Process for the preparation of a viral protease inhibitor and intermediates thereof

The invention relates to the prepn. of cyclopenta[c]pyrrole derivs. I (R is OH or an ester, P is H or a protecting group ), which are intermediates in the synthesis of viral protease inhibitor telaprevir. Compd. I was obtained by oxidn. of II (R1 is H or Me) as a stereoisomeric mixt. or a single isomer via formation of the formyl or acetyl deriv. in the first step. Compds. II were prepd. by nitroalkylation of hexahydrocyclopenta[c]pyrrole and optional N-protection and resoln. via formation of diastereoisomeric salts with a chiral amine.