In our ongoing research of utilizing flow-generated diazomethane, we report the formation of diverse pyrazolines by combining the flow generation of diazomethane with its subsequent [3+2]-cycloaddition to electron-deficient alkenes. It was possible to obtain the corresponding pyrazolines in quantities exceeding one hundred grams for the first time. The stereochemical particulars, scope and limitation of the reaction, advantages of the synthetic procedure are demonstrated. The further photochemical fragmentation of obtained substrates to gem-disubstituted cyclopropenes was investigated (Scheme 1). The reaction is stereoselective, the structure of the formed cyclopropane is determined by the configuration of the starting alkene. Relevant new compounds have been isolated and characterized.

Flow-generated diazomethane in the synthesis of diverse pyrazolines as precursors of <i>gem-</i>disubstituted cyclopropanes

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Flow-generated diazomethane in the synthesis of diverse pyrazolines as precursors of gem-disubstituted cyclopropanes