Generation of simple methylenecyclopropenes as reactive intermediates |
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Authors: | WE Billups Andrew J Blakeney Nancy A Rao John D Buynak |
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Institution: | Department of Chemistry, Rice University, Houston, TX 77001, U.S.A. |
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Abstract: | The dehydrochlorination of either 1,2 - dichloro - 1 - methylcyclopropane or 1 - bromo - 2 - chloro - 2 - methylcyclopropane with potassium t-butoxide yields 2 - t - butoxy - 1 - methylenecyclopropane. These results are interpreted in terms of methylenecyclopropene as a reactive intermediate which is trapped by addition of nucleophile (t-butoxide) to the cyclopropenyl double bond. The introduction of methanethiol to the reaction medium yields 2 - thiomethyl - 1 - methylenecyclopropene 2,2 - Dichloro - 1 - methylenecyclopropane reacts with potassium t-butoxide in tetrahydrofuran to yield trans- and cis - t - butoxybut - 1 - ene - 3 - yne. The addition of thiomethide ion results in the formation of 2,2 - bis(thiomethyl) - 1 - methylenecyclopropane and 2 - t - butoxy - 2 - thiomethyl - 1 - methylenecyclopropane. Other evidence for simple methylenecyclopropenes as reactive intermediates comes from the observation that nucleophiles add nonregiospecifically to the reactive intermediate produced by the dehydrohalogenation of 2 - halo - 1 - alkylidenecyclopropanes. Novel methylenecyclopropane→ cyclopropene transformations were found in the reaction of 2 - halomethylenecyclopropanes with thiomethide ion. |
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