Electrophile-induced ring expansions of beta-lactams toward gamma-Lactams.
[reaction: see text] An efficient and straightforward route toward 3,4-cis-4-isopropenylazetidin-2-ones was developed from 4-(1-chloroalkyl)azetidin-2-ones. Starting from the latter beta-lactams, a new synthesis of pyrrolidin-2-ones was achieved. When 4-isopropenylazetidin-2-ones were treated with bromine in dichloromethane, diastereoselective electrophile-induced ring expansions toward 5-bromopyrrolidin-2-ones were performed. Further oxidation of 3-benzyloxypyrrolidin-2-ones with bromine toward 3-bromopyrrolidin-2-ones was also established. When 4-isopropenyl-beta-lactams were added to a mixture of NBS and TMSN(3), 5-azidopyrrolidin-2-ones were obtained in moderate to high yields.
Van Brabandt
Willem
W
Department of Organic Chemistry, Faculty of Bioscience Engineering, Ghent University, Belgium.
De Kimpe
Norbert
N
D001384:Azetidines / Q000737:chemistry; D001966:Bromine / Q000737:chemistry; D004583:Electrons; D007769:Lactams / Q000737:chemistry*; D015394:Molecular Structure
D001384:Azetidines; D007769:Lactams; D001966:Bromine