New process for the manufacture of mdm2-p53 antagonists

A process for the manufacturing of a compound of formula (1)

• or a salt thereof,
• comprising the oxidative ring-opening of a compound of formula (13)
• wherein
• R* is a cleavable carboxyl protecting group, preferably an optionally substituted C1-6alkyl or an optionally substituted benzyl group, most preferably selected from the group consisting of methyl, ethyl, iso-propyl and benzyl, and
• PG is a suitable amino protective group, preferably a group —C(═O)—R, wherein R is R′ or —O—R′ and R′ is an optionally substituted linear, branched or cyclic aliphatic or aromatic group or combinations thereof, most preferably a protective group selected from the group consisting of acetyl (Ac) and tert-butyloxy carbonyl (Boc).