81581-02-4Relevant articles and documents
Addition Reactions of Benzothiophen. Part 3. Addition and Ring-opening Reactions with Phenolic Ethers
Clark, Peter David,Ewing, David F.,Kerrigan, Frank,Scrowston, Richard M.
, p. 615 - 622 (2007/10/02)
In the presence of aluminium chloride, anisole, phenetole, diphenyl ether, and (methylthio)benzene are added rapidly across the 2,3-bond in benzothiophen to give, inter alia, a mixture of 2- and 3-(p-substituted aryl)-2,3-dihydrobenzothiophens (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 unambigiuously.It is believed that benzothiophen is S-methylated by PhOMe-AlCl3 in 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.
