| abstract |
A process for the preparation of compounds of formula (I) wherein R 1 is unsubstituted or substituted C 1 -C 8 alkyl, R 2 , R 3 , R 4 and R 5 are each independently of the others hydrogen, unsubstituted or substituted C 1 -C 8 alkyl, C 1 -C 8 alkoxy, phenoxy or benzyloxy, or halogen, Y 1 and Y 2 are each independently of the other hydrogen or a protecting group, or Y 1 and Y 2 together form a protecting bridge, and X 1 is hydrogen, an organic radical or a cation, in which process a compound of formula (II) wherein R 1 R 2 , R 3 , R 4 and R 5 are as defined above and Z 1 is a leaving group, is reacted, in the presence of a catalytically effective amount of a palladium catalyst, with a compound of formula (III) wherein R 6 is hydrogen, bromine, chlorine, iodine, —OSO 2 CF 3 , —COCI, —B(OH) 2 or a mono- or di-ester derived from —B(OH) 2 , Y 3 and Y 4 are each a protecting group, or Y 3 and Y 4 together form a protecting bridge, and X 1 is as defined above, to form a compound of formula (IV) and if desired the radicals Y 3 and Y 4 are converted into the radicals Y 1 and Y 2 where Y 1 and Y 2 are hydrogen. |