Iodinations dibenzothiophene

Miscellaneous routes to dibenzothiophene include ring closure of the disulfide (35) with iodine (64%),treatment of biphenyl sulfone with... 

The synthesis of the four monocarboxylic acids of dibenzothiophene has been recorded in the previous review. However, several modified preparations have since been described. Ethyl 1-dibenzothiophene-carboxylate has been synthesized from 2-allylbenzo[6]thiophene (Section IV,B, 1) hydrolysis afforded the 1-acid (57% overall). In a similar manner, 3-methyl-1-dibenzothiophenecarboxylic acid was obtained from the appropriately substituted allyl compound. This method is now the preferred way of introducing a carbon-containing substituent into the 1-position of dibenzothiophene. 2-Dibenzothiophenecarboxylic acid has been prepared by oxidation of the corresponding aldehyde or by sodium hypoiodite oxidation of the corresponding acetyl compound. Reaction of 2-acetyldibenzothiophene with anhydrous pyridine and iodine yields the acetyl pyridinium salt (132) (92%), hydrolysis of which yields the 2-acid (85%). The same sequence has been carried out on 2-acetyldibenzothiophene 5,5-dioxide. The most efficient method of preparing the 2-acid is via carbonation of 2-lithio-... 

Disulfides were shown to be intermediates in the iodine oxidation of 1,3-butadiene-l-thiols and related compounds to form thiophenes (56JOC39). Several simple disulfides were converted to thiophene derivatives under these same conditions (64JOC2372). For example, bis(2-biphenyl) disulfide (13) produced dibenzothiophene (14) in 64% yield when heated with iodine in ethylene glycol for one hour. Treatment of (13) in benzene with aluminum bromide gave (14) in 76% theoretical yield, with an equivalent amount of the thiol, 2-biphenylthiol (62JOC4111). Thus the iodine reagent is more efficient, since it oxidizes the mercaptan, formed by the Friedel-Crafts reaction of disulfide on the adjacent aromatic ring, to disulfide for further reaction, and also serves as a catalyst for the initial reaction. 

Alkyl- or aryl-dibenzothiophenes are conveniently prepared from the 2-arylthio-cyclohexanones, which are readily cyclized and dehydrogenated to yield the respective 1-, 2-, 3- or 4-substituted dibenzothiophenes (382 equation 9 Section 3.15.2.3.2). More complex polycyclic systems are available, using suitable aryenethiols, such as naph-thalenethiols, and 2-bromo-l-tetralone to synthesize the appropriate 2-arylthio ketones. Diaryl sulfides can be converted to dibenzothiophene derivatives in satisfactory yields by photolysis in the presence of iodine (equation 10) (75S532). Several alkyldibenzothiophenes with substituents in the 2- and/or 3-positions were prepared in satisfactory yield by the condensation of dichloromethyl methyl ether with substituted allylbenzo[6]thiophenes (equation 11) (74JCS(P1)1744). 

Fluorescence quenching of fluorene, dibenzofuran, and dibenzothiophens by aromatic nitriles and aliphatic amines is the result of electron transfer with exciplex formation,177 and ion-pair formation in pyromellitic dianhydride-ethylbenzene is followed by dissociation into separated ion pairs in their highly excited states.178 Photochemical iodination of aromatic hydrocarbons may proceed by way of an electronically excited Ia-aromatic charge-transfer complex.179 Modulation excitation spectrophotometry has been used to analyse the nature of some complexes between polycyclic aromatic hydrocarbons and chloranil.180... 

Carbazoles, dibenzofurans, and dibenzothiophene derivatives 10 have been obtained via photocyclization of the corresponding diphenylamine, diphenylether, or diphenylthioether precursors 9 (Scheme 3). In these reactions, the lone pair of heteroatoms contributes to the 6jr—electrons engaged in the electro-cyclization. The re-aromatization occurred under oxidative conditions in the presence of oxygen or iodine. When irradiated in acetonitrile solution containing aqueous HCl, compounds 11 were transformed into... 

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