<p>Novel diastereomers of the Formula I <IMAGE> which are useful as intermediates in the preparation of thienamyan, are prepared in a process which comprises removing the ethylene ketal group from a compound of the general Formula III <IMAGE> [wherein R<1> is hydrogen or (as an amide protecting group) a phenyl or benzyl group optionally substituted by one or more methoxy group(s)] and reducing the new compound of the general Formula <IMAGE> thus obtained.</p>
