Novel Diastereoselective Synthesis of Bicyclic β-Lactams through Radical Cyclization and Their Reduction toward 2-(1-Alkoxy-2-hydroxyethyl)piperidines and 2-(1-Alkoxy-2-hydroxyethyl)azepanes

1-Allyl- and 1-(3-phenylallyl)-substituted 4-(2-bromo-1,1-dimethylethyl)azetidin-2-ones were transformed
into 3-substituted 7-alkoxy-5,5-dimethyl-1-azabicyclo[4.2.0]octane-8-ones through radical cyclization by
means of n-tributyltin hydride and AIBN in toluene with excellent diastereocontrol (≥99%). The radical
cyclization of 4-(2-bromo-1,1-dimethylethyl)-1-(2-methylallyl)azetidin-2-ones afforded 8-alkoxy-3,6,6-trimethyl-1-azabicyclo[5.2.0]nonan-9-ones in good diastereomeric excess (75−78%). The reductive ring
opening of 1-azabicyclo[4.2.0]octane-8-ones and 1-azabicyclo[5.2.0]nonan-9-ones with lithium aluminum
hydride resulted in novel 2-(1-alkoxy-2-hydroxyethyl)piperidines and -azepanes, which were isolated as
single isomers.