[N:1]1[CH:6]=[CH:5][CH:4]=[CH:3][CH:2]=1.[BH4-].[Na+].Cl[C:10]([O:12][CH2:13][C:14]1[CH:19]=[CH:18][CH:17]=[CH:16][CH:15]=1)=[O:11]>O1CCCC1>[CH2:13]([O:12][C:10]([N:1]1[CH:6]=[CH:5][CH:4]=[CH:3][CH2:2]1)=[O:11])[C:14]1[CH:19]=[CH:18][CH:17]=[CH:16][CH:15]=1A solution of pyridine (4.0 g., 0.050 mol) and NaBH4 (1.0 g, 0.026 mol) in 20 ml of tetrahydrofuran is treated with benzyl chloroformate (8.5 g, 0.05 mol) over about 1 hour followed by stirring for 1.5 hour at -78° C. The mixture is added to ice-water and extracted with ether, and the extract is washed with 3% HCl solution and 3% NaOH solution. After the extract is dried and evaporated, 8.0 g of N-benzyloxycarbonyl-1,2-dihydropyridine is obtained in 74% yield. A 5% solution of N-benzyloxycarbonyl-1,2-dihydropyridine is then irradiated using a Rayonet photochemical reactor (RP-300 lamps) until the NMR spectrum shows consumption of the starting materials. The solvent is evaporated to give the crude product, N-(benzyloxycarbonyl)-2-azabicyclo[2.2.0]hex-5-ene (VIII). Pure (VIII) is obtained by passing the crude product through basic alumina with ether. (VIII) is then reacted with ozone in methanol at -78° C. followed by reaction with peroxyacetic acid to form cis-N-(benzyloxycarbonyl)-azetidine-2,3-dicarboxylic acid.
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