Electrophilic substitution tropolones

Tropolone complexes (20) also undergo electrophilic substitution, but the numerous positions for reaction give rise to mixtures of products. The p-keto imine complexes (21) and (22)32 have been brominated successfully using )V-bromosuccinimide. 

Most tropolones give sparingly soluble, yellow or orange sodium salts, green cupric chelates, and colored ferric complexes. Although easily acetyl-ated or methylated and frequently precipitated by picric acid, tropolones only exceptionally react with carbonyl reagents. Electrophilic substitution reactions occur readily however, sulfonation or nitration is inhibited... 

With monocyclic tropolone, electrophilic substitutions preferentially occur at the 5-position. One major exception to this rule is halogenation, which takes place at C-3 and then at C-7 (55CRV9, p. 40). In fused derivatives, aside from the heteroring, the positions vicinal to the oxygen functionalities are preferred. 

Tris(l, 10-phenanthroline) complexes structure, 63 Tropolone metal complexes electrophilic substitution, 422 Tungstate, pcntachlorothio-stereochemistry, 50 Tungsten, octacyano-photoreactivity, 406 structure, 84... 

Tropolones resemble the latter compounds in their reactivity towards electrophiles. They readily undergo electrophilic substitution, which takes place at the 3-, 5- and 7-positions, by a mechanism analogous to that for electrophile substitution in 8-diketones ... 

Benzotropolones take part in electrophilic substitution reactions, for example halogenation [293,328,331] and coupling with aryldiazonium salts [332]. They may undergo rearrangement to benzenoid compounds in some instances, for example treatment of 3,4-benzotropolone with excess bromine gives 2,3-dibromonaphtho-quinone and with excess concentrated nitric acid leads to 2,4-di-nitro-l-naphthol [333]. Like other tropolones, 3,4-benzotropolone is photochemically converted into a bicycloheptadienone [334]... 

Not surprisingly, since both contain conjugated systems linking the hydroxyl and carbonyl groups, 3-hydroxytropone CXXXVII) and 4-hydroxytropone CXXXVIII) closely resemble tropolone in their chemical properties. They undergo electrophilic substitution, for... 

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