Effects of an Electron-Withdrawing Group on Thermal Decomposition of 4-Alkylidene-1-pyrazolines: A Novel Stereoselective Formation of Alkylidenecyclopropane Due to Participation of π-Electrons on the Methylene Carbon in Decomposition
es 7 arising from the bond formation between the exo-methylene carbon and the 5-carbon. The selective formation and the configurations of the products are rationalized in terms of the concerted process via the folded conformation of the pyrazolines. Introduction of an electron-withdrawing group at the 3-position of the 4-alkylidenepyrazoline system causes the polarization of the C(3)-N(2) bond inducing