When X3 in general formula (VI) represents a group --CR1 R2 X5 -- this may be reduced to a group --CR1 R2 (CH2)m-1 -- using hydrogen in the presence of a catalyst such as platinum or palladium on a support such as charcoal in a solvent such as an alcohol, e.g. ethanol or methanol, or an ester, e.g. ethyl acetate, or an ether, e.g. tetrahydrofuran, at normal or elevated temperature and pressure.