Simple and Condensed β-Lactams. Part 32. Base- and Acid-Catalyzed Ring Expansions of 3-Substituted 4-Acetylazetidin-2-ones and Related Compounds

On treatment with bases, the C3-C4 bonds of the 3-substituted 4-(1-iminoethyl)- or 4-acetylazetidin-2-ones 8f, 8g and 8i are cleaved heterolytically to afford, depending on the nature of the 3-substituent, ring expansion or other products (14, 19 and 27, respectively). Related compound 8h undergoes a base-induced ring transformation to afford compound 23 only after oxidation to the stereoisomeric disulfanes 20. Compound 8d, when treated with HCl, undergoes a ring transformation to pyrrolidin-2-one 32.