Alkylation of (8) with compounds of formula R4X2 wherein X2 is halogen, triflate or tosylate, in the presence of a base such as potassium carbonate, sodium hydride, potassium hydroxide or potassium tert-butoxide, and in a solvent such as N,N-dimethylformamide, acetonitrile, tetrahydrofuran or acetone, provides compounds of structure (9).