6484 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA J. Org. Chem. 1994,59, zyxwvu 6484-6486 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONML Synthesis of Extended Linear Aromatics Using Tandem Diels-Alder Aromatization Reactions J. Larry Morris, Calvin L. Becker, Frank R. Fronczek, William H. Daly, and Mark L. McLaughlin* Louisiana State University, Department zyxwvutsr of Chemistry, Baton Rouge, Louisiana 70803 Received May 31, 1994 Introduction Extended aromatic structures such as the naphthyl and anthryl nucleus have interesting physical and chemi- cal characteristics. Anthracenes generally fluoresce be- tween 400 and 680 nm.l Molecules with variously substituted anthracene nuclei react as Diels-Alder dienes.2 Anthracene also undergoes photochemical zyxwvu 4 zyxwvu + 4 cycloaddition reactions across the 9,lO positions to form a thermoreversible dimer. This reaction of anthracene has been known for more than a centurye3 This note describes an efficient synthesis of extended aromatics such as 2,3-disubstituted naphthalenes and 2,3,6,7- tetrasubstituted anthracenes, which were previously difficult and expensive to synthesize. These compounds may now be readily exploited as a result of this simple methodology. To illustrate the potential of the tandem Diels-Alder aromatization reaction, we synthesized benzflindanone, 2,3:6,7-dibenzofluorenone, and 2,3,6,7- tetrakis( methoxycarbony1)anthracene. Benzmindanone was synthesized by a five-step pro- ce~s.~,~ Friedel-Crafts reaction of indan with succinic acid gave an indan keto acid derivative that underwent a Clemmensen reduction and acid-catalyzedcyclization. The semicarbazone was formed from the resulting ketone which was decomposed to benzmindane. Benzmindane was then brominated in the 1 position by NBS and oxidized with chromic acid to benzmindan-1-one in an overall yield of less than 1%. A potential modern improvement to this synthesis is that of Carpino and Lin6 who synthesized 10-bromobenzmindan-1-one in six steps. Their initial bromination of both the 1 and the benzylic positions of 2-methylnaphthalene was followed by dis- placement of the benzylic bromide with sodium diethyl malonate. Hydrolysis, decarboxylation, and a Friedel- Crafts ring closure yielded the 10-bromobenzflindanone in a 23% yield overall. Obtaining benzmindan-1-one, however, requires dehalogenation of 10-bromobenzm- indan-1-one. This operation would reduce the overall yield, but such a method should yield products in greater than 1% overall. 2,3:6,7-Dibenzofluorenone was synthesized by Martin7 from methyl 3-bromo-2-naphthoate. Copperhronze cou- pling was employed to assemble the tetraphenyl ring sequence. Basic ester hydrolysis then yielded the di- sodium salt. The formation of an intramolecular lead (1) Cundall, R. B.; Gilbert, A. Photochemistry; Pitman Press: Lon- don, 1970; p 73. (2)Wagner-Jauregg, T. Synthesis 1980, 165. Kiasekev, V. D.; Shakirov, I. M.; Konovalov, A. I. zyxwvutsrqpon Zh. zyxwvutsr Og. Khim. 1986,22, 1034. (3) Fritzsche. J. Pruk. Chem. 1867, 101, 333-343. (4) McQuillin, F. J.; Robinson, R. J. Chem. zyxwvutsrq SOC. 1941, 586. (5)Horner, L.; Muth, K.; Schmelzer, H.-G. Chem. Ber. 1969, 92, (6) Carpino, L. A.; Lin, Y. J. Org. Chem. 1990, 55, 247. (7)Martin,R. H. J. Chem. SOC. 1941,679. 2953. dicarboxylate aligned the rings for subsequent pyrolysis of the lead salt. Pyrolysis introduced the bridging ketone to finish the synthesis. The overall yield was 8%. We were able to locate only three methods for the synthesis of 2,3,6,74etrasubstituted anthracenes. The first synthesis of 2,3,6,7-tetrasubstituted anthracene was by Morgan and Coulson,8 who reacted 2,3-disubstituted butadienes with p-benzoquinone. The resulting quinone was reduced with zinc and ammonia and aromatized with sulfur to give the corresponding anthracene. The second published synthesis was by Marschalk? who synthesized 2,3,6,7-anthracenetetracarboxylic acid in five steps from 2,3,6,74etramethylanthracene. Oxi- ation of the methyl substituents was accompanied by anthraquinone formation. The synthesis entailed reduc- tion to 9,10-dihydro-2,3,6,7-anthracenetetracarboxylic acid. Aromatization required conversion of the tetraacid to the bis-anhydride followed by dehydrogenation of the 9,lO positions with sulfur. Hydrolysis of the resultant anhydride gave 2,3,6,7-anthracenetetracarboxylic acid. This synthesis is difficult to conduct on a large scale because the 2,3,6,7-tetramethylanthracene is not readily available. The third method based upon a benz0[1,2,-~:4,5-c’]- difuran intermediate was developed by Luo and Hart.lo Reaction of anthracenediene dioxide with tetraphenyl- cyclone produced an adduct which liberated benzo- [1,2-~:4,5-c’]difuran upon heating in decalin. If the thermolysis is conducted in the presence of dienophiles such as dimethyl fumarate, 2,3,6,7-tetrakis((alkyloxy)- carbony1)anthracenes are formed along with carbon monoxide and tetraphenylbenzene. This is a very elegant synthesis, but rather expensive reagents are required. Regiospecific annulation of o-quinodimethane deriva- tives is the best approach to the synthesis of 2,3- disubstituted naphthalenes and 2,3,6,7-tetrasubstituted anthracenes. The concept was defined by Cava, Deana, and Muth,ll who published a synthesis of 2,3-disubsti- tuted naphthalenes via a tandem Diels-Alder aromati- zation reaction. In their synthesis, a,a,a’,a’-tetrabromo- o-xylene is reacted with a dienophile in the presence of NaI in DMF, such as N-phenylmaleimide or maleic anhydride, to give the correspondingnaphthalene deriva- tive. The Diels-Alder aromatization reaction, based on o-quinodimethane intermediates, provides remarkable flexibility. Not only can 2,3-disubstituted naphthalenes by synthesized with remarkable regiospecificitybut a bis- annulation with 2 mol of an o-quinodimethane inter- mediate yields molecules containing two 2,3-disubstituted naphthalene subunits. In a similar manner, bis-annu- lation with a difunctionalo-quinodimethane intermediate yields 2,3,6,7-tetrasubstituted anthracenes. Experimental Section All reagents were purchased from the Aldrich Chemical Co. and used without further purification. NJV-dimethylformamide (DMF) and Nfl-dimethylacetamide (DMAc) were purchased as anhydrous grade. Melting points were taken on a Fischer-Johns melting point apparatus and are uncorrected. NMR spectra were recorded with zyxwv an IBM/Bruker AR-100 MHz or AC-200 MHz ~ ~ ~~~~~ ~ ~ (8) Morgan, G. T.; Coulson, E. A. J. Chem. SOC. 1931, 2323. (9) Marschalk, C. Bull. SOC. Chim. Fr. 1960, 311. (10) Luo, J.; Hart, H. J. Og. Chem. 1988, 53, 1341. (11) Cava, M. P.; Deana, A. A,; Muth, K. J. Am. Chem. SOC. 1959, 81, 6458. 0022-326319411959-6484$04.50/0 0 1994 American Chemical Society