Abstract Diazomethane reacts with trisubstituted ethylenes of 5-nitrofurane series within the temperature range-60 C to+ 20 C with direct formation of cyclopropane derivatives IV without pyrazoline intermediates. This reaction does not proceed as a 1, 3-dipolar cycloaddition but goes via nonfinished stepwise mechanism discussed in the present paper. The cyclopropane derivative IVa has been prepared as a model substance via the new ...