Process for preparing hydromorphone and derivatives thereof

A process for the preparation of a compound of formula I,

• or a pharmaceutically acceptable salt thereof;
• wherein:
• R1 represents hydrogen, C1-12 alkyl, C2-12 alkenyl, C2-12 alkynyl or C3-12 cycloalkyl, wherein the alkyl, alkenyl, alkynyl and cycloalkyl (which latter four groups are optionally substituted by one or more halogen atoms or phenyl groups;
• the process comprises contacting a compound of formula II,
• or a salt thereof, wherein R1a is defined according to R1,
• with a mixture comprising water, a carboxylic acid, a sulfonic acid, and a sulfide compound;
• wherein the water is present in the mixture at from about 0.1% to about 70% by weight relative to combined weight of the water and the compound of formula II, and the sulfide compound is selected from the group consisting of cyclic sulfur-containing compounds and sulfides of formula III,
• X1—S—X2 III
• wherein X1 and X2 each independently represent hydrogen, phenyl, —C(O)R3 or a C1-12 alkyl group, wherein the phenyl, R3 and alkyl are each independently optionally substituted by one or more substituents selected from the group consisting of halogen, —OH, —NH2, phenyl, —O—C1-4 alkyl, —C(O)R4 and —S(O)m—C1-4 alkyl;
• R3 and R4 independently represent —OH, —C1-4 alkyl or —O—C1-4 alkyl;
• and
• m represents from 0 to 2.