| http://www.w3.org/ns/prov#value | - Compounds of formula I wherein R3 is lower alkyl, e.g. methyl can be prepared by reacting the corresponding compounds of formula I wherein R3 represents hydrogen with lower alkyl or phenyl lower alkyl haloformates, such as ethyl chloroformate, to obtain compounds of formula I wherein R3 is lower alkoxycarbonyl or lower phenylalkyloxycarbonyl, and reducing said acyl derivatives with simple or compl
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