Patent ID: 7045641

Claim:
A process for preparing compounds of the formula I in which a) a compound of the formula II is reacted with a reagent of the formula III to obtain a compound of the formula IV, b) optionally, the compound of the formula IV is treated to hydrolyze the acetal function thereof, and reacted with a reagent of the formula V to obtain a compound of the formula VI c) the compound of the formula IV or VI is reduced to obtain a compound of the formula VII d) the compound of the formula VII is oxidized to obtain the compound of the formula I, in which R 1 and R 2 are, independently of one another, C 1 –C 8 -alkyl or, together with the oxygen atoms to which they are bonded, and with the carbon atom located between them, are in which R 3 , R 4 and R 5 are, independently of one another, hydrogen or C 1 –C 4 -alkyl, R 6 is C 1 –C 8 -alkyl, is a triarylphosphonium or phosphonic acid dialkyl ester radical, and k is 0 or 1.