SYNTHESIS OF CHLOROTROPONES
Feb. 5 , 1961 [CONTRIBUTION FROM
THE
SCHOOL O F CHEMISTRY, UXIVERSITY
OF
603
MINNESOTA, MISNEAPOLIS 14,MINN.]
The Reaction of Halocarbenes with Aromatic Systems : Synthesis of Chlorotropones BY WILLIAM E. PARHAM, DONALD A. BOLON',~ AND EDWARD E . SCHWEIZER~ RECEIVED AUGUST19, 1960 The reaction of dichlorocarbene with 1-methoxynaphthalene, 2-methoxynaphthalene and 9-methoxyphenanthrene is discussed. Chlorotropones result by elimination of methyl chloride from the intermediate 1,l-dichlorocyclopropyl adducts.
We previously observed3 that dichlorocarbene reacts with indenes t o give cyclopropyl adducts, which subsequently afford chloronaphthalenes, in high yield, by ring expansion and elimination of hydrogen chloride. By-products in such reactions are azulenes which establish that aromatic double
gested that ring expansion to a benz-chlorotropone (I11 or V) had resulted as shown in scheme A or B.
CH,
CH,
acl
_+ I
"1
I11
q-&&
I
0
bonds, while far less reactive than aliphatic double bonds, are susceptible to reaction with dichlorocarbene. Quite recently Closs and Closs4 have reported the reaction of chlorocarbene with phenoxide ions and with benzene, and Murray5 has reported the reaction of dichlorocarbene with anthracene. We now wish to report studies of the reaction of dichlorocarbene with 1- and 2-methoxynaphthalene and with 9-methoxyphenanthrene. Dichlorocarbene was generated by reaction of ethyl trichloroacetate and sodium methoxide,6 and was allowed to react with 1-methoxynaphthalene in petroleum ether a t 0 to 25". The products isolated from the reaction mixture were: recovered 1-methoxynaphthalene (ca. 85%), methyl chloride and a ketone (11.5%, m.p. 95-96") with the molecular formula C11H70Cl. This ketone was characterized by conversion to the corresponding oxime, and by its infrared and ultraviolet spectra. The four peaks observed in the infrared spectrum of the ketone a t 1636, 1611, 1592 and 1523 ern.-' are consistent with the benztropone s t r u ~ t u r e ~and - ~ compare to absorptions a t 1638, 1618, 1575 and 1542 cm.-I for 4,5-benztropolone. These results sug-
-
IV
c1
c1
v
VI
While we favor path A, and consequently structure I11 for the ketone, no formal decision between these structures has been possible. Unequivocal evidence for the ring expansion reaction was, however, obtained by the catalytic reduction of 111 (or V) to benzsuberol (VI). Unsuccessful attempts were made to isolate the intermediate cyclopropyl adduct (I1 or IV) by elution chromatography. It was concluded, however, that this intermediate is unstable and decomposes to methyl chloride and the benzchlorotropone under the reaction conditions (20"). The ring expansion reaction noted is analogous to that involving the conversion of indene to chloronaphthaleneI3and dihydropyran to 2,3-dihydro-6chlorooxepine.l2 Particular reference is made to the study reported by McElvain and Weyna,13who showed that cyclopropanes such as VI1 are decomposed thermally to give methyl chloride and esters such as VIII, a reaction formally analogous to the ring expansion described above. CI
Cl (1) In part from the Ph.D. thesis Ijf Donald A. Bolon, The University of Minnesota, 1960. Ethyl Corporation Fellow, 1958-1959; National Science Foundation Fellow, 1959-1960. (2) Part of this work was supported by a grant (G-7382) from the National Science Foundation. (3) (a) W. E. Parham and H. E. Reiff, THIS JOURNAL, 77, 1177 (1955); (b) W. E. Parham, H. E . Reiff and P. Swartzentruber, ibad., 78, 1437 (1950); (c) W. E . Parham and R. R . Twelves, J . Ovg. Chem., 22, 730 (1957); (d) W. E. Parham and C. D. Wright, ibid., 22, 1473 (1957). (4) (a) G. L. Closs and L. E. Closs, Abstracts of the Meeting of the A.C.S., April, 1960, p. 8 3 - 0 ; (b) G. L. Closs and L. E. Closs, Tetrahedron Letters, 10, 38 (1960). (5) R. W. Murray, ibid., 7,27 (1960). (6) W. E. Parham and E. E. Schweizer, J. Org, Chem., 24, 1733 (1959). (7) P. L. Pauson, C h e w Revs., 66, 9 (1955). (8) D . S. Tarbell, G . P. Scott and A. D. Kemp, THIS J O U R N A L , 7 2 , 379 (1950). (9) L. J. Bellamy, "The Infrared Spectra of Complex Molecules," John Wiley and Sons, Inc., New York, N.Y.,1 9 2 , p. 130.
\
C1
OCH3 VI1
VI11
+ CHaCl
(10) I t was hoped that a decision between structures 111 and V could be made by use of n.m.r. spectroscopy. However, due to the aromatic character of the hydrogens on the seven-membered ring no positive answer was possible due to overlap with the benzenoid hydrogens. (11) For reaction of carbethoxycarbene with 1-methoxynaphthalene and anisole see (a) G. B. R . DeGraaff, J. H. Van Dijck-Rothuis and G. Van De Kolk, Rec. Irav. chim., 74, 143 (1955); (b) N.E. Searle, U. S. Patent 2,532,575, Dec. 5, 1950; C. A , , 45, 3873 (l'J5l) ; (c) E. Baltazzi, Comp. rend., 241, 321 (1955). (12) E. E. Schweizer and W. E. Parham, THIS JOURNAL, 82, 4085 (1960). (13) S. M. hlcElvain and P. L. Weyna, ibid., 81, 2570 (1959).
3,4-Benztropolone (IX) was prepared, as prcviously described by Cook,14 0
C)fi
(I
I;;
bene.
c I
I11
and numerous unsuccessful attempts were made to convert this tropolone to 7-chloro-2,:3-benztropone (111) using thionyl chloride in benzene, and phosphorus pentachloride in phosphorus oxychloride. This behavior is in sharp contrast to the facile conversion of tropolone t o 2-ch!orotroponc!~11y reaction with thionyl chloride in bcn7ene. .Ittempts were also made to effect hydrolysis of I11 (or Tt') with aqueous hydrochloric acid"' a t l i i ( i o , :tiid with hot potassium hydroxide in methanol1 however, no isolahlc products other than starting material r es u 1t ed . The reaction of dichlorocarbene with 2-niethoxynaphthalene was effected in the same mancer as described for 1-methoxynaphthalene, except that benzene was used as the reaction solvent, and s h i lar results were noted. In addition to recovered starting ether (ca. 757,) there was obtainecl a ketone (XI1 or XIV, 137,), isomeric with I11 or IT. The ketone was characterized by conversion into the corresponding oxime, and by its infrared and ultraviolet spectra.
lT,,~+r~uur3 1 -I-
c;=i- . . ~ '
x
-I
- -*
-L c'('l2
1. C: i \
The efTect ol' the iiiethoxy group w)uld be to activate the I ,'-double t~ondto attack i)y c!ichlorocar-
CI
YIY While two different ketones, XI1 aiid XIV, could result from this reaction (path A and path B), the latter appeared less likely and consequently structure XI1 was preferrcd on the basis of the following arguments: (1) The ketone is white (m.p. 105106'), and its infrared spectrum is similar to I11 (or V). The quinone structure XIV moulcl be expected to be colored, and to possess a spectrum quite different from benztropolone. (2) The electrons of dichlorocarbene are paired and the carbenes seek centers of highest electron density. l8.I9 XI11 c1
(14) J. W.Cook, A. R. XI.Gibb, A. R. Somerville an
