A facile and efficient ultrasound-assisted stereospecific synthesis of novel bicyclo-cyclopropanes

The regispecific synthesis of pyrazolines has been accomplished through the 1,3-dipolar cycloaddition of 2-diazopropane to pyridazine-3,6-dione derivatives. A convenient and inexpensive ultrasound-assisted preparation of bicyclo-cyclopropanes in a completely stereoselective manner in almost quantitative yields has been realized. The highly stereoselective extrusion of nitrogen suggests a concerted mechanism.