In the presence of aluminium chloride, anisole, phenetole, diphenyl ether, and (methylthio)benzene are added rapidly across the 2,3-bond in benzo[b]thiophen to give, inter alia, a mixture of 2- and 3-(p-substituted aryl)-2,3-dihydrobenzo[b]thiophens (3) and (4). Contrary to expectation, the 2-isomer predominates in all cases, and the addition is irreversible. Reaction with anisole also leads to a novel ring-opened product, viz.(E)-4-methoxy-2′-methylthiostilbene (9a), which was synthesised unambiguously. It is believed that benzo[b]thiophen is S-methylated by PhOMe–AlCl3in a 'push–pull' reaction, and that the resulting positive charge is delocalised into the ring, thus allowing the 2-position to participate in electrophilic attack on a second molecule of anisole. The resulting quadrivalent sulphur intermediate achieves stabilisation by means of a rapid ring-opening reaction. Other aromatic methyl ethers give analogous products, but phenetole, diphenyl ether, and (methylthio)benzene do not promote ring-opening. The ring-opening reaction is aided by the addition of MeBr– or EtBr–AlCl3; even phenetole will then undergo ring-opening. Under these conditions the S-alkyl group in the ring-opened product comes from the starting ether, and not from the added MeBr or EtBr.

AbstractDie Reaktion entsprechender Benzothiophene (I) mit Benzol bzw. Toluol (II) in Gegenwart von AlCl3 führt zu regioisomeren Deri‐ ,raten (II) und (III); teilweise werden als Nebenprodukte auch entsprechend substituierte dimere Verbindungen (V)‐(IX) gebildet (Tabelle; Zahlenangaben bezeichnen die prozentualen Produktanteile).

Heating acetoxybenzo[b]thiophens with AICl3–benzene can give the normal Fries-rearranged products (for the 4-OAc and 7-OAc isomers); these sometimes react further to give their 2,3-dihydro-(for 4-OAc and 7-OAc) or 2-phenyl derivatives (for 6-OAc). Alternatively, benzene can add across the 2,3-double bond of the acetoxycompound, to give the 2-(for 6-OAc) or 3-phenyl-2,3-dihydrobenzo[b]thiophens (for 7-OAc). With AICl3 in dichloromethane, 6-acetoxybenzo[b]thiophen undergoes intermolecular transfer of an acetyl group to give a mixture of 6-acetoxy-2- and 3-acetylbenzo[b]thiophens and 6-hydroxybenzo[b]thiophen. With AICl3 in benzene at room temperature, 4-acetoxybenzo[b]thiophen gives a rearranged product, 4,5-dihydro-2,4-diphenylbenzo[b]thiophen-7(6H)-one (3a)(17%).In the presence of AICl3 for 0.5 h, 4-, 5-, 6-, and 7-hydroxybenzo[b]thiophens undergo addition of benzene or toluene, to give the appropriate 2-aryl-2,3-dihydrohydroxybenzo[b]thiophens (1). Yields are high for the 4- and 6-hydroxy-isomers (80–-85%), but lower for the 5-(55%) and 7-isomers (10%). In each of these reactions the starting hydroxybenzo[b]thiophen is partly converted into its 2,3-dihydro-derivative. 5- and 7-Hydroxybenzo-[b]thiophen also each give the same 4,5-dihydro-2,4-diarylbenzo[b]thiophen-7(6H)-one (3)(25%) in this reaction. When the reaction period with benzene or toluene is extended to 5 days, the amount of solvent addition product (1) decreases, but all four hydroxy-isomers now give the same rearranged product (3). The mechanism of of this unusual rearrangement is discussed in terms of a spiro-intermediate.

AbstractDie Ether bzw. Thioether (II) addieren sich in Gegenwart von AlCl3 an Benzothiophen (I) in irreversibler Reaktion unter Bildung der Produkte (III)+(IV), wobei unerwarteterweise das 2‐Isomere (III) jeweils überwiegt.

Naphtho[2,1-b]thiophene undergoes addition of aromatic hydrocarbons across the 1,2-bond in the presence of aluminum chloride. At 20 °C 1-aryl-1,2-dihydronaphtho[2,1-b]thiophenes are the major products and at higher temperatures 2-arylnaphtho[2,1-b]thiophenes result. 1-Arylnaphtho[2,1-b]thiophenes may be prepared by treatment of the dihydro-addition products with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone thus giving a new synthesis of 1- and 2-arylnaphtho[2,1-b]thiophenes from the parent heterocycle.

AbstractBeim Umsetzen mit AlCl3 in organischen Lösungsmitteln bei Ooder 20°C geht Benzo[b]thiophen (I) leicht Additionsreaktionen an dem 2‐C‐ und/oder 3‐C‐Atom ein.

AbstractZur Diskussion der Beziehung zwischen der elektronischen Natur der Substituenten und ihrer Stellung werden die Nitrierung, Bromierung und Friedel‐ Crafts‐Acetylierung der Benzo[b lthiophene (I) untersucht.

AbstractAll carbon resonances in the title compounds have been unequivocably assigned. Steric effects in the peri substituted compounds have been compared with analogous effects in naphthalene and benzo[b]furan. The observed effects are not explained by current theory. Unusual deshielding steric shifts are observed at some carbons. Methyl substituent effects are not additive at any position in the sterically crowded 2,3‐disubstituted compounds.