Regio- and stereoselective synthesis of key 1-methyl carbapenem intermediates via hydroformylation using a zwitterionic rhodium catalyst

The asymmetric hydroformylation of a 4-vinyl ?-lactam catalyzed by a rhodium catalyst with a chiral phosphine ligand was investigated. The catalytic system consisting of a zwitterionic rhodium catalyst, (NBD)Rh+(C6H5B-Ph3) 4, and (S,S)-2,4 bis(diphenylphosphino)pentane, (S,S)-BDPP, gave branched aldehydes in high regio- and stereoselectivity. The hydroformylated products are key intermediates in the synthesis of 1-methylcarbapenem antibiotics. Using (3S,4R)-3-[(R)-1-(tert-butyldimethyl-silyloxy)ethyl]-4-vinyl-2-azetidinone (5a) as the reactant afforded aldehydes in a 97:3 branched-to-linear ratio and 91:9 to ?- to ?-branched isomers. The regio (branched/linear)- and stereoselectivity (?/?) was >99:1 when (3S,4R)-1-N-BOC-3-[(R)-1-methoxyethyl]-4-vinyl-2-azetidinone was used as the substrate (5q).