Aminoethylene

Aziridines are organic compounds containing the aziridine functional group, a three-membered heterocycle with one amine group (-NH-) and two methylene bridges (-CH2-). The parent compound is aziridine (or ethylene imine), with molecular formula C2H5N. Aziridines are organic compounds containing the aziridine functional group, a three-membered heterocycle with one amine group (-NH-) and two methylene bridges (-CH2-). The parent compound is aziridine (or ethylene imine), with molecular formula C2H5N. The bond angles in aziridine are approximately 60°, considerably less than the normal hydrocarbon bond angle of 109.5°, which results in angle strain as in the comparable cyclopropane and ethylene oxide molecules. A banana bond model explains bonding in such compounds. Aziridine is less basic than acyclic aliphatic amines, with a pKa of 7.9 for the conjugate acid, due to increased s character of the nitrogen free electron pair. Angle strain in aziridine also increases the barrier to nitrogen inversion. This barrier height permits the isolation of separate invertomers, for example the cis and trans invertomers of N-chloro-2-methylaziridine. There are several syntheses of aziridines (aziridination). An amine functional group displaces the adjacent halide in an intramolecular nucleophilic substitution reaction to generate an aziridine. Amino alcohols have the same reactivity, but the hydroxy group must first be converted into a good leaving group. The cyclization of an amino alcohol is called a Wenker synthesis (1935), and that of a haloamine the Gabriel ethylenimine method (1888). Nitrene addition to alkenes is a well-established method for the synthesis of aziridines. Photolysis or thermolysis of azides are good ways to generate nitrenes. Nitrenes can also be prepared in situ from iodosobenzene diacetate and sulfonamides, or the ethoxycarbonylnitrene from the N-sulfonyloxy precursor. Thermal treatment or photolysis of triazolines expels nitrogen, producing an aziridine. Triazolines can be generated by cycloaddition of alkenes with an azide. One method involves the ring-opening reaction of an epoxide with sodium azide, followed by organic reduction of the azide with triphenylphosphine accompanied by expulsion of nitrogen gas: The other method involves the ring-opening reaction of an epoxide with amines, followed by ring closing with the Mitsunobu reaction. The Hoch-Campbell ethylenimine (Aziridine) synthesis is the reaction of certain oximes with Grignard reagents: