C([N-]C(C)C)(C)C.[Li+].[CH3:9][O:10][CH:11]([O:22][CH3:23])[CH2:12][N:13]1[CH2:16][CH2:15][CH:14]1C(OCC)=O.[O:24]=O>O1CCCC1.ClCCl.[Zn]>[CH3:9][O:10][CH:11]([O:22][CH3:23])[CH2:12][N:13]1[CH2:16][CH2:15][C:14]1=[O:24]To a solution of 2.2 mmol of lithium diisopropylamide in 15 ml tetrahydrofuran at -78° was added dropwise 0.43 g (2 mmol) of N-(2,2-dimethoxyethyl)-2-carbethoxy azetidine in 3 ml of tetrahydrofuran. After stirring at -78° for 30 minutes, the deep yellow anion was silylated in the usual way and warmed to room temperature. Removal of all volatiles by rotary evaporation with a high vacuum pump gave a purple residue which was redissolved in dichloromethane. Internal photooxidation using 5 g of Photox (trademark for photoconductive lead-free zinc oxides available from The New Jersey Zinc Co.) as the sensitizer required less than 5 minutes for oxygen uptake. The mixture was then filtered free of sensitizer and worked up by aqueous extraction in the usual manner. The pink residue obtained was applied to a 17×2 cm neutral alumina column. Elution with 10:3 ethyl acetate-hexane yielded 0.18 g (56%) of pale yellow liquid, which by NMR analysis was greater than 90% pure. Comparison of its spectral properties (IR, NMR) with those of an authentic known sample confirmed the identity of the product as the expected beta-lactam.
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