Process for preparation and purification of misoprostol

Preparation of the compounds of general formula I, among them misoprostol where R represents a straight- or branched-chain C1-4 alkyl group by cuprate coupling of the vinyl cuprate of general formula II prepared by reacting the vinyl stannane of general formula III with copper halide CuX and alkyllithium R1Li wherein: R2 stands for H or an alcohol-protecting group which may contain silicium atom, as for instance trimethylsilyl-, triethylsilyl-, tert.-butyldimethylsilyl- group, or a cyclic or open-chain alkyl group containing oxygen atom, as for instance tetrahydropyranyl-, methoxymethyl- or ethoxymethyl- group; X means I, Br, CN, SCN, OSO2 CF3 group, R1 represents C1-6 alkyl group, n >2, if R2 is not hydrogen atom, n>3, if R2 is hydrogen atom, and the protected enone of the general formula IV 30 22 IV where R3 represents THP- or trialkylsilyl- group and the meaning of R is as defined above takes part in the cuprate reaction 5 in a manner that a.) the excess of the alkyllithium, which is applied as compared to the Cu(I) iodide in the case of R2 ≠ H in 2-2.4 molar ratio, in the case of R2 = H in 3-3.4 molar ratio, is decomposed before the coupling reaction of II and IV, b.) the protecting groups of the resulting compound of the general formula V 15 V where the meanings of R, R2 and R3 are as defined above are removed, the obtained compound of the general formula I is purified by chromatography.