Improved processes for preparing intermediates useful for preparing antibacterial N-[1-oxo-2-alkyl-3-(N-hydroxyformamido)-propyl}-(carbonylamino-aryl or -heteroaryl)-azacyclo4-7alkanes or thiazacyclo4-7alkanes, which have one or more of the following features: (1) make use of a particular .beta.-lactam intermediate; (2) which make use of a particular resolving agents, enantiomerically pure substituted propionic acids, especially (R)-2-butyl-3-hydroxy-propionic acid; (3) which avoid the use of hydrogen peroxide; and (4) which facilitate selective debenzylation reducing production of waste by-products.