3,4-Benzotropolone and Related Compounds. II. Chloro and Iodo Derivatives of 3,4-Benzotropolone

One hundred years of benzotropone chemistry

“…Ebine studied in more detail the chlorination and iodination of 241A ( Scheme 69 , Scheme 70 and Fig. 17 ) [ 194 , 198 ]. Treatment of the benzotropolone 241A with one or two equivalents of chlorine in acetic acid afforded 5,7-dichloro-3,4-benzotropolone ( 378 ) in low to fair yield.…”

“…17 ). 7-Iodo-3,4-benzotropolone ( 382 ) was also obtained in 40% yield by the reaction between benzotropolone 241A and sodium iodide/sodium iodate in acetic acid ( Scheme 70 ) [ 195 ].…”

“…Reaction of halobenzotropolones: Dehalogenation of halobenzotropolones: Hoshino and Ebine reported that palladium-catalyzed hydrogenation of bromobenzotroponoids 369 and 370 resulted in debromination of halogen atoms to give 239B as depicted in Scheme 71 [ 194 ]. However, hydrogenation of 375 gave 241A in low yield ( Scheme 72 ) [ 195 ]. Debromination of monobromide 290 with hydrobromic acid in acetic acid afforded 241A in 73% yield, whereas the reaction of dibromide 375 under the same conditions provided monobromide 383 in 85% yield as the debromination product ( Scheme 72 ) [ 198 ].…”

“…However, hydrogenation of 375 gave 241A in low yield ( Scheme 72 ) [ 195 ]. Debromination of monobromide 290 with hydrobromic acid in acetic acid afforded 241A in 73% yield, whereas the reaction of dibromide 375 under the same conditions provided monobromide 383 in 85% yield as the debromination product ( Scheme 72 ) [ 198 ].…”

“…Oxidation of halobenzotropolones: Oxidation reactions of halo-benzotropolones were often used to determine the structures of benzotroponoids [ 194 , 198 – 199 ]. For clarification of the positions of substituents in the final compounds, Ebine reported that oxidation of dihalo-benzotropones 370 and 381 with alkaline hydrogen peroxide gave phthalic acid ( 385 ) in 40% and 35% yields, respectively, while that of monohalobenzotropolenes 369 , 384 , and 290 afforded o -carboxycinnamic acid ( 273 ) in 47%, 33%, and 33% yields, respectively ( Fig.…”