Three-membered Rings.-The existence of a high barrier to nitrogen inversion in aziridines, which contain a hetero-atom attached to the ring nitrogen, may be inferred from n.m.r. spectroscopy.l An elegant demonstration of this effect is provided by 1-chloro-2-methyla~iridine~ and 7-chloroazabicyclo[4,1,0] although the adducts generally undergo rearrangement. For example, 2,4diphenylpyrrole is formed from 2-phenyl-1-azirine and acetophenone in the presence of a strong base,g diazomethane and 3-methyl-2-phenyl-1-azirine react to give a mixture of cis-and transl-azido-2-phenyl-but-2-ene together with 3-azido-2-phenyl-but-1 -ene, l o while a-ammoniumisobutyrophenone anil perchlorate is obtained from 3,3-dimethyl-2-phenyl-l-azirine and anilinium perchlorate." Even acid chlorides and acid anhydrides will add to the azirine double-bond :' the N-acylchloroaziridines derived from benzoyl chloride and 3-methyl-2-phenyl-1-azirine are stable in benzene, although they readily rearrange to 4-methyl-2,5-diphenyloxazole and the dichloro-amide (4) in acetone .
Ph,CH .CO* NPh. CH(0Me)Ph