There is provided a process for the preparation of a compound of formula (7) wherein R1 represents an alkyl group R2 represents an aryl group R3 represents hydrogen, a protecting group or an alkyl group and R4 represents hydrogen, a protecting group or a SO2R5 group where R5 is an alkyl group, which comprises a) hydroxylating a compound of formula (1) wherein Y represents a halo group P1 represents hydrogen or a protecting group, and W represents =O or -OP2, in which P2 represents hydrogen or a protecting group, to give a compound of formula (2), b) oxidising the compound of formula (2) to give a compound of formula (3), c) coupling the compound of formula (3) with a compound of formula (4), wherein R3 represents a protecting group or an alkyl group R4 represents a protecting group or a SO2R5 group where R5 is an alkyl group and R6 represents (PR7R8)+X- or P(=O)R7R8 in which X is an anion and R7 and R8 each independently is an alkyl, aryl.
