thylating agent, e.g. diazomethane,dimethyl sulphate or a compound of formula (X)wherein Y represents a leaving group, e.g. a halogen atom such as chlorine, bromine or iodine or an acyloxy group, e.g. a hydrocarbylsulphonyloxy group such as mesyloxy or tosyloxy, or a haloalkanoyloxy group such as a dichloroacetoxy group); or(F) alkylating a compound of formula (XI) ##STR10## (wherein R, R.sub.1, R