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Abstract

A process for the preparation of a compound of the formula ##STR1## wherein R.sub.1 is alkyl of 1 to 3 carbon atoms, R.sub.2 is alkyl of 1 to 12 carbon atoms, R.sub.3 is alkyl of 1 to 4 carbon atoms comprising reacting a compound of the formula ##STR2## wherein R.sub.4 is a remainder of an easily cleavable ether, K is a protected ketone function in the form of ketal, thioketal or mixed ketal and R.sub.1 has the above definition with a magnesium organic compound reagent of the formula HalMg--CH.sub.2 --R.sub.2 A wherein Hal is a halogen and R.sub.2 is defined as above to obtain a compound of the formula ##STR3## wherein R.sub.1, R.sub.2 and K are defined as above, reacting the latter with an acylation agent to obtain a compound of the formula ##STR4## wherein R.sub.5 is alkyl of 1 to 6 carbon atoms or aryl of 6 to 10 carbon atoms and R.sub.1, R.sub.2 and K are defined as above, reacting the latter with an appropriate alkylation agent to obtain a compound of the formula ##STR5## wherein R.sub.1, R.sub.2, R.sub.3 and K are defined as above, subjecting the latter to autoxidation to obtain a compound of the formula ##STR6## wherein R.sub.1, R.sub.2, R.sub.3 and K are defined as above, reacting the latter with an acid to obtain a reconjugated 3-keto compound of the formula ##STR7## wherein R.sub.1, R.sub.2 and R.sub.3 are defined as above and reacting the latter with a regio- and enantioselective reducing agent to obtain a compound of formula I and intermediates formed therein.

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