Asymmetric Induction in Friedel-Crafts Reaction with (+)-1,2-Epoxybutane and (−)-2-Chloro-1-butanol

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The alkylation of benzene with (+)-1,2-epoxybutane in the presence of Lewis acid gave a mixture of optically active 2-phenyl-1-butanol (I) and 3-phenyl-1-butanol (II) together with a mixture of optically active 2-chloro-1-butanol (III), 3-chloro-1-butanol (IV) and 1-chloro-2-butanol (V). The formation of (−)-I and (−)-III suggests that the ring opening of the epoxide proceeds with an inversion of configuration, while that of optically active II and IV suggests an asymmetric induction at the carbon adjacent to the terminal methyl group of the epoxide. The reactions with aluminum chloride at 20 °C and with stannic chloride at −20 °C gave (+)-II in 10% and (−)-IV in 56% optical yield, respectively. In the reaction of (−)-III with benzene, such an asymmetric induction was also found to give (+)-II in 21–24% optical yield. The probable mechanism of this induction was discussed on the basis of the stability of the transition state conformations.
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