Patent ID: 6169178
Filing Date: 2001-01-02
Classification: C07J

Abstract:
Process for the preparation, with control of the epimeric distribution at the C-22 position, of acetals of formula (I) where R.sub.1 is a linear or branched alkyl having from 1 to 12 carbon atoms; R.sub.2 is H, or a --CO--Z.sub.1 acyl group, in which Z.sub.1 is H or a linear or branched alkyl having from 1 to 12 carbon atoms, the said process comprising the following steps: a) acetalization with control of the epimeric distribution at the C-22 position, starting from a compound of formula (II-A) where R.sub.2 has the meaning seen above; R.sub.3 and R.sub.4 may both be H, or R.sub.3 and R.sub.4, taken together, may be: (i) --C(R.sub.5) (R.sub.6)--, where R.sub.5 and R.sub.6, which are the same or different from one another, are linear or branched alkyl groups having from 1 to 12 carbon atoms; or (ii) --CH(R.sub.1)--, where R.sub.1 is an alkyl group as defined above; in which the said compound of formula (II-A) is treated with an aldehyde of formula R.sub.1 CHO, where R.sub.1 has the meaning seen above, in the presence of an aqueous hydrogen halide chosen from between HBr and HI, and the corresponding acetals of formula (I-A) are obtained wherein R.sub.1 and R.sub.2 have the above meaning; b) the acetals of formula (I-A) thus obtained are treated with a halogenating agent in an acid environment in the presence of a hydroxylating agent or in the presence of an acyloxylating agent, thus obtaining the corresponding acetals of formula (I-C) where Y is an .alpha.-halogen and X is .beta.-OH when the reaction is carried out in the presence of a hydroxylating agent, or X is .beta.-OR.sub.7, where R.sub.7 is a CO--Z.sub.2 acyl in which Z.sub.2 is H or a linear or branched alkyl having from 1 to 12 carbon atoms, when the reaction is carried out in the presence of an acyloxylating agent; c) the so obtained acetals of formula (I-C) in which Y is .alpha.-halogen, are treated with a dehalogenating agent to yield the corresponding acetals of formula (I) reported above when X is .beta.-OH, and to yield the acetals of formula (I-D) in which R.sub.1, R.sub.2 have the above meaning, and X is .beta.-O R.sub.7, where R.sub.7 is as defined above; d) the acetals of formula (I-A), (I-C), (I-D), or formula (I) coming from step a), b) or c) where R.sub.2, R.sub.7 or both, are acyl groups as defined previously, and the other substituents are as defined previously, are subjected to removal of the ester group, when the corresponding acetals of formula (I-A), (I-C), (I-D), or formula (I) in which R.sub.2 and R.sub.7 are H have to be obtained.