82194-85-2Relevant academic research and scientific papers
Addition Reactions of Benzothiophen. Part 4. Reactions of Some Acetoxy- and Hydroxy-benzothiophens with Benzene or Toluene
Clark, Peter David,Rahman, Loay K.A.,Scrowston, Richard M.
, p. 815 - 822 (2007/10/02)
Heating acetoxybenzothiophens with AlCl3-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 acetoxy-compound, to give the 2- (for 6-OAc) or 3-phenyl-2,3-dihydrobenzothiophens (for 7-Oac).With AlCl3 in dichloromethane, 6-acetoxybenzothiophen undergoes intermolecular transfer of an acetyl group to give a mixture of 6-acetoxy-2- and 3-acetylbenzothiophens and 6-hydroxybenzothiophen.With AlCl3 in benzene at room temperature, 4-acetoxybenzothiophen gives a rearranged product, 4,5-dihydro-2,4-diphenylbenzothiophen-7(6H)-one (3a) (17percent).In the presence of AlCl3 for 0.5 h, 4-, 5-, 6-, and 7-hydroxybenzothiophens undergo addition of benzene or toluene, to give the appropriate 2-aryl-2,3-dihydrohydroxybenzothiophens (1).Yields are high for the 4- and 6-hydroxy-isomers (80-85percent), but lower for the 5- (55percent) and 7-isomers (10percent).In each of these reactions the starting hydroxybenzothiophen is partly converted into its 2,3-dihydro-derivative. 5- and 7-Hydroxybenzothiophen also each give the same 4,5-dihydro-2,4-diarylbenzothiophen-7(6H)-one (3) (25percent) 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 this unusual rearrangement is discussed in terms of a spiro-intermediate.
