Chemoenzymatic Preparation of a Key Intermediate for Carbapenem Synthesis Starting from Asymmetrized Bis(hydroxymethyl)acetaldehyde (BHYMA*)

4-Unsubstituted 2-azetidinones 3a,b, which are useful intermediates for the synthesis of carbapenem antibiotics, have been enantiospecifically and diastereoselectively prepared starting from asymmetrized bis(hydroxymethyl)acetaldehyde (BHYMA*) 4. a new chiral building block obtained through biological methods. The key steps are the highly diastereoselective addition of Me2CuLi to 4 (diast. ratio = 95 : 5), and the regioselective deblocking of tBuMe2Si ether in the presence of a (iPr)3Si ether, by using a novel methodology.