Intermediates and processes are disclosed which are useful for the preparation of a substantially pure compound of the formula: ##STR1## wherein R.sub.6 and R.sub.7 are each hydrogen or R.sub.6 and R.sub.7 are independently selected from ##STR2## wherein R.sub.a and R.sub.b are independently selected from hydrogen, loweralkyl and phenyl and R.sub.c, R.sub.d and R.sub.e are independently selected from hydrogen, loweralkyl, trifluoromethyl, alkoxy, halo and phenyl; and ##STR3## wherein the naphthyl ring is unsubstituted or substituted with one, two or three substitutents independently selected from loweralkyl, trifluoromethyl, alkoxy and halo; orR.sub.6 is as defined above and R.sub.7 is R.sub.7a OC(O)-- wherein R.sub.7a is loweralkyl or benzyl; orR.sub.6 and R.sub.7 taken together with the nitrogen atom to which they are bonded are ##STR4## wherein R.sub.f, R.sub.g, R.sub.h and R.sub.i are independently selected from hydrogen, loweralkyl, alkoxy, halogen and trifluoromethyl and R.sub.8 is hydrogen or --C(O)R" wherein R" is loweralkyl, alkoxy, benzyloxy or phenyl wherein the phenyl ring is unsubstituted or substituted with one, two or three substituents independently selected from loweralkyl, trifluoromethyl, alkoxy and halo; or an acid addition salt thereof.