This invention relates to a compound of Formula I, a method for its preparation and its use in the preparation of a compound of Formula II ##STR00001## wherein R.sup.1, R.sup.2, R.sup.3, X and n are as defined in the disclosure.This invention also discloses preparation of compounds of Formula III ##STR00002## wherein R.sup.1, R.sup.2, R.sup.6, R.sup.7, R.sup.8 and n are as defined in the disclosure. Also disclosed are certain intermediates of Formula 4 for the preparation of compounds of Formula I ##STR00003## wherein X is N and R.sup.2, R.sup.3 and n are as defined in the disclosure.