Process for the preparation of intermediates useful in the synthesis of statin derivatives

A process for the preparation of an intermediate compound of formula VI suitable for the preparation of statin derivatives, which process comprises reaction of an intermediate of formula I

• wherein X is halogen, acyloxy, activated hydrocarbyloxy, activated hydrocarbylthio or —N(CH3)—OCH3, Ra is a hydroxy-protecting group and Rb is a carboxy-protecting group, with chain lengthening, including the following reaction steps, as described below, wherein the intermediate of formula I reacts with an ethylene of formula II
• wherein Ya is halogen or hydrogen;
• there being obtained a keto compound of formula III
• wherein Ya is halogen or hydrogen, Xa is halogen or acyloxy, Ra is hydrogen, obtainable after removal of a hydroxy-protecting group Ra, or a hydroxy-protecting group and Rb is a carboxy-protecting group;
• the compound of formula III is reacted further in accordance with the following method (3), wherein
• a compound of formula III wherein Xa is halogen or acyloxy, Ya is hydrogen, Ra is hydrogen and Rb is a hydroxy-protecting group is reacted diastereoselectively by means of a suitable reagent to form a syn-diol compound of formula Va
• wherein Xa is halogen or acyloxy, and Ra′ and Rc′ are as defined for compounds of formula V and Rb is as defined for compounds of formula III;
• and the compound of formula Va is then reacted with a salt of hydrazoic acid to form a compound of formula V
• wherein Ra′ and Rc′ are each hydrogen or, after subsequent introduction of protecting groups, Ra′ and Rc′ are each independently of the other hydrogen or a protecting group, with the proviso that at least one of the two radicals is a protecting group, or Ra′ and Rc′ together are a bridging hydroxy-protecting group, and Rb is as defined above for compounds of formula III
• and the compound of formula V so obtainable is then reduced to the corresponding amino compound of formula VI
• wherein Ra′ and Rc′ are each independently of the other hydrogen or a hydroxy-protecting group or together are a bridging hydroxy-protecting group, and Rb is a carboxy-protecting group;
• wherein in the processes mentioned above, at any stage, even where not explicitly mentioned, if necessary one or more or all of the protecting groups present in the compounds of formulae I to VI in question are removed or one or more or all of the functional groups that are not to participate in a reaction, or that would interfere with the reaction, are converted into protected groups by the introduction of suitable protecting groups, and it being possible for the compounds of formulae Ito VI, where salt-forming groups are present and the reaction in question is not impaired, also to be in salt form.