ACID-CATALYZED ISOMERIZATION OF 1-ACYL- AND 1-THIOACYLAZIRIDINES .2. ORIENTATION OF RING OPENING

The isomerization of 1-(N-phenylcarbamyl)- (IlIa) and 1-(N-phenylthiocarbamyl)-2-methylaziridines (Illb) with acids was investigated. In the isomerization of (IlIa), 2-anilino-5-methy1-2-oxazoline (IVa) was obtained as the major product along with the isomeric 2-anilino-4-methyl-2-oxazoline (Va). Illb gave a mixture of almost equal amounts of 2-anilino-5-methyl-2-thiazoline (IVb) and 2-anilino-4-methyl-2-thiazoline (Vb). The orientation of the ring opening of IlIa or Illb seems to be nearly independent of acids and solvents. Investigation using optically active IlIa and Illb suggests that IVa is formed by an Sn2 mechanism with protonic acids and by a front-side attack mechanism when boron trifluoride etherate is used, and IVb would either be an Sn2 or Sn1 mechanism depending upon the acid and solvent used. These results clearly indicate that the mechanism of ring opening is not determined by the orientation. Such an Sn2 mechanism is considered to be a “modified” Sn2 in which substituents exhibit an Sn1-like effect. An interpretation in which the difference in the orientation of the ring opening between IlIa and Illb on the assumption that the site of the protonation would be different from IlIa to Illb was also considered. © 1969, American Chemical Society. All rights reserved.