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Abstract

Process for the synthesis of compounds of the formula ##STR1## in R[R*,S*] enantiomeric form, wherein each P.sub.1 is independently an hydroxy group-protecting group, and R.sub.2z is C.sub.1-4 alkyl, benzyl or allyl, comprising, as a key step when R.sub.2z is R.sub.2x, the reaction of the compound of the formula ##STR2## in (S) enantiomeric form with a compound of the formula Mg.sup. .circle.+2 (.sup..crclbar. OOC--CH.sub.2 --COOR.sub.2x).sub.2 to obtain a compound of the formula ##STR3## in (S) enantiomeric form, and, as a key step when R.sub.2z is R.sub.2y, the reaction of a compound of the formula ##STR4## in (S) enantioimeric form with a compound of the formula Li.sup..sym..crclbar. CH.sub.2 --COOR.sub.2y to obtain a compound of the formula ##STR5## in (S) enantiomeric form, wherein R.sub.2x is primary or secondary C.sub.1-4 alkyl, benzyl or allyl, R.sub.2y is C.sub.1-4 alkyl not containing an asymmetric carbon atom, and R.sub.3 ' is methyl or ethyl, processes for the synthesis of compounds of the formula ##STR6## comprising reacting a compound of the formula ##STR7## with the reaction product of a strong base and a compound of the formula ##STR8## optionally followed by, when R.sub.2z is allyl, cleavage of the allyl and P.sub.1 groups to obtain the corresponding compound of the formula ##STR9## wherein each R.sub.7 is methyl or ethyl, R is as defined in the specification, and each P.sub.1 independently and R.sub.2z are as defined above, and the compounds of the formula ##STR10## wherein R and each R.sub.7 are as defined above.

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First Claim