. "the intermediate compound (IIA).In one aspect of the invention, a compound of formula (II) may be prepared by reaction of a compound of formula (III): wherein R1 is as hereinbefore defined for a compound of formula (I), P is a protecting group, typically a tetrahydro-2H-pyran-2-yl group, and R3 is as hereinbefore defined for a compound of formula (IIA), with a s" . . . .