| Abstract
| - An efficient and straightforward route toward 3,4-cis-4-isopropenylazetidin-2-ones was developedfrom 4-(1-chloroalkyl)azetidin-2-ones. Starting from the latter β-lactams, a new synthesis ofpyrrolidin-2-ones was achieved. When 4-isopropenylazetidin-2-ones were treated with bromine indichloromethane, diastereoselective electrophile-induced ring expansions toward 5-bromopyrrolidin-2-ones were performed. Further oxidation of 3-benzyloxypyrrolidin-2-ones with bromine toward3-bromopyrrolidin-2-ones was also established. When 4-isopropenyl-β-lactams were added to amixture of NBS and TMSN3, 5-azidopyrrolidin-2-ones were obtained in moderate to high yields.
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