Process for preparing tert-butyl (3r,5s)-6-hydroxy-3,5-o-...

Details Process for preparing tert-butyl (3r,5s)-6-hydroxy-3,5-o-... Process for preparing tert-butyl (3r,5s)-6-hydroxy-3,5-o-...

C - Chemistry, Metallurgy

07

D

C07D 319/06 (2006.01)

Patent

CA 2099444

Process for preparing tert-butyl (3R,5S)-6-hydroxy-3,5-O- isopropylidene-3,5-dihydroxyhexanoate A novel process is described for preparing tert-butyl (3R,5S)6-hydroxy-3,5-O-isopropylidene-3,5-dihydroxyhexan- oate of the formula I (See formula I) which is a valuable structural element for preparing inhibitors of HMG-CoA reductase. In particular, the present invention relates to a process for preparing the compound of the formula I, wherein ethyl .omega. benzyloxyacetoacetate of the formula II (See formula II) is asymmetrically hydrogenated at substrate/catalyst molar ratio greater than 1000:1, using an in-situ ruthenium (II) chloride -(R)-BINAP catalyst and hydrogen pressure of less than 5 atm H2 to give ethyl 2(S)-hydroxy-3-benzyloxybutyrate of the formula III, Image the .beta.-hydroxy ester of the formula III is converted by means of a Claisen condensation into the .beta.-keto-.delta.-(S)-hydroxy ester of the formula IV, Image the resultant ester of the formula IV is converted by diastereoselective reduction into tert-butyl 3(R),5(S)- dihydroxy-6-benzyloxyhexanoate of the formula V, Image the hydroxyl groups in the dihydroxy ester of the formula V are protected, with the formation of the acetonide of the formula VI, Image and the benzyl protective group is removed from the acetonide of the formula VI, with the formation of the compound of the formula I.

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