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 wherein R₁, R₂, R₃, X and n are as defined in the disclosure. This invention also discloses preparation of compounds of Formula III wherein R₁, R₂, R₆, R₇, R₈ and n are as defined in the disclosure. Also disclosed are certain intermediates of Formula 4 for the preparation of compounds of Formula I wherein X is N and R₂, R₃ and n are as defined in the disclosure. ##STR1##