β-Lactams. 2. Diastereoselective Alkylative Discrimination of Racemic 3-Substituted 4-Acetoxyazetidin-2-ones and Its Application to the Synthesis of a Chiral Key Intermediate for Carbapenem Syntheses

Article abstract of DOI:10.1021/jo00041a032

Alkylation of rac 3-substituted 4-acetoxyazetidin-2-one 4 with chiral tin(II) enolate 8 derived from 3-acetyl-(4S)-ethyl-1,3-thiazolidine-2-thione (ETT) (7) proceeded in a highly diastereoselective manner to give alkylated products 9, 10, and 11 in 42percent, 20percent, and 9percent yields, respectively, after chromatographic purification.Similar alkylation of rac-5 with 8 gave 16, 17, and 18 in 45percent, 29percent, and 5percent yields, respectively.Compound 9 was readily converted to 33, a chiral key intermediate for the synthesis of carbapenems.Analytical separation of rac-4 was effectively done with an HPLC technique employing a chiral column packed with A(S)MBC.