A process for preparing compounds of the formula ##STR13## wherein R-R.sup.5 are as defined in claim 1 which process comprises reductively alkylating: ##STR14## or alkylating compounds of Formula VI with .alpha.-halo compounds of theformula: ##STR15## wherein R-R.sup.5, are as defined above and X is a good leaving group such as Br or I, followed by removal of protecting groups, if necessary, to yi