C.Compounds of formula IB wherein R.sub.1 is not hydrogen can be prepared by the alkylation of a compound of formula IA wherein R.sub.1 is hydrogen, and W, n, and m are as defined above with an alkylating agent of the formula R.sub.1 -LG and a basein an inert solvent, where LG is a suitable leaving group and R.sub.1 is as defined above except for hydrogen.