Stereospecific method for the preparation of dioxa-bicyclooctane nitrate compounds

A method for the preparation of a compound of formula (I):

• wherein Z represents a C1-6-alkyl, C2-6-alkenyl, C3-8-cycloalkyl, aryl, heteroaryl, aryl C1-6-alkyl, or heteroaryl-C1-6-alkyl group, optionally substituted by one to three groups independently chosen from the group consisting of halogen, C1-6-alkyl and C1-6-alkylthio,
• comprising the following steps:
• (a) reacting a compound of formula (II):
• with a sulfonic derivative of formula (III)
• wherein R is chosen from the group consisting of C1-3-alkyl, C1-3-alkyl substituted with 1 to 3 halogen atoms, phenyl, C1-3-alkyl-phenyl and C1-3-alkyl-phenyl;
• wherein the alkyl is substituted with 1 to 3 halogen atoms and G is a halogen atom or —O—SO2—R;
• wherein R is as hereinabove defined, to yield a compound of formula (IV)
• wherein R has the meaning defined for formula (III);
• (b) treating compound (IV) with a thiocarboxylic acid of formula (V) or a salt thereof:
• wherein Z is as defined for formula (I), to yield compound (VI);
• wherein Z is as defined for formula (I) and R is as defined for formula (III);
• and
• (c) treating compound (VI) with tetrabutylammonium nitrate to yield a compound of formula (I).