Structures of abnormal- and normal-addition 1-pyrazolines produced from 2-cyano-3,3-di-(or mono-)-substituted-acrylates with diazoalkanes

Reactions of methyl 2-cyano-3-methyl-3-(p-substituted-phenyl)acrylates ( 1 ) with 1-phenyldiazoethane ( 2 ) produced the stable abnormal-addition 1-pyrazolines, AP, 4 1]. The structure of cis-syn- 4a (X = NO₂) was determined by X-ray crystallography. Thermal decomposition of 4 results in “true cycloreversion” to the starting materials. Stereochemistry and decomposition of the normal-addition 1-pyrazolines, NP , produced in situ from 2-cyano-3-(p-substituted-phenyl)acrylates and diazoalkanes, are also discussed.