Methylenecyclopropenes synthesis

The well-known Peterson olefination reaction has been utilized in the synthesis of several unusually substituted methylenecyclopropenes The precursor methoxycyclo-propenyl triflates can be obtained as stable crystalline salts by addition of methyl triflate to the appropriate cyclopropenone (equation 75). The reaction of these triflates with a variety... 

Despite intense theoretical interest, surprisingly few attempts to prepare the parent hydrocarbon were reported prior to its synthesis in 1984 however, evidence for simple alkyl methylenecyclopropenes can be found in the base-induced elimination-isomerization reactions of gem-dichlorocyclopropanes " " . 

The synthesis of methylenecyclopropene under conditions which allow complete spectral characterization was finally reported in 1984 Dehydrohalogenation of either 104 or 105 in the gas phase at 10 mtorr over potassium r-butoxide supported on Chromosorb provided nearly pure methylenecyclopropene (equation 82). The remarkable... 

One of the earliest useful applications of eliminations in the cyclopropane series is the two-step synthesis of l-alkenyl-2-alkylidenecyclopropanes from simple alkenes. The first step consists of addition of dichlorocarbene to the alkene to give a 1,1-dichlorocyclopropane. This is then followed by double dehydrochlorination with potassium /ert-butoxide in dimethyl sulfoxide at room temperature (Table 6). The product diene contains one double bond exo to the cyclopropane ring and the other in the vinyl position, presumably through the intermediacy of an undetected, highly strained methylenecyclopropene. The method is illustrated by the synthesis of l-methylene-2-vinylcyclopropane (3) starting from pent-2-ene (1). ... 

Triafulvene (methylenecyclopropene) 2, the smallest member of the fulvenes, is of particular interest not only for its aromatic character but also for its highly strained nature. Since the first synthesis of derivatives of 2 about 50 years ago [16],... 

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