1926). ( t i ) S. Sugasawa, K . Kakemi a n d H , K a z u u i , Proc. imp, .Acud. ( T o k y o ) , 16, 223 (1939). (7) C. E . Teague a n d A . R o e , THISJ O U R N A L73, , 089 (1951).
: (
VII. R = H
VIII. R = C H ,
IX, R = H X.R=CH,
Mihen hydrobromic acid solutions of either of the two benz[b]acridizinium salts, IX and X , were refluxed for one or two hours the corresponding dimers V arid VI were isolated in good yield. T h e salts IX and X resembled acridizinium bromide i n undergoing photodimerization. The photodiniers obtained were identical with the dimers formed by the action of hydrobromic acid. The ultraviolet absorption spectra (Fig. 1) of benz [blacridizinium bromide (IX) and its dimer V are quite different in that V does not absorb a t the (8) C. K . Bradsher, I,, E. Beavers a n d James I € . Jones, J . 01'8 C h e m . , 22. 1740 (1957). (9) F o r f u r t h e r examples u f t h e cyclization 01 oximes to l u r i i i acridizinium derivatives, see C. K. Bradsher, T. W. C;, Solornuns and 1'. R. Vaughan, i b i d . , 24, in press (1959). (10) I n this regard i t should be s t a t e d t h a t cycliratiuti
